Decadal Variation of Rainfall Seasonality in the North American Monsoon Region and Its Potential Causes

2012 ◽  
Vol 25 (12) ◽  
pp. 4258-4274 ◽  
Author(s):  
Paola A. Arias ◽  
Rong Fu ◽  
Kingtse C. Mo
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
North American ◽  
Southeastern United States ◽  
Atmospheric Stability ◽  
Cyclonic Circulation ◽  
North American Monsoon ◽  
Monsoon Region ◽  
The North ◽  
Anomalous Cyclonic Circulation

Abstract This study shows that the North American monsoon system’s (NAMS) strength, onset, and retreat over northwestern Mexico exhibit multidecadal variations during the period 1948–2009. Two dry regimes, associated with late onsets, early retreats, and weaker rainfall rates, occurred in 1948–70 and 1991–2005, whereas a strong regime, associated with early onsets, late retreats, and stronger rainfall rates, occurred in 1971–90. A recovery of the monsoon strength was observed after 2005. This multidecadal variation is linked to the sea surface temperature anomalies’ (SSTAs) variability, which is a combination of the Atlantic multidecadal oscillation (AMO) and the warming SST trends. These SST modes appear to cause an anomalous cyclonic circulation and enhanced rainfall over the southeastern United States and the Gulf of Mexico, which in turn increases the atmospheric stability over the monsoon region. However, these SST modes cannot fully explain the circulation and rainfall anomalies observed during the early-retreat monsoons. An expansion of the North Atlantic surface high (NASH) in recent decades also contributes to the anomalous circulation associated with the early retreats of the NAMS. A northwestward expansion of the NASH further enhances the anomalous cyclonic circulation and rainfall over the southeastern United States and the Gulf of Mexico. Its associated northwestward shift of the subtropical jets over the western United States enhances subsidence over the NAMS region. The combined effects of the AMO, the warming trends, and the NASH expansion on atmospheric circulation contribute to a stronger and more persistent earlier retreat during the recent dry regime (1991–2005), while the earlier dry regime (1948–70) appears to be only influenced by the positive phase of the AMO.

Observed relation between evapotranspiration and soil moisture in the North American monsoon region

2008 ◽  
Vol 35 (22) ◽  
Author(s):  
Enrique R. Vivoni ◽  
Hernan A. Moreno ◽  
Giuseppe Mascaro ◽  
Julio C. Rodriguez ◽  
Christopher J. Watts ◽  
...  
Keyword(s):  
Soil Moisture ◽  
North American ◽  
North American Monsoon ◽  
Monsoon Region ◽  
The North

Hydroclimatology of the North American Monsoon region in northwest Mexico

2006 ◽  
Vol 316 (1-4) ◽  
pp. 53-70 ◽  
Author(s):  
David J. Gochis ◽  
Luis Brito-Castillo ◽  
W. James Shuttleworth
Keyword(s):  
North American ◽  
North American Monsoon ◽  
Monsoon Region ◽  
Northwest Mexico ◽  
The North

Observational Analysis of an Upper-Level Inverted Trough during the 2004 North American Monsoon Experiment

2010 ◽  
Vol 138 (9) ◽  
pp. 3540-3555 ◽  
Author(s):  
Zachary O. Finch ◽  
Richard H. Johnson
Keyword(s):  
North American ◽  
Cyclonic Circulation ◽  
Primary Data ◽  
North American Monsoon ◽  
The West ◽  
Colorado State University ◽  
Downward Motion ◽  
The North ◽  
Northwestern Mexico ◽  
Upper Level

Abstract Upper-level inverted troughs (IVs) associated with midlatitude breaking Rossby waves or tropical upper-troposphere troughs (TUTTs) have been identified as important contributors to the variability of rainfall in the North American monsoon (NAM) region. However, little attention has been given to the dynamics of these systems owing to the sparse observational network over the NAM region. High temporal and spatial observations taken during the 2004 North American Monsoon Experiment (NAME) are utilized to analyze a significant IV that passed over northwestern Mexico from 10 to 13 July 2004. The Colorado State University gridded dataset, which is independent of model analysis over land, is the primary data source used in this study. Results show that the 10–13 July IV disturbance was characterized by a warm anomaly around 100 hPa and a cold anomaly that extended from 200 to 700 hPa. The strongest cyclonic circulation was in the upper levels around 200 hPa. Quasigeostrophic (QG) diagnostics indicate that the upper-level low forced weak subsidence (weak rising motion) to the west (east) of its center. Net downward motion to the west was a result of the Laplacian of thermal advection (forcing subsidence) outweighing differential vorticity advection (forcing weak upward motion). Despite the QG forcing of downward motion west of the upper-level IV, enhanced convection occurred west of the IV center along the western slopes of the Sierra Madre Occidental (SMO). This seemingly contradictory behavior can be explained by noting that the upper-level IV induced a midlevel cyclonic circulation, with northeasterly (southeasterly) midlevel flow to the west (east) of its center. Increased mesoscale organization of convection along the SMO foothills was found to be collocated with IV-enhanced northeasterly midlevel flow and anomalous northeasterly shear on the western (leading) flank of the system. It is proposed that the upper-level IV increased the SMO-perpendicular midlevel flow as well as the wind shear, thereby creating an environment favorable for convective storms to grow upscale as they moved off the high terrain.

