scholarly journals Understanding the Dominant Sources and Tracks of Moisture for Summer Rainfall in the Southwest United States

2018 ◽  
Vol 123 (10) ◽  
pp. 4850-4870 ◽  
Author(s):  
Srijita Jana ◽  
Balaji Rajagopalan ◽  
Michael A. Alexander ◽  
Andrea J. Ray
Keyword(s):  
United States ◽  
Summer Rainfall ◽  
Southwest United States

scholarly journals The Contribution of Eastern North Pacific Tropical Cyclones to the Rainfall Climatology of the Southwest United States

2009 ◽  
Vol 137 (8) ◽  
pp. 2415-2435 ◽  
Author(s):  
Kristen L. Corbosiero ◽  
Michael J. Dickinson ◽  
Lance F. Bosart
Keyword(s):  
United States ◽  
New Mexico ◽  
Tropical Cyclones ◽  
North Pacific ◽  
Southern California ◽  
Warm Season ◽  
Direct Interaction ◽  
Summer Rainfall ◽  
Southwest United States ◽  
Rainfall Climatology

Abstract Forty-six years of summer rainfall and tropical cyclone data are used to explore the role that eastern North Pacific tropical cyclones (TCs) play in the rainfall climatology of the summer monsoon over the southwestern United States. Thirty-five TCs and their remnants were found to bring significant rainfall to the region, representing less than 10% of the total number of TCs that formed within the basin. The month of September was the most common time for TC rainfall to occur in the monsoon region as midlatitude troughs become more likely to penetrate far enough south to interact with the TCs and steer them toward the north and east. On average, the contribution of TCs to the warm-season precipitation increased from east to west, accounting for less than 5% of the rainfall in New Mexico and increasing to more than 20% in southern California and northern Baja California, with individual storms accounting for as much as 95% of the summer rainfall. The distribution of rainfall for TC events over the southwest United States reveals three main categories: 1) a direct northward track from the eastern Pacific into southern California and Nevada, 2) a distinct swath northeastward from southwestern Arizona through northwestern New Mexico and into southwestern Colorado, and 3) a broad area of precipitation over the southwest United States with embedded maxima tied to terrain features. Differences in these track types relate to the phasing between, and scales of, the trough and TC, with the California track being more likely with large cutoff cyclones situated off the west coast, the southwest–northeast track being most likely with mobile midlatitude troughs moving across the intermountain west, and the broad precipitation category generally exhibiting no direct interaction with midlatitude features.

scholarly journals Decadal Variation of the Southwest U.S. Summer Monsoon Circulation and Rainfall in a Regional Model

2007 ◽  
Vol 20 (18) ◽  
pp. 4702-4716 ◽  
Author(s):  
Qi Hu ◽  
Song Feng
Keyword(s):  
United States ◽  
Moisture Transport ◽  
Gulf Of California ◽  
Monsoon Rainfall ◽  
Summer Rainfall ◽  
Western United States ◽  
Low Level ◽  
Southwest United States ◽  
Dry Conditions ◽  
Rainfall Variations

