Interannual Variability of the North American Warm Season Precipitation Regime

Abstract Extratropical cyclones play a principal role in wintertime precipitation and severe weather over North America. On average, the greatest number of cyclones track 1) from the lee of the Rocky Mountains eastward across the Great Lakes and 2) over the Gulf Stream along the eastern coastline of North America. However, the cyclone tracks are highly variable within individual winters and between winter seasons. In this study, the authors apply a Lagrangian tracking algorithm to examine variability in extratropical cyclone tracks over North America during winter. A series of methodological criteria is used to isolate cyclone development and decay regions and to account for the elevated topography over western North America. The results confirm the signatures of four climate phenomena in the intraseasonal and interannual variability in North American cyclone tracks: the North Atlantic Oscillation (NAO), the El Niño–Southern Oscillation (ENSO), the Pacific–North American pattern (PNA), and the Madden–Julian oscillation (MJO). Similar signatures are found using Eulerian bandpass-filtered eddy variances. Variability in the number of extratropical cyclones at most locations in North America is linked to fluctuations in Rossby wave trains extending from the central tropical Pacific Ocean. Only over the far northeastern United States and northeastern Canada is cyclone variability strongly linked to the NAO. The results suggest that Pacific sector variability (ENSO, PNA, and MJO) is a key contributor to intraseasonal and interannual variability in the frequency of extratropical cyclones at most locations across North America.

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

Journal of Climate ◽

10.1175/jcli-d-11-00215.1 ◽

2012 ◽

Vol 25 (11) ◽

pp. 3953-3969 ◽

Cited By ~ 5

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.

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Simulations of the 2004 North American Monsoon: NAMAP2

Journal of Climate ◽

10.1175/2009jcli3138.1 ◽

2009 ◽

Vol 22 (24) ◽

pp. 6716-6740 ◽

Cited By ~ 27

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.

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Atmospheric Responses to North Atlantic SST Anomalies in Idealized Experiments. Part II: North American Precipitation

Journal of Climate ◽

10.1175/jcli-d-14-00751.1 ◽

2016 ◽

Vol 29 (2) ◽

pp. 659-671 ◽

Cited By ~ 7

Author(s):

Qi Hu ◽

Michael C. Veres

Keyword(s):

North America ◽

North Atlantic ◽

North American ◽

North Atlantic Ocean ◽

Warm Season ◽

The North ◽

Precipitation Anomalies ◽

Sst Anomaly ◽

The North Atlantic ◽

Sst Anomalies

Abstract This is the second part of a two-part paper that addresses deterministic roles of the sea surface temperature (SST) anomalies associated with the Atlantic multidecadal oscillation (AMO) in variations of atmospheric circulation and precipitation in the Northern Hemisphere, using a sequence of idealized model runs at the spring equinox conditions. This part focuses on the effect of the SST anomalies on North American precipitation. Major results show that, in the model setting closest to the real-world situation, a warm SST anomaly in the North Atlantic Ocean causes suppressed precipitation in central, western, and northern North America but more precipitation in the southeast. A nearly reversed pattern of precipitation anomalies develops in response to the cold SST anomaly. Further examinations of these solutions reveal that the response to the cold SST anomaly is less stable than that to the warm SST anomaly. The former is “dynamically charged” in the sense that positive eddy kinetic energy (EKE) exists over the continent. The lack of precipitation in its southeast is because of an insufficient moisture supply. In addition, the results show that the EKE of the short- (2–6 day) and medium-range (7–10 day) weather-producing processes in North America have nearly opposite signs in response to the same cold SST anomaly. These competing effects of eddies in the dynamically charged environment (elevated sensitivity to moisture) complicate the circulation and precipitation responses to the cold SST anomaly in the North Atlantic and may explain why the model results show more varying precipitation anomalies (also confirmed by statistical test results) during the cold than the warm SST anomaly, as also shown in simulations with more realistic models. Results of this study indicate a need to include the AMO in the right context with other forcings in an effort to improve understanding of interannual-to-multidecadal variations in warm season precipitation in North America.

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

Journal of Climate ◽

10.1175/jcli4098.1 ◽

2007 ◽

Vol 20 (9) ◽

pp. 1608-1627 ◽

Cited By ~ 54

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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Can a Regional Climate Model Improve the Ability to Forecast the North American Monsoon?

Journal of Climate ◽

10.1175/jcli-d-11-00441.1 ◽

2012 ◽

Vol 25 (23) ◽

pp. 8212-8237 ◽

Cited By ~ 48

Author(s):

Christopher L. Castro ◽

Hsin-I Chang ◽

Francina Dominguez ◽

Carlos Carrillo ◽

Jae-Kyung Schemm ◽

...

Keyword(s):

North American ◽

Large Scale ◽

Dynamical Downscaling ◽

Warm Season ◽

Regional Model ◽

Precipitation Anomaly ◽

Early Summer ◽

North American Monsoon ◽

The North ◽

Temperature And Precipitation

Abstract Global climate models are challenged to represent the North American monsoon, in terms of its climatology and interannual variability. To investigate whether a regional atmospheric model can improve warm season forecasts in North America, a retrospective Climate Forecast System (CFS) model reforecast (1982–2000) and the corresponding NCEP–NCAR reanalysis are dynamically downscaled with the Weather Research and Forecasting model (WRF), with similar parameterization options as used for high-resolution numerical weather prediction and a new spectral nudging capability. The regional model improves the climatological representation of monsoon precipitation because of its more realistic representation of the diurnal cycle of convection. However, it is challenged to capture organized, propagating convection at a distance from terrain, regardless of the boundary forcing data used. Dynamical downscaling of CFS generally yields modest improvement in surface temperature and precipitation anomaly correlations in those regions where it is already positive in the global model. For the North American monsoon region, WRF adds value to the seasonally forecast temperature only in early summer and does not add value to the seasonally forecast precipitation. CFS has a greater ability to represent the large-scale atmospheric circulation in early summer because of the influence of Pacific SST forcing. The temperature and precipitation anomaly correlations in both the global and regional model are thus relatively higher in early summer than late summer. As the dominant modes of early warm season precipitation are better represented in the regional model, given reasonable large-scale atmospheric forcing, dynamical downscaling will add value to warm season seasonal forecasts. CFS performance appears to be inconsistent in this regard.

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

Journal of Climate ◽

10.1175/2007jcli1642.1 ◽

2008 ◽

Vol 21 (4) ◽

pp. 771-787 ◽

Cited By ~ 16

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.

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