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 (CTT
_{4 km}
) and 50 km (CTT
_{50 km}
) resolutions in terms of GCOS requirements by validating them with concurrent measurements from ground-based hyper-spectral microwave radiometer (MWR). CTT
_{4 km}
and CTT
_{50 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 CTT
_{50 km}
and CTT
_{4 km}
. Analysis shows deviation of 7 K between CTT
_{50 km}
and CTT
_{4 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.