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UNIVERSITY OF HONG KONGLIBRARY
Hong Kong CollectionGift from
E.K, loyal Observatory
.V \
Page
INTRODUCTION
1. METECrvGLjUGlCAL CbciEKVATION
1 • 1 Euuii^i'iteui: 3
1.1.1 Surface wind Sensor at Tsim Bei Tsui
1.1*2 Upper-air Measurement Systems- at King's Park
1.1.3 Monostatic Acoustic Radar at Junk Bay
1.2 Operation of Meteorological Instruraents 7
1.2.1 Observation Period
1.2.2 normal Operation of Instruments
1.2.3 Calibration ana Maintenance
1.3 Data processing ' 9
1.3.1 vvino Recoras
1.3*2 cloua Observations
1*3.3 Upper-air Radiosonae/Rawin Records
1.3.4 Acoustic Radar Recoras
2* METEOROLOGICAL ASSESSMENTS
2.1 General Climatology of Hong Kong 12
2-2 Meteorological Data Bases ' 14
2.2*1 Surface wind . :
2.2-2 Cloua Data
2«2» 3 Upper-air Wind, arid' Temperature profiles.
2 * 2.4 Mixing Height
2,3 Wind and Temperature Analyses 17
2.3.1 Monthly and Annual Surface Wind Roses
2» 3 « 2 Monthly and Annual Diurnal 'Variationsof Surface Wind
2*3-3 Spells of Light Wind
2.3-4 Seasonal Variation of Vertical windand Comparison with GEPB Data
2*3«5 Seasonal Variation of Vertical Temperatureprofiles and Comparison with GEPB Data
2*4 Stability Analysis 22
2.4.1 Monthly and Annual Variations of Stability
2*4*2 Monthly and Annual Stability-Wind Roses
2«5 Mixing Height Climatology 26
2«6 Model Simulation of Wind Flow overthe Deep Bay Air Shed 28
2.6*1 Use of the Topographic Air PollutionAnalysis System (TAPAS) Models
2*6*2 Model Results and Their Interpretation
3-. CONCLUDING REMARKS 32
ACKNOWLEDGEMENTS 34
REFERENCES 34
FIGURES
Fig* 1*1 Tsim Bei Tsui anemometer locationand the nearby terrain.
Fig* 1*2 Locations of meteorological stationsmentioned in this report*
Fig. 2*1 Typical surface patterns for northeast monsoonin winter and for southwest monsoon in summer.
Fig. 2.2 Annual wind roses for Tsim Bei Tsui (1975-82),Tate8s Cairn (1971-80) and Chiwan (1976-80)*
Fig. 2.3 Monthly wind roses for Tsim Bei Tsui (1975-82),Tate's Cairn (1971-80) and Chiwan (1976-80).
Fig. 2.4 Diurnal variation of surface windat Tsim Bei Tsui (1975-1982).
Fig. 2.5 Monthly mean wind speed at Tsim Bei Tsui (1975-1982)
Fig. 2-6 Cumulative probabilities of light wind spellsat Tsim Bei Tsui and at the Hong Kong InternationalAirport during 1982*
Fig. 2.7 Seasonal percentage distribution of upper-airwind direction at King's Park, 1981-1982.
Fig« 2.8 Seasonal percentage distribution of upper-airwind direction' at Shenzhen, 1981-1982.
Fig. 2.9 Mean seasonal vertical temperature profilesat King's Park, 1981-1982.
Fig. 2.10 Mean seasonal vertical -temperature .profliesat Shenzhen, 1981-1982.
Fig. 2.11 Monthly and annual stability-wind rosesat Tsim Bei Tsui (1975-1982)*
Fig. 2.12 Resultant flow when daytime onshore flow issuperimposed on the prevailing flowduring winter and during summer.
Fig. 2.13 Diurnal variation of the mixing heightestimated from monostatic acoustic radarrecords at Junk Bay (1982/1983).
Fig* 2.14 Wind field simulated with a background flow of 5-knotnorth-northeast winds•
Fig* 2*15 Wind field simulated with a background flow of 5-knotnortheast winds*
Fig. 2*16 Wind field simulated with a background flow of 5-knoteast-northeast winds.
Fig« 2.17 Wind field simulated with a background flow of 5-knoteasterly winds*
Fig. 2.18 Wind field simulated with a background flow of 5-knoteast-southeast winds.
Fig* 2*19 'Wind field simulated with a background flow of 5-knotsouth-southeast winds.
Fig* 2*20 Wind field simulated with a background flow of 5-knotsoutherly winds.
Fig- 2*21 Wind field simulated with a background flow of 5-knotsouth-southwest winds.
Fig* 2*22 Wind field simulated with a background flow of 5-knotwesterly winds*
Notes (Fig* 2,14-2*22) :-
1. A full barb in the wind arrow represents a speed of 10knots. A half barb represents 5 knots*
2. The numerical value, of the wind force is plottedalongside the wind arrow and is expressed to the nearestknot.
TABLES
TABLE 2.1 DIURNAL VARIATION OF WIND {KNOTS}AT TSIM BEI TSUI (1975-1982)
TABLE 2.2 FREQUENCY DISTRIBUTION OF LIGHT WIND SPELLSAT TSIM BEI TSUI DURING THE PERIOD 1975-1982
TABLE 2.3 DIURNAL VARIATION OF ATMOSPHERIC STABILITYAT TSIM BEI TSUI (1975-1982).STABILITY A = 1, B = 2,..., G=7
TABLE 2.4 OCCURRENCES OF INVERSION AT SHENZHENDURING ABOUT 80 OBSERVATION DAYS IN 1981-1982
TABLE 2«5 PERCENTAGE FREQUENCY DISTRIBUTION OF INVERSIONSWITH BASE IN SPECIFIED HEIGHT RANGES ABOVE KING8S PARK(1971-1980)
TABLE 2,6 UPPER-AIR CLIMATOGICAL SUMMARIES OF UPPER-AIR DATAMEASURED AT KINGgS PARK DURING 1971-1980.
TABLE 2*7 LIST OF MEAN' METEOROLOGICAL SITUATIONS SELECTED FORWIND FLOW SIMULATION USING THE 'TAPAS1 MODELS
PHOTOGRAPHS
Plate l.l Anemograph at the Tsim Bei Tsui Police post
plate 1*2 Radiosonde operation at Kingfs Park
Plate 1.3 Monostatic acoustic radar at Junk Bay
Plate 2.1 Topographic features surrounding the -Deep Bay air shed,
INTRODUCTION
As part of a collaborative work plan to protect the
atmospheric and aquatic enivornment of Deep Bay, the Royal
Observatory Hong Kong has examined the following aspects relatinc
to atmospheric transport in the areas-
i) Meteorological Observation
and ii) Meteorological Assessment.
This report covers the work carried out on the above topics*
The essential meteorological observation within the Deep
air shed comes from a weather station at Tsim Bei Tsui . The
station was set up by the Royal Observatory in 1975 to monitor
early indications of arrival of cold surges from the north* Other
supporting data are derived from observations outside tine air
shed. These include upper-air sounding records obtained at Kingrs
Park and monostatic acoustic radar records obtained at Junk Bay«
Section 1 of this report describes in detail the various
instruments, their operation , site conditions and data processing
of the .records. Section 2 presents analyses of various
meteorological parameters carried out with a view to constructing
a data base for further application studies of air pollution ir
Deep Bay, e.g. pollution dispersion and the air shed.8 s dispersive
capability.
Because of the steep and rugged terrain to the .h-outa of Deej
Bay, it is necessary to investigate the effect of topography on
the mean wind flow pattern in the air shed. For this reason/ wind
tlow simulations using an established model were carried out ana
the results are presented at the end of Section 2«
1. METEOROLOGICAL OBSERVATION
1*1 Equipment and Siting
1*1*1 Surface Wind Sensor at Tsim Bei Tsui
A Dines pressure-tube anemograph was installed at the Tsirt
Bei Tsui Police Post (Plate 1.-1) in January 1975. It is at e
height of 17-5 in above ground, or 43-7 ra above mean sea level.
The site condition has been described by Lara (1981)* The locatior
of the anemograph and the nearby terrain are shown in Fig. 1.1.
The site is well exposed to all directions but is slightly
obstructed to the southwest and west-southwest (Pig* 1.1).
The anemograph makes use of the difference of pressure set
up between two pipes * one of which is kept facing the wind by the
action of a wind vane, while the other is connected to a systen
of suction holes on a vertical tube. The ppressure dif f'erenential
causes the movement of a float carrying a pen, the height oi
which above the zero position is proportional to wind speed.
