Uncertainties in Space-Based Estimates of Clouds and Precipitation: Implications for Deriving Global Diabatic Heating (original) (raw)

The Earth's weather and climate is driven by the exchange of energy between the sun, atmosphere, surface, and space and energy transport required to establish a global balance. Clouds and precipitation play an integral role in this exchange, enhancing reflection of solar radiation to space, trapping thermal emission from the surface, and providing a mechanism for the direct transfer of energy to the atmosphere through the release of latent heat in precipitation. As a result, there is an intimate coupling between the climate, energy budget, and global hydrologic cycle. The problem of establishing observational evidence for these connections and climate change in general, poses a significant challenge to the observational community. This dissertation seeks to address the components of this problem related to observing the hydrologic cycle and its role in modulating the tropical energy budget, from space-based measurements. This work reports on a new technique which makes use of cloud and precipitation information from the Tropical Rainfall Measuring Mission to estimate the principal components of the tropical energy budget and to examine the mechanisms by which clouds and precipitation modify it. First, three distinct retrieval algorithms are employed to determine the three-dimensional structure of cloud and precipitation in the tropical atmosphere. The first retrieves cloud and precipitation profiles from passive microwave observations from the TRMM Microwave Imager while the second applies a different technique to the same observations in an effort to derive estimates of non-precipitating liquid cloud. Finally, the third algorithm makes use of infrared radiances from the Visible and Infrared Scanner to infer-ice cloud optical properties in non-precipitating regions. The reSUlting representation of the three-dimensional strucure of cloud and precipitation in the tropical atmosphere is then used as input to a broadband radiative transfer model to derive profiles of short-and longwave fluxes. These flux profiles are composited to present a TRMM-based estimate of the short-term tropical energy budget for oceanic regions over the month of February 1998. On average, over this period, the tropical atmosphere absorbs 51 Wm-2 or 13 % of the 393 Wm-2 of solar radiation it receives. A further 112 Wm-2 is reflected by atmospheric particles, clouds, and the surface, leaving 230 Wm-2 to be absorbed by the ocean. At thermal wavelengths, it is found that the ocean emits 436 Wm-2 of energy to the atmosphere while the atmosphere emits a total of 639 Wm-2 units, 407 Wm-2 downward toward the surface and 231 Wm-2 to space. Accounting for latent heat release which amounts to an exchange of 82 Wm-2 of energy between the surface and atmosphere, the results imply a deficit of 70 Wm-2 of energy in the atmosphere and a surplus of 121 Wm-2 at the Earth's surface. The implied net gain of 51 Wm-2 in the Earth-atmosphere system is consistent iii IV