Microphysical properties of frozen particles inferred from Global Precipitation Measurement (GPM) Microwave Imager (GMI) polarimetric measurements

Abstract

Abstract. Scattering differences induced by frozen particle microphysical properties are investigated, using the vertically (V) and horizontally (H) polarized radiances from the Global Precipitation Measurement (GPM) Microwave Imager (GMI) 89 and 166 GHz channels. It is the first study on frozen particle microphysical properties on a global scale that uses the dual-frequency microwave polarimetric signals.From the ice cloud scenes identified by the 183.3 ± 3 GHz channel brightness temperature (T b ), we find that the scattering by frozen particles is highly polarized, with V-H polarimetric differences (PDs) being positive throughout the tropics and the winter hemisphere mid-latitude jet regions, including PDs from the GMI 89 and 166 GHz TBs, as well as the PD at 640 GHz from the ER-2 Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) during the TC4 campaign. Large polarization dominantly occurs mostly near convective outflow regions (i.e., anvils or stratiform precipitation), while the polarization signal is small inside deep convective cores as well as at the remote cirrus region. Neglecting the polarimetric signal would easily result in as large as 30 % error in ice water path retrievals. There is a universal "bell curve" in the PD-TB V relationship, where the PD amplitude peaks at ∼ 10 K for all three channels in the tropics and increases slightly with latitude (2-4 K). Moreover, the 166 GHz PD tends to increase in the case where a melting layer is beneath the frozen particles aloft in the atmosphere, while 89 GHz PD is less sensitive than 166 GHz to the melting layer. This property creates a unique PD feature for the identification of the melting layer and stratiform rain with passive sensors.Horizontally oriented non-spherical frozen particles are thought to produce the observed PD because of different ice scattering properties in the V and H polarizations. On the other hand, turbulent mixing within deep convective cores inevitably promotes the random orientation of these particles, a mechanism that works effectively in reducing the PD. The current GMI polarimetric measurements themselves cannot fully disentangle the possible mechanisms.

SLALOM: An All-Surface Snow Water Path Retrieval Algorithm for the GPM Microwave Imager

“…Previous studies on the GMI snowfall detection capability assessment [18,26,33,43] demonstrate that GMI has great potential for snowfall observation. In this work, we have shown that, through the exploitation of all 13 GMI channels and the optimal use of ancillary variables describing the atmospheric conditions (and no ancillary information on the background surface conditions), SLALOM is able to predict snowfall occurrence and SWP, with a very good agreement with the Cloudsat 2CSP product, and has the advantage of ensuring a much larger spatial coverage, corresponding to the GMI swath.…”

“…These sensors have high frequency channels that are highly sensitive to snowfall due to the scattering by snowflakes of upwelling terrestrial and radiation, originating in the lower levels of the atmosphere [15][16][17][18]. In addition, passive microwave radiometers have a large swath and have been installed on many platforms over the last decades, ensuring a good global coverage with a fair spatial resolution and lengthy data records.…”

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

“…In particular, studies of PD from passive and active spaceborne measurements at visible and microwave wavelengths show that nonspherical ice crystals are not randomly oriented but usually horizontally oriented (Davis et al, , ; Defer et al, ; Prigent et al, , ; Zhou et al, ). Gong and Wu () (GW17 hereafter) first identified the similar features from the GPM‐GMI 166 and 89 GHz observations. Taking advantage of GPM's precession orbit, this paper aims to better understand the diurnal variation of PDs in the tropics and its implication for ice crystal's microphysical properties and how they vary together with macroscopic quantities such as cloud occurring frequency and mass.…”

Representing Precipitation Ice Species With Both Spherical and Nonspherical Particles for Radiative Transfer Modeling of Microphysics‐Consistent Cloud Microwave Scattering Properties

“…Only the use of spheres for both snow and graupel leads to simulated brightness temperatures at 91.7 GHz which are colder than that at 183 GHz in the area of the hurricane precipitation (Figure b versus Figure b). Also, all of the CRTM simulations at 91.7 GHz (Figure ) have a cold bias to observations, even as the use of randomly oriented cloud and precipitation particles should be a source of positive bias to observations in 91.7 GHz simulations at horizontal polarization (e.g., Defer et al, ; Gong & Wu, ).…”