1.1.2 Upper-air Measurement Systems at King8s Park
The upper-air station at King's Park was established in 195]
arid is located on a hill about 1 km north of the 'Royal
Observatory (Fig* 1.2)* Twice a day* a free, unmanned balloor
carrying a radiosonde is launched for the purpose .of rueasurinc
the wind, pressure, temperature and relative humidity . in • the
upper atmosphere. Plate 1*2 shows an upper-air ascent being made
at King * s Park*
.During the period 1971-1980, upper-wind measurements'' were
made by means of a 30-ram Plessey WP2 wind-finding radar tracking
a Vacuum Reflex type 336 W corner reflector attached to the
balloon. The range and angles of elevation and azimuth were
determined at intervals of one minute. The wind at a given height
or pressure level was measured over an interval of 2 or 3 minutes
chosen so that the midpoint almost coincided with the instant at
which the balloon attained that particular height or pressure-1
level. The rate of ascent was approximately 6 m s
Upper-air temperature, pressure and relative humidity were
measured by means of radiosondes* Vaisala RS-13 radiosondes with
pressure, temperature and humidity sensors were used prior to and
until 17 November 1974* after which the RS-18 radiosondes were
brought into use. The RS-18 radiosondes provided a better
resolution in the pressure range of 100 mbar and above* The
various transducers in a radiosonde include a nickel-alloy
aneroid capsule for measuring pressure, a bimetallic thermometer
for temperature and chemically-treated human hair for humidity*
Radiosonde ascents were made using 0«7-kg balloons, while
rawin ascents were made using Q*5~kg balloons.
The Plessey WP2 wind-finding system was replaced by a
Vaisala CORA upper-air sounding system on 1 January 1981• At the
same time, the RS-21-12CN radiosondes were brought into use. The
CORA system makes use of the International OMEGA navigational aid
network which consists of several high-power VLF time signal
transmitters located in different parts of the world* A
transponder inside the radiosonde receives signals from three or
more transmitters and relays them to the ground station.. The
location of the radiosonde is calculated from the phase
differences among the relayed signals. The upper winas are
computed by tracking the radiosonde's flight. Pressure*
temperature ana humidity data from the radiosonde are sampled
every 6 to 9 s and transmitted to the ground station for
processing on a microcomputer equipped with a quality control
program and a 'significant point1 identification program* A
8 significant point8 at a certain level represents temperature
and/or humidity data (at that level) which are required for the
reasonably accurate reproduction of the radiosonde observation *
1.1.3 Monostatic Acoustic Radar at Junk Bay
In 1982i an Aerovironment 300C monostatic acoustic radar
(plate 1*3) was installed at Junk Bay (Fig* 1.2) on the roof top
of the Haven of Hope Sanatorium. The site is about 150 m inland
of the west coast of junk Bay and is about 30 m above mean sea
level. The electronic equipment for the radar system- was 'housed
in an air-conditioned shed, located also on the'roof.
The acoustic radar operates by emitting a sound pulse
vertically upward and then processes the echo which comes back
from the turbulent region aloft. It allows the detection of
turbulence structures, such as the height of the convectively
mixed layer and characterisitics of atmospheric waves and
layering.
The acoustic antenna (Model 302) consists of a vertically
pointing parabolic dish with a speaker mounted on a horn, and is
housed within a dense acoustic enclosure to cut out external
noise. The acoustic sounder operates at 1 600 Hz with a :pulse
repetition rate of once every 15 s* The pulse length is 200 ms,
providing a height resolution of 33 m. The maximum detectable
range is 1 000 m.
The central component of the system is a 300C transceiver-
display unit whose purpose is to continuously record the return
echoes on a chart recorder. In addition to recording at tne site,
the signal is also telemetered via a pair of private telephone
wires to another chart recorder (Model 322A) at the Royal
Observatory.
6
1.2 Operation of Meteorological Instruments
1.2.1 Observation Period
The anemograph at Tsim Bei Tsui has been in operation since
January 1975.
Routine radiosonde and rawin soundings were made at King's
Park since 1 June 1951 and 1 January 1955 respectively*
As part of the Junk Bay air shed study carried out by the
Air Pollution Meteorological Research Unit^ the operation of the
monostatic acoustic radar started on 1 December 1982 and was
terminated on 30 Novemeber 1983* The representativeness of the
observation period is discussed in the Final Report of the Air
Shed Meteorological Study at Junk Bay* prepared by the Unit in
1984.
1*2*2 Normal Operation of the Instruments
The pressure-tube anemograph at Tsim Bei Tsui is manned by
the staff of the Tsim Bei Tsui Police Post and maintained by the
Meteorological Instruments and Equipment Section of the Royal
Observatory* In addition to continuous recording on charts,
routine wind information is passed to the Royal Observatory by
the staff at the Tsim Bei Tsui police Post every three hours
during daylight hours*
The upper-air station at King's Park is also operated by the
Meteorological Instruments and Equipment Section* During the
period 1971-1980, upper-air wind speed; direction, temperature,
humidity and pressure were measured twice daily at 00 Z and 1225.
Two 'additional rawin ascents were scheduled daily at 062 and 18Z.
During the period 1981-1983, four radiosonde ascents were made
daily, at 00, 06, 12 and 182. The 06 and 18Z ascents were
additional ones made during the period.
The monostatic acoustic radar at Junk Bay was operated by
the Air Pollution Meteorological Research Unit, Royal
Observatory.
1.2.3 Calibration and Maintenance
Calibration of the anemograph at Tsira Bei Tsui is conducted
once every quarter* Routine maintenance is carried out once every
month* Emergency repair work is made on receiving reports of
equipment malfunctioning.
The maintenance arid emergency repair of the entire upper-air
measurement equipment are carried out by a technical staff
stationed at King's park. On occasions when the equipment is
unserviceable and the cloud base is sufficiently high, upper-
winds are determined by a pilot balloon with a single theodolite *
Prior to each radiosonde ascent, a 'ground check4 is
performed on the pressuref temperature and humidity sensors of
the radiosonde *
Calibration of the acoustic radar system was conducted
approximately once every month. Routine maintenance was carried
out at a frequency of about twice a week*
1,3 Data Processing
1.3.1 Wind Recoras
Hourly wind information is extracted manually from the
autographic chart of the anemograph and then transferred onto
computer carets* The information on the computer cards is
processed by the computer at the Royal Observatory into a
standard format and then stored on a magnetic tape.
1*3*2 Cloud Ooservations
Visual observations of cloud type and amount, and estimates
of the height of the cloud base are made at the Royal
Observatory. These cloud data are transcribed onto computer cards
before being processed by a computer at the Government Data
processing Agency. The data are then stored on magnetic tapes.
Because of the volume of -data, only the total cloud amount is
tabulate in 'Meteorological Results Part I Surface
Observations8 published annually by the Royal Observatory*
1*3*3 Upper-air Radiosonde/Rawin Records
Prior to 1981, upper-air information obtained at each
radiosonde/rawin ascent was transcribed onto computer cards
before being processed and quality-controlled by a mainframe
computer at the Government Data Processing Division (now the
Government Data processing Agency)• The processed information was
stored on magnetic tapes and published annually by the Royal
Observatory in ' 'Meteorological Results Part II -— upper-Air
Observations1,
Since 1981, upper-air data acquired by the CORA system is
processed and quality-controlled automatically in real time by a
minicomputer. The minicomputer produces coded messages containing
the data and relay them via telephone wires to the Royal
Observatory main computer for direct archival on magnetic tapes*
1*3*4 Acoustic Radar Records
The maximum operable range of the acoustic radar is 1 000 m.
Hourly mixing height values were extracted from the acoustic
radar chart records. During extraction, vertical wind and
temperature data obtained at King *s Park were taken into
consideration *
The mixing height is defined as the thickness of the
atmospheric layer through which pollutants are assumed to mix by
virtue of convection caused by daytime heating at the surface * It
is usually taken to be the height measured from the surface
upward to the lowest elevated temperature inversion. (A
temperature inversion is a stable condition in which the
temperature increases with height.) Temperature inversions
normally showed up on the acoustic radar as ground-based or
elevated echoing layers*
Extraction of data from the acoustic radar records was not
possible under the following meteorological situations:-
i) mixing layers exceeding 1 000 m;
ii) rain or showers; and
iii) windy conditions, with fresh winds or stronger.
As these situations normally result in efficient removal of
10
airborne pollutants from the ambient atmosphere, the mixing
height was given the value of the maximum operable range of the
instrument, namely 1 000 m. This renders a conservative estimate
of the mean mixing height.
11
2. METEOROLOGICAL ASSESSMENTS
2.1 General Climatology of Hong Kong
The climatology of Hong Kong has been described by Malone
(1977). It is summarized in the following paragraphs•
Although Hong Kong lies just within the tropics and is in
the same latitude as Honolulu, it enjoys a variey of weather
unusual in tropical regions. Seasonal changes are well-marked and
are due to Hong Kong's position on the southeast coast of the
Asiatic land mass. The cooling of the continent in winter and its
heating in summer give rise to seasonal monsoon winds on a very
large scale . These winds exert a profound influence on the
climate of south China.
The winter period in Hong Kong is loosely referred to as the
period from mid-October to early April. Starting from October, a
cold anticyclone forms over-Siberia and Mongolia (Fig. 2.1) and
normally reaches its maximum intensity in January, South China
experiences frequent cold outbursts of winter nionsoon during
which winds blow from the northeast quadrant* During monsoon
surges, the radiosonde ascent normally show a dry and stable
atmosphere aloft*
The period from mid-April to mid-May is usually termed the
'spring transition period', and is marked'by very changeable
weather. In March and April the continental anticyclone gradually
weakens and cold surges become indistinct and less frequent.
