scholarly journals Assessment of CMIP5 Model Simulations of the North American Monsoon System

2013 ◽  
Vol 26 (22) ◽  
pp. 8787-8801 ◽  
Author(s):  
Kerrie L. Geil ◽  
Yolande L. Serra ◽  
Xubin Zeng
Keyword(s):  
North American ◽  
Geopotential Height ◽  
General Circulation ◽  
Large Scale ◽  
North American Monsoon ◽  
Monthly Precipitation ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Monsoon System

Abstract Precipitation, geopotential height, and wind fields from 21 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are examined to determine how well this generation of general circulation models represents the North American monsoon system (NAMS). Results show no improvement since CMIP3 in the magnitude (root-mean-square error and bias) of the mean annual cycle of monthly precipitation over a core monsoon domain, but improvement in the phasing of the seasonal cycle in precipitation is notable. Monsoon onset is early for most models but is clearly visible in daily climatological precipitation, whereas monsoon retreat is highly variable and unclear in daily climatological precipitation. Models that best capture large-scale circulation patterns at a low level usually have realistic representations of the NAMS, but even the best models poorly represent monsoon retreat. Difficulty in reproducing monsoon retreat results from an inaccurate representation of gradients in low-level geopotential height across the larger region, which causes an unrealistic flux of low-level moisture from the tropics into the NAMS region that extends well into the postmonsoon season. Composites of the models with the best and worst representations of the NAMS indicate that adequate representation of the monsoon during the early to midseason can be achieved even with a large-scale circulation pattern bias, as long as the bias is spatially consistent over the larger region influencing monsoon development; in other words, as with monsoon retreat, it is the inaccuracy of the spatial gradients in geopotential height across the larger region that prevents some models from realistic representation of the early and midseason monsoon system.

scholarly journals Mechanisms Controlling Precipitation in the Northern Portion of the North American Monsoon

2011 ◽  
Vol 24 (11) ◽  
pp. 2771-2783 ◽  
Author(s):  
Ruth Cerezo-Mota ◽  
Myles Allen ◽  
Richard Jones
Keyword(s):  
Climate Change ◽  
North American ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Regional Model ◽  
North American Monsoon ◽  
Low Level ◽  
The North ◽  
Northern Portion

Abstract Key mechanisms important for the simulation and better understanding of the precipitation of the North American monsoon (NAM) were analyzed in this paper. Three experiments with the Providing Regional Climates for Impacts Studies (PRECIS) regional climate model, the Hadley Centre Regional Model version 3P (HadRM3P), driven by different boundary conditions were carried out. After a detailed analysis of the moisture and low-level winds derived from the models, the authors conclude that the Gulf of Mexico (GoM) moisture and the Great Plains low-level jet (GPLLJ) play an important role in the northern portion of the NAM. Moreover, the realistic simulation of these features is necessary for a better simulation of precipitation in the NAM. Previous works suggest that the influence of moisture from the GoM in Arizona–New Mexico (AZNM) takes place primarily via the middle- and upper-tropospheric flow (above 700 mb). However, it is shown here that if the GoM does not supply enough moisture and the GPLLJ at lower levels (below 700 mb) does not reach the AZNM region, then a dry westerly flow dominates that area and the summer precipitation is below normal. The implications of these findings for studies of climate change are demonstrated with the analysis of two general circulation models (GCMs) commonly used for climate change prediction, which are shown not to reproduce correctly the GPLLJ intensity nor the moisture in the GoM. This implies that the precipitation in AZNM would not be correctly represented by a regional model driven by these GCMs.

scholarly journals Effects of Increased Horizontal Resolution on Simulation of the North American Monsoon in the NCAR CAM3: An Evaluation Based on Surface, Satellite, and Reanalysis Data

2007 ◽  
Vol 20 (9) ◽  
pp. 1843-1861 ◽  
Author(s):  
J. Craig Collier ◽  
Guang J. Zhang
Keyword(s):  
North American ◽  
Large Scale ◽  
Monsoon Season ◽  
The United States ◽  
Horizontal Resolution ◽  
North American Monsoon ◽  
Sierra Madre Occidental ◽  
The North ◽  
Sierra Madre ◽  
Monsoon System

