Decadal variations in the season advancement of sp

Authors: RuiXia Zhao Hong Zhang GuoXiong Wu WeiPing Li AiLi Shi

Publish Date: 2012/04/15

Volume: 55, Issue: 8, Pages: 1358-1370

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Abstract

Spring is the critical period for atmospheric circulation transition from winter to summer The spring water cycle is very important to agriculture in planting crop and the initial growth of crop Note that there was a significant abrupt decadal change in the water budget increase during early spring over eastern China in the late 1970s Studied here are the decadal variations of water budgets over the key regions and the associated change of water cycle over East Asia and atmospheric circulation over AsiaWest Pacific region in early spring using the observed OBS precipitation the ECMWF ERA and NCEP/NCAR reanalysis NRA and the Mantua’s Pacific decadal oscillation index PDOI The water budget increments from March to April exhibited a sharp decrease over the key region around Huaihe River basin HHR 111°–120°E 31°–36°N after year 1978 Before 1977 the water vapor flux through south boundary of the HHR region increased greatly during March to April by 152 mm d−1 in ERA and 188 mm d−1 in NRA Concurrently the moisture convergence and precipitation over the region also increased greatly The increment for the moisture convergence was 111 mm d−1 in ERA and 122 mm d−1 in NRA and for the precipitation was 108 mm d−1 in observation and 105 mm d−1 in ERA April was the time that the water budgets over HHR increased most rapidly before 1977 But after 1978 the water budgets decreased conversely from Mach to April The water vapor flux increment through the south boundary was −003 mm d−1 in ERA and 001 mm d−1 in NRA the moisture convergence increment was −091 mm d−1 in ERA and −053 mm d−1 in NRA and precipitation increment was −008 mm d−1 in observation and −015 mm d−1 in ERA Further investigation has shown that the largescale atmospheric circulation in the early spring has correspondingly changed significantly after the late 1970s During March to April the weakening of the trough over East Asia became significantly slower and the strengthening of the ridge over the west China became significantly faster in the middle troposphere after the late 1970s At the same time in the lower troposphere the strengthening and northward extending of the west part of the subtropical high and the weakening of the trough over the southwest part of the Aleutian low in the early spring became slower and the weakening of the main part of Asian high became slower but the strengthening of its west part became faster This significant decadal change of circulation caused a sharp decrease in the northward extending speed of water vapor transport and in the water budgets increasing speed over the southeastern China during early spring after the late 1970s

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