STATISTICAL ANALYSIS OF ORGANIZED CLOUD CLUSTERS ON WESTERN NORTH PACIFIC

AND THEIR WARM CORE STRUCTURE

KOTARO BESSHO*1

Tetsuo Nakazawa1

Shuji Nishimura2

Koji Kato2

and

Shunsuke Hoshino1

1 Meteorological Research Institute

2 JMA / Meteorological Satellite Center

1. Using Early stage Dvorak Analysis data and reanalysis data of JRA-25, statistical analyses were done for Organized Cloud Clusters on western North Pacific in 2002-2005.

- There are big differences of physical parameters between clusters developing and not developing to TS.

- Vertical wind shear showed small difference between clusters.

2. Warm core structure of the clusters estimated from Advanced Microwave Sounding Unit (AMSU) in 2004

- Almost clusters developing to TS have warm core structure.

- Almost clusters staying at L have no warm core structure.

- Lead time from detection of warm core to TS is 28 hours.

- Large possibility to detect and forecast the genesis of TS by AMSU retrieved air temperature anomalies

Conclusions

Motivation and GoalDvorak technique- Excellent and reasonable work, but subjective

Motivation- To supplement the Dvorak technique by objective method especially in the genesis stage of TS

- To investigate the difference between clusters developing and not developing to TS

- Inspired by Zehr (1992) and so many preceding papers

- To use data from microwave sensors, especially of AMSU

Goal- Development of objective method to predict the tropical cyclone genesis by satellite microwave observation

Data and MethodologyData

- Early stage Dvorak Analysis (EDA) log files

- Reanalysis data of JRA-25 with the spatial resolution of 1.25o

- Air temperature retrieved from AMSU data by DDK algorithm

Methodology

- Statistical analysis of Organized Cloud Clusters from 2002 to 2005 by JRA-25

- Analysis of warm core structure of the clusters in 2004 by AMSU data

Definition of OCC - OCC (Organized Cloud Cluster)

Cloud Clusters with CSC (Cloud System Center)

OCCs staying with the stage of L or TD, or developing to TS

- OCCs are classified by T# and Maximum Wind Speed (MWS)

Low pressure area (L; Tropical Disturbance) T#<1

Tropical Depression (TD) T#>=1 and MWS < 34kt

Tropical Storm (TS; Named Tropical Cyclone)

T#>=1 and MWS >=34kt

Early stage Dvorak Analysis (EDA) - Including the position and T# of OCCs

- Subjective analysis for warning the genesis of Tropical Cyclones

- After Dvorak (1975), Dvorak (1984) and Tsuchiya et al. (2001)

- Edited by Japan Meteorological Agency / Meteorological Satellite Center (JMA/MSC) from 2002

- 2 steps procedure

1. Detecting the CSC to find OCC itself

2. T-number 1 (T1) diagnosis to find the stage of OCC

Statistical Analysis of OCCs by JRA-25

- Following Zehr (1992)

