A Synoptic Climatology of the Elevated Mixed-Layer Inversion over the Southern Great Plains in Spring. Part I: Structure, Dynamics, and Seasonal Evolution

Lanicci, John M.; Warner, Thomas T.

doi:10.1175/1520-0434(1991)006<0181:ascote>2.0.co;2

Cited by 62 publications

(21 citation statements)

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“…9). Drylines are often characterized by a large component of westerly or southwesterly midlevel flow off the higher terrain of the Rockies or the Mexican plateau, which can result in a drier, warmer, and more capped midlevel environment due to the eastward advection of the elevated mixed layer (Lanicci and Warner 1991). Moreover, unlike slab ascent (Bryan and Fritsch 2000;James et al 2005) frequently associated with cold fronts, the lift along a dryline is confined to a narrow zone with localized areas of enhanced low-level convergence.…”

Section: Type Of Initiating Boundarymentioning

confidence: 99%

Short-Term Convective Mode Evolution along Synoptic Boundaries

Dial¹,

Racy²,

Thompson³

2010

Weather and Forecasting

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This paper investigates the relationships between short-term convective mode evolution, the orientations of vertical shear and mean wind vectors with respect to the initiating synoptic boundary, the motion of the boundary, and the role of forcing for ascent. The dominant mode of storms (linear, mixed mode, and discrete) was noted 3 h after convective initiation along cold fronts, drylines, or prefrontal troughs. Various shear and mean wind vector orientations relative to the boundary were calculated near the time of initiation. Results indicate a statistical correlation between storm mode at 3 h, the normal components of cloud-layer and deeplayer shear vectors, the boundary-relative mean cloud-layer wind vector, and the type of initiating boundary. Thunderstorms, most of which were initially discrete, tended to evolve more quickly into lines or mixed modes when the normal components of the shear vectors and boundary-relative mean cloud-layer wind vectors were small. There was a tendency for storms to remain discrete for larger normal shear and mean wind components. Smaller normal components of mean cloud-layer wind were associated with a greater likelihood that storms would remain within the zone of linear forcing along the boundary for longer time periods, thereby increasing the potential for upscale linear growth. The residence time of storms along the boundary is also dependent on the speed of the boundary. It was found that the boundary-relative normal component of the mean cloud-layer wind better discriminates between mode types than does simply the ground-relative normal component. The influence of mesoscale forcing for ascent and type of boundary on mode evolution was also investigated. As expected, it was found that the magnitude and nature of the forcing play a role in how storms evolve. For instance, strong linear low-level convergence often contributes to rapid upscale linear growth, especially if the boundary motion relative to the mean cloud-layer wind prevents storms from moving away from the boundary shortly after initiation. In summary, results from this study indicate that, for storms initiated along a synoptic boundary, convective mode evolution is modulated primarily by the residence time of storms within the zone of linear forcing, the nature and magnitude of linear forcing, and secondarily by the normal component of the cloud-layer shear.

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Section: Type Of Initiating Boundarymentioning

confidence: 99%

Short-Term Convective Mode Evolution along Synoptic Boundaries

Dial¹,

Racy²,

Thompson³

2010

Weather and Forecasting

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“…Region 4 corresponds to the regime examined by Cavazos (1997). Both regimes are strongly controlled by the north Atlantic subtropical anticyclone and its interaction with regional air masses and the continental elevated mixed layer (Cavazos & Hastenrath 1990, Lanicci & Warner 1991, Cavazos 1997, and both experience the mid-summer dry spells known in Mexico as caniculas. The 2 maxima in regions 3 and 4 are partly associated with tropical storms and hurricanes over the Caribbean/Atlantic basin.…”

Section: Regionsmentioning

confidence: 99%

Principal components-based regionalization of precipitation regimes across the southwest United States and Northern Mexico, with an application to monsoon precipitation variability

