TY - JOUR
T1 - Landform controls on low level moisture convergence and the diurnal cycle of warm season orographic rainfall in the Southern Appalachians
AU - Wilson, Anna M.
AU - Barros, Ana P.
N1 - Funding Information:
The first author acknowledges support by NSF Graduate Research Program Grant 1106401 and the Pratt School of Engineering . The research was funded by NASA Grant NNX13AH39G with the second author. For allowing us to set up instrumentation, we are grateful to Greg Wilson and Pamela McCown, to Asheville-Buncombe Technical Community College, to Paul Super and the National Park Service, and to Neil Carpenter and the Maggie Valley Sanitary District. We thank the University of North Carolina at Asheville and Duke University students who assisted with maintenance and deployment of our RG network and the other instrumentation used in this research. WRF simulations were conducted using computing resources at NCAR (Yellowstone) available through the first author’s NSF grant. Xiaoming Sun provided valuable help with initial model set-up. Last, generous support was provided by Florida International University with funds from the National Science Foundation for the first author to present some of this work at the Weather Radar and Hydrology 2014 International Conference.
Publisher Copyright:
© 2015 Elsevier B.V.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2015/12/1
Y1 - 2015/12/1
N2 - The Advanced Weather Research and Forecasting (WRF) model was used to simulate two warm season events representative of reverse orographic enhancement of warm season precipitation in the Southern Appalachians under weak (9-12 July, 2012) and strong (12-16 May, 2014) synoptic forcing conditions. Reverse orographic enhancement refers to significant enhancement of rainfall intensity (up to one order of magnitude) at low elevations in the inner mountain valleys, but not in the ridges. This is manifest in significant increases of radar reflectivity observations and associated integral quantities (rain rate) at low levels (within 500 m of the surface), as well as changes in the observed microphysical properties of rainfall (raindrop size distribution). Analysis of high-resolution (1.25 km × 1.25 km) WRF simulations shows that the model captures the march of observed rainfall, though not the timing in the case of strong synoptic forcing. For each event, the results show that the space-time variability of rainfall in the inner region is strongly coupled to the development and persistence of organized within-valley low-level moisture convergence that is a necessary precursor to valley fog and low level cloud formation. Microphysical interactions among precipitation from propagating storm systems, and local low-level clouds and fog promote coalescence efficiency through the seeder-feeder mechanism leading to significant enhancement of rainfall intensity near the ground as shown by Wilson and Barros (2014). The simulations support the hypothesis that ridge-valley precipitation gradients, and in particular the reverse orographic enhancement effects in inner mountain valleys, are linked to horizontal heterogeneity in the vertical structure of low level clouds and precipitation promoted through landform controls on moisture convergence.
AB - The Advanced Weather Research and Forecasting (WRF) model was used to simulate two warm season events representative of reverse orographic enhancement of warm season precipitation in the Southern Appalachians under weak (9-12 July, 2012) and strong (12-16 May, 2014) synoptic forcing conditions. Reverse orographic enhancement refers to significant enhancement of rainfall intensity (up to one order of magnitude) at low elevations in the inner mountain valleys, but not in the ridges. This is manifest in significant increases of radar reflectivity observations and associated integral quantities (rain rate) at low levels (within 500 m of the surface), as well as changes in the observed microphysical properties of rainfall (raindrop size distribution). Analysis of high-resolution (1.25 km × 1.25 km) WRF simulations shows that the model captures the march of observed rainfall, though not the timing in the case of strong synoptic forcing. For each event, the results show that the space-time variability of rainfall in the inner region is strongly coupled to the development and persistence of organized within-valley low-level moisture convergence that is a necessary precursor to valley fog and low level cloud formation. Microphysical interactions among precipitation from propagating storm systems, and local low-level clouds and fog promote coalescence efficiency through the seeder-feeder mechanism leading to significant enhancement of rainfall intensity near the ground as shown by Wilson and Barros (2014). The simulations support the hypothesis that ridge-valley precipitation gradients, and in particular the reverse orographic enhancement effects in inner mountain valleys, are linked to horizontal heterogeneity in the vertical structure of low level clouds and precipitation promoted through landform controls on moisture convergence.
KW - Complex terrain
KW - Numerical weather simulations
KW - Orographic enhancement
KW - Precipitation microphysics
KW - Seeder-feeder mechanism
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U2 - 10.1016/j.jhydrol.2015.10.068
DO - 10.1016/j.jhydrol.2015.10.068
M3 - Article
AN - SCOPUS:84964510433
SN - 0022-1694
VL - 531
SP - 475
EP - 493
JO - Journal of Hydrology
JF - Journal of Hydrology
ER -