Incursions of warm moist tropical air from .the southeast become
more frequent* Since the coastal waters are still relatively
cold, the incoming warm moist air, produces widespread stratus,
' ' ' ' • ' ' ' . . - • - ' ' . ' . ' • ' " ' ' • • • 12"..' ' ' '•-" - -.:' : . : ; . . - . : / . . - ' • ' . - ",':
drizzle and fog.
Summer in Bong Kong lasts from approximately mid-May until
mid-September, but may be split into three fairly well defined
periods. From mid-May until June, trough ana light wind
conditions dominate over south China• Rain and thunderstorms
reach a maximum in June. By June, a deep depression forms over
the Indian continent* giving rise to warm and moist west to
southwesterly surface winds over the south China coast (Fig.
2.1) .
From mid-June to raid-August, tropical cyclones affect Hong
Kong with increasing frequency, although the summer monsoon
remains relatively persistent.
During the period raid-August to mid-September, trough and
light wind conditions return. Also, tropical cyclones become more
frequent.
Overall,, summer monsoon is less persistent than winter
monsoon.
The autumn transition period normally lasts from mid-
September to mid-October. During this period there is a rapid
decrease in precipitation* The cold anticyclone starts to develop
again over Siberia and Mongolia and there are weak outbursts of
cool air. The monsoon depression over India generally disappears.
During this period tropical cyclones reach their maximum
frequency, and then rapidly fall off in both frequency and
intensity*
13
2*2 Meteorological Data Bases
2-2*1 Surface Wind
Hourly wind aata obtained at Tsira Bei Tsui during the period
1975-1982 are usea. These are ID-minute means ending on the hour.
Unless otherwise stated,^ all mean winds derived in the analyses
refer to the vector means.
Hourly wind data obtained during 1982 at the Hong Kong
International Airport (Fig * 1*2) are used in the comparison of
light wind conditions* These are chosen because the station
exposure is good and the anemometer mast head is at a comparable
altitude .
The wind flow at Tate8s Cairn, which is 575 m above mean sea
level provides a good representation of unobstructed flow over
Hong Kong. Monthly and annual wind roses for Tate's Cairn are
used in the comparison of mean distribution in wind speed ana
direction.
A description of the site conditions of trie anemometer
stations at the Airport and at Tate8 s Cairn can oe found in Chen
(1975).
Monthly and annual mean speed-direction distributions of
winds measured at a hydroraeteorological station in Chiwan during
the period 1976-1980 have been supplied by the Guangdong
Environmental Protection Bureau. Chiwan is located on a peninsula
to the west of Deep Bay (near Ch1 ih-wan-rniao on plate 2.1).
Available information of the station indicates that it is located
on the slope of a hill and the surface flow there may not be.
adequately represented* . . . . . .
' ' . • • • . ' • • . ' : ' . • • . • • • • • • 14.:' . ;•'• - . . • . - ' • . ' " ' . ' • • ' • ' ' • • ' . . • '•'" . ' • . ' • : . • ' " • .
2.2 * 2 Cloud Data
As no clouu ooservations in the vicinity of Tsim Bei Tsui
are available, hourly cloua data ootaineci at the Royal
Observatory ciuriny the period 1975-1982 are useu. Tne clouci aata
consist of clouci type ana amount, and estimates of the height of
the cloua
2»2*3 Upper-air wind ana Temperature profiles
The Guangdong Environmental Protection Bureau has made
available vertical wind and temperature data ootained at bnenznen
City (Luonu District) during the period 1981-1982. Wind data were
obtained using Model CFJ-II optical theodolites ana temperature
data usin^ tooae! TK-II low-level sorides. Both the wina and
temperature were measured up to an altitude of about: 1 uOU ru.
During each season of the period, observations were made on about
20 days, at a frequency of three times daily: at around local
time 0700, 1300 and 1900 hours respectively.
For comparison purposes, upper-air wind and temperature data
obtained at King's Park on the same observation clays during 1981-
1982 are used.
2.2*4 Mixing Height
Hourly estimates of the mixing height at Junk Bay during the
period December 1982-Noveiuber 1983 are used*
Statistics of inversions detected during 1971-1980 using
radiosondes released at King's Park. (Li 1984)"; are also used. In
15
accordance with practice ^ 'cue worla Meteorological
Organization, an inversion is aefinea as a layer of atmosphere
with a temperature increase with height ana with a thickness of
at least 20 rabar .
16
2.3 Wind and Temperature Analyses
2*3«1 Monthly and Annual Surface Wind Roses
The annual wind rose for Tsim Bex Tsui is shown in Fig. 2.2.
For comparison purposes^ the wind roses for Tate8s Cairn (in 12-
point compass directions) and Chiwan have oeen included in the
figure* The wind rose for Chiwan shows apparent biases
towards occurrences of winds in the direction of the eight major
compass points.
At Tsim Bei Tsui, the prevailing wind comes from the sector
NNE-NE-ENE-E (47% annually). Easterly and northerly winds are
less frequent when compared with the winds at Tate's Cairn, This
is probably related to channelling effects of the roughly
northeast-southwest oriented mountain ridges in China and in Hong
Kong (Plate 2*1).
Winds from the southwest quadrant are relatively less
frequent when compared with those at Tate*s Cairn. As already
discussed in Section 1.1.I/ this is due to partial blocking by a
hill to the southwest of Tsim Bei Tsui* As noted, by Lam (1981)*
the general flow in the Deep Bay area is probably southwesterly
during some of the time when southerly wina is reported at Tsim
Bei Tsui *
Winds from the west-northwest occur as much as 5% of the
time* As will be discussed further in Section 2*4*2f this is
considered to be caused by onshore sea breezes during light wind
conditions* Onshore flow has the effect of recirculatixig
pollutants which otherwise would have been transported.away 'from
land by an offshore prevailing flow*
•'17' . ' • ' : . " ; - , - ' "• . • • • ' ; - . • • ' •
Comparison of the monthly wind roses (Pig. 2.3) suggests
similar observations to the above. Fig* 2*3 further reveals that
the general flow at Deep Bay is probably southerly or west-
southwest south-southeast winds are blowing at Tsim Bei
Tsuif particularly in the months of April to August.
The monthly wind roses in Fig. 2.3 suggest that the
anemometer station at Chiwan is sheltered from southerly winds,
which hardly occur at all*
Also, the average 101 occurrence, of westerly winds annually
at Chiwan is considerably higher than those at Tsim Bei Tsui and
Tatess Cairn. Inspection of the monthly wind roses (Fig* 2«3)
indicates that the westerly winds occurred mostly during the
cooler months with a maximum frequency of about 16% in December.
The reason for this is not immediately apparent * A further look
into the raw data and possibly the site conditions may be
necessary in order to explain this in meteorological terms*
2*3*2 Monthly and Annual Diurnal variations of Surface wind
The monthly and annual diurnal variations of surface wind
measured at Tsira Bei Tsui are presented in Fig* 2*4* The length
of wind arrows in the figure is proportional to the wind
strength* The following observations have been madie:*-
i) It can be seen that during the day in the months March-August,
winds generally veer (i.e. turn clockwise) and that during the
rest of the months the reverse is generally true* In' Section
2.4«2# an attempt is made to explain this phenomenon in terms
of the seasonal prevailing flow and local circulations due to
18
diurnal effects;
ii) The diurnal variation of the mean wind speed is separately
tabulated in Table 2.1f which shows different, distinct trends
between the period from March to September and the period from
October to February. During the first period^ the mean maximurn
wind speed occurs between 2 p.m. and 6 p.m. in the afternoon
and the minimum occurs between around midnight and 7 a«m* in
the morrving. During -the second period, the maximum' wind speed
occurs at around 10 and 11 a.m. before midday and the minimum
occurs at around 8 p*in» in the evening; and
iii) The maximum diurnal variation in the wind speed occurs in
May and June^ when there is a mean increase of about 4 knots
during day time. The minimum variation occurs in January and
February, when there is a mean increase of less than 2 knots
during day time.
In Section 2*4«2* attempts are raade to explain the phenomena
described in i) and ii) in terms of the seasonal prevailing flow
and local circulations due to diurnal effects®
As shown in Fig* 2*5* the maximum mean monthly wind speed of
7*2 knots occurs in March and the minimum of 5*2 knots occurs in
August and December.
2.3*3 Spells of Light wind
The annual mean wind speed of 5*9 knots at Tsim Bei Tsui is
relative low when compared to 7*6 knots at the Hong Kong
International Airport (victoria Harbour area).. ' ' ' ' ••
A comparison has been made of the' frequency of light wind
spells (i«e* duration over which the wind speeds ••/are less than 7
• • • • • • • • . ' ' ' ' ' . • / • ' . ' -19' • ' . ' ' • • • : • • - • > • • . • ' " • • : . - . . • . ' : ' ' • ' . • • ' ' •
knots) using 1982 data obtained at both stations• During data
extraction, a light wind spell is considered to be terminated
when the succeeding hourss wind is 7 knots or higher or when the
data is missing. Plotted on a double-exponential probability
paper, the cumulative probability of light wind spells (Fig. 2.6)
shows clearly that light wind occasions at Tsim Bei Tsui are more
frequent and usually last longer than those at the Airport.
