Abstract

The sensitivity of microwave brightness temperatures (TBs) to hydrometeors at frequencies between 89 and 190 GHz is investigated by comparing Fengyun-3C (FY-3C) Micro-Wave Humidity Sounder-2 (MWHS-2) measurements to radar reflectivity profiles and retrieved products from Global Precipitation Measurement’s (GPM) Dual-frequency Precipitation Radar (DPR). Scattering-induced TB depressions (ΔTBs), calculated by subtracting simulated cloud-free TBs from bias-corrected observed TBs for each channel, are compared to DPR-retrieved hydrometeor water path (HWP) and vertically integrated radar reflectivity (ZINT). We also account for the amount of hydrometeors actually visible in each MWHS-2 channel by weighting HWP with the channel’s cloud-free gas transmission profile and the observation slant path. We denote these transmission-weighted, slant-path-integrated quantities with a superscript asterisk (e.g. HWP*). The so-derived linear sensitivity of ΔTB with respect to HWP* increases with frequency roughly to the power of 1.78. A retrieved HWP* of 1 kg/m2 at 89 GHz on average corresponds to a decrease in observed TB, relative to a cloud-free background, of 11 K. At 183 GHz, the decrease is about 34 – 53 K. We perform a similar analysis using the vertically integrated, transmission-weighted slant-path radar reflectivity ZINT* and find that ΔTB also decreases approximately linearly with (ZINT*)0.58. The exponent of 0.58 corresponds to the one we find in the purely DPR-retrieval-based ZINT-HWP-relation. The observed sensitivities of ΔTB with respect to ZINT* and HWP* allow for the validation of hydrometeor scattering models.

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Current affiliation: Earth & Environmental Sciences Department, Vanderbilt University, Nashville, TN, 37235

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