18th Conference on Climate Variability and Change


Diurnal cycles of the surface radiation budget data set

Pamela E. Mlynczak, SAIC, Hampton, VA; and G. L. Smith, P. W. Stackhouse, and S. K. Gupta

There are two strong cycles of solar radiation: the annual cycle and the diurnal cycle. An examination of the response of the weather/climate system to radiative forcing at the annual and daily time scales provides insight into the process which constitute the weather/climate system. At the daily time scale, the insolation interacts strongly with the surface, heating the land and transfering heat to the lower atmosphere. The present paper examines the diurnal cycles of radiation fluxes at the surface, using the Surface Radiation Budget Data Set, which was developed by the Langley Research Center of NASA as part of the Global Energy and Water Experiment (GEWEX). The Surface Radiation Budget Data Set contains seven components describing radiation flux: shortwave up, down and net, longwave up, down and net, and total radiation net. These parameters are given for every third hour, starting at midnight GMT. The analysis began by interpolating to get the parameters at each location for each hour. A principal component analysis was used to study the diurnal cycles of these components for an average July. The large thermal inertia of the ocean causes the diurnal cycle of its temperature to be quite small, so the globe was partitioned into land and ocean for this study. For land a single term describes the time variation of the diurnal cycle of SRB components for 97% of the power and greater, except for longwave, for which the first term accounts for 92.6% percent of the power for longwave down and 94.5% for net longwave. Asymmetries of SW about local noon are small, showing that globally diurnal variations of clouds play a minor role in SW. The longwave components have a peak after noon due to warming of the surface and of the air. Geographically, the strongest diurnal cycles are over the deserts for the upward and downward shortwave and longwave, but these regions have average net shortwave, net longwave and net total radiation fluxes. For ocean the maximum diurnal variability of downward and net shortwave flux is over the regions of climatological high pressure, with the absence of clouds. The downward longwave flux has a small but complex variation in time of day. Terms accounting for 1% or less do not have clear physical interpretation. Many of these small terms can be identified as artifacts of the data set and of the interpolation from 8 GMT times to 24 times.

extended abstract  Extended Abstract (2.1M)

Poster Session 1, Observed climate change
Monday, 30 January 2006, 2:30 PM-4:00 PM, Exhibit Hall A2

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