First observations of polarized scattering over ice clouds at close‐to‐millimeter wavelengths (157 GHz) with MADRAS on board the Megha‐Tropiques mission

Abstract

Polarized scattering by frozen hydrometeors is investigated for the first time up to 157 GHz, based on the passive microwave observations of the Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS) instrument on board the Indo-French Megha-Tropiques satellite mission. A comparison with time-coincident Tropical Rainfall Measurement Mission Microwave Imager records confirms the consistency of the coincident observations collected independently by the two instruments up to 89 GHz. The MADRAS noise levels of 1.2 K at 89 GHz and of 2.5 K at 157 GHz are in agreement with the required specifications of the mission. Compared to the 89 GHz polarized channels that mainly sense large ice particles (snow and graupel), the 157 GHz polarized channel is sensitive to smaller particles and provides additional information on the cloud systems. The analysis of the radiometric signal at 157 GHz reveals that the ice scattering can induce a polarization difference of the order of 10 K at that frequency. Based on radiative transfer modeling the specific signature is interpreted as the effect of mainly horizontally oriented ice cloud particles. This suggests that the effects of the cloud particle orientation should be considered in rain and cloud retrievals using passive radiometry at microwave and millimeter wavelengths.

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

“…Compared with 166 GHz, the 89 GHz TB V has a narrower dynamic range (∼ 60 K) before reaching the PD peak for both oceanic and land conditions. This result is consistent with the TMI 85 GHz PD behavior reported by Prigent et al (2005), but Defer et al (2014) reported a somewhat smaller PD peak amplitude (∼ 8 K) at 89 GHz using the MADRAS instrument onboard the Indo-French MeghaTropiques satellite mission. At 166 GHz, PD does not reach its peak until about 80 K colder than the clear-sky radiance.…”

“…This finding is consistent with Defer et al (2014) using MADRAS's 157 GHz polarization channel pairs. The PD bell curve gradually diminishes at clear-sky scenes (TB V ∼ 280 K), but approaches ∼ +2 K at very thick convective clouds (TB V ∼ 100 K).…”

“…Previous research (Defer et al, 2014) using another fully polarized RTM also recognized that other ice microphysical properties, including density and size, would impact the simulation results seriously. Therefore, more observations from higher-frequency microwave or even IR channels are very much needed, and would greatly facilitate the decoding of the microphysical information of frozen particle shape and orientation at different portions of the crystal size spectrum.…”

“…For spaceborne remote sensing, Prigent et al (2001Prigent et al ( , 2005 analyzed the polarimetric observations at 37 and 85 GHz from SSMI/S (Special Sensor Microwave Imager Sounder) and 85 GHz from TRMM-TMI (Tropical Rainfall Measurement Mission Microwave Imager), where they attributed significant polarimetric differences to horizontally oriented non-spherical liquid or frozen precipitating particles (Prigent et al, 2001(Prigent et al, , 2005. Defer et al (2014) found similar amplitudes of polarimetric signals at 89 and 157 GHz using the MADRAS (Microwave Analysis and Detection of Rain and Atmospheric Structures) instrument onboard the Megha-Tropiques Mission. Studies using groundbased radar also suggested similar polarimetric difference distribution (e.g., Homeyer and Kumjian, 2015).…”

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

“…Recently, the polarimetric data have been used to study ice microphysical properties (e.g., Hioki et al, 2016;Homeyer & Kumjian, 2015;Skofronick-Jackson et al, 2015). 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, 2005(Davis et al, , 2007Defer et al, 2014;Prigent et al, 2001Prigent et al, , 2005Zhou et al, 2012). Gong and Wu (2017) (GW17 hereafter) first identified the similar features from the GPM-GMI 166 and 89 GHz observations.…”