Cloud Cover and Surface Radiation Budget
J. Key1, Y. Liu2, R. Stone3,4, C. Cox4, V. Walden5
1Center for Satellite Applications and Research, NOAA/NESDIS, Madison, WI, USA
2Cooperative Institute for Meteorological Satellite Studies, University of Wisconsin, Madison, WI, USA
3Global Monitoring Division, NOAA/ESRL, Boulder, CO, USA
4Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
5Department of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA
November 21, 2013
- There was considerably less winter cloud cover in early 2013 over the western Arctic Ocean relative to the last decade, and above average cloud cover in late spring/early summer.
- The cloud cover anomalies had a cooling effect on the surface, particularly where sea ice persisted during summer 2013.
Winter 2012-2013 was characterized by below average cloud cover over the western Arctic Ocean, particularly in January (Fig. 6a) and February. In contrast, late spring and early summer cloud cover was above average. (Fig. 6b). The cloud cover anomalies are consistent with large-scale pressure and circulation patterns, where positive 850 hPa geopotential height anomalies (Fig. 7) occurred in winter (January-March 2013) and negative anomalies occurred in the late spring and early summer (May-June). Positive wintertime geopotential height anomalies generally result in less cloud cover, while negative anomalies are associated with increased cyclonic activity and greater cloud cover (Liu et al. 2007).
Over the Arctic Ocean, clouds warm the surface during winter and cool the surface in mid-summer (e.g., Stone 1997). The effect of the observed cloud cover anomalies on the radiation budget is one of decreased net longwave radiation during winter that results in cooling at the surface, and decreased solar insolation during summer, which also results in cooling. This can be seen in the January net radiation at the surface from the European Centre for Medium-range Weather Forecasts (ECMWF) Reanalysis project (ERA-Interim; Fig. 8a), when relatively low net radiation prevailed over the entire Arctic Basin. There is empirical evidence of a decrease in net radiation in response to reduced cloud cover (Fig. 6a) at Barrow, Alaska, where the surface radiation budget has been monitored for many years. During January 2013, for instance, there was a reduction in net radiation at the surface of approximately 12 W/m-2 (Fig. 9), consistent with the ERA-Interim analysis for that location (Fig 8a).
In June, the net surface radiation distribution (Fig. 8b) is consistent with the cloud cover (Fig. 6b) and the sea ice distribution, with high net radiation around the margins of the Arctic Basin, where the sea ice retreated away from the coast, and low net radiation where sea ice persisted all summer (see the essays on Air Temperature and Sea Ice). Overall, however, the cloud radiative effect on the surface energy budget is larger in January than in June.
Dee, D. P., and 35 others, 2011: The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q. J. Roy. Met. Soc., 137, 553-597.
Liu, Y., J. Key, J. Francis, and X. Wang, 2007: Possible causes of decreasing cloud cover in the Arctic winter, 1982-2000. Geophys. Res. Lett., 34, L14705, doi:10.1029/2007GL030042.
Stone, R. S., 1997: Variations in western Arctic temperature in response to cloud radiative and synoptic-scale influences. J. Geophys. Res., 102(D18), 21769-21776.