Regional Wind Patterns Research Articles

Mars Global Digital Dune Database and initial science results

A new Mars Global Digital Dune Database (MGD3) constructed using Thermal Emission Imaging System (THEMIS) infrared (IR) images provides a comprehensive and quantitative view of the geographic distribution of moderate‐ to large‐size dune fields (area >1 km2) that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of Mars. MGD3 extends from 65°N to 65°S latitude and includes ∼550 dune fields, covering ∼70,000 km2, with an estimated total volume of ∼3,600 km3. This area, when combined with polar dune estimates, suggests moderate‐ to large‐size dune field coverage on Mars may total ∼800,000 km2, ∼6 times less than the total areal estimate of ∼5,000,000 km2 for terrestrial dunes. Where availability and quality of THEMIS visible (VIS) or Mars Orbiter Camera narrow‐angle (MOC NA) images allow, we classify dunes and include dune slipface measurements, which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification. For dunes located within craters, the azimuth from crater centroid to dune field centroid (referred to as dune centroid azimuth) is calculated and can provide an accurate method for tracking dune migration within smooth‐floored craters. These indicators of wind direction are compared to output from a general circulation model (GCM). Dune centroid azimuth values generally correlate to regional wind patterns. Slipface orientations are less well correlated, suggesting that local topographic effects may play a larger role in dune orientation than regional winds.

Effects of mesoscale physical processes on thin zooplankton layers at four sites along the west coast of the U.S.

Within the coastal marine environment, populations of phytoplankton, zooplankton, bacteria, viruses, and aggregations of marine snow are frequently concentrated beneath the surface in discrete, vertically thin layers. Thin layers range in vertical dimension from a few centimeters to three meters, and have been observed to extend horizontally for kilometers. They appear in the water column episodically and can persist for days. We present some of the results of an investigation of four coastal sites along the west coast of the United States to assess frequency of occurrence of thin layers of zooplankton. Our study sites included coastal sites near East Sound, Washington; Cape Perpetua, Oregon; Monterey Bay, California; and Santa Barbara, California. At each site, we collected several, weeks-long time series of hydrography, current velocity, and acoustic backscatter due to mesozooplankton. Our results show that thin layers were common features at all four sites. Across all study sites, a change in the predominant physical regime, usually precipitated by a change in the wind pattern, corresponded with an absence of thin zooplankton layers. In order to make a first-order prediction about when thin layers have the possibility of occurring in a coastal environment, we found it useful to examine regional wind and circulation patterns and to determine how they affect stratification in each local environment.

Palaeowind patterns during the latest Jurassic–earliest Cretaceous in Gondwana: Evidence from aeolian cross-strata of the Botucatu Formation, Brazil

The direction of sediment transport in the aeolian sandstones of the Botucatu Formation (latest Jurassic–earliest Cretaceous of the Paraná Basin) has been interpreted on the basis of cross-strata dip directions, which allowed the reconstruction of regional wind patterns in midwestern Gondwana. Regionally, cross-strata dip directions indicate variations of palaeowind directions across the outcrop area of the Botucatu palaeoerg. The northern portion of the palaeoerg was characterized by palaeowinds blowing from the NNE, whereas the southern portion was under the influence of palaeowinds coming from the SW. A wind convergence zone occurred at palaeolatitudes around 24° to 26°S. The identified wind pattern agrees with general circulation models for the Late Jurassic, which predict that, during the summer months (December through February), strong monsoonal winds to the S existed at low latitudes in Gondwana. Southerly winds converged at the ITCZ (at around 24°S) with winds blowing toward the northeast.

Regional wind fields and dunefield migration, southern Brazil

AbstractThis paper examines a seemingly anomalous situation in southern Brazil where the dunefields on Santa Catarina Island (e.g. Joaquina Beach) migrate to the NNW, almost completely the opposite direction (c. 160) to the dunefields immediately to the south (e.g. Pinheira Beach), and some much further to the north (e.g. Cabo Frio) which migrate to the SSW. A variety of mechanisms are examined to explain the differences in dunefield migration including grain size variations, topographic effects on local winds, shoreline orientation, and regional wind field changes. The mean grain sizes of the two beaches, Pinheira and Joaquina, are not sufficiently different to restrict aeolian sediment transport in either place, nor to account for a lack of transport from the NNE to the SSW in the case of Joaquina. Some topographic steering of the wind is likely but could not account for the long‐term average difference in migration trends of the island dunefields compared to the mainland dunefields. While the orientation of the shoreline to prevailing winds is an important control on beach and dune sediment transport, it is not the dominant controlling mechanism. An analysis of the regional wind patterns demonstrates that there is a major shift in the regional wind field near the island such that the dominant island winds blow from the SW/SSW while those further south blow from the NE. It is concluded that this is the predominant reason for the divergence in the direction of migration of the dunefields. Copyright © 2006 John Wiley & Sons, Ltd.

