Regional cloud cover change associated with global climate change: Case studies for three regions of the United States

Land-based observations of cloud cover. for the period 1900-87 and averaged over three geographical regions of the United States (coastal southwest, c oastal northeast, and southern plains). show strong positive correlations w ith one estimate of global mean surface temperature, a finding consistent w ith prior investigations that suggest cloud cover over land has increased d uring global warm periods relative to cold periods. it is also found that t he strengths of three permanent high/low pressure systems (North Pacific hi gh, Icelandic low, anti Azores high) are negatively correlated with global mean surface temperature, suggesting a possible connection between regional cloud cover, for certain locations, and the strengths of adjacent high/low pressure systems. Specifically, for the regions considered it is suggested that the coastal southwest cloud cover is related to changes in the streng th of the subtropical North Pacific high, that For the southern plains also to the strength of the North Pacific high, and that for the coastal northe ast to the strength of the Icelandic low. Thus the climate-induced change i n cloud cover for certain regions appears related, at least in part, to cli mate-induced change in the strengths of adjacent high/low pressure systems, and plausible physical explanations for this relation are provided for the three regions that have been studied. This does not, of course, provide a direct physical cause-and-effect explanation for the changes in regional cl oud cover, because the mechanisms that cause the intensities of the high/lo w pressure systems to change are not understood.