Southern Wind Research Articles

Long-term variability of surface temperature in the Black Sea, and its connection with the large-scale atmospheric forcing

Satellite, in situ and reanalysis data for the period of 1950–2005 were used to study the long-term variability of sea surface temperature (SST) in the Black Sea and its connection with the major large-scale atmospheric forcing (air temperature, surface wind and North Atlantic Oscillation — NAO). In contrast to the quasi-regular decadal oscillations of the SST typical for the Northern Atlantic, the pattern of long-term SST variability in the Black Sea is better described as an intermittent periods of SST increase/decrees with the duration of approximately 6–10 years and short (1–2 years) and quite abrupt transitions between them. Confirmed is a known fact of existence of the two major surface wind regimes over the Black Sea i.e., Southern–Western (SW) and Northern–Eastern (NE) and new details on the correlations between the zonal and meridional wind components in each regime are added. A new important finding is that the switch between two regimes occurs quite abruptly at values of NAO index slightly less then zero. It was shown that in weak to moderate positive NAO situation the SW wind regime prevail and wind components are well correlated with the NAO index. The long-term variability of winter-mean SST in the Black Sea is reasonably well correlated with the variability of surface air temperature (SAT), which in turn is highly correlated with the meridional component of surface wind. It is shown that strengthening/weakening of the Southern wind or weakening/strengthening of the Northern wind cause SAT and SST increase/decrease. Finally, a conceptual diagram of NAO impact on the meridional component of the surface wind, SAT and SST is presented.

屋久島河川水にあらわれる同位体高度効果と流出特性

Isotopic compositions were analyzed to grasp the altitude effect observed in and the discharge characteristics of river water in Yakushima Island, southwestern Japan. The isotopic characteristics of the river water are similar to those of precipitation in summer; a regression line for the river water is δ D = 7.68 δ18O + 10.06 and d values are in a range of 6.5 ∼ 16.1‰. Moreover, the altitude effects are -0.17‰/100 m for δ18O and-1.3‰/100 m for δ D irrespective of river drainage size. These altitude effects are well concordant with the values in the previous report in Japan, strongly indicating that the river water in Yakushima Island is scarcely affected by the processes of evaporation and mixing with groundwater having long residence time. This idea is not contradict with verifications using mass ratio of potential evapotranspiration in precipitation as an index. Such discharge characteristics of the river might be attributed to hydrological setting of Yakushima Island, i.e., lower permeability of granite and high amounts of precipitation up to 10,000 mm/yr in the mountainous area. Some river water samples in central-northern and western parts of the Island have apparently light isotopic compositions against the average altitudes of drainage basin. Considering landforms of Yakushima Island and meteoric conditions, such isotopic data would be caused by rain shadow effect in which vapor mass as a source of these river water samples has been brought across a ridge by seasonal southern wind.

Quantification of Water, Salt and Nutrient Exchange Processes at the Mouth of A mediterranean Coastal Lagoon

Vassova lagoon is a typical Mediterranean (small, shallow, micro-tidal, well-mixed) coastal lagoon, receiving limited seasonal freshwater inflows from direct precipitation and underground seepage. An intensive study was carried out in order to quantify the mechanisms responsible for the intra-tidal and residual transport of water, salt, nutrients and chlorophyll at the mouth of this lagoon and to assess the lagoon's flushing behavior. Results indicated that although the system is micro-tidal, tidal effects appeared to be the dominant factor for the longitudinal distribution of physical and chemical parameters, while the associated residual flow is also important and serves as a baseline measure of overall circulation. However, analysis of the net longitudinal currents and fluxes of water, salt and nutrients revealed the importance of non-tidal effects (wind effect and precipitation incidents) in the mean tidal transport. It is shown that the Eulerian residual currents transported water and its properties inwards under southern winds, while a seaward transport was induced during precipitation incidents and northern winds. The Stokes drift effect was found an order of magnitude lower than the Eulerian current, directed towards the lagoon, proving the partially-progressive nature of the tide. Nutrients and chlorophyll-alpha loads are exported from the lagoon to the open sea during the ebb phase of the autumn and winter tidal cycles, associated with the inflow of nutrient-rich freshwater, seeped through the surrounding drainage canal. The reverse transport occurs in spring and early summer, when nutrients enter the lagoon during the flood tidal phase, from the nutrient-rich upper layer of the stratified adjacent sea. Application of a tidal prism model shows that Vassova lagoon has a mean flushing time of 7.5 days, ranging between 4 to 18 days, affected inversely by the tidal oscillation.

