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.

scholarly journals Atmospheric Moisture Transport over the United States and Mexico as Evaluated in the NCEP Regional Reanalysis

2005 ◽  
Vol 6 (5) ◽  
pp. 710-728 ◽  
Author(s):  
Kingtse C. Mo ◽  
Muthuvel Chelliah ◽  
Marco L. Carrera ◽  
R. Wayne Higgins ◽  
Wesley Ebisuzaki
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
Great Plains ◽  
Moisture Transport ◽  
Gulf Of California ◽  
Phase Relationship ◽  
The United States ◽  
Low Level ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The large-scale atmospheric hydrologic cycle over the United States and Mexico derived from the 23-yr NCEP regional reanalysis (RR) was evaluated by comparing the RR products with satellite estimates, independent sounding data, and the operational Eta Model three-dimensional variational data assimilation (3DVAR) system (EDAS). In general, the winter atmospheric transport and precipitation are realistic. The climatology and interannual variability of the Pacific, subtropical jet streams, and low-tropospheric moisture transport are well captured. During the summer season, the basic features and the evolution of the North American monsoon (NAM) revealed by the RR compare favorably with observations. The RR also captures the out-of-phase relationship of precipitation as well as the moisture flux convergence between the central United States and the Southwest. The RR is able to capture the zonal easterly Caribbean low-level jet (CALLJ) and the meridional southerly Great Plains low-level jet (GPLLJ). Together, they transport copious moisture from the Caribbean to the Gulf of Mexico and from the Gulf of Mexico to the Great Plains, respectively. The RR systematically overestimates the meridional southerly Gulf of California low-level jet (GCLLJ). A comparison with observations suggests that the meridional winds from the RR are too strong, with the largest differences centered over the northern Gulf of California. The strongest winds over the Gulf in the RR extend above 700 hPa, while the operational EDAS and station soundings indicate that the GCLLJ is confined to the boundary layer.

Redescription of the holotype of Bostrichoclerus bicornus Van Dyke, 1938, a rare species of the New World Tillinae Fauna (Coleoptera: Cleridae), with some taxonomic notes

Zootaxa ◽  
2019 ◽  
Vol 4544 (4) ◽  
pp. 548
Author(s):  
ALAN F. BURKE ◽  
JOHN M. JR. LEAVENGOOD ◽  
CLARKE H. SCHOLTZ ◽  
CATHERINE L. SOLE
Keyword(s):  
United States ◽  
Rare Species ◽  
Gulf Of California ◽  
Southern California ◽  
New World ◽  
Original Description ◽  
San Bernardino County ◽  
Southwest United States ◽  
Northwest Mexico ◽  
San Bernardino

Bostrichoclerus bicornus Van Dyke is known from southwest United States and northwest Mexico. To date, only two specimens have been captured: the holotype, collected on Isla Angel de la Guarda, in the Gulf of California, Mexico, and a second individual collected in San Bernardino County, California, United States. The original description of B. bicornus is brief and lacks any images. Considering its rarity, we present the redescription of this species based on the examination of the holotype and compare this taxon to similar genera of New World Tillinae. Images of the holotype and the Bostrichoclerus specimen collected in southern California are given. We conclude that B. bicornus is undoubtedly a member of the subfamily Tillinae with unclear intergeneric relations in the group. 

scholarly journals Variation of the North American Summer Monsoon Regimes and the Atlantic Multidecadal Oscillation

2008 ◽  
Vol 21 (11) ◽  
pp. 2371-2383 ◽  
Author(s):  
Qi Hu ◽  
Song Feng
Keyword(s):  
United States ◽  
North American ◽  
Summer Rainfall ◽  
Atlantic Multidecadal Oscillation ◽  
North American Monsoon ◽  
Western North America ◽  
The North ◽  
West Mexico ◽  
Central United States ◽  
Rainfall Variations

