A method for defining monsoon onset and demise in the southwestern USA

Ellis, Andrew W.; Saffell, Erinanne M.; Hawkins, Timothy W.

doi:10.1002/joc.996

Cited by 37 publications

(33 citation statements)

References 34 publications

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“…5). Some investigators in the United States, including U.S. National Weather Service forecast offices in Arizona, prefer to use humidity as a smoother, less transient indicator of the onset of the ''wet'' season (Ellis et al 2004). As a complement to additional research on seasonal predictability in the CORE subregion, the definition of ''monsoon onset'' itself in the United States and Mexico requires additional investigation.…”

Section: Discussionmentioning

confidence: 99%

Simulations of the 2004 North American Monsoon: NAMAP2

et al. 2009

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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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Section: Discussionmentioning

confidence: 99%

Simulations of the 2004 North American Monsoon: NAMAP2

et al. 2009

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“…The two active phases of the NAM are separated by a dry period (typically one-two weeks) commonly known as the midsummer drought (Magna et al 1999). The PF2 distribution pattern suggests that the 1999 monsoon onset in central Mexico takes place during the second week of June, whereas the monsoon demise evolves slowly from late August to early September (Ellis et al 2004). Specifically, heavy rainfall occurred during the periods of 13-26 June, 2-15 July, and 6-14 August in 1999.…”

Section: North American Monsoon Over Central Mexicomentioning

confidence: 98%

“…The NAM refers to the dramatic increase in precipitation associated with the summertime shift in atmospheric circulation stretching from the Caribbean Sea to Mexico and into the southwestern United States (Douglas et al 1993;Stensrud et al 1995;Ellis et al 2004; more information is available online at http:// www.cpc.ncep.noaa.gov/products/precip/monsoon/ NAME.html).…”

Section: North American Monsoon Over Central Mexicomentioning

confidence: 99%

A Numerical Study to Investigate the Relationship between Moisture Convergence Patterns and Orography in Central Mexico*

Bhushan

Barros

2007

Journal of Hydrometeorology

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This study examines small-scale orographic effects on atmospheric moisture convergence at the ridgevalley scale in the Grande de Santiago River basin in central Mexico during a major monsoon storm on 13-14 August 1999. The simulation was performed using a coupled land-cloud resolving model on three nested grids (at 12-, 3-, and 1-km resolutions). The specific objective is to investigate the physical mechanisms that explain the regional space-time organization of orographic precipitation and cloudiness identified in the region from satellite data. The overarching goals of the research were 1) to characterize the effects of landform and topography-flow geometry relationships on the spatial distribution of precipitation and clouds, especially with regard to the role of mountain winds and lateral drainage flows, and 2) to assess the influence of land-atmosphere interactions (specifically latent and sensible heat fluxes) on moisture convergence patterns during monsoon storms.The model results indicate that large-scale moisture convergence dominates the distribution of total water in the troposphere during monsoon storms, which is modulated by topographically induced gravity waves and thermodynamic gradients associated with the land-sea contrast in the coastal zone. In the Grande de Santiago River basin, mountain-plain differences in thermodynamic response control mesoscale moisture convergence patterns leading to nocturnal buildup in the valleys. At the ridge-valley scale, strong convergence and strong winds (up to 15 m s Ϫ1 ) occur on the lee side of ridges oriented perpendicularly to the impinging synoptic flow with the development of transient flow conditions (from supercritical to subcritical) in the valley, independently of the time of day. In turn, this localized hydraulic-jump-like circulation drives strong return winds (i.e., cold outflows in the downvalley direction) that converge in the central lowlands preceding nighttime rainfall, lifting warm moist air at the mouth of the valley, thus initiating nocturnal convection. Simulated moisture convergence patterns are clustered along the ridges and against the foot slopes at the outlet of the north-south oriented catchments consistent with the space-time distribution of satellite observations of precipitation and clouds in the region overall, and with precipitation features detected during the simulated event in particular.

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“…A monsoon is a seasonal pattern of wind shift often accompanied by an abrupt transition in the amount of precipitation. In southern Arizona, site of the present study, frequent thunderstorms associated with the North American summer monsoon system (Adams and Comrie 1997;Ellis et al 2004) contribute most of the annual precipitation in the region and result in a rapid Xush of vegetative growth in desert biota. In the present study, we examined how monsoonal eVects on host and host environment inXuenced patterns of oviposition by pipevine swallowtail butterXies (Battus philenor L.; Papilionidae).…”

Section: Introductionmentioning

confidence: 84%

Extreme weather change and the dynamics of oviposition behavior in the pipevine swallowtail, Battus philenor

2007

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Prospects of global increases in extreme weather change provide incentive to examine how such change influences animal behavior, for example, behavior associated with resource use. In this study, we examined how oviposition behavior in a southern Arizona population of pipevine swallowtails (Battus philenor L.) responded to changes in their Aristolochia host resource and vegetative background caused by the North American monsoon system. Summer monsoon rains resulted in a flush of non-host vegetation and a more than doubling in rate of landings by host-searching females on non-host vegetation. Rates of discovery of the host species A. watsoni Woot. Standl. decreased by 50% after monsoon rains. Rains did not alter host density appreciably, but resulted in significant increases in host plant size and new growth, two indicators of host suitability for B. philenor larvae. After the rains, mean clutch size on individual host plants increased by a factor of 2.5; the mean proportion of host plants encountered on which a female laid eggs also increased significantly. Females were discriminating about the host plants on which they laid eggs after alightment; plants accepted for oviposition were larger, bore more new growth, and bore fewer larvae than rejected plants. Contrary to predictions from foraging theory, degree of discrimination did not change seasonally. Finally, the rate at which eggs were laid increased seasonally, suggesting that oviposition rates were limited more before monsoon rains by the relatively low quality of hosts than they were after the rains by the relatively low rate at which hosts were found. This latter result suggests that, while butterflies possess behavioral flexibility to respond to extreme weather change, such flexibility may have limits. In particular, expected increases in the severity and frequency of droughts may result in reduced oviposition rates, reductions that could have adverse demographic consequences.

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A method for defining monsoon onset and demise in the southwestern USA

Cited by 37 publications

References 34 publications

Simulations of the 2004 North American Monsoon: NAMAP2

Simulations of the 2004 North American Monsoon: NAMAP2

A Numerical Study to Investigate the Relationship between Moisture Convergence Patterns and Orography in Central Mexico*

Extreme weather change and the dynamics of oviposition behavior in the pipevine swallowtail, Battus philenor

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