Tropical Outgoing Longwave Radiation and Longwave Cloud Forcing Diurnal Cycles from CERES

Abstract

The diurnal cycle is a fundamental earth system variability driven by daily variations in solar insolation. Understanding diurnal variability is important for characterizing top-of-atmosphere and surface energy budgets. Climatological and seasonal first diurnal cycle harmonics of outgoing longwave radiation (OLR) and longwave cloud forcing (LWCF) are investigated using the Clouds and the Earth's Radiant Energy System (CERES) synoptic 3-hourly data. A comparison with previous studies indicates generally similar results. However, the results indicate that the CERES OLR diurnal cycle amplitudes are 10%-20% larger in desert regions than previous analyses. This difference results from the temporal interpolation technique overestimating the daily maximum OLR. OLR diurnal cycle amplitudes in other tropical regions agree with previous work. Results show that the diurnal maximum and minimum OLR variability contributes equally to the total OLR variance over ocean; however, over land the diurnal maximum OLR variance contributes at least 50% more to the total OLR variability than the minimum OLR. The differences in maximum and minimum daily OLR variability are largely due to differences in surface temperature standard deviations at these times, about 5-6 and 3-4 K, respectively. The OLR variance at diurnal maximum and minimum is also influenced by negative and positive correlations, respectively, between LWCF and clear-sky OLR. The anticorrelation between LWCF and clear-sky OLR at diurnal OLR maximum indicates smaller cloud fractions at warmer surface temperatures. The relationship between LWCF and clear-sky OLR at diurnal minimum OLR appears to result from a preference for deep convection, more high clouds, and larger LWCF values to occur with warmer surface temperatures driving a narrower diurnal minimum OLR distribution.

The Atmospheric Infrared Sounder version 6 cloud products

“…A climate change signal in either the amplitude or phase of the diurnal cycle can have profound impacts on climate trends through the modulation of the daily timing of maximum (or minimum) cloud reflection, and the absorption and re-emission of infrared radiation by high ice clouds (e.g., Cairns, 1995). Convective precipitation (Nesbitt and Zipser, 2003;Dai, 2006), cloud frequency/amount (Chen and Houze, 1997;Rossow and Schiffer, 1999;Tian et al, 2004), and outgoing longwave radiation (e.g., Taylor, 2012) are perhaps the best-observed cloud-related quantities over the diurnal cycle. It has been well documented that there is a clear landsea contrast for the diurnal cycle of high clouds (cloud tops above 440 hPa) (e.g., Yang and Slingo, 2001;Tian et al, 2004).…”

Variability of Monthly Diurnal Cycle Composites of TOA Radiative Fluxes in the Tropics

“…One fundamental Earth system forcing is solar insolation, which drives a 24-h periodicity in Earth system variability referred to as the diurnal cycle. The diurnal cycle contributes significantly to variability in many geophysical variables including clouds, temperature, radiation, and precipitation (e.g., Gray and Jacobson 1977;Minnis and Harrison 1984;Hartmann and Recker 1986;Harrison et al 1988;Yang and Slingo 2001;Taylor 2012) and influences many geophysical processes (e.g., cloud formation, surface turbulence, and surface evaporation rates; Caldwell et al 2005;Strong et al 2005). Understanding and characterizing diurnal cycle features is critical for both Earth system modeling (Bechtold et al 2004;Del Genio and Wu 2010) and placing satellite observations of Earth into proper context (Raschke and Bandeen 1970;Short and Wallace 1980;Loeb et al 2009;Taylor and Loeb 2013).…”

“…The strongest surface temperature diurnal cycles on Earth are found in subtropical deserts (e.g., Atacama Desert) and drive significant diurnal cycle Denotes Open Access content. amplitudes more than 35 W m 22 in top-of-the-atmosphere (TOA) outgoing longwave radiation (OLR; Harrison et al 1988;Smith and Rutan 2003;Taylor 2012). Significant differences in the land and ocean convective diurnal cycle timing have also been identified: an early morning peak in oceanic convection (Gray and Jacobson 1977;Janowiak et al 1994) and a late afternoon-to-early evening convective peak over tropical land (Riehl and Miller 1978;Lin et al 2000;Nesbitt and Zipser 2003).…”

Insights into the diurnal cycle of global Earth outgoing radiation using a numerical weather prediction model

“…This is perhaps manifested most clearly in the strong diurnal signatures that EOR exhibits, a direct result of the rapidly evolving scene from which the radiation originates. Diurnal variability in the Earth system that defines such signatures has been studied extensively (e.g., Nitta and Sekine, 1994;Webster at al., 1996;Soden, 2000;Yang and Slingo, 2001;Wood et al, 2002;Nesbitt and Zipser, 45 2003;Taylor, 2012). However, discrepancies persist when comparing the diurnal cycles in observations and models (e.g., Betts and Jakob, 2002;Dai and Trenberth, 2004;Slingo et al, 2004;Tian et al, 2004;Itterly and Taylor, 2014).…”