Roles of 10 20-day oscillation in sustained rainstorms of October 2010 over Hainan, China Maoqiu Jian Yunting Qiao (Center for Monsoon and Environment Research //Department of Atmospheric Sciences, Sun Yat-sen University, China)
Outline 1. Motivation 2. Circulation systems for the sustained rainstorms in October 2010 in Hainan 3. Roles of 10-20-day oscillation in the sustained rainstorms 4. Impact of Indo-Pacific SSTA on the 10-20-day oscillations 5. Summary
1. Motivation The summer sustained rainstrom events in southern China are closely related to the intraseasonal oscillation (ISO) propagation activities. 10-20-day and 30-60-day oscillations are often dominant in the SCSSM evolution and the south Asian summer monsoon activities. 10-20-day oscillation may also modulate the tropical cyclone activities in the northwestern Pacific. This study is going to examine the ISO s influence in the sustained rainstorms over Hainan in autumn, based on an extreme case occurred in Oct. 2010. 3
Hainan Island
300 R(mm) 200 100 Climatological seasonal march of monthly rainfall at Haikou( 海口 ) 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 month Rainfall anomalies in October at Haikou(mm) 5
Time series of regional mean daily rainfall over Hainan from August to October 2010 200 13 days 10-20-day Oscillation in October? 150 mm 100 50 0 31Jul 15Aug 30Aug 14Sep 29Sep 14Oct 29Oct Questions: 1) Is there any connection between the ISO and the sustained rainstorms of Hainan? 2) If so, how does the ISO influence the Hainan sustained rainstorms? 6
Spatial distribution of accumulated rainfall (mm) for two subperiods over Hainan in October 2010 Haikou Lingao 817 308 Chengmai Dingan 473 Danzhou 866 Wenchang 328 Tunchang 1459 Changjiang Baisha 647 Qionghai Dongfang 198 390 Qiongzhong 1490 70 808 Ledong Wuzhishan Wanning 285 486 1142 Baoting Lingshui 701 931 Sanya 607 1000 600 300 100 0 Haikou Lingao 394 343 Chengmai Dingan 692 Danzhou 457 355 Tunchang Changjiang Baisha 569 Qionghai Dongfang 96 201 Qiongzhong 404 35 546 Ledong Wuzhishan Wanning 71 259 579 Baoting Lingshui 307 386 Sanya 246 Wenchang 401 1000 600 300 100 0 Sub-period I: 30 Sep-09 Oct, 2010 Sub-period II: 13-18 Oct, 2010 7
2 Circulation systems for the sustained rainstorms in October 2010 1-8 Oct 15-17 Oct Wind at 850 hpa and p-velocity at 500hPa for the two periods of 1-8 Oct and 15-17 Shading area for the up motion blank for down motion; thick dashed lines note the low-level convergence belts 8
Power spectrum analysis for time series of Aug to Oct 2010 Power 0.5 0.4 0.3 0.2 0.1 0.3 95% 95% power 0.4 0.2 0.1 0.0 0 100 20 10 Period(day) 2 1 100 20 10 2 1 period(day) U-wind(110 o E, 17.5 o N)at 850hPa Daily rainfall averaged over Hainan Island 9
3 Roles of 10-20-day oscillation in the sustained rainstorms Sep Oct (a) Latitude-time section of 10-20-day u-component at 850 hpa along 110 o E (b) Time-longitude section of 10-20-day u-component at 850 hpa along 18 o N 10
Sep25 10-20-day filtered wind at 850hPa for the first rainstrom event (shading for ascending motion anonalies) Oct 3 Sep28 Oct 6 Oct 1 Oct 9 11
Evolution of 10-20-day filtered wind at 200hPa Oct 1 Oct 6 Oct 3 Oct 9 Shading for negative 10-20-day component of OLR 12
10-20-day filtered wind at 850hPa for the second rainstrom event (shading for ascending motion anomalies) Oct 11 C A Oct 15 C A C Oct 13 C A Oct 18 A C 13
Evolution of 10-20-day filtered wind at 200hPa for the second rainstrom Oct 11 Oct 15 Oct 13 Oct 18 Shading for negative 10-20-day component of OLR 14
Sep 29 Filtered wind at 700hPa Oct 3 and OLR(shaded area is negative ) 700 hpa Sep 20 Sep 25
Oct 7 Oct 11 Oct 17 Filtered wind at 700hPa Oct 23 and OLR(shaded area is negative)
Oct Sep Aug (a)hovmöller diagram of 10-20-day filtered OLR and (b)time-latitude section of filtered OLR(W/m 2 ;interval is 10) Propagation of filtered OLR in the tropical western Pacific
eastward propagation of the unstable Kelvin-Rossby mode D C C D D C C the frictional moisture convergence in the boundary layer is essential for the growth of the unstable Kelvin-Rossby mode. Lagged regression coefficients of the OLR (contours) and 850-hPa wind anomalies (left panel), moisture divergence(right panel),with respect to the normalized 10 20-day component of OLR(X(-1)) at (85 o E, 5 o S)
Low frequency components of OLR at (110E,18N)
(a)hovmöller diagram of 30-60-day filtered OLR and (b)time-latitude section of filtered OLR (W/m 2 ;interval is 10)
4 Impacts of Indo-Pacific SSTA on the 10-20-day oscillations Hovmöller diagram of SSTA along equator( o C) 21
Anomalies of SST and OLR in Oct 2010 SSTA( o C) OLR (W/m 2 ) 22
Vertical shear of zonal wind in Oct 2010: (a)u850-u200 and (b) U850-U200 anomalies (based on 1979-2010)(m/s)
5 Summary Influence of QBWO in the first sustained raintrom event: 30-60-day oscillation strong northeasterlies intensified QBWO QBWO QBWO
Influence of QBWO in the second rainstrom event: strong easterlies intensified QBWO QBWO
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