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NOAA SEARCH Element 1: Retrospective Analysis of Arctic Clouds and Radiation from Surface and Satellite Measurements

Jeff Key Taneil Uttal Robert Stone Institution: NOAA NESDIS

Abstract

Recent studies have shown that Northern Hemisphere sea ice extent and thickness have been decreasing (cf., Parkinson et al., 1999; Vinnikov et al., 1999), while land surface air temperature has increased markedly over the last 30 years (Serreze et al., 2000). Arctic climate change has also been noted in the horizontal flux of precipitable water snowfall, and vegitation (Groves and Francis, 2002; Chapman and Walsh, 1993; Myneni et al., 1997). While these studies indicate that the Arctic has been warming, it is not clear how other aspects of the climate system have forced the change. In particular how do changes in surface and cloud properties interact and affect the surface radiation budget; i.e., what is the cloud-radiation feedback?

Answers to these questions will only come through an analysis of multi-decadal datasets. Surface-based meteorological and radiation data have been collected at various locations across the Arctic for many years, with some observations dating back to the 1920s. However, surface stations are sparse, and many are scaling back operations. Satellite meteorological datasets that now span two decades provide a pan-Arctic perspective. While the measurement principles are very different, both types of observations offer the potential to detect and monitor climate change. For example, long-term measurements from meteorological stations have shown that the surface temperature of the Arctic land areas has been increasing over the past few decades. These trends have been verified by satellite data for the past 20 years, and trends in satellite-derived cloud amount and the cloud radiative effect have recently been reported. In turn, similar trends found at surface stations corroborate the satellite findings.

Nevertheless, there is still much that can be learned from the historical surface and satellite datasets. Cloud and radiation fields need to be examined in more detail, other geophysical parameters should be examined, similarities and differences in surface and satellite-derived measurements need to be assessed, and regional trends must be explained. Furthermore, the interactions between parameters, i.e., the ice/snow albedo and cloud radiation feedbacks, are poorly understood. The objective of this element is to evaluate the degree to which historical and ongoing measurements can be used to answer SEARCH science questions and to aid in the evaluation of optimum locations for an expansion of the Arctic observing network (Element 3). The task is to perform a retrospective analysis of coincident surface measurements and satellite-derived quantities, comparing one to the other, and assessing the spatial and temporal variability in each parameter.