Abstract The North American summer monsoon holds the key to understanding warm season rainfall variations in the region from northern Mexico to the Southwest and the central United States. Studies of the monsoon have pictured mosaic submonsoonal regions and different processes influencing monsoon variations. Among the influencing processes is the “land memory,” showing primarily the influence of the antecedent winter season precipitation (snow) anomalies in the Northwest on summer rainfall anomalies in the Southwest. More intriguingly, the land memory has been found to vary at the multidecadal time scale. This memory change may actually reflect multidecadal variations of the atmospheric circulation in the North American monsoon region. This notion is examined in this study by first establishing the North American monsoon regimes from relationships of summer rainfall variations in central and western North America, and then quantifying their variations at the multidecadal scale in the twentieth century. Results of these analyses show two monsoon regimes: one featured with consistent variations in summer rainfall in west Mexico and the Southwest and an opposite variation pattern in the central United States, and the other with consistent rainfall variations in west Mexico and the central United States but different from the variations in the southwest United States. These regimes have alternated at multidecadal scales in the twentieth century. This alternation of the regimes is found to be in phase with the North Atlantic Multidecadal Oscillation (AMO). In warm and cold phases of the AMO, distinctive circulation anomalies are found in central and western North America, where lower than average pressure prevailed in the warm phase and the opposite anomaly in the cold phase. Associated wind anomalies configured different patterns for moisture transport and may have contributed to the development and variation of the monsoon regimes. These results indicate that investigations of the effects of AMO and its interaction with the North Pacific circulations could lead to a better understanding of the North American monsoon variations.

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.

Roles of water vapor sources and transport in the intraseasonal and interannual variation in the peak monsoon rainfall over East China

2021 ◽  
Author(s):  
Qucheng Chu ◽  
Qiguang Wang ◽  
Guolin Feng ◽  
Zikang Jia ◽  
Gang Liu
Keyword(s):  
Water Vapor ◽  
South China ◽  
Moisture Transport ◽  
Interannual Variation ◽  
Monsoon Rainfall ◽  
Summer Precipitation ◽  
Summer Rainfall ◽  
East China ◽  
Source Water

Abstract ERA-Interim reanalysis data from 1979–2017 are utilized to analyze the intraseasonal and interannual variabilities in the moisture transport associated with the summer rainfall over East China. Three key issues of moisture sources for East China summer precipitation are discussed in this study: the identification of the primary moisture sources of summer precipitation, determination of their individual contributions to the intraseasonal variation in summer precipitation, and determination of the extent to which each source affects the interannual variation in precipitation during the peak monsoon rainfall period (PMRP). Through the Lagrangian method, the water vapor is divided into six sources, namely, the land area source (LD source), East China source (EC source, except for the target region), Indian Ocean source (IO source), Pacific Ocean source (PO source), South China Sea source (SCS source), and regional evapotranspiration sources. This study proposes that the rainfall over South China (SC) during the PMRP is mainly influenced by the IO source water vapor transport (52.4%). For the middle and lower Yangtze River valley (YRV), the rainfall contribution from southwesterly moisture transport accounts for approximately 50% of the total rainfall during the PMRP and determines the intraseasonal and interannual variation in the summer rainfall. The water vapor from terrestrial evaporation, which includes EC source water vapor (38.9%) and NC source water vapor (21.8%), is the most important moisture source for rainfall over North China (NC) during the PMRP.

Seasonal Shifts in the North American Monsoon

2007 ◽  
Vol 20 (9) ◽  
pp. 1923-1935 ◽  
Author(s):  
Katrina Grantz ◽  
Balaji Rajagopalan ◽  
Martyn Clark ◽  
Edith Zagona
Keyword(s):  
United States ◽  
North American ◽  
Gulf Of California ◽  
Monsoon Rainfall ◽  
Monsoon Season ◽  
North American Monsoon ◽  
Southwestern United States ◽  
Monsoon Period ◽  
The North ◽  
Ocean Conditions

