Precipitation efficiency and its dependence on physical factors A look into the cloud response to climate warming Chung-Hsiung Sui 1 Institute of Hydrological and Oceanic Sciences, 2 Department of Atmospheric Sciences, National Central University, Taiwan

How do tropical clouds/rain change in response to climate warming ? Global warming scenario Natural climate change Equilibrium convective- radiative response SST L-S Ocean- atmospheric circulation Thermostat hypothesis iris hypothesis GCM modeling CRM experiments

How do tropical clouds/rain change in response to climate warming ? 1. A drying trend in the subtropics and reduction in tropical cloudiness [e.g. Schroeder and McGuirk, 1998; Bates and Jackson, 2001], increase in OLR (Weilicki et al. 2002). 2. A possible increase in precipitation over tropical oceans but reduction over tropical land (Kumar et al. 2003, Wang and Ding 2006), confirmed by model (Bosilovich et al. 2005) 3. Warm clouds vs cold clouds? 4. Extreme weather events ?

Lau and Wu (2007) CMAP (thin line) GPCP (thick line) Annual heavy rain (top 10% rainrate) Annual light rain (bottom 5% rainrate) CMAP GPCP Cumulative rain (mm) Pentad, tropical mean rainfall linear trend in tropical rain as a function of rain rate linear trend in tropical rain FOC as a function of rain rate GPCP (solid bar) CMAP (outlined bar) How do warm clouds change in climate warming?

How do extreme weather events react to climate warming ? Webster et al. 2005, Emanuel 2005, …. Increasing tropical SST and measures of TC activity have been reported to be strongly correlated since at least 1950.

Knutson et al. 2007: Simulated reduction in Atlantic hurricane frequency under 21st-century warming conditions Atlantic hurricane and tropical storm frequencies are reduced. At the same time, near-storm rainfall rates increase substantially. Obs. Control Exp warm climate Exp a. tropical storms b. hurricanes c. major hurricanes c (Pc< 965 hPa)

How do warm and cold clouds/rain change in response to climate warming? Does its precipitation efficiency increase ?  Ambiguity in defining warm clouds/rain,  Lack of long record,  Need a more complete set of definition Application to estimate PE of clouds in the tropics as a function of sea surface temperature (for studying the response of tropical water cycle to climate warming)

PE based on conservation of cloud water SI qv = [P CND ]+[P DEP ]+ [P SDEP ]+[P GDEP ] SO qv = [P REVP ]+[P MLTG ]+ [P MLTS ] [  t q C ]  [CONV C ] local stotorage  t q C

      Cloud W.V. + cloud PE

An estimate of LSPE based on available data NCEP reanalysis at 6 hour and 2.5 o x2.5 o resolution and interpolated to 1 o x1 o grids JMA-25 reanalysis (Onogi et al. 2007; Hatsushika et al. 2006, Takahashi et al. 2006) at 6 hour and 1.25 o x1.25 o resolution and interpolated to 1 o x1 o grids

GPCPTMI3B42R2 Surface Grid360 x x x x 94 Spatial resolution 1º x 1º0.25º x 0.25º 1.875º x Gausian Temporal coverage 1997/01 ~ 2007/ /12 ~ now 1998/01 ~ 2008/ /01 ~ now Temporal resolution 1 dy12 hr3 hr6 hr First point0.5, , , , Unitmm/daymm/hr An estimate of LSPE based on available data Precipitation data (averaged to 1 o x1 o grids)

Conv -tqv-tqv

EsEs Total P s sources

Types< to 0.4> 0.4 downward upward Freq.84 %12 %4 %60 %40 % Precipitation Range (mm/hr) ω 500 How to define warm clouds 1.Based on satellite data like TRMM retrieved cloud water content, SST, ….. (e.g. Lau and Wu) 2.This study

S = water source P PE = P/S P > 0.4 mm/hr 0.1 < P < 0.4 P < 0.1

RR < < RR < 0.4 RR > 0.4

Discussion 1.A more complete set of PE is defined for studying cloud response to climate warming 2. One hypothesis: the change of warm clouds affect cold clouds (Lau and Wu 2007) 3. Another hypothesis is possible