scholarly journals A Numerical Investigation of Wet and Dry Onset Modes in the North American Monsoon Core Region. Part I: A Regional Mechanism for Interannual Variability

2012 ◽  
Vol 25 (11) ◽  
pp. 3953-3969 ◽  
Author(s):  
Cuauhtémoc Turrent ◽  
Tereza Cavazos
Keyword(s):  
Interannual Variability ◽  
Diurnal Cycle ◽  
North American ◽  
Gulf Of California ◽  
Deep Convection ◽  
Core Region ◽  
Eastern Pacific ◽  
North American Monsoon ◽  
The Core ◽  
The North

In this study the results of two regional fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) simulations forced at their boundaries with low-pass-filtered North American Regional Reanalysis (NARR) composite fields from which synoptic-scale variability was removed are presented. The filtered NARR data are also assimilated into the inner domain through the use of field nudging. The purpose of this research is to investigate wet and dry onset modes in the core region of the North American monsoon (NAM). Key features of the NAM that are present in the NARR fields and assimilated into the regional simulations include the position of the midlevel anticyclone, low-level circulation over the Gulf of California, and moisture flux patterns into the core monsoon region, for which the eastern Pacific is the likely primary source of moisture. The model develops a robust diurnal cycle of deep convection over the peaks of the Sierra Madre Occidental (SMO) that results solely from its radiation scheme and internal dynamics, in spite of the field nudging. The wet onset mode is related to a regional land–sea thermal contrast (LSTC) that is ~2°C higher than in the dry mode, and is further characterized by a northward-displaced midlevel anticyclone, a stronger surface pressure gradient along the Gulf of California, larger mean moisture fluxes into the core region from the eastern Pacific, a stronger diurnal cycle of deep convection, and the more northward distribution of precipitation along the axis of the SMO. A proposed regional LSTC mechanism for NAM onset interannual variability is consistent with the differences between both onset modes.

scholarly journals The Diurnal Cycle of Precipitation over the North American Monsoon Region during the NAME 2004 Field Campaign

2008 ◽  
Vol 21 (4) ◽  
pp. 771-787 ◽  
Author(s):  
Emily J. Becker ◽  
Ernesto Hugo Berbery
Keyword(s):  
Diurnal Cycle ◽  
North American ◽  
Gulf Of California ◽  
Warm Season ◽  
Moisture Flux ◽  
North American Monsoon ◽  
The Core ◽  
The North ◽  
Eta Model ◽  
Diurnal Cycle Of Precipitation

Abstract The structure of the diurnal cycle of warm-season precipitation and its associated fields during the North American monsoon are examined for the core monsoon region and for the southwestern United States, using a diverse set of observations, analyses, and forecasts from the North American Monsoon Experiment field campaign of 2004. Included are rain gauge and satellite estimates of precipitation, Eta Model forecasts, and the North American Regional Reanalysis (NARR). Daily rain rates are of about the same magnitude in all datasets with the exception of the Climate Prediction Center (CPC) Morphing (CMORPH) technique, which exhibits markedly higher precipitation values. The diurnal cycle of precipitation within the core region occurs earlier in the day at higher topographic elevations, evolving with a westward shift of the maximum. This shift appears in the observations, reanalysis, and, while less pronounced, in the model forecasts. Examination of some of the fields associated with this cycle, including convective available potential energy (CAPE), convective inhibition (CIN), and moisture flux convergence (MFC), reveals that the westward shift appears in all of them, but more prominently in the latter. In general, warm-season precipitation in southern Arizona and parts of New Mexico shows a strong effect due to northward moisture surges from the Gulf of California. A reported positive bias in the NARR northward winds over the Gulf of California limits their use with confidence for studies of the moist surges along the Gulf; thus, the analysis is complemented with operational analysis and the Eta Model short-term simulations. The nonsurge diurnal cycle of precipitation lags the CAPE maximum by 6 h and is simultaneous with a minimum of CIN, while the moisture flux remains divergent throughout the day. During surges, CAPE and CIN have modifications only to the amplitude of their cycles, but the moisture flux becomes strongly convergent about 6 h before the precipitation maximum, suggesting a stronger role in the development of precipitation.