Abstract Analysis is performed on the spatiotemporal attributes of North American monsoon system (NAMS) rainfall in the southwestern United States. Trends in the timing and amount of monsoon rainfall for the period 1948–2004 are examined. The timing of the monsoon cycle is tracked by identifying the Julian day when the 10th, 25th, 50th, 75th, and 90th percentiles of the seasonal rainfall total have accumulated. Trends are assessed using the robust Spearman rank correlation analysis and the Kendall–Theil slope estimator. Principal component analysis is used to extract the dominant spatial patterns and these are correlated with antecedent land–ocean–atmosphere variables. Results show a significant delay in the beginning, peak, and closing stages of the monsoon in recent decades. The results also show a decrease in rainfall during July and a corresponding increase in rainfall during August and September. Relating these attributes of the summer rainfall to antecedent winter–spring land and ocean conditions leads to the proposal of the following hypothesis: warmer tropical Pacific sea surface temperatures (SSTs) and cooler northern Pacific SSTs in the antecedent winter–spring leads to wetter than normal conditions over the desert Southwest (and drier than normal conditions over the Pacific Northwest). This enhanced antecedent wetness delays the seasonal heating of the North American continent that is necessary to establish the monsoonal land–ocean temperature gradient. The delay in seasonal warming in turn delays the monsoon initiation, thus reducing rainfall during the typical early monsoon period (July) and increasing rainfall during the later months of the monsoon season (August and September). While the rainfall during the early monsoon appears to be most modulated by antecedent winter–spring Pacific SST patterns, the rainfall in the later part of the monsoon seems to be driven largely by the near-term SST conditions surrounding the monsoon region along the coast of California and the Gulf of California. The role of antecedent land and ocean conditions in modulating the following summer monsoon appears to be quite significant. This enhances the prospects for long-lead forecasts of monsoon rainfall over the southwestern United States, which could have significant implications for water resources planning and management in this water-scarce region.

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

Integrated Approach to Remediatiion of Multiple Uranium Mill Tailing Sites for the US DOE in the Western United States

2003 ◽  
Author(s):  
Bill Van Dyke ◽  
Tom Dabrowski
Keyword(s):  
United States ◽  
Public Involvement ◽  
The United States ◽  
Lessons Learned ◽  
Department Of Energy ◽  
Western United States ◽  
Maximum Efficiency ◽  
Small Scale ◽  
Remedial Action ◽  
Low Level

This paper provides a case history of a highly successful approach that was developed and implemented for the U.S. Department of Energy (DOE) for the cleanup and remediation of a large and diverse population of uranium mill tailings sites located in the Western United States. The paper addresses the key management challenges and lessons learned from the largest DOE Environmental Management Clean-up Project (in terms of number of individual clean-up sites) undertaken in the United States. From 1986 to 1996, the Department of Energy’s Grand Junction Projects Office (GJPO) completed approximately 4600 individual remedial action site cleanup projects for large- and small-scale properties, and sites contaminated with residual hazardous and radioactive materials from former uranium mining and milling activities. These projects, with a total value of $597 million, involved site characterization, remedial design, waste removal, cleanup verification, transportation, and disposal of nearly 2.7 million cubic yards of low-level and mixed low-level waste. The project scope included remedial action at 4,200 sites in Grand Junction, Colorado, and Edgemont, South Dakota; 412 sites in Monticello, Utah; and, 44 sites in Denver, Colorado. The projects ranged in size and complexity from the multi-year Monticello Millsite Remedial Action Project, which involved investigations, characterization, remedial design, and remedial action at this uranium millsite along with design of a 2.5 million cubic yard disposal cell, to the remediation and reconstruction of thousands of smaller commercial and residential properties throughout the Southwestern United States. Because these projects involved remedial action at a variety of commercial facilities, businesses, churches, schools and personal residences, and the transportation of the waste through towns and communities, an extensive public involvement program was the cornerstone of an effort to promote stakeholder understanding and acceptance. The Project established a DOE model for rapid, economical, and effective remedial action. During the ten years of the contract, the management operations contractor (Duratek) met all project milestones on schedule and under budget, with no cost growth from the original scope. By streamlining remediation schedules and techniques, ensuring effective stakeholder communications, and transferring lessons learned from one project to the next, the contractor achieved maximum efficiency and the lowest remediation costs of any similar DOE environmental programs at the time.

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