1. Role of cold pool formation on the diurnal cycle of precipitation over the maritime continent Tomonori Sato (CCSR, Univ of Tokyo) Hiroaki Miura (JAMSTEC & CSU) Masaki Satoh (CCSR & JAMSTEC) Yukari N. Takayabu (CCSR & JAMSTEC) Yuqing Wang (IPRC, Univ of Hawaii) Submitted to Journal of Climate 090305Workshop@Vietnam

2. Diurnal cycle (DC) is a dominant mode in convective features over tropics which plays an important role in driving a global-scale atmospheric circulation. Conventional GCMs, that use cumulus parameterizations, fail to simulate the amplitude and phase of the precipitation DC (e.g., Dai, 2006). Heating anomaly over the maritime continent has significant impact on the global atmospheric circulation (Neale and Slingo, 2003). Background - importance of the diurnal cycle -

3. Diurnal cycle of rainfall in GCM-TL959 Arakawa and Kitoh (2005) PR 12-24LT /PR 00-24LT Land Coast offshore Land Coast offshore (1) High resolution GCMs

4. Tao et al. (2009) Observations Original GCM Goddard's MMF CSU's MMF DJFJJA (2) Multi-scale Modeling Framework (MMF or Super parameterization)

5. NICAM (Nonhydrostatic ICosahedral Atmospheric Model ) Satoh et al. (2008) -Developed at Frontier Research Center for Global Change (FRCGC) and Center for Climate System Research (CCSR), University of Tokyo. -Simulation by Miura et al. (2008, Science) Period: 15th Dec. 2006 through 14th Jan. 2007 Initial: NCEP final analysis Grid size: 14 km (31 days), 7 km (31 days), and 3.5 km (7days) Cumulus parameterization: Not used Experiments (3) Global cloud resolving model Satellite Model

6. Satellite data used TRMM 3B42 (31days; 15 Dec.2006 - 14 Jan.2007 ) –Grid size: 0.25 x 0.25 degree –Interval: 3 hourly (+/- 90 minute) –optimal combination of 2B-31, 2A-12, SSMI, AMSR and AMSU precipitation estimates, to adjust IR estimates from geostationary IR observations. TRMM 3G68 (DJF climatology, 1998-2007) –Grid size: 0.5 x 0.5 degree –Based on PR observation –Interval: 3-hourly composite

8. Averaged diurnal cycle over 15 o S-15 o N

9. Significant improvement in the higher resolution run. DC over ocean is less influenced by the horizontal resolution.

10. Diurnal cycle of rainfall (NICAM-7km) 00 LT 03 LT 06 LT 09 LT 12 LT 15 LT 18 LT 21 LT [mm/day]

11. [10 -5 sec -1 ] conv. div. Evening Morning Contrast of 10m-level wind and divergence pattern

12. Frequency of cold pool formation over oceans Cold pool definition: dT/dt < -1.5 o C/90min [counts/month] [mm/day] Precipitation rate

13. DC of cold pool formation over oceans Diurnal change of cold pool distribution is very much consistent to that of precipitation. [counts/month] 18-24LT 06-12LT

14. Conclusion This is the first study to investigate DC in GCRM. GCRM well simulates the DC in tropical regions. Prominent resolution dependence is recognized in phase and amplitude of the DC, in particular over land. The highest resolution run (3.5km mesh) shows very similar phase to the observed one. Spatio-temporal characteristics of the cold pool is shown using NICAM simulation. We found the cold pools are often formed over the oceans with high rainfall rate, such as ITCZ and SPCZ. Near the offshore regions around the maritime continent, the formation of cold pool is consistent to the low-level atmospheric circulation and the convectively active areas.

16. Mean diurnal cycle of precipitation in warm season. Dai (2006) Observation TRMM3B42(1998-2003) CCSM2 GFDL-CM2.0 GISS-ER MIROC3.2(hires) MRI-CGCM2.3.2a 25-70N; Land25-70N; Ocean 25S-25N; Land25S-25N; Ocean 25S-50S; Land25S-50S; Ocean

19. Impact of horizontal resolution on phase and amplitude of DC

20. Dynamics (grid-scale) Governing equationsFull compressible non-hydrostatic system Spatial discretization Horizontal grid configuration Vertical grid configuration Topography 2 nd -order centered scheme (Tomita et al. 2002, JCP) 2 nd -order upwind biased scheme (Miura, 2007, MWR) Icosahedral grid (Tomita et al. 2001/2002, JCP) Lorenz grid Terrain-following coordinate Conservationmass, tracers, total energy (Satoh 2002,2003, MWR) Temporal scheme Slow mode － explicit scheme （ RK2 ） Fast mode － Horizontal Explicit Vertical Implicit scheme Physics (subgrid-scale) Turbulence / surface fluxYamada and Mellor (1979) /Louis(1979), Uno et al.(1995) Radiation / aerosolMSTRNX (Sekiguchi 2004) / SPRINTARS (Takemura et al. 2003) Cloud physicsGrabowski(1998), Lin (1983) Surface processBucket land model / fixed SST, MATSIRO / slab ocean Nakanishi and Niino (2004)

21. Studying diurnal cycle in GCMs (1) High resolution GCM –Maritime continent: Arakawa and Kitoh (2005) –Continental US: Lee et al. (2007) (2) Multi-scale Modeling Framework (MMF or Super parameterization) –Khairoutdinov et al. (2005) –Tao et al. (2009) (3) Global cloud resolving model  This study