A Two-Dimensional Simulation of the Iberian Summer Thermal Low

Gaertner, Miguel Ángel; Fernández, C.F. González; Castro, Manuel de

doi:10.1175/1520-0493(1993)121<2740:atdsot>2.0.co;2

Cited by 58 publications

(10 citation statements)

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“…Of course, the peak intensity may occur a few hours earlier or later, the temporal resolution of the data being too coarse to be more precise. The work of Portela and Castro (1996), based on three-hourly surface observations, indicates that the peak hour is between 15 and 18 UTC which is corroborated by the numerical simulation of Gaertner et al (1993). A characteristic of the Iberian thermal low is the moderate anisotropy in the radial horizontal gradients.…”

Section: Horizontal Structurementioning

confidence: 74%

“…In order to analyse regional characteristics that primarily in uence the formation of summer thermal lows, Gaertner et al (1993) performed a numerical study using a two-dimensional numerical model. They showed that the most prominent factors determining the intensity of thermal lows are the surface aridity during summer and the elevated height of the central Iberian plateau.…”

Section: Introductionmentioning

confidence: 99%

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The Iberian Peninsula thermal low

Hoinka¹,

Castro

2003

Quart J Royal Meteoro Soc

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SUMMARYStatistics of the thermal low above the Iberian Peninsula are presented for the period between 1979 and 1993, based on gridded data from the European Centre for Medium-Range Weather Forecasts reanalysis project. The sample of days with a thermal low above the Iberian Peninsula was selected objectively using criteria applied to mean-sea-level pressure and 925 hPa geopotential elds. The synoptic-and regional-scale horizontal structure is characterized by the climatology of the 500 hPa geopotential and mean-sea-level pressure distributions. The diurnal evolution of the mean-sea-level pressure is portrayed by mean elds at 00, 06, 12 and 18 UTC. The climatological vertical structure of the thermal low is shown by relation to meridional and zonal crosssections passing through the thermal low's centre. The diurnal evolution of the divergence, relative vorticity, potential temperature and vertical velocity is investigated. Statistics are presented also for the monthly frequency, geographical location, vertical extent and intensity of the Iberian thermal low.

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Section: Horizontal Structurementioning

confidence: 74%

Section: Introductionmentioning

confidence: 99%

The Iberian Peninsula thermal low

Hoinka¹,

Castro

2003

Quart J Royal Meteoro Soc

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“…This thermal low is one of several around the world, including the Iberian low (Gaertner et al 1993;Hoinka and Castro 2003), the Australian thermal low (Leslie 1980), the India-Pakistan low (Joshi and Desai 1985), and the Saudi Arabian low (Blake et al 1983). Between the persistent southwest U.S. thermal low and the nearby Pacific high, there is often a large pressure gradient over the Pacific coast that is typically most intense over northern California and southern Oregon (Mass and Albright 1987).…”

Section: Background and Prior Researchmentioning

confidence: 99%

The West Coast Thermal Trough: Climatology and Synoptic Evolution

Brewer

Mass

Potter

2012

Monthly Weather Review

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Although the West Coast thermal trough (WCTT) is the most important mesoscale feature over the U.S. west coast during the warm season, its initiation, evolution, and structure are not well understood. Originating in the southwest United States, this inverted trough can extend northward into Oregon, Washington, and British Columbia, with large impacts on temperature, wind, humidity, and air quality.Using NCEP's North American Regional Reanalysis (NARR), annual and diurnal climatologies of WCTTs reaching the northwest United States were constructed. For the entire year, WCTTs are most frequent along the coast near the California-Oregon border, with weaker maxima west of the Cascade and coastal mountains. Over the coastal region, they occur most often during autumn, while east of the Cascade Mountains, the highest frequency is during summer. There is strong diurnal variability in WCTT frequency during the summer, with little diurnal variation in winter.Though compositing revealed important seasonal differences in WCTT evolution, some common features emerged. An upper-level ridge moves over the northwest United States and associated high pressure builds in the lower troposphere over southwest Canada, resulting in the development of near-surface easterlies and downslope flow over the western slopes of major terrain barriers of the region. Simultaneously, the WCTT extends northward from California into the Pacific Northwest. As the synoptic configuration changes, the WCTT either moves eastward and merges with the larger thermal low over the Great Basin region, which is most common in summer, or it recedes back into California and dissipates, as often happens in winter.

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“…While the work described in this paper has been motivated by observations acquired in the Australian subtropics, the processes are fundamental in nature and most likely operate in other regions of the world where heat lows are common. These regions include the Iberian Peninsula (Morris 1986;Gaertner et al 1993;Alonso et al 1994;Portela and Castro 1996;Serrano et al 1999;Hoinka and Castro 2003), Saudi Arabia (Ackermann and Cox 1982;Blake et al 1983;Smith 1986a,b;Bitan and Sa'aroni 1992), north Africa (Thorncroft and Flocas), south-west Africa (Pedgley 1972), Pakistan and north India (Joshi and Desai 1985), the QinghaiXizang plateau in China (Junning et al 1986), and the south-western United States (Rowson and Colucci 1992;Douglas and Li 1996).…”

Section: Introductionmentioning

confidence: 99%

The dynamics of heat lows in simple background flows

Spengler¹,

Reeder²,

Smith³

2005

Quart J Royal Meteoro Soc

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SUMMARYA three-dimensional numerical model is used to study the evolution of an idealized heat low that develops over an isolated level land mass surrounded by sea. Calculations are carried out without a background flow and for simple background flows. In all cases, the flow shows a significant diurnal variation in which the sea-breeze circulations are the prominent feature during the daytime and the nocturnal low-level jet is the prominent feature at night. If the land area is large enough so that the sea breezes do not cover it entirely during the diurnal cycle, strong convergence associated with the low-level jet leads to the formation of intense, but shallow, cold fronts along the inland boundaries of sea-breeze air. These fronts decay rapidly after sunrise when surface heating leads to renewed vertical mixing, which destroys the low-level stable layer.The presence of a uniform easterly flow leads to the formation of a west-coast trough, similar to the situation commonly observed over Western Australia. The trough broadens during the day due to the heating of the land, while at night it sharpens and again frontogenesis occurs at low levels near the leading edge of the sea breezes to form shallow cold fronts. In these calculations there is an east-west asymmetry in the sea-breeze circulations: the cool air behind the west-coast sea breeze is shallower than that behind the east-coast sea breeze, but the vertical circulation associated with the west-coast sea breeze is deeper. The east-coast sea-breeze front penetrates further inland, but is more diffuse and is recognizable more by its signature in the relative vorticity than by that in the horizontal temperature gradient.The presence of a horizontal shear-flow leads to the deformation of the heat trough, a process that appears to play an important role in the formation of cold fronts over central Australia. Again the calculations show the formation of shallow fronts over the land during the night, which frontolyse rapidly after sunrise. Despite the idealized nature of the calculations, the associated patterns of low-level vorticity, divergence and horizontal temperature gradient that develop overnight show remarkable similarity to those observed over central Australia. Indeed, the calculations help to interpret the observations of nocturnal frontogenesis over this region.

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A Two-Dimensional Simulation of the Iberian Summer Thermal Low

Cited by 58 publications

References 0 publications

The Iberian Peninsula thermal low

The Iberian Peninsula thermal low

The West Coast Thermal Trough: Climatology and Synoptic Evolution

The dynamics of heat lows in simple background flows

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