Table 2® 2 presents the frequency distribution of light wind
spells at Tsim Bei Tsui during the period 1975-1982• Light wind
spells lasting more than 50 hours are most frequent during the
period November-January.
2-3*4 Seasonal Variation of Vertical Windand Their Comparison with GEPB Data
The seasonal variation of the vertical wind at King ' s Park
over periods in 1981-1982 coinciding with observations ' carried
out at Shenzhen by GEPB are given in- Fig* 2*7« Those for Shenzhen
are reproduced in Fig** 2«S* Apart from differences which are
discussed later on/ there is broad agreement between these two
sets of data* In generalf the predominant flow in spring, autumn
and winter is easterly and in summer is southwesterly. .The
consistency in the wind direction from surface up to about 200 in
suggests that surface wind data are adequate in describing the
wind direction within this layer.
Compared with data at King' s Park, easterly and east-
northeast winds at the lowest 200 m are relatively infrequent at
Shenzhen. The more predominant flow over Shenzhen is 'east-
southeasterly throughout the year>. While Wutong- Shan (Wu-t'ung.
• : ' . . ' - ' . ' - " • • • ' - - . 20 ' • • '• ' ' . . . ' " : ' : , ' ; / ' . ; - ' ' : ' • • ' - . ' ' . . : : V
Shan In plate 2«1) and a hill to its south may be a reason for
obstruction of- easterly flow towards Shenzhen, further
substantiation of this is required as. these topographic features
are about 10 .km from Shenzhen,
2*3.5 Seasonal Variation of Vertical TemperatureProfiles and Comparison with GEPB Data
The seasonal vertical temperature profiles at King's Park
over periods in 1981-1982 coinciding with observations carried
out at Shenzhen are given in Fig* 2*9. Those for Shenzhen are
reproduced in Fig* 2*10* Allowing for a difference of about one
hour in the observation times (e.g., 7 a..m. at Shenzhen and 8
a«m. at King 's Park), there is broad agreement between these two
sets of data.
It is observed that, throughout the year, the temperature
near the surface at King's Park (66 m) is slightly higher than
those taken at Shenzhen at approximately the same altitude* This
is probably due to the different degrees of urbanization^ hence
different degrees of temperature change in the two places. This
urbanization effect probably also accounts for the absence of an
average inversion at 8 p»rn* at Kinga s park during autumn^ whereas
at Shenzhen, an average nocturnal inversion is observed as early
as 7 p.nu Partly because of increased cloudiness during winter/
such an average inversion is not observed for .the ' winter
temperature profiles at these hours*
In view of similar land uses in Shenahen and in Deep Bay, it
is considered that vertical temperature structures•at, Shenzhen
are representative of the Deep Bay air shed* ' ;
. - - , . - •". "./ • -' ' • • .- - ' - : ' • ' • ' - 21' ' ' . . • : • ,' : • • ' • • ' • • • ' . . • • / ' • • : : - - . • • ' ' . ' :.;-, , "
2e4 Stability Analysis
One of the roost important parameters in assessing the
atmosphere's dispersive capability during a certain time of the
day is the atmospheric stability. Pollutants are readily
dispersed under an unstable atmospheric condition* Dispersion is
still possible under a neutral condition but gets progressively
more difficult as the atmosphere becomes more stable. When an
inversion exists, the vertical mixing of pollutants is severely
limited.
Estimation of the hourly atmospheric stability at Tsim Bei
Tsui is carried out using the conventional Turner's (1964)
method. This method is based on the consideration that stability
is dependent primarily on the net radiation and wind speed*
Without the influence of clouds, the insolation (incoming
radiation) 'during the day depends on the solar elevation! which
is a function of the time of day and time of year. When clouds
exist their amount and thickness reduce incoming and outgoing
radiation• In this method insolation is estimated from the sun's
elevation and modified for existing conditions of total cloud
cover and cloud ceiling height. At night estimates of outgoing
radiation are made by considering cloud cover and wind speed
only*
The sun*s elevation permits differentiation into daytime and
nighttime cases• The solar data for Hong Kong are given by
Peacock (1978)* in which/ for each day of the year, the solar
declination • as'well as the sun's elevation for the time of the
day are given. • :
22'
Turnerfs method divides stability into seven classes A to G,
with A representing the most unstable conditions, D neutral and G
the most stable. Stability classes for day time are A to D* and
for night time D to G« To facilitate computation, these classes
are assigned the values 1 to 7 for A to G respectively.
2«4*1 Monthly and Annual Variations of Stability
The monthly .and annual mean stability variations at Tsira Bei
Tsui are presented in Table 2*3* Over a 24-hour period, the
atmosphere is on the average most unstable at around midday*
Among the different months, it becomes most unstable during the
day , in around August and most stable during night time in around
December. The relatively stronger wind speeds in around March
results in a less unstable atmosphere on the average • for that
month.
2.4*2 Monthly and Annual Stability-Wind Roses
Stability-wind roses are constructed in order to aid, among
other pollution investigations, analysis of worst pollution
cases*
The relationship between the stability and wind (direction
and speed) is best depicted by plotting the stability-wind roses,
as shown in Fig* 2*11. In this analysis, the stability "has been
classified into three broad categories, viz* unstable (A-C),
neutral (D) and stable (E-G). The following observations are
noted s-
i) Under unstable conditions, light winds from the northwest
quadrant become prominent* Also, the occurrence of west-
• ' • • . • • ' ' . - • ' . ' • ' . • • • 23 •'" ' . . - - • . . . . . , ; , - - . • • • • ' • • ; ' ' . V . • : •
northwest winds far exceeds other winds from the same
quadrant•
ii) During the cooler months of November to March, winds from
the south are relatively infrequent unaer unstable
conditions when compared with neutral or stable conditions;
and
iii) During the cooler months, there seems to be more
occurrences of stable condition with winds coining from the
northeast quadrant•
The observation described in i) above indicates an onshore
unstable flow during day time (sea breeze)* with a preferred
direction from the west-northwest. Such flow is also evident from
time sequences of hourly wind at Tsiia Bei Tsui, especially during
light wind conditions- As land-sea circulations are 3-eiimensional
in nature, the impact of such effect on the local air quality
would have to be assessed in full by means of 3-dimensional wind
flow and dispersion modelling. However, this is outside the scope
of this report.
Point ii) above hints at a stable' nocturnal, offshore flow.
However, even if this exists at Tsim Bei Tsui it is not as well-
defined and also not as frequent as the onshore flow during day
time.
The stable conditions noted in iii) above are normally
associated with cool winter monsoon near the surface undercutting
the warmer westerly or southwesterly winds at higher level, thus
creating a temperature inversion*
Having identified a daytime sea-breeze circulation at Tsim
. ' . . • • • ' " . . • - ' '' . . ' - ' 2 . 4 - • - ' • . ' ' ' . ' . • . - ' - . ; V : ' • • : ' ' '
Bei Tsui^ it would be appropriate to offer here an explanation to
the diurnal changes observed in the wind direction, as noted in
observation i) of Section 2*3.2* Fig« 2.12 shows the resultant
wind field when a daytime sea-breeze flow is superimposed on the
prevailing flow at different seasons* The results indeed show
winds veering (i.e. turning clockwise) when the prevailing flow
is from the south or southwest quadrant during the warmer months
and winds backing (i.e. turning counter-clockwise) when the
prevailing flow comes from the northeast during the cooler
months *
Also, it can be s.een from Fig* 2*12 that, with the
establishment of a day-time sea bree.ze circulation, the wind
speed is decreased during the cooler months, but increased during
the warmer months. This, coupled with the fact that winds are
usually stronger during neutral conditions (see Table 2.3 for the
time of day when average neutral conditions occur), generally
explains observation ii) in Section 2*3.2*
25
2*5 Mixing Height Climatology
Pig* 2.13 depicts results of mixing height analysis for Junk
Bay (Koo et al. 1984). The mixing height is primarily derived
from acoustic radar records.
For all months! the minimum mixing height occurs during
night time and the .maximum in the afternoon .
Concerning the seasonal trend of mixing height variation*
the mean maximum' mixing height is as low as 426 m in February and
as high as 1 000 m and beyond in July* The mean mixing height is
low during the cooler months and high during the warmer months *
No attempt is made to' assess the effect of different
topography in Junk Bay and in Deep Bay on the mixing height •
However! for the purpose of modelling pollution dispersion, Aron
il983) noted in his studies of maximum oxidant concentrations in
a number of cities in United States that the mixing height has a
lower correlation to the concentration than other parameters such
as temperature9 inversion characteristics, geopotential height
and pressure gradient. On this consideration, it would appear
that the mixing height data obtained at Junk Bay would suffice
for modelling purposes.
As already discussed in Section 2.3«5# th^ temperature data
obtained at Shenzhen are considered to be representative of the
Deep Bay area. Inversion statistics at Shenzhen for local time
0700, 1300 and 1900 are presented in Table 2.4. At 0700 local
time, inversions are observed during more than 90% of the time,
irrespective of the season* of these, around 40% are ground-based
inversions, which are more frequent during summer and autumn.
