Recent progress in the development of Upper air Systems

© Crown copyright 2004

Recent progress in the development of Upper air Systems

Catherine Gaffard

Met Office Upper Air Team, University of Reading With contributions from

J.Nash, T.Hewison, Richard Smout and T Oakley


Introduction

Upper air observations are required to improve climate and weather prediction

Climate observations require “reference” quality , and improved reliability in new generation measurements

Observations need to be provided at higher temporal and spatial resolution than in earlier networks for understanding processes for improved data assimilation

- (1km grid, update every 15 minutes)

Achievable by a mix of in situ measurements (Radiosondes, aircraft) and ground based remote sensing stations to complement satellite observations.


Outline of talk

Progress in radiosonde technology Progress in ground base remote sensing for operational use.

Expected results from integration Conclusion


Progress in radiosonde technology


Temperature sensors

Thermistor or thermocapacitor devicesnow have fast response, small radiation error. time response = Function of (density, speed of the flow, specific heat, size of sensor, shape of sensor) small and thin sensor will be fast

radiation error = Function of (infrared and visible emissivity, total incoming flux in infrared and visible, surface of the sensor, sensor temperature) compensation by radiation correction scheme, however small aluminised coated sensor will have small radiation error thus small error in the correction .


thermistor

Modem radiosonde

in Brazil,WMO test 2001Modem radiosonde

2006

white paint coating,fine for short wave.but 0.8 emissivity in IR


capacitor

RS80 Vaisala temperature Sensor, 1.2mm diameter

RS92 Vaisala temperature Sensor, 0.1mm diameter


Mauritius comparison Temperature sensor evaluation.

Systematic differences in nighttime temperature referenced to the average of Graw, Meisei, Sippican, SRS-adjusted and Vaisala

WMO High Quality Radiosonde Comparison Test, Mauritius 2005

0

5

10

15

20

25

30

35

-2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50

Temperature difference [K]

Hei

gh

t [

km]

Vaisala RS92

SRS

Meisei

Modem

Sippican

Graw

3 Therm

SRS-adj

nearly all RS fall within ±0.20K bias (sip and 3 therm are <0.1K)Graw and Srs had a calibration problemModem white coating induced strongradiative cooling (replaced now by

aluminized coating)

10 years ago bias >1k were commonly observed in the stratosphere (above 25km)

The reference is obtained bya careful editing of each flight rejecting data when conta-

mination is identified. Night time

-0.5

0.5


Estimated random errors in nighttime temperature measurements, WMO High Quality Radiosonde Comparison, Mauritius 2005,

assuming Vaisala random errors were as shown

0

5

10

15

20

25

30

35

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Random Error in Temperature [K]

Hei

ght

[km

]

Vaisala RS92

SRS

Meisei

Modem

Sippican

Graw

3 Therm

std less than 0.1K for RS92 and 3 therm up to 35km, in general very good reproducibility for all sensors

0.4 0.2 0.0


Evaporative cooling, well prevented by RS92 hydrophobic coating

cloud top


Geopotential height comparison

GPS heights are very consistent with themselves. This seems to indicate that GPS heights are reliable. At 10hPa (31 km) in the tropics an error of 0.1hPa introduces an error of70m in height


Progress in humidity sensor

The majority of modern radiosondes use thin film capacitors e.g. Vaisala(Finland), Meisei (Japan) Modem (France) and Graw (Germany), Sippican (USA), Intermet (USA)

Carbon hygristor sensors are much larger than the thin film capacitors. These were distributed widely in the past by Sippican/VIZ [USA], being used by many national radiosonde designs. Sensors also now developed in China and India

Gold-beater’s skin sensors have much slower response than the capacitors and hygristors but are still used in Russia and China [ to a limited extent].

Snow white is a chilled mirror hygrometer which measures dew and frost point.


Vaisala RS80 - H Humicap, main UK sensor, 1996 -thin film polymer, capacitance changes with relative humidity


Sippican Carbon Hygristor,resistance very high at high relative humidity, low at low relative humidity


Vaisala RS90 in 2000,No cover, heating pulses applied alternately to sensors to drive off contamination

Sensors

In Mauritius in 2005 , bare circuit board near sensors aluminised to reduce heating of sensor surrounds, but may not yet be available

In operational radiosondes


Vertical structures are very similar in the middle troposphere


Mauritius Intercomparison

when temperature <-60C agreement between sensor often diverges


RS 92 against reference very good agreement. Still some discrepancies at very low temperature


Bias for day time larger than at night time (underestimation) Day night difference ~5% for RS92 in the lower troposphere


World wide radiosonde network

China is developing new generation of RS


Progress in remote sensing technology


Remote sensing technology may provide :-

high time and space resolution data for model validation and initialisation (assimilation)

automated unattended system for operational use

complement to radiosonde (time evolution), AMDAR (aircraft), and satellite data

Instruments considered hereMicrowave radiometerwind profilerGPScloud radar, ceilometer


Microwave radiometer : example of radiometer retrieved profile

Integrated water vapour with optimum accuracy of ~0.7kg/m^2 (against rs)

Integrated liquid water with optimum accuracy ~20g/m^2 (estimated error)

temperature better than 1.5K (std) up to 3km (against rs)

relative humidity accuracy 20% std (against rs)

12 channelsaround watervapour lineand oxygencomplex +IR channel•automated•unattended•high time resolution•low verticalresolution


Wind profiler and VAD winds are assimilated in most of NWP centres

weather radar VAD windwind profiler network mixture ofoperational and research instruments


Wind profiler used for AMMA(African Monsoon Multidisciplinary Analysis)

4 UHF ( 2 are permanently installed for airport security)1 VHF


example of diurnal cycle during dry seasonBamako (march 2005)

north easterly LLJ

south easterly MLJ

convective turbulence

shear,friction turbulence


FMCW radar ( affordable technology)

Example of low stratus/fog evolution captured by the 78 GHZ cloud radar.