Daily and monthly averaged aerosol optical properties and diurnal variability deduced from AERONET sun-photometric measurements at Thala site (Tunisia)

Spectral aerosol optical thickness have been measured at Thala site (central West of Tunisia) from March to October 2001. The measurement site is located in a continental and non industrialized region, approximately 150 km from the North coast of the Mediterranean Sea and nearby the Algerian border. Thala site could be then influenced by the dust content of the continental air masses carried by western and southern winds. A second pollution source is constituted by industrial and/or maritime particles carried by northern and eastern winds. AOT measurements acquired through the ground-based AERONET are analyzed. The diurnal cycle over Thala and two other areas within the network showed various trends and a prevailing pattern of the optical thickness increase by 10–40% during the day. Daily AOT and monthly averaged aerosol optical thickness, Angstrom coefficient and precipitable water vapor are computed and compared with those of other sites. Measured meteorological parameters represent a valuable supplement to the data sets with the sunphotometer measurements. The analysis of the results shows that there is a high correlation between aerosol optical properties (AOT and Angstrom coefficient) and the local weather conditions, essentially wind speed and direction and air specific humidity.

Uranus in 2003: Zonal winds, banded structure, and discrete features

Imaging of Uranus in 2003 with the Keck 10-m telescope reveals banded zonal structure and dozens of discrete cloud features at J and H bands; several features in the northern hemisphere are also detectable at K′. By tracking features over four days, we extend the zonal wind profile well into the northern hemisphere. We report the first measurements of wind velocities at latitudes − 13 ° , + 19 ° , and northward of + 43 ° , the first direct wind measurements near the equator, and the highest wind velocity seen yet on Uranus ( + 218 m / s ). At northern mid-latitudes ( + 20 ° to + 40 ° ), the winds appear to have accelerated when compared to earlier HST and Keck observations; southern wind speeds ( − 20 ° to − 43 ° ) have not changed since Voyager measurements in 1986. The equator of Uranus exhibits a subtle wave structure, indicated by diffuse patches roughly every 30° in longitude. The largest discrete cloud features on Uranus show complex structure extending over tens of degrees, reminiscent of activity seen around Neptune's Great Dark Spot during the Voyager encounter with that planet. There is no sign of a northern “polar collar” as is seen in the south, but a number of discrete features seen at the “expected” latitudes may signal the early stages of development of a northern collar.

Simulation of West African monsoon circulation in four atmospheric general circulation models forced by prescribed sea surface temperature

The mean evolution of the West African monsoon (WAM) circulation and its interannual variability have been studied using an ensemble of 21 simulations (common period 1961–1994) performed with four different atmospheric general circulation models (AGCMs) (European Center/Hamburg (ECHAM) 3, ECHAM 4, Action de Recherche Petite Echelle Grande Echelle (ARPEGE), and Goddard Institute for Space Studies (GISS)) and forced by the same observed sea surface temperature (SST) data set. The results have been compared with European Centre for Medium‐Range Weather Forecasts reanalyses (ERA‐40). The climatological means of WAM winds for the AGCMs are similar to the ERA‐40 ones. However, the AGCMs tend to underestimate the southern wind component at low levels around 10°N compared to the ERA‐40. The simulated Tropical Easterly Jet (TEJ) is usually shifted northward and also too weak for ECHAM 3 and ECHAM 4 compared to ERA‐40. The interannual variability of an atmospheric WAM index (WAMI) is quite successfully reproduced (the correlations between the mean ensemble of each AGCM and ERA‐40 time series over 1961–1994 range between 0.51 and 0.64). In particular, the four AGCMs reproduce quite well the mean teleconnection structure with El Niño–Southern Oscillation, i.e., a strong (weak) monsoon during La Niña (El Niño) events, even if the largest absolute correlations between WAMI and SST in the eastern and central equatorial Pacific are weaker than in ERA‐40. On a yearly basis, WAMI is more predictable and skillful during the cold ENSO years than during the warm ENSO ones. The unskillful warm ENSO events are associated with a significant cooling over the equatorial Atlantic and Western Pacific Ocean and a significant warming in the tropical Indian Ocean.