26
Also,, at 1900 local time there are more ground-based inversion in
autumn than in other seasons* This probably accounts for the
average inversion appearing as early as 1900 local time in
autumn, as noted' in Section 2®3*5*
Also included are the statistics obtained from 0800H and
2000H radiosonde ascents at King§s park during 1971-1980 (Li
1984) which show a predominance in the occurrence of low-level
inversions in the cooler months (Table 2.5)* Within an altitude
of 600 m the majority of the inversions are concentrated in the
range from 360 m to 600 m.
Apart from ground-based inversions which are normally
results of radiative cooling overnight, inversions observed in
the cooler months are usually caused by the cool winter monsoon
undercutting the warmer westerly or southwesterly aloft* This is
shown in the upper-air climatological summaries at King's Park
(Table 2*6).
27
2*6 Model Simulation of Wind Flowover the Deep Bay Air Shed
2«6*1 The Topographic Air Pollution Analysis System (TAPAS)
To study pollution transport processes in the Deep Bay air
shedf it is necessary to characterize the local wind flow. The
topographic "features surrounding the air shed is such that
deviations from the prevailing broad—scale flow are possible in
the vicinity of hilly terrain• In the absence of a comprehensive
network of anemometer stations in the air shed, model simulation
is often employed to study the effects of terrain on air flow.
Such simulation can either be 'physical modelling., i.e. putting a
scaled model of the topography in a simulated aerodynamic
environraentf or computer modelling! i»e* using using numerical
fnethods to solve the dynamic equations which account for as many
as possible various atmospheric processes required to adequately
describe pollutant transport phenomena. Physical modelling is
normally cost-prohibitive* For this reason, therefore* computer
modelling remains as the only alternative* As in the previous
junk Bay study (Koo et al, 1984), the computer models of the
Topographic Air Pollution Analysis System (TAPAS) organized "by
the Colorado State University are found to be suitable. With the
appropriate input, these models provide- estimates of the terrain-
induced wind flow (speed and direction) and pollution plume
trajectories* These are important factors in pollution
dispersion* The results would allow adjustments to be made when
the more rudimentary straight-line-trajectory dispersion models
a r e -used, ' . . . - • . - . . ' - - " . . ' • . ' ' • • ' • . ' * • • • - : : ' • . • • •
28
Also, the wind simulation results are given at grid points.
It is thus possible to interface them to a topographical
dispersion model*
A full description of the TAPAS models can be found in
Fosberg et al. (1976).
Results of wind field provided by the models have undergone
validation in the United States (Fosberg et al. 1976) which
provides indication of their accuracy* Separate validation using
wind data from a number of surface stations in Hong Kong exhibits
a similar degree of accuracy*
Specific data required by the models are the background wind
flow, temperatures and contour heights at two specific pressure
levels* as well as elevation and roughness length of the
underlying surface for all computational points* The number of
grid points are 1024 (32 x 32) and the' grid size used is 1 km*
2.6.2 Model Results and Their Interpretation
Several meteorological conditions typical of the mean
situations in Hong Kong have been selected for simulation* In
particular, light winds are used because these are normally
associated with poor dispersion conditions and ..because the mean
wind at Tsim Bei Tsui is about 6 knots. pollution transport will
be more efficient in the case of stronger winds*. In-the choice of
cases, due considerations have been given to prevailing flows at
Tsim Bei Tsui. The cases are listed in Table 2.7. Typical
resultant wind fields are presented in Pigs. 2.14 to 2.22 and
represent winds at 10 m above ground, in the Figures, a full barb
29
stands for 10 knots and a half barb stands for 5 knots. The
numerical value of the wind force is also plotted alongside the
wind barb,
In relation to air pollution aspects, the assessment of
topographical effects on the wind flow is based on two main
considerations:-
i) whether there is any reduction in speed; and
ii) whether there, are significant deviations from the mean flow
resulting in localized, circulation.
The former will result in poorer pollution transport and the
latter is conducive to local stagnation conditions *
Resultant wind fields as presented in Figs* 2*14 to 2*22
show virtually undisturbed flow over the relatively flat area in
the vicinity of Tsim Bei Tsui• However s strong topographic
control of the wind pattern is observed near terrain features. In
general, stronger winds 'are observed on the windward sides of
hills and ridgetops, while depressed wind speeds are simulated on
the leeward sides.
During 'the cooler months with light winds from the northeast
quadrant, it can be seen from Figs. 2*14 to 2*18 that over the
Hong Kong side the flow is dominated by Tai Mo Shan and, in
general, areas within the air shed which are affected most by
stagnant flow and reduced wind speeds are• :-
i) the area bounded by Kai Keung Leng, Tai To Yan and
Ma On Kong; and
ii) Tuen Mun.
Less severely affected are Nan Shan (China) and "Tanglang Shan
(China) and the hilly area to the north of Castle Peak*
- ' • • • •-" • ' • " . ' ' . - - ; - : • • " ' • 30',. - • - - ! - ' - . ' ---::••:--. • : • - . •"...:.'': '': .';:/-
During the warmer months with winds from the southern
quadrant, resultant wind fields presentee! on Figs. 2.19-2.21
indicate that the area i) above is also most affected. Nan Shan
(China) is less severely affected, Tuen Mun is affected only by
westerly winds (Fig. 2.22)*
In areas where the effects of topography on the prevalent
flow are appreciable, the above model results will form the basic
input to a variable-trajectory dispersion model. The model will
provide quantitative estimates of the pollution impact due to
identified sources inside or outside the air shed* However, this
is outside the scope of the present report.
31
3. CONCLUDING
Meteorological analyses have been carried out for the Deep
Bay air shed based on available data collected by the Royal
Observatory.
The prevailing flow in the area is found to be different
from that of other locations outside air shed» The flow is
characterized by winds from the northeast quadrant during the
cooler moriths and by southerly winds during the warmer months.
During day time there is an onshore sea-breeze component from the
west-northwest direction at Tsim Bei Tsui.
The onshore flow is a 3-*dimensional phenomenon and has the
effect of recirculating pollutants over which otherwise
would have been transported away from land by an offshore
prevailing flow. The full effect on the local air quality would
have to be assessed by means of appropriate 3-diioensional
modelling• However, this is outside the scope of this report*
Drainage flow during night time is not apparent from the
available data*
Comparison with records at the international Airport
indicates that the mean wind speed is lower and that light wind
spells are more frequent and normally last longer at Deep Bay.
These are considered to be factors that may cause poor
ventilation condition in the air shed,*
In the diurnal cycle, dispersion'of pollutants is especially
limited in the early morning9 when inversions are,observed more
than 90% of the time throughout the'year* Of these, about 40% are
ground-based inversions* Under such conditions, vertical mixing
32
of pollutants from near-ground sources will be severely
restricted.
Findings on the seasonal variation in the atmospheric
stability^ wind speed, mixing height and the number of light wind
spells all indicate less favourable dispersion conditions in the
early winter months than in the summer months* However, the
maximum mean wind speed occurs around March and this suggests
slightly better ventilation during the late winter months*
The rugged terrain in soEie parts of the air shed warrants a
simulation of the year-round spatial, wind distribution by the use
of an established computer model. The model output reveals that
the steep terrain in the vicinity of Tai Mo Shan causes the
dispersive capability of the southeastern part of the air shed
near Ma On Kong and Kara Tin to 'be severely limited as a result of
the generally depressed wind speed and stagnation flow in the
area throughout the year *
It is "believed that the collected data and analyses
presented in this report will form an adequate meteorological
data base and provide a framework for future pollution
investigation and dispersion modelling work*
33
ACKNOWLEDGEMENTS
Thanks are due to the Guangdong Environmental Protection-
Bureau for making available the relevant meteorological.data at
Shenzhen and Chiwan«
The authors are indebted to Prof. W.E. Marlatt, Dept. of
Earth Resources, Colorado State University, who kindly provided
the TAPAS computer models*
REFERENCES
Aronf R,
Chen, T.Y *
Fosberg, M»&«, 1976W. Marlatt andL. Krupnak
Koo, E., 1984B * Y. Lee andC.M* Tarn
Lam, C. Y.
Li, T.S.
Malone, D.J.
peacock, J.E*
Turner, D.B.
1983 Mixing height — an inconsistentindicator of potential air pollutionconcentrations, A tin. Environ,, vol. 17,pp 2193-2197*
1975 Comparison of surface winds in Hong:Kong, Royal Observatory Technical NoteNo, 41*
Estimating airflow patterns over complexterrain,. Forest Service Reseach PaperRM-162, U*S* Dept* of Agriculture.
Final report of the air shedmeteorological study at Junk Bay,Royal Observatory Occasional paper(to be published).
1981 A preliminary report on themeteorological conditions in the DeepBay area, Royal Observatory OccasionalPaper No. 47 (restricted).
