Remote Sensing of TTL Radiation Balance

Determining the level of zero net radiative heating (Qnet_0) is critical to understanding parcel trajectory in the Tropical Tropopause Layer (TTL) and associated stratospheric hydration processes. The advent of a wealth of remote sensing measurements from polar-orbiting satellites may provide the relevant horizontal and vertical information for assessing TTL solar heating and infrared cooling rates. Formal error budget analysis for the determination of radiative heating and cooling rates from remote sensing instruments is presented with a focus on thermal infrared sounders such as AIRS and TES and active sounders such as CloudSat. It is found that the exact details of the water vapor profile are less important to determining Qnet_0 than understanding the temperature structure between 50 and 200 mbar, the ozone profile, and the underlying cloud profile structure. Nevertheless, determination of the contribution of the far-infrared bands (15 to 100 μm) may be problematic especially for scenes where total cloud cover is significant. A priori and a posteriori maps of Qnet_0 are presented with the former derived from ECMWF climatology and the latter derived from AIRS and CloudSat products. Selected comparisons of Qnet_0 derived from in situ measurements are also presented.