Abstract Previous studies have identified several major causes for summer rainfall variations over the southwest United States, for example, land memory (i.e., relationships between antecedent winter season precipitation and snow cover anomalies and subsequent summer rainfall anomalies over the southwest United States; these anomalies are likely most important in the northwest United States, although antecedent anomalies in the southwest United States also may be important in determining summer rainfall variations) and sea surface temperature (SST) anomalies in the North Pacific. Atmospheric responses to these “boundary forces” interact with moisture flows from the Gulf of Mexico and from the Gulf of California to influence the rainfall in the Southwest. The land memory and the SST effects were further found to be “naturally separated,” in the sense that they each played a dominant role influencing the monsoon rainfall variation during different periods of the last century. This separation was also manifested by different dominant low-level moisture transport anomalies in those periods. Several new questions have arisen from these findings: How have the land memory and the SST effects been “separated,” so as to affect the monsoon rainfall variations during different periods, or “regimes”? And, what are the corresponding changes of low-level flows, and hence moisture transports into the southwest United States that help achieve the land memory or the SST effects on the rainfall variations during these different regimes? These questions, and related issues, are addressed using a numerical model of regional climate. The model was used to simulate 14 individual warm seasons (April–October) in each of the postulated regimes. Analyses of the simulation results showed systematic and significant changes in atmospheric circulation anomalies between the two regimes. In the early regime (1961–90), when the land memory effect was strong, the average geopotential height was lower and storm activity was more intense over the central and western United States than in the more recent regime (from 1990 on), indicating reduced eddy energy and momentum exchanges between high and low latitudes in the western United States. The effects of these changes on the monsoon rainfall were achieved by very different low-level flow and moisture transport anomalies. In the earlier regime, low-level flow and moisture transport anomalies in the southwest United States were primarily due to easterlies and southeasterlies into the Southwest for its wet monsoon conditions, with reversed anomalies for dry conditions. In the recent regime, these anomalies changed, with primarily southerlies and southwesterlies from the Gulf of California into the Southwest during its wet monsoon conditions, and reversed flow anomalies for dry conditions. These changes indicate that different physical processes, including those responsible for the planetary-scale atmospheric circulation, led to monsoon rainfall variations during each of these regimes.

Understanding grower perceptions and attitudes on the use of nontraditional water sources, including reclaimed or recycled water, in the semi-arid Southwest United States

2019 ◽  
Vol 170 ◽  
pp. 500-509 ◽  
Author(s):  
Jessica L. Dery ◽  
Channah M. Rock ◽  
Rachel Rosenberg Goldstein ◽  
Cathy Onumajuru ◽  
Natalie Brassill ◽  
...  
Keyword(s):  
United States ◽  
Water Sources ◽  
Recycled Water ◽  
Southwest United States ◽  
Perceptions And Attitudes ◽  
Arid Southwest ◽  
Semi Arid

Investigation of the Summer Climate of the Contiguous United States and Mexico Using the Regional Atmospheric Modeling System (RAMS). Part II: Model Climate Variability

2007 ◽  
Vol 20 (15) ◽  
pp. 3866-3887 ◽  
Author(s):  
Christopher L. Castro ◽  
Roger A. Pielke ◽  
Jimmy O. Adegoke ◽  
Siegfried D. Schubert ◽  
Phillip J. Pegion
Keyword(s):  
United States ◽  
Climate Model ◽  
Weather Prediction ◽  
Regional Climate ◽  
Summer Rainfall ◽  
Atmospheric Modeling ◽  
Regional Atmospheric Modeling System ◽  
Prediction Mode ◽  
Regional Atmospheric Modeling ◽  
Seasonal Weather

Abstract Summer simulations over the contiguous United States and Mexico with the Regional Atmospheric Modeling System (RAMS) dynamically downscaling the NCEP–NCAR Reanalysis I for the period 1950–2002 (described in Part I of the study) are evaluated with respect to the three dominant modes of global SST. Two of these modes are associated with the statistically significant, naturally occurring interannual and interdecadal variability in the Pacific. The remaining mode corresponds to the recent warming of tropical sea surface temperatures. Time-evolving teleconnections associated with Pacific SSTs delay or accelerate the evolution of the North American monsoon. At the period of maximum teleconnectivity in late June and early July, there is an opposite relationship between precipitation in the core monsoon region and the central United States. Use of a regional climate model (RCM) is essential to capture this variability because of its representation of the diurnal cycle of convective rainfall. The RCM also captures the observed long-term changes in Mexican summer rainfall and suggests that these changes are due in part to the recent increase in eastern Pacific SST off the Mexican coast. To establish the physical linkage to remote SST forcing, additional RAMS seasonal weather prediction mode simulations were performed and these results are briefly discussed. In order for RCMs to be successful in a seasonal weather prediction mode for the summer season, it is required that the GCM provide a reasonable representation of the teleconnections and have a climatology that is comparable to a global atmospheric reanalysis.

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