1984 Hong Kong upper-air climatologicalsummaries :•1971-198O, RoyalObservatory Climatological Note(to. be published)*
1977 Hong Kong Forecasters' Manual/ RoyalObservatory Forecasters1 Note .No* 2.
1978 Solar data for Hong Kong, RoyalObservatory Technical Mote No'. 14.
1964 A diffusion model for an • urban area/;J. Appl, Met;, Vol. 3, pp 83-91V
34
Fig. 1*1 Tsim Bei Tsui anemometer locationand the nearby terrain*
*' ^ ~
.' '* 4 •, i« Vf / , ,P- «' '"'i '-'"
^ Cf ^"A. '.JsTarfftlN.. *'''
t*fmww&
J IlHong KongInteratLtiona
ROYAL OBSERVATORY HONG KONG
Fig. 1.2 Locations of meteorological stationsmentioned in this report.
r Hof 10 I 20
H I G H
a* LOW
type (HE)6 IBB. 1948
Southerly type(S)27 JOKE 1948
Fig. 2.1 Typical surface patterns for northeast monsoonin winter and for southwest monsoon in summer.
s
7-16 1 7 - 2 7 ^ 2 8 IN KNOTS
Bei
w-Chiwan
-"- E
Fig. 2.2 Annual wind roses for Tsim Bei Tsui (1975-82),-n^.u^'1.^ r»^4V^ /.I .Q*71-.fl'fl \ an/i nHi^yan M
Tote's Cairn
Tsim Bei Tsui
T f T
C hi wan
V
0 10 20 30 40 50 */,
2&3 Monthly wind roses for Tsim Bei Tsui (1975-82)fTatess Cairn (1971-80) and Chiwan (1976-80).
IN IN 9N 4N 8N 6N 7M SH OH ION i«4 I8H S» 14N S« SSH |7N tiff SON f«l
JAN
FEB
HAR
APB
NAY
/
\ \ \ \ \
T T / t ^ ^ ^ ^ ^ ^ ^ ^ \AUG
SEP
OCT
NOV>s >s s s s ^ ^ / / / / / ^ ^ • ^ ^ ^ ^
DEC
10 20 knots
Fig. 2.4 Diurna l variat ion of surface windat Tsim Bei Tsui (1975-1982).
oc
J£~ 4•o
XIC
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Fig. 2.5 Monthly mean wind speed at Tsim Bei Tsui (1975-1982).
Hr
40
SO
10
„_
;- • -
„
.:
—
-
-.
— .,.-
,1 * 5 \ 0
: ill 1 IlllllFig. 2*6 Curr
atA tr
1 i
i 1 - ; - • • - • • •
1
jj,} - !J~
-jj
• • •
"""-"" - - . . , . -. .. — „ - . . - - ,
Lj^jJal^5 10. 20 30
lllllllHIIulative probahTsim Bei Tsuiport during 19
j; * "*
* |
i *
i . i ~
1 • ! : • • - .
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9 9 9
Bei Tsui
InltrnatAirport
PROBABILITY
Spring Summer
-1-320
960
840
720
660
MO
420
360
240
120
66
Heirht(m)
v
A
H
3 *
2
2
2
2
2
0
0
V.NW
5
5
5
v.5'
3
3
2
2
2
0
0
NW
1020 1
960 1
0.10 o
Y20 0
6bO 0
540 0
420 0
360 0
240 0
120 0
66 0
Height fe(m)
10
110
0
0
0
0
0
0
HW
106 10
10 15\ 80J
o
11
11
11\.J
11
11
151515
6\15 10 1.0 10 ir 138 "10 16\J) 11 13 11
8 8\11 10 16^15 1
N' NN1 ME E ESE SE SSE S SSW SW
Autumn
1
0
0
0
1
1
0
0
0
33
0
0
1
1
1
1
1
1
0
3
3
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
5
2
2
2
0
2
2
2
2
2
3
2
3
3
5
5
5
3
3
3
3
1020
960
840
720
660
540
420
360
240
120
66
W Height Vf'NW NVi NNVi(m)
S fO
M Mm MB- SHE E ESB SE SSI S
. 2 . 7
0
0
0
0
0
0
0
0
0
0
0
SW WSW W Height(m)
0
0
0
0
0
0
0
0
0
3
3
0
0
0
0
0
0
0
0
0
1
1
1020
960
840
720
660
540
420
360
240
120
66
0
0
0
0
0
0
0
2
0
0
0
/^8 12 15 M/2y
8 8 18 15 18
KNE NE EH1 E ESE SE
Winter
tO '012 7 10 13 I 7 10. .15
17
15
15 12 7 2 0 1 3 18
2 12 1.2 18) P7 15
7\15 7 22 18
8 10 1 3 2 0 20 17
22\17
7
7
8
8
8
7
10. n*""™""-r
6
6
/0 28 110 10
8/
/3
11
11
14
y
A"8
8
6
4
7
7 8
7 6
10 6 //
10
10
10
10
10
11
10
0 2$26
28
28
28
28
26
25
10 51
6
6
6
6
7
7
V11 rf 14""'
11 10 19 /
11 10 19
>E SSE S "SSW SW WSW
22
m HNW N NE E ESB SE SSE S SSW SW WSW
Seasonal percentage distribution of upper-air.wind direction at King ' s Park, 1981-1982.
Spring Slimmer
h( m )950
850
750
650
550
450
350
250
150
50
h( m )950
850
750
650
550
450
350
250
150
50
WNW NW NNW N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW N NNE NE ENE E ESE SE SSE S SSW SW WSW W
Autumnh
(m)950
850
750
650
550
450
350
250
150
SO
Winter
WNW NW NNW N NNE NE ENE E ESE SE SSE S SSW SW WSW W
17 16 ,1 IS 15 i*"f3 19 2
WNW NW NNW N NNE NE ENE E ESE SE SSE S SSW SW WSW W
Fig, 2.88 Seasonal percentage distribution of upper-airwind direction at Shenzhen, 1981-1962-
SPRING
020
960
900
840
780
720
660
BOO
540
480
420
360
300
240
180
120
66
0
OOOOZ0600Z1200Z
12 13 14 15 16 17 18 19 20 21 22 23 24 T(*C)
z(m)1020
960
900
840
780
720
660
600
540
480
420
360
300
240
180.
120
66
0
SUMMER
. * . . « -*.— » «08H 20H 14H
-I L 1 L.19 20 21 22 23 24 25 26 27 28 29 30 31 T(fflC)
2m)020 -
960
900
B40
780
720
560
BOO
540
480
420
360
300
240
180
120
66
0
AUTUMN WINTER
\08H 20H 14H
16 17 18 19 20 21 22 23 24 25 26 27 28 T(*C) 19 20 21 TC*C)
Fig. 2.9 Mean seasonal vertical temperature profilesat King's Park, 1981-1982.
h(m)
1000
900
800
700
600
500
400
300
200
100
Surface
h(m)
1000
900
800
700
600
500
400
300
200
100
Surface
h(m)
1000
900
800
700
600
500
400
300
200
100
- Surface
07:0013:0019:00
Autumn Winter
13 14 15 16 17 18 19 20 21 22 23 24 (eO T 21 22 23 24 25 26 27 28 29 30 31 32 33 ( e C) Th
(m)1000
900
800
700
600
500
400
300
200
100
Surface17 18 19 20 21 22 23 24 25 26 27 28 29 30 POT 11 12 13 14 IS 16 17 18 19 20 21 PC
Fig* 2.10 Mean seasonal vertical temperature profilesat Shenzhen, 1981-1982*
WinterPrevailingNE flow
/ Onshore flowfrom WNW
Resultant
SummerPrevailingSW flow
Onshore flowfrom WNW
Resultant
Fig. 2.12 Resultant flow when daytime onshore flow issuperimposed on the prevailing flowduring winter and during summer.
DEC1982
JAN1983
FEB
MAR
APR
MAY
JUN
JUL
Itsr 400H200
AUG
SEP
OCT
NOV
1 2 3 4 5 8 7 8 9 10 11 12 13 U IS 16 17 16 19 20 21 22 23 24 IHOURIJ-J~-J-JL~J--a^—L-JL-JL.JL-J l^J^±^J^
•827
371
529
,422
MONTHLY MEANHEIGHT Cm)
366
258
211
267
218
342
427
441
418
437
420
331
MEAN DAILY
Fig. 2.13 Diurnal variation of the mixing heightestimated from monostatic acoustic radarrecords at Junk Bay (1982/1983).
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
y
y y
y, yJ J J
(\y3§9 /
J , x20Q300^
^3"
,300
f200
y
<10Q-
14
,/ ,/ a/ a/ a/ a/ a/ a/ a/ 7
,/ ./ aTV a/ =/ a/ a/ a/ a/ a/ a/ /<_
s/ a/ a/ A/ a/ a/ / a/ / ,/ a/ a/
y a/././
a/ y y y
y,/ y
100
6/ 6/ 5/ 4/ 5/ 5/ 4/ 6/
5/ y y ,/,/ y
5/ 4/ 4/ 4/ 4/ 4/ 4/
4/ 4/ 4/ 4/ 4/ 4/ ^
/ / >/ /'a/v
y / j y-y/ y
4/ 4/ 4/ 5/ 5/ J *f- J- h h f- f*F
4/ 4/ Z !/ 5/ 4/ ,*5/
V
/y
y y
r/VY
Oa//
y
y.
/ / / BEEP BAY/ / /4/ 4/ 4/ 4/ 4/ 4/ 4/ 4/ 4/ 4/ X< y ,/L/
shear4/ 5/ Jq)
XtaonartShanr?
£/ 4/ 4/ 4/
4/ 4/ 4/
y / y y y
4/ 4/ 4/ 4/ 4/ /4/ 4/ 4/
4/ SW 4/ 3/( 3/ 3/ 3\
\C^hV N100 ; ,X, 4Xxf?/fring/ T O O -
/La/4/ y 4.