Thermally driven circulation in a region of complex topography: comparison of wind-profiling radar measurements and MM5 numerical predictions

Abstract. The diurnal variation of regional wind patterns in the complex terrain of Central Italy was investigated for summer fair-weather conditions and winter time periods using a radar wind profiler. The profiler is located on a site where interaction between the complex topography and land-surface produces a variety of thermally and dynamically driven wind systems. The observational data set, collected for a period of one year, was used first to describe the diurnal evolution of thermal driven winds, second to validate the Mesoscale Model 5 (MM5) that is a three-dimensional numerical model. This type of analysis was focused on the near-surface wind observation, since thermally driven winds occur in the lower atmosphere. According to the valley wind theory expectations, the site – located on the left sidewall of the valley (looking up valley) – experiences a clockwise turning with time. Same characteristics in the behavior were established in both the experimental and numerical results. Because the thermally driven flows can have some depth and may be influenced mainly by model errors, as a third step the analysis focuses on a subset of cases to explore four different MM5 Planetary Boundary Layer (PBL) parameterizations. The reason is to test how the results are sensitive to the selected PBL parameterization, and to identify the better parameterization if it is possible. For this purpose we analysed the MM5 output for the whole PBL levels. The chosen PBL parameterizations are: 1) Gayno-Seaman; 2) Medium-Range Forecast; 3) Mellor-Yamada scheme as used in the ETA model; and 4) Blackadar.

Holocene palaeoecology and shoreline displacement on the Biskopsmåla Peninsula, southeastern Sweden

High-resolution palaeoecological proxies of pollen, macrofossils and diatoms from an isolation lake provide a long-term record of the Holocene landscape history and shoreline displacement on the Biskopsmala Peninsula in central Blekinge, SE Sweden. During the Preboreal/Boreal transition, the peninsula was sparsely vegetated by woodlands, along with lateglacial dwarf shrub/steppe communities. The lake basin was isolated from the shallow Yoldia Sea during this time. The regional climate improved from 10 700 cal. BP, evident as progressive expansion of Pinus -dominated mixed forest with deciduous trees. The lake basin was probably connected with the Ancylus Lake during the period 10 700-10 100 cal. BP. Subsequently the basin became isolated again, corresponding to the Early Littorina Sea phase. Replacement of freshwater diatoms by those with brackish-water affinity at 8100 cal. BP indicates the initial transgression of the Littorina Sea in this basin. But not until 7500 cal. BP were brackish conditions fully established. Peaks of brackish-marine diatoms and dinoflagellates during 7500-7000 cal. BP indicate increased saltwater inflow to the Baltic Sea in response to global meltwater pulse 3. However, interactive changes in seagrass and stonewort macrofossil concentrations suggest that three minor transgressions during 5900-5300, 5000-4700 and 4400-4000 cal. BP occurred locally, associated with centennial-scale variations in regional wind pattern or coastal storminess. By 3000 cal. BP, the lake basin was finally isolated from the Baltic, and thereafter the landscape on the peninsula became gradually more influenced by human activities.

Holocene palaeoecology and shoreline displacement on the Biskopsmåla Peninsula, southeastern Sweden

High‐resolution palaeoecological proxies of pollen, macrofossils and diatoms from an isolation lake provide a long‐term record of the Holocene landscape history and shoreline displacement on the Biskopsmåla Peninsula in central Blekinge, SE Sweden. During the Preboreal/Boreal transition, the peninsula was sparsely vegetated by woodlands, along with lateglacial dwarf shrub/steppe communities. The lake basin was isolated from the shallow Yoldia Sea during this time. The regional climate improved from 10 700 cal. BP, evident as progressive expansion of Pinus‐dominated mixed forest with deciduous trees. The lake basin was probably connected with the Ancylus Lake during the period 10700–10 100 cal. BP. Subsequently the basin became isolated again, corresponding to the Early Littorina Sea phase. Replacement of freshwater diatoms by those with brackish‐water affinity at 8100 cal. BP indicates the initial transgression of the Littorina Sea in this basin. But not until 7500 cal. BP were brackish conditions fully established. Peaks of brackish‐marine diatoms and dinoflagellates during 7500–7000 cal. BP indicate increased saltwater inflow to the Baltic Sea in response to global meltwater pulse 3. However, interactive changes in seagrass and stonewort macrofossil concentrations suggest that three minor transgressions during 5900–5300, 5000–4700 and 4400–4000 cal. BP occurred locally, associated with centennial‐scale variations in regional wind pattern or coastal storminess. By 3000 cal. BP, the lake basin was finally isolated from the Baltic, and thereafter the landscape on the peninsula became gradually more influenced by human activities.

