**6. Microphysical effects of ice clouds: CNIM versus CNIR**

The calculations of model domain mean simulation data show the decreases in *PEWV* and *PEH* from CNIR to CNIM during the life span of pre-summer heavy rainfall event (Figs. 9a-10a). On 4 June, the exclusion of microphysical effects of ice clouds decreases *PEWV* and *PEH* through the hydrometeor change from loss in CNIR to gain in CNIM and the weakened local atmospheric cooling (Figs. 11a-17a). On 5 June, the decrease in *PEWV* is associated with the intensification in local atmospheric moistening and the hydrometeor change from loss in CNIR to gain in CNIM. The reduction in *PEH* is related to the hydrometeor change from loss in CNIR to gain in CNIM. On 6 June, the decrease in *PEWV* corresponds to the strengthened hydrometeor gain. *PEH* is barely changed in the two experiments because of similar rates of rainfall source from thermal processes. On 7 June, the decreases in *PEWV* and *PEH* result from the hydrometeor change from loss in CNIR to gain in CNIM although water vapor divergence and local atmospheric cooling are weakened.

Over convective regions, *PEWV* and *PEH* are increased from CNIR to CNIM during the life span of pre-summer heavy rainfall event (Figs. 9b-10b). The exclusion of microphysical effects of ice clouds increases *PEWV* and *PEH* through the weakened transport of hydrometeor concentration from convective regions to raining stratiform regions during 4-6 June (Figs. 11b-17b). The decrease in local atmospheric cooling also contributes to the increases in *PEWV* and *PEH* on 6 June. On 7 June, the removal of microphysical effects of ice clouds increases *PEWV* through the weakened transport of hydrometeor concentration from

Thermodynamic Aspects of Precipitation Efficiency 89

the removal of microphysical effects of ice clouds barely impacts local atmospheric cooling on 5 June and it decreases local atmospheric cooling on 6 June, the decreases in stratiform rainfall are associated with the slowdown in transport of hydrometeor concentration from convective regions to raining stratiform regions. As a result, the decreases in stratiform rainfall lead to the decreases in *PEH* from CNIR to CNIM. On 7 June, the elimination of microphysical effects of ice clouds increases *PEWV* through the weakened water vapor divergence and increases *PEH* through the weakened local

Precipitation efficiency can be well defined through diagnostic surface rainfall budgets. From thermally related surface rainfall budget, precipitation efficiency associated with heat processes (*PEH*) is first defined in this study as the ratio of surface rain rate and the rainfall source from heat and cloud budgets. Precipitation efficiency associated with water vapor processes (*PEWV*) was defined by Sui et al. (2007) as the ratio of surface rain rate to the rainfall source from water vapor and cloud budgets. In this study, both precipitation efficiencies and their responses to effects of ice clouds are investigated through an analysis of sensitivity cloud-resolving modeling data of a pre-summer heavy rainfall event over

 The calculations of model domain mean simulation data show that *PEH* is lower than *PEWV* because heat divergence contributes more to surface rainfall than water vapor convergence does. Precipitation efficiencies are lower during the decay phase than during the development of rainfall. *PEH* is generally lower than *PEWV* over convective regions, whereas it is generally higher than *PEWV* over raining stratiform regions.

 *PEWV* has different responses to radiative effects of ice clouds during the different stages of the rainfall event. The exclusion of Microphysical effects of ice clouds generally decreases *PEWV* in the calculations of model domain mean simulation data,

 The exclusion of radiative effects of ice clouds generally decreases *PEH*. The removal of microphysical effects of ice clouds generally decreases *PEH* except that it increases *PEH*

 Effects of ice clouds on precipitation efficiencies can be explained by the analysis of surface rainfall budgets. The changes in *PEWV* are mainly associated with the changes in local atmospheric moistening and transport of hydrometeor concentration from convective regions to raining stratiform regions during the life span of presummer heavy rainfall event and the change in water vapor divergence on 7 June. The changes in *PEH* are mainly related to the changes in local atmospheric cooling and radiative cooling and transport of hydrometeor concentration from convective regions to raining stratiform regions during the life span of pre-summer heavy

The authors thank W.-K. Tao at NASA/GSFC for his cloud resolving model, and Dr. N. Sun at I. M. Systems Group, Inc. for technical assistance to access NCEP/GDAS data. This study

southern China during June 2008. The major results include:

Precipitation efficiencies increase as surface rain rate increases.

whereas it generally increases *PEWV* over raining regions.

over convective regions.

rainfall event.

**8. Acknowledgment** 

atmospheric cooling.

**7. Conclusions** 

convective regions to raining stratiform regions, whereas it barely changes *PEH* because of the offset between the weakened transport of hydrometeor concentration from convective regions to raining stratiform regions and the enhanced local atmospheric cooling (Figs. 14b and 15b).


Table 3. Thermally related surface rainfall budget (*PSWV*, *SHT*, *SHF*, *SHS*, *SRAD*, and *QCM*) averaged daily and over model domain, convective regions, and raining stratiform regions in C, CNIR, and CNIM. Unit is mm h-1.

Over raining stratiform regions, the elimination of microphysical effects of ice clouds decreases *PEWV* through the weakened local atmospheric moistening and reduces *PEH* through the weakened local atmospheric cooling on 4 June. During 5-6 June, the exclusion of microphysical effects of ice clouds increases *PEWV* because all rainfall processes favors rainfall in CNIM but the local atmospheric moistening reduces rainfall in CNIR. Although the removal of microphysical effects of ice clouds barely impacts local atmospheric cooling on 5 June and it decreases local atmospheric cooling on 6 June, the decreases in stratiform rainfall are associated with the slowdown in transport of hydrometeor concentration from convective regions to raining stratiform regions. As a result, the decreases in stratiform rainfall lead to the decreases in *PEH* from CNIR to CNIM. On 7 June, the elimination of microphysical effects of ice clouds increases *PEWV* through the weakened water vapor divergence and increases *PEH* through the weakened local atmospheric cooling.