Dynamics of a Simulated North American Monsoon Gulf Surge Event

2013 ◽  
Vol 141 (9) ◽  
pp. 3238-3253 ◽  
Author(s):  
Andrew J. Newman ◽  
Richard H. Johnson
Keyword(s):  
United States ◽  
North American ◽  
Gulf Of California ◽  
Dynamical Evolution ◽  
North American Monsoon ◽  
The Core ◽  
Southwest United States ◽  
Northwest Mexico ◽  
The North ◽  
Internal Bores

Abstract Gulf surges are transient disturbances that propagate along the Gulf of California (GoC) from south to north, transporting cool moist air toward the deserts of northwest Mexico and the southwest United States during the North American monsoon. They have been shown to modulate precipitation and have been linked to severe weather and flooding in northern Mexico and the southwest United States. The general features and progression of surge events are well documented but their detailed dynamical evolution is still unclear. In this study, a convection-permitting simulation is performed over the core monsoon region for the 12–14 July 2004 gulf surge event and the dynamics of the simulated surge are examined. Initially, convection associated with the tropical easterly wave precursor to Tropical Cyclone Blas creates a disturbance in the southern GoC on early 12 July. This disturbance is a precursor to the gulf surge on 13 July and is a Kelvin shock (internal bore under the influence of rotation) that dissipates in the central GoC. The surge initiates from inflow from the mouth of the GoC along with convective outflow impinging on the southern GoC. Continued convective outflow along the GoC generates multiple gravity currents and internal bores while intensifying the simulated surge as it propagates up the GoC. As the core of the surge reaches the northern GoC, a Kelvin shock is again the best dynamical fit to the phenomenon. Substantial low-level cooling and moistening are associated with the modeled surge along the northern GoC as is observed.

Simulations of the 2004 North American Monsoon: NAMAP2

2009 ◽  
Vol 22 (24) ◽  
pp. 6716-6740 ◽  
Author(s):  
D. S. Gutzler ◽  
L. N. Long ◽  
J. Schemm ◽  
S. Baidya Roy ◽  
M. Bosilovich ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
North American ◽  
Warm Season ◽  
North American Monsoon ◽  
Regional Models ◽  
Global Models ◽  
Low Level ◽  
The Core ◽  
The North ◽  
Low Level Jet

Abstract The second phase of the North American Monsoon Experiment (NAME) Model Assessment Project (NAMAP2) was carried out to provide a coordinated set of simulations from global and regional models of the 2004 warm season across the North American monsoon domain. This project follows an earlier assessment, called NAMAP, that preceded the 2004 field season of the North American Monsoon Experiment. Six global and four regional models are all forced with prescribed, time-varying ocean surface temperatures. Metrics for model simulation of warm season precipitation processes developed in NAMAP are examined that pertain to the seasonal progression and diurnal cycle of precipitation, monsoon onset, surface turbulent fluxes, and simulation of the low-level jet circulation over the Gulf of California. Assessment of the metrics is shown to be limited by continuing uncertainties in spatially averaged observations, demonstrating that modeling and observational analysis capabilities need to be developed concurrently. Simulations of the core subregion (CORE) of monsoonal precipitation in global models have improved since NAMAP, despite the lack of a proper low-level jet circulation in these simulations. Some regional models run at higher resolution still exhibit the tendency observed in NAMAP to overestimate precipitation in the CORE subregion; this is shown to involve both convective and resolved components of the total precipitation. The variability of precipitation in the Arizona/New Mexico (AZNM) subregion is simulated much better by the regional models compared with the global models, illustrating the importance of transient circulation anomalies (prescribed as lateral boundary conditions) for simulating precipitation in the northern part of the monsoon domain. This suggests that seasonal predictability derivable from lower boundary conditions may be limited in the AZNM subregion.