Loess in Europe—mass accumulation rates during the Last Glacial Period

Upper Pleistocene loess/palaeosol sequences provide excellent high-resolution terrestrial archives of climate forcing. Due to improvements in numerical age determinations, especially in luminescence dating methods, a more reliable time-based reconstruction of the past climate and environmental change has become available for the loess record in Europe. Chronological information was collected from 43 sites along a northwest to southeast transect in Europe. Thirty-three of these sites had sufficient age information to allow estimation of mass accumulation rates, and it was possible to isolate the mass accumulation rates of primary loess during the Last Glacial Period (∼28–13 ka BP) at 21 of these locations. These sites fall along a coarse climatic gradient from the relatively coastal climate of Belgium and France to the drier, more continental climate of Central Europe. Interpreting mass accumulation rates of loess in terms of this climatic gradient is not straightforward as these deposits are dominated by sources in floodplains and large river systems. Thus accumulation rates are influenced strongly by regional wind and precipitation patterns, but mostly by the availability of glacially derived material from the Alps and the periglacial terrains that characterized European fluvial systems during and immediately following glaciation.

Internal structure of a trough blowout, determined from migrated ground‐penetrating radar profiles

Ground‐penetrating radar (GPR) was used to investigate the relationship between the geomorphological development of a large aeolian trough blowout and the stratigraphy and internal sedimentary structure of its associated deposits. Although analogous, many of the data‐processing techniques routinely applied in seismic reflection are very rarely applied in GPR studies. In this study, a simple migration program was used that significantly enhanced the quality of GPR images from a large trough blowout at Raven Meols on the Sefton coast, northwest England. These improvements aided subsequent data interpretation, which was achieved through application of the principles of radar stratigraphy. GPR shows the pre‐blowout dunes to have a complex internal structure that suggests they were formed in the presence of at least a partial vegetation cover. Subsequent to stabilization of these dunes a thin soil developed. This dune soil forms an important radar sequence boundary and delineates a complex topography beneath the depositional lobe of the blowout. The internal structure of the depositional lobe of the blowout does not conform to a model of simple radial foreset deposition, as derived from contemporary process studies reported in the literature. Instead, the pattern of deposition has been extensively modified by the antecedent dune topography and by varying spatial and temporal exposure to important sand‐transporting winds that is partly controlled by interactions between the regional wind pattern and local dune morphology. Trough blowout deposits in coastal aeolian sedimentary sequences are likely to be recognized by the presence of laterally continuous packets of relatively high‐angle cross‐strata, which often display a spatially‐variable radial dip pattern that is only very poorly or partially developed. In addition, a soil, or other surface representing a significant hiatus in dune deposition, is likely to underlie the blowout deposits, the topography of which will show a clear relationship to the dip and orientation of the overlying cross‐strata.

Wintertime Surface Wind Patterns in the Colorado River Valley

Abstract The diurnal variation of regional wind patterns in the complex terrain of the Grand Canyon area was investigated for wintertime fair weather days using a network of wind sensors on 10-m towers. Thermally driven along-slope and along-valley circulations were present at all sites within the region, but wind characteristics varied from site to site depending on nearby topography and exposure. Along the Colorado River upstream from the Grand Canyon, a series of subbasins produce a regional circulation system characterized by convergence of low-level air into the subbasins at night and divergence of air from the subbasins during the day. Contrary to valley wind theory expectations, locations down valley from the subbasin centers experience up-valley winds during nighttime and down-valley winds during daytime.

Determination of repose-period patterns of volcanoes from sequences of ash layers

The repose-period patterns of volcanoes have been studied earlier from the historical records of their eruptions. This paper analyzes the necessary conditions for using observed sequences of ash layers instead of such records. The temporal distribution of preserved ash falls at a point is a function of: (1) the number of active volcanoes of the region; (2) their locations within the region; (3) the regional wind pattern; and of accidental erosion and redeposition at the point. The distribution of ash layers is derived if only one volcano must be considered and factor (4) can be neglected. Explicit functions are complicated; ash falls from a “Poissonian volcano” are, however, also Poissonian but with a different wind pattern-dependent parameter. A correction for factor (3) is rarely possible because the present wind pattern may differ from the pattern at the time of ash falls. By determining the chronostratigraphy of the ash falls all around the volcano, factor (3) may be eliminated. The example of several volcanoes producing origin-indistinguishable ash layers, is briefly discussed. The time sequence of such “pooled” ash falls practically always shows pronounced memory effects of previous eruptions.

A Climatological Study of the Urban Temperature Anomaly in the Lakeshore Environment at Toronto

Metropolitan Toronto (population of about 2,160,000 and area of 2282 km2) is on the north shore of Lake Ontario (area of 19,400 km2). The interaction between the daytime urban heat island and the lake circulation is studied using several years of records of daily maximum temperatures from a network of about 23 observing stations, pre-stratifying the data according to the regional wind patterns at the geostrophic level and according to the daily sunshine total. The results show that the heat island exists and is detectable during the time of maximum heating in Toronto. Further, the position of the heat island, although a result of urban influence (automobile traffic, industry, home heating units, etc.), is displaced in response to regional and lake breeze wind patterns and the modification of the lake breeze as it moves across the built-up area.