Surface Moistening Trends in the Northern North American Great Plains Increase the Likelihood of Convective Initiation
Surface Moistening Trends in the Northern North American Great Plains Increase the Likelihood of Convective Initiation
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DOI：
10.1175/jhm-d-17-0117.1
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发表时间：
2018-01-01
影响因子：
3.8
通讯作者：
Stoy, Paul C.
中科院分区：
文献类型：
--
作者：
Gerken, Tobias;Bromley, Gabriel T.;Stoy, Paul C.
土地管理影响大气边界层过程，最近减少夏季休耕的趋势导致加拿大大草原各省夏季降水增加，气温下降。目前还不清楚这种趋势是否也影响了邻近的美国北方大平原的水文气象，其中部分地区的土地管理也发生了类似的变化。在这里，MERRA-2再分析数据，涡度协方差观测，和混合层（ML）的大气模拟框架相结合，以证明对流预处理条件的可能性增加了约10%，自20世纪80年代中期以来，现在更敏感的进一步减少的鲍文比（Bo）和最大日净辐射Rn，R-max在蒙大拿州东北部。在研究区的对流季节波从20世纪80年代到现在已经从大约2减少到1，这主要是由于潜热通量的同时增加和显热通量的减少，与观察到的夏季休耕减少和种植增加一致。尽管从20世纪80年代到现在，5月和6月的湿度递减率显著下降，但日净辐射Rn没有变化。未来的研究应确定美国大平原地区的大气边界层高度的动态变化和解除凝结水平及其交叉作为对流降水发生的必要条件，并确定土地管理的持续变化是否会导致对流结果的未来变化。
Land management impacts atmospheric boundary layer processes, and recent trends reducing the practice of summer fallow have led to increases in precipitation and decreases in temperature in the Canadian Prairie provinces during summer. It is unclear if such trends also impact the hydrometeorology of the adjacent U.S. northern Great Plains, parts of which have seen similar changes in land management. Here, MERRA-2 reanalysis data, eddy covariance observations, and a mixed-layer (ML) atmospheric modeling framework are combined to demonstrate that the likelihood of convectively preconditioned conditions has increased by approximately 10% since the mid-1980s and is now more sensitive to further decreases in the Bowen ratio (Bo) and maximum daily net radiation R-n,R-max in northeastern Montana. Convective season Bo in the study area has decreased from approximately 2 to 1 from the 1980s until the present, largely due to simultaneous increases in latent heat flux and decreases in sensible heat flux, consistent with observed decreases of summer fallow and increases in cropping. Daily net radiation Rn has not changed despite a significant decrease in May and June humidity lapse rates from the 1980s to present. Future research should determine the area of the U.S. Great Plains that has seen changes in the dynamics of the atmospheric boundary layer height and lifted condensation level and their crossings as a necessary condition for convective precipitation to occur and ascertain if ongoing changes in land management will lead to future changes in convective outcomes.