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.

scholarly journals Comments on “Regional Impacts of Irrigation in Mexico and the Southwestern United States on Hydrometeorological Fields in the North American Monsoon Region”

2018 ◽  
Vol 19 (2) ◽  
pp. 477-481 ◽  
Author(s):  
Theodore J. Bohn ◽  
Enrique R. Vivoni
Keyword(s):  
North American ◽  
Gulf Of California ◽  
Wrf Model ◽  
Summer Precipitation ◽  
Atmospheric Modeling ◽  
Irrigated Agriculture ◽  
North American Monsoon ◽  
Impact Surface ◽  
The North ◽  
The Impact

Abstract For their investigation of the impact of irrigated agriculture on hydrometeorological fields in the North American monsoon (NAM) region, Mahalov et al. used the Weather Research and Forecasting (WRF) Model to simulate weather over the NAM region in the summer periods of 2000 and 2012, with and without irrigation applied to the regional croplands. Unfortunately, while the authors found that irrigated agriculture may indeed influence summer precipitation, the magnitude, location, and seasonality of their irrigation inputs were substantially inaccurate because of 1) the assumption that pixels classified as “irrigated cropland” are irrigated during the summer and 2) an outdated land cover map that misrepresents known agricultural districts. The combined effects of these errors are 1) an overestimation of irrigated croplands by a factor of 3–10 along the coast of the Gulf of California and by a factor of 1.5 near the Colorado River delta and 2) a large underestimation of irrigation by a factor of 7–10 in Chihuahua, particularly in 2012. Given the sensitivity of the WRF simulations conducted by Mahalov et al. to the presence of irrigated agriculture, it is expected that the identified errors would significantly impact surface moisture and energy fluxes, resulting in noticeably different effects on precipitation. The authors suggest that the analysis of irrigation effects on precipitation using coupled land–atmospheric modeling systems requires careful specification of the spatiotemporal distribution of irrigated croplands.

scholarly journals Analysis of the 13–14 July Gulf Surge Event during the 2004 North American Monsoon Experiment

2007 ◽  
Vol 135 (9) ◽  
pp. 3098-3117 ◽  
Author(s):  
Peter J. Rogers ◽  
Richard H. Johnson
Keyword(s):  
North American ◽  
Gulf Of California ◽  
Leading Edge ◽  
North American Monsoon ◽  
Strong Wind ◽  
Kelvin Wave ◽  
High Resolution Data ◽  
Low Level ◽  
Second Stage ◽  
The North

Abstract Gulf surges are disturbances that move northward along the Gulf of California (GOC), frequently advecting cool, moist air from the GOC or eastern tropical Pacific Ocean into the deserts of the southwest United States and northwest Mexico during the North American Monsoon (NAM). Little attention has been given to the dynamics of these disturbances because of the lack of reliable high-resolution data across the NAM region. High temporal and spatial observations collected during the 2004 North American Monsoon Experiment are used to investigate the structure and dynamical mechanisms of a significant gulf surge on 13–14 July 2004. Integrated Sounding Systems deployed along the east coast of the GOC and an enhanced network of rawinsonde sites across the NAM region are used in this study. Observations show that the 13–14 July gulf surge occurred in two primary stages. The first stage was preceded by anomalous low-level warming along the northern GOC on 13 July. Sharp cooling, moistening, and increased low-level south-southeasterly flow followed over a 12–18-h period. Over the northern gulf, the wind reached ∼20 m s−1 at 750 m AGL. Then there was a brief respite followed by the second stage—a similar, but deeper acceleration of the southerly flow associated with the passage of Tropical Storm (TS) Blas on 14 July. The initial surge disturbance traversed the GOC at a speed of ∼17–25 m s−1 and resulted in a deepening of the mixed layer along the northern gulf. Dramatic surface pressure rises also accompanied the surge. The weight of the evidence suggests that the first stage of the overall surge itself consisted of two parts. The initial part resembled borelike disturbances initiated by convective downdrafts impinging on the low-level stable layer over the region. The secondary part was characteristic of a Kelvin wave–type disturbance, as evident in the deeper layer of sharp cooling and strong wind that ensued. Another possible explanation for the first part is that the leading edge of this Kelvin wave steepened nonlinearly into a borelike disturbance. The second stage of the surge was associated with the increased circulation around TS Blas.

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