1998

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We determine precipitation regions for the United States-Mexico border region based on seasonality and variability of monthly precipitation at 309 stations for the period 1961 to 1990. Using a correlation matrix of input data to avoid the effect of elevation on precipitation, we apply principal components analysis with oblique rotation to regionalize this large, climatologically complex study area. We examine the applicability of the method, 2 techniques for defining region boundaries, the various defined regions themselves, and the effects of transforming input data and changing obliquity of component rotation. We obtain 9 consistent and largely contiguous regions from each of the analyses, including regions for the North American monsoon, the low deserts, the California Mediterranean regime, and for summer precipitation regimes adjoining the Gulf of Mexico. The derived regions and associated boundaries make physical sense in terms of the driving atmospheric processes, and they are robust to transformed input data and changes in rotation procedures. The central border regions are remarkably consistent across analyses, with small changes to peripheral regions. We also identify 4 monsoon sub-regions, and we illustrate the applicability of the regionalization via an analysis of relationships between monsoon precipitation variability and 500 mb pressure heights. Significantly different 500 mb circulation patterns are associated with wet and dry monsoon seasons in each of the subregions, and it appears that shifts in 500 mb circulation relative to the geographic position of each sub-region influence seasonal precipitation variability, directly or indirectly. There are important differences between some sub-regions, but in general wet monsoons are associated with northward meridional bulging of the subtropical anticyclone over the continental monsoon areas, while dry monsoons are associated with zonal stretching of the subtropical anticyclone over adjacent oceans with slightly higher pressure-heights. Overall, the study provides a clear regionalization of the precipitation climatology for the southwest United States and northern Mexico, and shows its utility for studies of climate variability.

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“…Although this study focused on the convective precipitation processes in Texas, the impacts of EMLs on convection emphasized in this study are not limited to Texas and can be applied to the south-central United States and the southern Great Plains (Lanicci and Warner 1991). In NOAA (2001), it was reported that Texas and the adjacent areas have had a higher frequency of droughts than other states in the western United States, northern plains, and southeastern United States during the 15-yr period from 1985 to 2000.…”

Section: Discussionmentioning

confidence: 99%

“…If the diabatically heated area to the west of Texas is important, the paths rather than the origins of particles may be more relevant for affecting Tlt. According to Lanicci and Warner (1991), the elevated mixed layer (EML) that develops over the high terrain of the Mexican Plateau and the Rocky Mountains tends to induce a capping inversion and suppresses convection over the south-central United States most frequently in spring and early summer. Deep and strong capping inversions tend to suppress convection directly.…”

Section: Causes Of Low-tropospheric Warmingmentioning

confidence: 99%

The Convective Instability Pathway to Warm Season Drought in Texas. Part II: Free-Tropospheric Modulation of Convective Inhibition

Myoung

Nielsen‐Gammon

2010

Journal of Climate

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This study is concerned with the modulation by convective instability of summertime precipitation in Texas as a mechanism for maintaining or enhancing drought. The important role of convective inhibition (CIN), its dependence on the temperature at 700 hPa and the surface dewpoint, and the mechanism by which soil moisture modulates precipitation through CIN were described in Part I of this two-part series study. This study, Part II, examines the dynamic and physical processes controlling the temperature at 700 hPa and elucidates the large-scale influences on convective instability and precipitation integrating the principal processes found in both Parts I and II.Back-trajectory analysis indicates that a significant contributor to warming at 700 hPa is the inversion caused by warm air transport from the Rocky Mountains and the Mexican Plateau where the surface potential temperature is greater than 307.5 K, rather than by subsidence. It was found that downward motion and warm air transport are enhanced in Texas when an upper-level anticyclonic circulation develops in the southern United States.Upper-level anticyclonic circulations in the southern United States, one of the distinctive features of central U.S. droughts, strongly affect Texas summertime precipitation by modulating the thermodynamic structure of the atmosphere and thus convective instability. Stationary anticyclonic anomalies increase CIN not only by enhancing warm air transport from the high terrain but also by suppressing the occurrence of traveling disturbances. The resulting reduced precipitation and dry soil significantly modulate surface conditions, which elevates CIN and decreases precipitation. The aforementioned chain reaction of upper-level anticyclone influences that is expected to play an important role in initiating and maintaining Texas summer droughts can be understood within the context of CIN.

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A Synoptic Climatology of the Elevated Mixed-Layer Inversion over the Southern Great Plains in Spring. Part I: Structure, Dynamics, and Seasonal Evolution

Cited by 62 publications

References 0 publications

Short-Term Convective Mode Evolution along Synoptic Boundaries

Short-Term Convective Mode Evolution along Synoptic Boundaries

Principal components-based regionalization of precipitation regimes across the southwest United States and Northern Mexico, with an application to monsoon precipitation variability

The Convective Instability Pathway to Warm Season Drought in Texas. Part II: Free-Tropospheric Modulation of Convective Inhibition

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