GPS water vapour plot for Europe, showing current sites supplying data to E-GVAP hub in near real-time

12

32

3717

18


Actual GPS sensor site used to measure IWV in Africa


Integrated ground base remote sensing station- expected results


Integrated profiling systems

wind profiler SNR+ ceilometer could be used with radiometer to get better vertical structure in the humidity profile

RH retrieved by radiometer

RH measured by hourly RS

SNR measured by WP

Refractive (potential) index gradient computed from RS


convective scale: radiometer+ wind profiler

vertical speed updraft seen by WP

SNR (range corrected)from WP

unstable before the updraftstable and lower RH in the updraft event last ~10minin the future it will be possibleto assimilate such structure.


cloud radar and ceilometer integration

liquid content=Function (size and concentration) Cloud radar Zdb function of size( D^6)and concentration Ceilometer return, function of size(D^2) and concentration,The combination of the 2 allows an estimate of the water liquid profile for thin water cloud.

Cloud base


conclusion (radiosondes)

Radiosondes are the only instrument that can give detailed profiler of humidity, temperature collocated with wind.

It’s essential for climate reference that radiosonde biases are minimised and kept stable.

New generation of radiosondes have much better design which minimise radiation error for temperature sensor. In the night, the absolute accuracy of the temperature sensor is reaching 0.1K with a very good reproducibility 0.1K . Climate monitoring with selected type of radiosonde could be envisaged using night temperature.

China is developing new generation radiosondes .


conclusion (radiosonde)

There is no discrepancy between GPS height.

Pressure sensor might become obsolete unless accuracy in both sensor can become such that their information could be used for non-hydrostatic model.

For the humidity, in the middle troposphere,at night, the performance of sensors in Mauritius test was rather similar within ±5%. At higher level above 11km or when the temperature start to be lower than -60C, the agreement between all the radiosonde diverge. The best agreement with the snow white is obtained with RS92.


conclusion ( remote sensing)

The need for weather forecasting and understanding physical processes for climate prediction, requires data at high temporal and spatial resolution. This can only be achieved by a mixture of in situ and remote sensing.

With the help of European funding, the development of a European network of wind profiler has facilitated the use of wind profiler and VAD wind.

During AMMA, the deployment of wind profiler in Africa was successful, demonstrating the maturity of this remote sensing technique. Help from international funding will lead to sustainable development of wind profiler network, including training for technicians supporting the systems.


conclusion ( remote sensing)

With the evolution in the software and network architecture, GPS integrated water quantities are now available within 15 min. Integrated water quantities are now assimilated operational into NWP. This information is cheap and funding to help various regions to expand their actual networks is desirable.

While having a limited vertical resolution, radiometers have the potential to be useful for high time resolution description of physical processes.

FMCW cloud radars are becoming affordable as operational instruments.

An integrated approach has the prospective to deliver better products than independently retrieved quantities.


Conclusion : Future work

The Met office is currently working on costed option of a new upper air network which can deliver the user needs for new generation of NWP.

Several country in Europe including operational and research centre have expressed their interest for collaborative work to deliver an improved cost-effective European ground-based observing system design, providing essential atmospheric observations for both climate and weather from one integrated operational network for the decade 2010-2020.


Questions & Answers


1c

Estimated random errors in nighttime temperature measurements, WMO High Quality Radiosonde Comparison, Mauritius 2005,

assuming Vaisala random errors were as shown

0

5

10

15

20

25

30

35

0.00 0.20 0.40 0.60 0.80 1.00 1.20


Hei

ght

[km

]

Vaisala RS92

SRS

Meisei

Modem

Sippican

Graw

3 Therm

std less than 0.1K for rs92 and 3 therm up to 35km, in general very good reproducibility for all sensors


Estimated random errors in daytime temperature measurements, WMO High Quality Radiosonde Comparison, Mauritius, 2005

assuming Vaisala errors were as shown

0

5

10

15

20

25

30

35

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00


Heig

ht [

km]

Vaisala RS90

SRS

Meisei

Modem

Sippican

Graw

3 Therm

std larger at day time than at night time above 15km for all the sensors due tosolar heating


Wind Profiler UK Model Assimilation

Wind Profiler Sites Assimilated in UK Met Office Model

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Month

To

tal n

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ber

of s

ites

Sites Assimilated

Total sites Reporting

7 sites

Other NWP Centres

DWD – 20 Sites

Meteo France – 26 Sites (with restrictions)

ECMWF – 13 Sites


Weather Radar UK Model Assimilation

Weather Radar Wind sites being Assimilated in UK Met Office Model

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70

80

90

Month

To

tal S

ite

s

Sites Assimilated

Total sites

27 sites

Other NWP Centres

Only SMHI (local)

Recent progress in the development of Upper air Systems

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