Abstract Simulation of the North American monsoon system by the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM3) is evaluated in its sensitivity to increasing horizontal resolution. For two resolutions, T42 and T85, rainfall is compared to Tropical Rainfall Measuring Mission (TRMM) satellite-derived and surface gauge-based rainfall rates over the United States and northern Mexico as well as rainfall accumulations in gauges of the North American Monsoon Experiment (NAME) Enhanced Rain Gauge Network (NERN) in the Sierra Madre Occidental. Simulated upper-tropospheric mass and wind fields are compared to those from NCEP–NCAR reanalyses. The comparison presented herein demonstrates that tropospheric motions associated with the North American monsoon system are sensitive to increasing the horizontal resolution of the model. An increase in resolution from T42 to T85 results in changes to a region of large-scale midtropospheric descent found north and east of the monsoon anticyclone. Relative to its simulation at T42, this region extends farther south and west at T85. Additionally, at T85, the subsidence is stronger. Consistent with the differences in large-scale descent, the T85 simulation of CAM3 is anomalously dry over Texas and northeastern Mexico during the peak monsoon months. Meanwhile, the geographic distribution of rainfall over the Sierra Madre Occidental region of Mexico is more satisfactorily simulated at T85 than at T42 for July and August. Moisture import into this region is greater at T85 than at T42 during these months. A focused study of the Sierra Madre Occidental region in particular shows that, in the regional-average sense, the timing of the peak of the monsoon is relatively insensitive to the horizontal resolution of the model, while a phase bias in the diurnal cycle of monsoon season precipitation is somewhat reduced in the higher-resolution run. At both resolutions, CAM3 poorly simulates the month-to-month evolution of monsoon rainfall over extreme northwestern Mexico and Arizona, though biases are considerably improved at T85.

scholarly journals Convective forcing of the North American Monsoon Anticyclone at intraseasonal and interannual time scales

2021 ◽  
Author(s):  
Kai-Wei Chang ◽  
Kenneth P. Bowman ◽  
Leong Wai Siu ◽  
Anita D. Rapp
Keyword(s):  
Time Scales ◽  
North American ◽  
Time Scale ◽  
General Circulation ◽  
Large Scale ◽  
Vertical Structure ◽  
Lower Stratosphere ◽  
North American Monsoon ◽  
The North ◽  
Circulation Anomalies

AbstractIn the upper troposphere and lower stratosphere (UTLS), large-scale anticyclones associated with monsoons play major roles in tropospheric and stratospheric transport and mixing. To understand the forcing of the North American Monsoon Anticyclone (NAMA), this study examines the connection between precipitation over the tropics and subtropics of the North American longitude sector and the variability of the troposphere and lower stratosphere. Using ERA5 reanalysis and outgoing longwave radiation (OLR) data from 1979 to 2019, we assess the relationship at the intraseasonal time scale using pentad-mean time series. We show that OLR anomalies are correlated with circulation anomalies northwest and northeast of the region of precipitation. Decreased OLR (increased precipitation) corresponds to increased geopotential heights and anticyclonic circulation anomalies in the 300 – 100 hPa layer and an opposite response in the lower tropospheric 850 – 600 hPa layer. The results are consistent with the established theory of the Rossby wave response to latent heating. The increase in height, which is strongest near 150 hPa, indicates that increased precipitation is associated with a strengthened NAMA. UTLS temperatures also have significant correlations with OLR, with cold (warm) anomalies occurring above (below) the core of the anticyclonic anomaly consistent with large-scale balance. The vertical structure of geopotential and temperature anomalies is compared to simulations using an idealized general circulation model, which shows that such a vertical structure is a consistent response to diabatic heating. Correlations at the interannual time scale resemble those at the intraseasonal time scale, demonstrating that precipitation is related to the NAMA at both time scales.

scholarly journals Impacts of Large-Scale Circulation on Urban Ambient Concentrations of Gaseous Elemental Mercury in New York, USA

2017 ◽  
Author(s):  
Huiting Mao ◽  
Dolly Hall ◽  
Zhuyun Ye ◽  
Ying Zhou ◽  
Dirk Felton ◽  
...  
Keyword(s):  
New York ◽  
North American ◽  
Large Scale ◽  
Measurement Data ◽  
Elemental Mercury ◽  
Urban Site ◽  
Large Scale Circulation ◽  
Gaseous Elemental Mercury ◽  
The North ◽  
The Impact

