Diurnal Variation of Tropical Ice Cloud Microphysics: Evidence from Global Precipitation Measurement Microwave Imager Polarimetric Measurements

Abstract

The diurnal variation of tropical ice clouds has been well observed and examined in terms of the occurring frequency and total mass but rarely from the viewpoint of ice microphysical parameters. It accounts for a large portion of uncertainties in evaluating ice clouds' role on global radiation and hydrological budgets. Owing to the advantage of precession orbit design and paired polarized observations at a high‐frequency microwave band that is particularly sensitive to ice particle microphysical properties, 3 years of polarimetric difference (PD) measurements using the 166 GHz channel of Global Precipitation Measurement Microwave Imager (GPM‐GMI) are compiled to reveal a strong diurnal cycle over tropical land (30°S–30°N) with peak amplitude varying up to 38%. Since the PD signal is dominantly determined by ice crystal size, shape, and orientation, the diurnal cycle observed by GMI can be used to infer changes in ice crystal properties. Moreover, PD change is found to lead the diurnal changes of ice cloud occurring frequency and total ice mass by about 2 h, which strongly implies that understanding ice microphysics is critical to predict, infer, and model ice cloud evolution and precipitation processes.

Modeling the Radiative Effect on Microphysics in Cirrus Clouds Against Satellite Observations

“…Gong et al. (2018) statistically analyzed the GMI 166PD versus 166V Tb in the tropics. When 166V Tb is ∼195 K, 166PD reaches the largest magnitude of ∼8.5 K. With 166V Tb decreasing from 195 to 100 K, 166PD decreases from 8.5 to 1.5 K. If 166V Tb is treated as a variable to approximately represent cloud top level, the correlation between 166PD and 166V Tb implies that the 166PD decreases with increasing cloud top level, supporting the PDF distributions in Figure 11 and the sensitivity of REM to altitude in Figure 8.…”

“…It also displays the image of the polarization difference (PD) at 166 GHz, where PD is defined as the difference in Tb between vertically and horizontally polarized channel radiance measurements (i.e., 166PD = 166V − 166H). Since the magnitude of PD at 166 GHz is caused mainly by ice crystal orientations (e.g., Adams et al., 2008; Defer et al., 2014; Roberti & Kummerow, 1999; Skofronick‐Jackson et al., 2008), the 166PD image exhibits the distribution of horizontally oriented ice crystals (HOICs or the ice crystals with long axis oriented in the horizontal plane) near cloud top, given that other ice microphysical properties (e.g., size, habit) are largely homogeneous (Gong et al., 2018; Zeng et al., 2019).…”

Spaceborne Middle‐ and Far‐Infrared Observations Improving Nighttime Ice Cloud Property Retrievals

“…This approach is robust for COT > 0.3 but can be performed only under daytime conditions. Since the ice cloud properties have diurnal variations (Gong et al, 2018; Iwabuchi et al, 2018), the climatologies of the ice cloud properties in the daytime may not be representative at night. Another major approach is the split‐window method (Inoue, 1987) based on middle‐infrared (MIR; wavelengths 5–15 μm) thermal emission, available day and night.…”

Radiatively Induced Precipitation Formation in Diamond Dust

“…The second assessment was applied to the arctic regions where η z is usually less than one (see section 4.1), addressing the formation of diamond dust. The third assessment was applied to thick‐cloud top from the low to high latitudes (Gong et al, ; Zeng et al, ), using the polarization difference data of Global Precipitation Measurement Microwave Imager (Skofronick‐Jackson et al, , ). The fourth assessment was applied to the tropical upper troposphere (Zeng, ), showing the consistency between the CloudSat observations of thin clouds and the prediction of REM‐induced precipitation (Zeng, ).…”