Estimation of Surface Air Specific Humidity and Air–Sea Latent Heat Flux Using FY-3C Microwave Observations

Latent heat flux (LHF) plays an important role in the global hydrological cycle and is therefore necessary to understand global climate variability. It has been reported that the near-surface specific humidity is a major source of error for satellite-derived LHF. Here, a new empirical model relating multichannel brightness temperatures ( $T_B$ ) obtained from the Fengyun-3 (FY-3C) microwave radiometer and sea surface air specific humidity ( $Q_a$ ) is proposed. It is based on the relationship between $T_B$ , $Q_a,$ sea surface temperature (SST), and water vapor scale height. Compared with in situ data, the new satellite-derived $Q_a$ and LHF both exhibit better statistical results than previous estimates. For $Q_a$ , the bias, root mean square difference (RMSD), and the correlation coefficient (R²) between satellite and buoy in the mid-latitude region are 0.08 g/kg, 1.76 g/kg, and 0.92, respectively. For LHF, the bias, RMSD, and R² are 2.40 W/m², 34.24 W/m², and 0.87, respectively. The satellite-derived $Q_a$ are also compared with National Oceanic and Atmospheric Administration (NOAA) Cooperative Institute for Research in Environmental Sciences (CIRES) humidity datasets, with a bias, RMSD, and R² of 0.02 g/kg, 1.02 g/kg, and 0.98, respectively. The proposed method can also be extended in the future to observations from other space-borne microwave radiometers.