Abstract. The impact of large-scale circulation on urban gaseous elemental mercury (GEM) was investigated through analysis of 2008–2015 measurement data from an urban site in New York City (NYC), New York, USA. Distinct annual cycles were observed in 2009–2010 with mixing ratios in warm seasons (i.e. spring–summer) 10–20 ppqv (~ 10 %–25 %) higher than in cool seasons (i.e. fall–winter). This annual cycle was disrupted in 2011 by an anomalously strong influence of the North American trough in that warm season and was reproduced in 2014 with annual amplitude enhanced up to ~ 70 ppqv associated with a particularly strong Bermuda High. North American trough axis index (TAI) and intensity index (TII) were used to characterize the effect of the North American trough on NYC GEM especially in winter and summer. The intensity and position of the Bermuda High had a significant impact on GEM in warm seasons supported by a strong correlation (r reaching 0.96, p 

scholarly journals Toward Identifying Subseasonal Forecasts of Opportunity Using North American Weather Regimes

2020 ◽  
Vol 148 (5) ◽  
pp. 1861-1875
Author(s):  
Andrew W. Robertson ◽  
Nicolas Vigaud ◽  
Jing Yuan ◽  
Michael K. Tippett
Keyword(s):  
North American ◽  
El Niño ◽  
Geopotential Height ◽  
Large Scale ◽  
El Nino ◽  
Lead Times ◽  
Seasonal Forecasts ◽  
The North ◽  
The Pacific ◽  
Graphical Tool

Abstract Large-scale atmospheric circulation regime structures are used to diagnose subseasonal forecasts of wintertime geopotential height fields over the North American sector, from the NCEP CFSv2 model. Four large-scale daily circulation regimes derived from reanalysis 500-hPa geopotential height data using K-means clustering are used as a low-dimensional basis for diagnosing the model’s forecasts up to 45 days ahead. On average, hindcast skill in regime space is found to be limited to 10–15 days ahead, in terms of anomaly correlation of 5-day averages of regime counts, over the 1999–2010 period. However, skill up to 30 days ahead is identified in individual winters, and intraseasonal episodes of high skill are identified using a forecast-evolution graphical tool. A striking vacillation between the West Coast and Pacific ridge patterns during December–January 2008/09 is shown to be predicted 20–25 days in advance, illustrating the possibility to identify “forecasts of opportunity” when subseasonal forecast skill is much higher than the average. The forecast-evolution tool also provides insight into the poor seasonal forecasts of California precipitation by operational centers during the 2015/16 El Niño winter. The Pacific trough regime is shown to be greatly overpredicted beyond 1–2 weeks in advance during the 2015/16 winter, with weather-scale features dominating the forecast evolution at shorter lead times. A similar though less extreme situation took place during the weaker El Niño of 2009/10, with the Pacific trough overforecast at S2S lead times.

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.

Recurrent Supersynoptic Evolution of the Great Plains Low-Level Jet

2011 ◽  
Vol 24 (2) ◽  
pp. 575-582 ◽  
Author(s):  
Scott J. Weaver ◽  
Sumant Nigam
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
Large Scale Circulation ◽  
Low Level ◽  
The North ◽  
Analysis Strategy ◽  
Precipitation Anomalies ◽  
North American Regional Reanalysis ◽  
Low Level Jet ◽  
Regional Reanalysis

Abstract The evolution of supersynoptic (i.e., pentad) Great Plains low-level jet (GPLLJ) variability, its precipitation impacts, and large-scale circulation context are analyzed in the North American Regional Reanalysis (NARR)—a high-resolution precipitation-assimilating dataset—and the NCEP–NCAR reanalysis. The analysis strategy leans on the extended EOF technique, which targets both spatial and temporal recurrence of a variability episode. Pentad GPLLJ variability structures are found to be spatially similar to those in the monthly analysis. The temporal evolution of the supersynoptic GPLLJ-induced precipitation anomalies reveal interesting lead and lag relationships highlighted by GPLLJ variability-leading precipitation anomalies. Interestingly, similar temporal phasing of the GPLLJ and precipitation anomalies were operative during the 1993 (1988) floods (drought) over the Great Plains, indicating the importance of these submonthly GPLLJ variability modes in the instigation of extreme hydroclimatic episodes. The northward-shifted (dry) GPLLJ variability mode is linked to large-scale circulation variations emanating from remote regions that are modified by interaction with the Rocky Mountains, suggesting that the supersynoptic GPLLJ fluctuations may have their origin in orographic modulation of baroclinic development.

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