JOO
4/ 4/ 4/ 4/ 4/ 4/ 4/ 4/ >
4/ 4/ 4/ 4/ 4/ 4/ 4/
4/ 4/ 4/ J J 3/X
24 (
25 (
/ Z - J /5/ 5^«i0h4* ar«4iri
a/ a/ a/ ./y y j jy a/ aA J
t f f""fir*« 4/ 4/ 4/
4/ 4/ 4/ 4/
4/ 3/ 2/
'/ /fM" / A4 / 4 / 1 4/ 4/ 3/ 2/
,A . A- i y
/K7 a/),/ AfC^
A/ .AA.XlU a/
^y xy.ng/v-5/ y / 3/\ (
200'
rti
\i10 0>
T
7
a/
u- X
?£!<
F« Tuan Mb
\)2t)0
M/t
>4A ,/
y j ia A , /
a / \
y,
r20Cj ,x.
y
3ng
*n^an^
Cil't
aoq13/
15/
900oF'
700feoo^
11\ fjl' ' 1 0 / 12'
,%e>S^orf/9/ TH \45\ /ytf
/30p
"Voq
NHedla.y/ / 4-. .. ,">y;11*//^7
s/ ./v,/./ /y yt
iLrfiCh^ I 13/ ^12/iOO
\30Q,
71 18 *" y r>6o z.1
a/^7^V/IUIj;H'H9
Fig. 2,14 Wind field simulated with a background flow of 5-knotnorth-northeast winds.
8 9 10 11 I'd 13 14 15 16 17 18 19 20- 21 22 23 24 25 26 27 28 29 30 31
, 5/5/5XI CJ • >-J' *•!'
X9XaX8 /5/X5X5X5/5/5/5// Bx ax ax ax ax sx
X5X5X5/5X5X5X
X X^l5/ 4/ .' (b a
X X X XX 4X 4X 4X 4
/ / x x^ 4/1 4/f 44
O 4/ 4/ 4/ 4/
4/ 4/ 4/ 4/
Fig. 2.15 Wind f ie ld s imulated wi th a background f low of 5-knotnortheast winds .
8 9 10 11 12 13 14 15 18 17 18 19 20 21 22 23 24 25 28 27 28 29 30 31
Fig. 2.16 Wind field simulated with a background flow of 5-knoteast-northeast winds.
10 ii 12 13 14 15 16 17 13 19 20 21 22 23 24 25 26 27 29 29 30 31
Fig. 2.17 Wind field simulated with; a. background floweasterly winds.
of 5-knot
5 0
10 11 12 13 14 15 24 25 26 27 23 23 30
Lau Fan Shan
Fig. 2.18 Wind field simulated with a background flow of 5-knoteast-southeast winds.
10 li 12 13 14 15 18 17 IB jg 20 21 22 23 24 25 26 27 ij«
( i , ()v
hoo , ' ,G i ) 5v 4 v
5 f5 v
o
"1M \°\ YA4 x vjf' - »
•\ ^tvV'\•\ \ \ r\ \\ ;\ 5\ \ \ s\ ;\\v\ v\5\\ \ \ \
10.,
B \ r \ H v R V
x 2 Q O .30Q
<&
,300 2£Q
20(3"tanoyShciF
\ \
<\ -\ A A ^ -7
\ \ \ !\ 'I )\ \ \ 5\ '\ '1 }\ \ "\ '\ \ \ 1
S 300 X
^o^r- looA
V)oo1 ' F
\ \T
\'\:\ \ \ \ \' XO.4
\ V'*\i/?;,"\6\ 5\ YN..:>, '•A M ( !" , » *> ' f') 1
\
\\
\
I A\•\5\
v\*\ ^ «\ «^ <\ >v
\ \ \ \ \ \ \ '\h
' ' \ \V\V
-\ ;\ ;\ ;\ ;\ ;\\V\\v\
\ i.-
, 3 - / ™ 9 < -\T
\ \ \ \ \ \ \ \ X A X \ \4\ 4\ 4\ 4\ 4\ 4\ 4\ 4\ 4\ 4\ Vv. X^5 4\ / 4\\ \ \ ^DE^P ^>AY\ \ \ \ T A i ^
\ \ \ \ \ \ \ \ \ \ y v\!\ \ \ \ \ \ \A \ Y\ 5\ "T\A A \ '» A \ fc ._. A •. • A .. • _ . A A A A5y 5v 4v 4x 4» 4v 4,7 ^\"?^ \X \ >5\ 4 \ j ^\
x x x x x VQU Pori SiXon ^i/ ^ ^' A X A
3, r)
16
-200") .N\ 5l '**\ A A \ \ \ \ .swjusM . * :4 A A A
\ \ \ \ \ \ Y V\ \X\\
24 c
25 (
29 t
\ \ \ji artgin mt^rti
A A A
\ \ V'\ \s\\ 7
\ \ \\ .\"R Congi
V \<a<n TirX-ry
\5, 5V 5X
5\ 5\ 6,\ \ 5\ \ ;\ 13, Ja"
VTueri Mur
'' ieak
-700reooj
#0 ^'
Tap Shek ^00300 5.
31 o\ \ \ \c\ \ \ \ \ \ \ \
0 30
Fig. 2,19 Wind field simulated with a background flow of 5-knotsouth-southeast winds.
10 11 12 13 14 15 16 17 IB 19 20 21 22 23 24 25 26 27 28 30 31
5, \ 4, } \A 4 5/ \4\ 4 4 4, „ 5,
hl' 1 ;\U, in4 i 'JaJ
" } 1 J 1 ]
] "j ] 1 17? 1
i
/ > / < >/ 7 (>zo°/ / W
J J
31 (
Fig, 2.20 Wind field simulated with a background flow of 5-knotsoutherly winds.
10 12 13 14 15 18 17 IB 19 20 21 22 23 24 25 28 27 28 29 30 31
7 ; °
n ) 1 1\ 5/ 5/ 5/ 6/ 5/ >\ 7 7 7 7/0 /•'
/;;;;; 7 ; ;v; j7 ;; 7 ) 7; 2.2, s )
o5. 5yH*iflhls are^in mt*r*s 4
7 7 * /
rrrrj
W i n d f i n l d n l i T W l n t r > d w i t h n bnak . j rmmd f l a w o f '5-knotsouth-southwest winds.
6 7 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Fig. 2.22^ simulated with a background flow of 5-knot
Hour
Month
Jan
Feb
Mac
Apr
May
Jun
Jul
Aug
Sep
Dot
Nov
Dec
Tear
10 11 12 15 14 15 16 1? 18 19 20 21 22 23 24
5.4 5.5 5.4 5.8 5.6 5.8 5.9^6.0 6.1 6.4 6.1\5.4 5.5 5.4 5.6 5.8
5.a/ClN\5.9/C?\5.9 5.9/6.2 6.1 6.6/7~72\6.6 6.1 6.1 6.3 6.2 6.1
5.5 5.6 5.3 5.3
t.5 6.2_6.0 5.9 5.9 6.0"1>. 7 s 7.8 8.0 8.1/7
'"57J) 4.2 4.3 4.1 4.3 4.3 4.7 \.1 5.4" 3 6.1 6.4 6.6\7.1 7.4 7.2
4.7 4.7 4.3 4.Q 8)4.3 4.3 4.?) 5.4 5.3\6.1 6.4 6.8/7.5 7.5 7.7
5.2 5«8 5.6 5.5 5.8 5.7
4.1 4.4 4.0-^5794.2 4.1 4.5 4.5
4.9 4.9 4.7 4.9 4.9 4.8 5.0 6.
5.2 5.3^5.04.8 5.0 4.8 4.9 6.0 6.7
7.4 7.5 7.5 7.5
5.2 5 . 5 7 ^ 6 . 3 6.5 6.7
.1 6.8 6.7 6.7 6.4 6.7 6.97.~ 6.8 6.9 6.6 6.6 6.3
5.0 5.5 5.3 5.5 5.6 5.9 5.6 (6.1 6.8(7.3/6.5/5.5 5.2 5.5 5.6 5.9
5.4 5.1 5.0 5.2 5.1 5.5 5.0 5.9\6.4 6.7 6.5(5.8 5.2 5.2 5.1 5.3
5.1 5.3 5.2 5.3 5.2 5.4 5.4 5.7 6.1 6.6 6.7 6.5 6.6 6.7 6.8 6.8 6.9 6.6 6.2 5.7 5.6 5.5 5.5 5-4
TABLE 2.1 DIURNAL VARIATION OF WIND SPEED (KNOTS)AT TSIM BEI TSUI (1975-1982)
Month
No. of Hours
0-10 11-15 16-20 21-25 26-30 51-35 56-40 41-45 46-50 ^51 Total
Jan
Peb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Mov
Dec
65
82
77
77
85
75
77
75
87
81
86
76
29
51
22
2?
