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KOTARO BESSHO* 1 Tetsuo Nakazawa 1 Shuji Nishimura 2 Koji Kato 2 and Shunsuke Hoshino 1

STATISTICAL ANALYSIS OF ORGANIZED CLOUD CLUSTERS ON WESTERN NORTH PACIFIC AND THEIR WARM CORE STRUCTURE. KOTARO BESSHO* 1 Tetsuo Nakazawa 1 Shuji Nishimura 2 Koji Kato 2 and Shunsuke Hoshino 1 1 Meteorological Research Institute 2 JMA / Meteorological Satellite Center.

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KOTARO BESSHO* 1 Tetsuo Nakazawa 1 Shuji Nishimura 2 Koji Kato 2 and Shunsuke Hoshino 1

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  1. 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

  2. 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

  3. Dvorak 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 Motivation and Goal

  4. Data and Methodology • Data • 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

  5. 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

  6. 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 CSCto find OCC itself 2. T-number 1 (T1) diagnosisto find the stage of OCC

  7. 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

  8. TS L TD Statistical Analysis of OCCs Total numbers and percentages of OCCs in 2002 - 2005

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

  10. 8.3 9.6 11.5 9.7 58.3 44.0 46.2 48.1 12.5 32.7 18.7 18.1 4.2 3.8 6.3 4.7 14.6 19.0 24.1 5.8 Geographical distribution of genesis of each stage OCCs L TD ALL TS

  11. Examples of OCCL and OCCTS GMS IR 250 TMP ANOM 850 VOR 850 COV 250 DIV Wind Shear Surf Pressure OCCL EDA 0413 00Z18Apr OCCTS EDA 0453 00z14Aug

  12. Some parameters in OCCs in 2002-2005

  13. EDA0413 0413 OCCL vs. 0453 OCCTS in AMSU GMS TPW CLW AMSU 250hPa TMI PCT TMI 10GHz TMP ANOM GOES-9 IR Weak Warm Core EDA0453 GMS TPW CLW TMP ANOM 10:27z19Aug 09:30z19Aug Strong Warm Core 06:35z25Aug 06:35z25Aug 08:30z25Aug

  14. OCCL EDA0413 OCCTS EDA0453 L Dissipation L TD TS Warm Core No Warm Core 17 Apr 18 13 Aug 14 15 16 Time series of Temp Anom of OCCL vs. OCCTS 0.9K 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

  15. 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

  16. Duration of each stage of OCCs OCCTS including WC CSC WC 51.1 hr TS 23.4 hr T1 19.4 hr 27.7 hr (Lead Time) OCCL not including WC CSC 13.6 hr Dissipation Large possibility to detect and forecast the genesis of TS by Warm Core structure retrieved from AMSU

  17. 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

  18. - 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. Detecting CSC

  19. - 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. T1 Diagnosis

  20. Warm Core and Low Level Circulation Average distance between the grids of maximum temp. anom. on 250 hPa and the grids of maximum vorticity on 850 hPa AMSU 250hPa TMI PCT TMI 10GHz GOES-9 IR 675 km 135 km 09:19z19Aug 10:27z19Aug 09:30z19Aug OCCLEDA0413 OCCTSEDA0453 08:37z25Aug 08:30z25Aug

  21. Future Work 1. 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

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