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 Multiscale Variability of the Flow during the North American Monsoon Experiment

2007 ◽  
Vol 20 (9) ◽  
pp. 1628-1648 ◽  
Author(s):  
Richard H. Johnson ◽  
Paul E. Ciesielski ◽  
Brian D. McNoldy ◽  
Peter J. Rogers ◽  
Richard K. Taft
Keyword(s):  
United States ◽  
North American ◽  
Gulf Of California ◽  
Large Scale ◽  
Regional Scale ◽  
North American Monsoon ◽  
Return Flow ◽  
Southwestern United States ◽  
The North ◽  
Upper Level

Abstract The 2004 North American Monsoon Experiment (NAME) provided an unprecedented observing network for studying the structure and evolution of the North American monsoon. This paper focuses on multiscale characteristics of the flow during NAME from the large scale to the mesoscale using atmospheric sounding data from the enhanced observing network. The onset of the 2004 summer monsoon over the NAME region accompanied the typical northward shift of the upper-level anticyclone or monsoon high over northern Mexico into the southwestern United States, but in 2004 this shift occurred slightly later than normal and the monsoon high did not extend as far north as usual. Consequently, precipitation over the southwestern United States was slightly below normal, although increased troughiness over the Great Plains contributed to increased rainfall over eastern New Mexico and western Texas. The first major pulse of moisture into the Southwest occurred around 13 July in association with a strong Gulf of California surge. This surge was linked to the westward passages of Tropical Storm Blas to the south and an upper-level inverted trough over northern Texas. The development of Blas appeared to be favored as an easterly wave moved into the eastern Pacific during the active phase of a Madden–Julian oscillation. On the regional scale, sounding data reveal a prominent sea breeze along the east shore of the Gulf of California, with a deep return flow as a consequence of the elevated Sierra Madre Occidental (SMO) immediately to the east. Subsidence produced a dry layer over the gulf, whereas a deep moist layer existed over the west slopes of the SMO. A prominent nocturnal low-level jet was present on most days over the northern gulf. The diurnal cycle of heating and moistening (Q1 and Q2) over the SMO was characterized by deep convective profiles in the mid- to upper troposphere at 1800 LT, followed by stratiform-like profiles at midnight, consistent with the observed diurnal evolution of precipitation over this coastal mountainous region. The analyses in the core NAME domain are based on a gridded dataset derived from atmospheric soundings only and, therefore, should prove useful in validating reanalyses and regional models.

Applications of Monsoon Research: Opportunities to Inform Decision Making and Reduce Regional Vulnerability

2007 ◽  
Vol 20 (9) ◽  
pp. 1608-1627 ◽  
Author(s):  
Andrea J. Ray ◽  
Gregg M. Garfin ◽  
Margaret Wilder ◽  
Marcela Vásquez-León ◽  
Melanie Lenart ◽  
...  
Keyword(s):  
United States ◽  
Decision Making ◽  
North American ◽  
Knowledge Exchange ◽  
The United States ◽  
North American Monsoon ◽  
Precipitation Regime ◽  
The North ◽  
Integrated Assessments ◽  
Inform Decision Making

Abstract This article presents ongoing efforts to understand interactions between the North American monsoon and society in order to develop applications for monsoon research in a highly complex, multicultural, and binational region. The North American monsoon is an annual precipitation regime that begins in early June in Mexico and progresses northward to the southwestern United States. The region includes stakeholders in large urban complexes, productive agricultural areas, and sparsely populated arid and semiarid ecosystems. The political, cultural, and socioeconomic divisions between the United States and Mexico create a broad range of sensitivities to climate variability as well as capacities to use forecasts and other information to cope with climate. This paper highlights methodologies to link climate science with society and to analyze opportunities for monsoon science to benefit society in four sectors: natural hazards management, agriculture, public health, and water management. A list of stakeholder needs and a calendar of decisions is synthesized to help scientists link user needs to potential forecasts and products. To ensure usability of forecasts and other research products, iterative scientist–stakeholder interactions, through integrated assessments, are recommended. These knowledge-exchange interactions can improve the capacity for stakeholders to use forecasts thoughtfully and inform the development of research, and for the research community to obtain feedback on climate-related products and receive insights to guide research direction. It is expected that integrated assessments can capitalize on the opportunities for monsoon science to inform decision making and, in the best instances, reduce regional climate vulnerabilities and enhance regional sustainability.

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