Abstract
Atmospheric temperature time series for the nine climate regions of the contiguous U.S. are accurately reproduced by the superposition of oscillatory modes, representing the Atlantic multidecadal oscillation (AMO) and the Pacific decadal oscillation (PDO), on a monotonic mode representing, at least in part, the effect of radiant forcing due to increasing atmospheric CO2. The relative importance of the different modes varies among the nine climate regions, grouping them into three mega-regions: Southeastern comprising the South, Southeast and Ohio Valley; Central comprising the Southwest, Upper Midwest, and Northeast; and Northwestern comprising the West, Northwest, and Northern Rockies & Plains. The defining characteristics of the mega-regions are: Southeastern – dominated by the AMO, no PDO influence; Central – influenced by the AMO, no PDO influence, Northwestern – influenced by both the AMO and PDO. Temperature vs. time curves calculated by combining the separate monotonic and oscillatory modes agree well with the measured temperature time series, indicating that the 1938-1974 small decrease in contiguous U.S. temperature was caused by the superposition of the downward-trending oscillatory mode on the upward-trending monotonic mode while the 1980-2000 large increase in temperature was caused by the superposition of the upward-trending oscillatory mode on the upward-trending monotonic mode. The oscillatory mode, mostly representing the AMO, was responsible for about 72% of the entire contiguous U.S. temperature increase over that time span with the contribution varying from 86 to 42% for individual climate regions.
Highlights
The atmospheric temperature of the contiguous U.S has increased by about 1.0 K since 1910, but not at a uniform rate, increasing between 1910 and 1938, decreasing slightly between 1938 and 1974, increasing between 1974 and 2000, and decreasing slightly since 2000
The nine National Climatic Data Center (NCDC) climate regions fall into three groups: Ohio Valley (OV), S, and SE—where the monotonic mode slopes are much smaller than for the other climate regions; Northern Rockies & Plains (NR&P), W, and NW—where the Pacific decadal oscillation (PDO) is a significant part of the oscillatory mode; and Upper Midwest (UMW), SW, and NE—where neither of these circumstances apply
The oscillatory mode amplitude decreases from 0.79 K for the OV, S, and SE group to 0.68 K for the UMW, SW, and NE group to 0.59 K for the NR&P, W, and NW group
Summary
The atmospheric temperature of the contiguous U.S has increased by about 1.0 K since 1910, but not at a uniform rate, increasing between 1910 and 1938, decreasing slightly between 1938 and 1974, increasing between 1974 and 2000, and decreasing slightly since 2000. Ocean Temperature Oscillations and Contiguous U.S Temperatures by Chen & Tung [1] and are mostly focused on change in radiative forcing due to volcanic or anthropogenic aerosols or change in ocean heat content. The latter is a reasonable explanation since, compared to the atmosphere, the ocean is able to store very large amounts of heat with little change in temperature (the heat capacity of the entire atmosphere is equal to that of only a few meters of ocean), but no fully satisfactory explanation has been offered for the mechanism by which heat might be captured or why it should be captured but was not between 1980 and 2000
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