Variability and trend of cloud parameters and OLR retrieved from the TOVS Pathfinder Path A dataset

Satellites provide a great platform to study the Earth-atmosphere system on practically all spatial and temporal scales. Thus, one may expect that their rapidly growing datasets could provide (or even could have provided) crucial insights not only for short-term weather processes/predictions but into the likely ongoing and potential future climate change processes as well. Though Earth-observing satellites have been around for decades, extracting climatically reliable information from their datasets faces rather formidable challenges. For example, satellite sensors can degrade, orbits can drift, and intercalibration of sensors on subsequent satellites may lack completely. However, efforts are under way to create and validate, or at least intercalibrate, satellite climatologies of atmospheric variables.

Clouds play an important role in the atmosphere on all spatial and temporal scales, and satellites can provide an ideal platform to access cloud and large scale atmospheric variables simultaneously and on comparable scales. This is extremely important for developing more reliable cloud models, which could help to improve the representation of cloud-climate feedbacks (probably the least known ones, still hindering global warming predictions, for example) in global general circulation models. The TOVS series of satellites were the first to provide this information since 1979 on. Cloud cover and cloud top pressure are among the key climatic parameters computed by the TOVS Path A algorithm using mainly the retrieved temperature and moisture profiles. Global energy balance of the Earth-atmosphere system may also change due to natural and man-made climate variations. Thus, changes in the OLR, also computed by TOVS, are crucial indicators of climate variations.

Here we present validation efforts of TOVS-retrieved cloud top pressures[P_c] and “effective” (A_eff, a product of infrared emissivity at 11 µm and physical cloud cover or A_c) cloud fractions. For example, the TOVS and ISCCP [available since 1983] cloud top pressures correlate strongly. Decadal trends in P_c and A_eff/A_c are also similar. However, validation of the TOVS Aeff time series requires further effort, since the ISCCP provides the Ac time series only. Currently we are pursuing this task using MODIS Aqua cloud retrievals for validating AIRS [which can be regarded as the “new and improved TOVS”] cloud products.

We also present TOVS OLR validation effort results. For instance, we take it as a very encouraging sign that global monthly mean OLR values computed by TOVS are in very good agreement with the available state-of-the-art CERES OLR measurements.