Quality Estimates of INSAT-3D Derived Cloud Top Temperature for Climate Data Record

Reliable measurements of cloud top temperature (CTT) are crucial for several applications including climate research and evaluation of cloud-resolving models. Being a relevant geophysical property of climate system, CTT is identified as an essential climate variable by global climate observing system (GCOS). This article evaluates quality of INSAT-3D retrieved CTT products at 4 km (CTT4 km) and 50 km (CTT50 km) resolutions in terms of GCOS requirements by validating them with concurrent measurements from ground-based hyper-spectral microwave radiometer (MWR). CTT4 km and CTT50 km agree with MWR retrieved CTTs at respective spatial resolutions, within 4 K and 5 K respectively, which are close to the GCOS required accuracy of CTT (1-5 K) for climate studies. The study also examines adequacy of GCOS standard spatial resolution for CTT (50 km) and dependence of spatial resolution on CTT, by comparing CTT50 km and CTT4 km. Analysis shows deviation of 7 K between CTT50 km and CTT4 km. It is observed that the effect of spatial resolution on CTT is relatively less for opaque clouds (with uncertainty within 3 K for 50% cloud fraction) compared to that for semitransparent cirrus (STC) clouds (within 9 K for 50% cloud fraction). These uncertainties are observed to be decreasing with increasing cloud fraction. Thus, our study shows that INSAT-3D CTT at 50-km resolution agrees with GCOS recommended spatial resolution for opaque clouds. However, caution should be taken in case of STCs. The results presented here are particularly important for scale-dependent approaches of cloud characterization and have significant implications for the parameterization of clouds in climate models.