Publication Date:
2015-08-03
Description:
In the long term, precipitation in the central U.S. decreases by about 25% during the seasonal transition from June to July. This precipitation decrease is observed to have intensified since 1979, and such intensification could have enhanced spring drought occurrences in the central U.S., in which conditions quickly evolve from being abnormally dry to exceptionally dry. Various atmospheric and land reanalysis datasets were analyzed to examine the trend in the June-to-July seasonal transition. It was found that the intensified deficit in precipitation was accompanied by increased downward shortwave radiation flux, tropospheric subsidence, enhanced evaporative fraction, and elevated planetary boundary layer height, all of which could and did lead to surface drying. The change in tropospheric circulation was characterized by an anomalous ridge over the western U.S. and a trough on either side – a pattern known to suppress rainfall in the central U.S. The pattern of these trends calculated from 1979 to 2011 shows similarity with the evolution of the 2012 record drought from spring to summer.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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