- Seasonal variation and Geophysical distribution

- Investigated the structure of OCCs　 Air temperature anomaly on 250 hPa

Wind convergence on 850 hPa

　Wind divergence on 250 hPa

　 Relative vorticity on 850 hPa

Wind shear between 250 hPa and 850 hPa

- Averaged the parameters within 5ox5o grid

Statistical Analysis of OCCs

Total numbers and percentages of OCCs in 2002 - 2005

LTD

TS

Seasonal variations of occurrence of each stage OCCs in 2002 - 2005

Geographical distribution of genesis of each stage OCCs

L TD

TS ALL

18.1

9.744.0 4.2 24.1 32.7

11.546.2 3.8 5.8

12.5

8.358.3 6.3 14.6 18.7

9.648.1 4.7 19.0

OCCL

EDA

041300Z18Apr

OCCTS

EDA

045300z14Aug

GMS

IR

250 TMP ANOM

850 VOR

850 COV

250 DIV

Wind Shear

Surf Pressure

Examples of OCCL and OCCTS

Some parameters in OCCs in 2002-2005

0413 OCCL vs. 0453 OCCTS in AMSU

WeakWarm Core

EDA0413

EDA0453

AMSU

250hPa

TMI

PCT

TMI

10GHz

GOES-9

IR

10:27z19Aug

06:35z25Aug 06:35z25Aug

09:30z19Aug

08:30z25Aug

GMS

GMS

TPW

TPW

CLW

CLW TMP ANOM

TMP ANOM

StrongWarm Core

Time series of Temp Anom of OCCL vs. OCCTS

Temp Anom = Temp - Average Temp on grid of 10ox10o

And Temp Anom is averaged in grid of 4ox4o

Warm Core : Temp Anom is greater than 0.9 K

TSTDL

OCCTS EDA0453

13 Aug 14 15 16

Warm Core

L

OCCL EDA0413

17 Apr 18

Dissipation

No Warm Core

0.9K

Warm core structure statistics

Total number of time series analysis by AMSU retrieved temp.

Total: 97 cases L: 56 TD: 13 TS: 28

Including WC structure L: 3 TD: 7 TS: 25

Not Including WC structure L: 53 TD: 6 TS: 3

Average period from genesis of OCC to TS in 25 OCCTS cases including WC 51.1 hours

Average period from genesis of OCC to first recognition of T1 in 25 OCCTS cases including WC 19.4 hours

Average period from genesis of OCC to the recognition of WC in 25 OCCTS cases including WC 23.4 hours

Average period from detection of CSC to the dissipation of L in 53 OCCL cases not including WC 13.6 hours

Duration of each stage of OCCs

Dissipation

OCCL not including WCCSC 13.6 h

r

TS

OCCTS including WCCSC WC23.4 h

r

51.1 hr

27.7 hr (Lead Time)

Large possibility to detect and forecast the genesis of TS by Warm Core structure retrieved from AMSU

19.4 hr

T1

1. Using Early stage Dvorak Analysis data and reanalysis data of JRA-25, statistical analyses were done for Organized Cloud Clusters on western North Pacific in 2002-2005.

- There are big differences of physical parameters between clusters developing and not developing to TC.

- Vertical wind shear showed small difference between clusters.

2. Warm core structure of OCC estimated from Advanced Microwave Sounding Unit (AMSU) in 2004

- Almost clusters developing to TS have warm core structure.

- Almost clusters staying at L have no warm core structure.

- Lead time from detection of warm core to TS is 28 hours.

- Large possibility to detect and forecast the genesis of TS by AMSU retrieved air temperature anomalies

Conclusions

Detecting CSC- OCC is defined as the cloud cluster with CSC.

- CSC has one of the features as below.

1. Dense and cold overcast bands that show some curvature around a relatively warm area.

2. Curved cirrus lines indicating a center of curvature within or near a dense, cold overcast.

3. Curved low cloud lines showing a center of curvature within two degrees of a cold cloud mass.

4. Cumulonimbus (Cb) clusters rotating cyclonically on animated images.

T1 Diagnosis- When OCC has ALL five conditions as below, T# is 1 1. The cloud clusters have persisted for 12 hours or more.

2. The accuracy of estimation of CSC in the clusters is 2.5o latitude or less.

3. The CSC has persisted for 6 hours.

4. The clusters have dense, cold overcasts that appear less than 2o latitude from CSC.

5. The extent of the overcasts is more than 1.5o latitude.

Warm Core and Low Level Circulation

OCCL　EDA0413

OCCTS　EDA0453

AMSU

250hPa

TMI

PCT

TMI

10GHz

GOES-9

IR

09:19z19Aug 10:27z19Aug

08:37z25Aug

09:30z19Aug

08:30z25Aug

Average distance between the grids of maximum temp. anom. on 250 hPa and the grids of maximum vorticity on 850 hPa

675 km

135 km

Future Work1. To investigate the relation between warm

core structure of OCCs retrieved from AMSU and their environmental condition

- Using other reanalysis data such as ERA-40 and NCEP

- Using other satellite microwave observational data such as QuikSCAT, AMSR-E and SSM/I

2. To expand the analysis period, especially for warm core analysis by AMSU data from 2002

3. To establish the objective method to detect and forecast the genesis of TS

- Need of validation by independent data set