35
52
52
32
28
52
55
24
20
15
16
15
15
14
6
13
10
15
18
22
7
9
3
12
6
6
6
7
6
8
10
10
4
5
5
4
5
3
1
7
3
2
3
2
5
5
0
0
4
1
1
5
3
2
5
1
2
3
0
0
1
1
0
0
1
1
4
3
1
1
1
0
1
0
0
4
0
1
1
1
2
0
0
0
0
1
0
1
1
2
1
4
3
0
1
0
0
0
1
0
0
3
3
3
138
147
123
133
152
133
124
142
139
147
166
146
Year 941 359 177 90 40 50 16 11 12 14 1690
TABLE 2.2 FREQUENCY DISTRIBUTION OF LIGHT WIND SPELLSAT TSIM BEI TSUI DURING THE PERIOD 1975-1982
Hour
South
Jan
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
HOT
Dec
Year
8
5.4 5.5
5.1 5.1
5.0 4.9
5.0 5.1
5.4 5.4
5.4 5.4
5.4 5.5
5.6 5.5
5.5 5.5
5.4 5.5
5.4 5.5
5.5 5.5
5.2 5.5
5.1 5.0
4.9 4.9
5.0 5.0
5.4 5.4
5.4 5.5
5.4 5.4
5.6 5.5
5.5 5.5
5.4 5.5
5.5 5.5
5.5 5.5
5.2 5.2
5.1 5.1
4.9 5.0
5.1 5.0
5.4 5.5
5.5 5.4
5.5 5.5
5.5 5.5
5.5 5.4
5.5 5.4
5.5 5.5
5.5 5.5
10 11 12 13 14 15 16 1? 18 19 20 21 22 25 24
41 5.2JJ5.5 5.5 5.1 5.0 5.0 5.0 3.1 3.4 5.
1 5.'0 /5.6 5.7 5.4 3.5 3-5 5.5 5.5 3.5 3.
/4.3/3.7 5.7 5.6 5.5 5.5 5.6 3.7 5.7 3.7 \.1 4.8 47
/%7 5.5 5.5 5.1 5.1 3.1 5.4 3.5 5.7 5.8 5.8\4«8 4.0
4
5.6 5.4
5.5 5.5
5.5 5.1/f f \
5.5 5.8 5.7 5.8
2.8 2.9 2.8 3.0 5^0 3.5 5.7 5.7 5.8
2.6 2.7 2.7 2.8 2.8 \5.2 5.6 5.7 5.8
5.5 5.'0 2.6 2.4 2.5 2.4 2.7/3.1 3.5 3.5 3.7
3.4 5;0-^S7ls\2.6 2.6 2.5/5T2 3.2 3.5 5.6
4.8 5.
4.8 510
.5 5.2 3.1 3\0 2.7 5.'o—5.0 3.1 5.2 3.6
3.5 5.0 /2.9 2.7 2.6 2.7\5.5 5.2 3.7.
5 5.5U5.4 5.0 5.0 2.8 2.6 2.7«>" ly X.<«
5.1 5.1 5.6
,575 5.6 5.6
5.4 5.5 5.6
5.7 5.9 5.9
4.9 5.0
5.0^5.2
5.
5.5 5.5 5.5 5.5 5.5 5.5 5.5 4.1 5.4 5.1 5.0 2.9 2.9 3.0 3.5 5.5 5.6 4.5 5.1 5.2 5.5 5.5 5.5 5.5
TABLE 2 .3 DIURNAL VARIATION OF ATMOSPHERIC STABILITYAT TSIM BE! TSUI (1975-1982).STABILITY A = 1, B = 2 , . . . , G=7
^-\TiiaeHt (mj\.
0-49
50-99
100-149
150-199
200-249
250-299
500-549
350-599
400-449
450-499
500-599
600-699
700-799
800-899
900-999
1000-1099
Total
Ho. of Oba
Bo. of Obewiifa ianrecgi
Spring
4331
11
5110
4
5
1
1
0
0
29
21
n19
07 h
Sassier
10
60
510
0
1101
1
1
2
1
0
28
19
18
tt*feUBD
11552
1
0
0
2
1
42
2
5
0
2
0
58
21
21
Winter
7411
2
2
1
2
2
1
5
1
4
2
1
0
54
20
20
pring
1
0
01
0
0
11401
1
5
0
0
0
15
19
10
13h
SdSffi^E
012
0
1
300
0
0
2
1
1
0
0
0
11
18
7
totaeaia
0
0
0
0
0
0
0
10
0
0
0
1
1
1
0
4
H
5
f
Winter
0
0
0
0
0
0
10
110
1
1
1
4
1
11
17
10
Spring
12
0
1
501
552
1
2
2
1
0
0
24
20
16
19b
Summer
0
0
111010
0
0
5
0
1
2
0
0
10
22
6
tataim
11
1
1
1
1
1
1
2
1
1
0
0
1
1
0
1
24
19
17
Vdneber
3551
0
01501
3
2
1
1
1
0
23
19
15
TABLE 2.4 OCCURRENCES OF INVERSION OBSERVED AT SHENZHENDURING ABOUT 80 OBSERVATIONS IN 1981-1982
OF ! 0600 AND 2000f 0000 AND 1?00 H
JAM FFH HAY JIIN JHL AMG SFP NOV OFC YEAR
6b«i19 "i-1NO. OF ocPupKFNrt
1PO-179 HMO, -CiF OLtU&KFI-jnt
NO.' OF OCfUPHFhCE
£4 0-2*) 9 H
300-5*19 I-,NO. OF 0£ruPNFi,itiLi<i00 fl'F A^PEMTS
fjO.-uF OCPUPRFMTE
NO. UF OcCURhFuCE
4^0-519 h
NO I UF .ACCENTS *
540*600 N
66-bOO MNO, OF OCCURRFNPfc.NO A UF A SCfc. NT $
.00 „ 0 0 .000 0 If
bPO 5 6 t»PO
S0(; .00 *lb0 U 1
9 3 1 ^ "PbPO bbh 6?0
1«13 .71 1.777 4 ! 1
bPG 56b 6?0
1 a^4 1 P^l P ?blif 7 1X1
6PO 5fcb b?0
"J? 6i^ s,'j!
*?b "13 "l26?U S66 b?U
6?U 566 620
°?9 e?H 812t>PO 566 6?0
142 112 157b?0 56b 6?0
v)
,000
efbOO
SbOO
bOO
s.so13
bOO
oOO
S1bbOO
600
lfl.0010dbOO
eoo0
b P U
0 0U
16?0
1
1 .137
@146?0
*ia
?J!
eii
0S96?0
0
.171
.00
eoo0
596
.67a
3
3
2
.50596
*16596
0616
65 o
,00U
616
eoo0616
.16616
3616
e^22
616
e a616
9616
.0819
616
.000
6?0
0
0b?0
.000
,000
6PO
a6PO
" 8
.656?0
1.136?0
3.7123
B o599
,00599
.00599
,000599
.000
5^9
a599
599
3
599
3.1719
599
.000
0
.000
6?0
."000
6?0
6?0
1 .6110
6?0
eio6?0
1.6110
620
b?0
,000
600
.000
600
,000
600
600
.17
600
B15bOO
@12600
3.0018
bOO
S15bOO
10.5063
bOQ
,000
6PO
0
06?0
.65a
6?0
1.137
0pq
6PO
*ln
3*M
120
,000
72^7
,03
9
.47
"§6
20472^7
2.66194
7297
72^7
19772^7
905
TABLE 2.5 PERCENTAGE FREQUENCY DISTRIBUTION OF INVERSIONSWITH BASE IN SPECIFIED HEIGHT RANGES ABOVE KING'S PARK(1971-1980)
Bai^ft
Dw Feist1000 8*lstiv*
lixlEc iatlo (Via* Bl»3ti«MM
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117.2(27.2)2l.0( 3,0*)18.7( 5.3)87.0( 8,9U.i( 3.1)093
59.9(26.3,
,2.3}, .87. 7( 6.5)17.5( 2.6
. . ,27.7 1.2
84. <»( 5.6)20.3( 1.2)
215
85, Lf e.o)16. 0( 2.3)040
123.X 34.023.1(ia.i( 4.574.9 13.313.7 3057
10
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9.7( 3.3044
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72.«(17.78.2( 3.0052
115.5(56.019.91 5.7i«-a( 7.380.3(14.0)I2.i( 5.2071
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TABLE 2.6 UPPER-AIR CLIMATOGICAL SUMMARIES OF UPPER-AIR DATAMEASURED AT KING!S PARK DURING 1971-1980...
TABLE 2*7 LIST OF METEOROLOGICAL SITUATIONSSELECTED FOR WIND FLOW SIMULATIONUSING ^APAS1 MODELS
Background Flow Applicable Situation
Direction Speed (knots)
1)
2)
3)
4)
5)
6)
7)
8)
9)
NNE
NE
ENE
E
ESE
SSE
S
SSW
W
5 Autumn, winter, spri
5
5 Winter, spring
5
5
5 Spring, summer
5 Summer, autumn
5
5
Plate 1.1 Anemograph at the Tsim Bei Tsui Police Post(viewed from southwest)
Plate 1.2 Radiosonde operation at King's ParkPlate 1.3 Monostatic acoustic radar at Junk Bay
"•i-fing-Mqg• "%
^ •'%
Plate 2.1 Topographic features surrounding the Deep Bay air shed
ft*
TOG