Extreme Weather Events and the Vertical Microhabitat of Rain Forest Anurans

Abstract When rapid changes in environmental factors occur in tropical rain forests, anurans may behaviorally alter their vertical microhabitat in response. Friajes are extreme weather phenomena that bring cold southern winds into Amazonia. Five friaje events during 1997 and 1998 in southern Peru were studied to examine whether anuran populations differed between visual encounter surveys conducted on friaje nights versus non-friaje nights. Anuran diversity, species richness, and number of hylid individuals were significantly greater during friajes in Peru. Friajes alter anuran vertical distributions by causing arboreal frogs to descend to lower levels in order to avoid the cold temperatures and desiccating winds associated with friajes.

Determination of Linke turbidity factor from solar radiation measurement in northern Tunisia

The attenuation of solar radiation through a real atmosphere versus that through a clean dry atmosphere gives an indication of the atmospheric turbidity. Study of atmospheric turbidity is important in meteorology, climatology and for monitoring of atmospheric pollution. The Linke turbidity factor refers to the whole spectrum, that is, overall spectrally integrated attenuation, which includes presence of gaseous water vapour and aerosols. In this work, a procedure for calculation of Linke turbidity factor is adopted using pyrheliometric measurements in a coastal tourist location in Tunisia (Sidi Bou Saïd), during three summer months (June, July and August 1999). Real diurnal and monthly variations of the T L turbidity factor are found in the three studied months, with a maximum in August afternoon and a minimum in July morning. The increase of T L is an indication for increasing atmospheric turbidity level (pollution). The correlation between atmospheric turbidity and the local weather conditions shows that this increase is essentially due to the heavy water vapour content of maritime air masses, carried by the north-eastern winds prevalent during the afternoon. A second pollution source is the dust content of the continental air masses carried by western and southern winds prevalent in the morning. Next to this can be added the influence of traffic at rush hours and during the afternoon of summer holidays.

PALEOVENTOS E PALEOCORRENTES SUBAQUOSAS DO SISTEMA DEPOSICIONAL PIRAMBÓIA NOS ESTADOS DE SÃO PAULO E PARANÁ, BACIA DO PARANÁ: ESTUDO BASEADO EM ANÁLISE ESTATÍSTICA DE DADOS AZIMUTAIS

Cross stratification dip directions data distributed along the outcrop area of the Pirambóia eolian depositional system (Permian and/Triassic of Paraná Basin), in the states of São Paulo and Paraná, South Brazil, were grouped according to stratigraphic interval, geographic position and depositional facies criteria. Paleowinds and subaquous paleocurrents directions were estimated from eolian and subaqueous (coastal and/or fluvial) facies data, through statistical analysis. The geographic distribution of these paleocurrents and paleowinds directions, during the development of the Pirambóia system, is discussed in terms of provenance and paleogeography, including aspects of atmospheric circulation and relief. The paleowind pattern shows a convergence zone, in the State of Paraná, characterized by eolian influx from NW and NE, in the northern area, and from SW, in the southern area. During the development of Pirambóia depositional system, this zone migrates from the central to the south-central portion of the Paraná State. About the subaqueous facies for the lower Pirambóia depositional system, the paleocurrents exhibit provenance from NE in the southwest of São Paulo State and north of Paraná State. Bidirectional paleocurrents (NNE-SSW) are observed in the central-eastern area of São Paulo State. For the upper Pirambóia depositional system, the paleocurrents found are from SE in the northern São Paulo State, and from NE and NNE in the central and southern areas of Paraná State. Paleocurrents with high dispersion, without a main dip direction, were observed in the central-eastern portion of São Paulo and northern Paraná. The observed paleowind pattern reflects air mass convergence, in global or regional scale of atmospheric circulation. In the regional scale, this convergence would be related to blockade exerted by a geographic barrier in Paraná, which acted as an obstacle to the southern winds, in its north flank, and to the northern winds, in its southern flanks. The coincidence between the zone with reversal of paleowinds and subaquous paleocurrents and the area with concentration of rudaceous facies und with thinning of the stratigraphic unit are suggestive of the existence of structural highs internally to the basin during the development of the Pirambóia depositional system.

PALEOVENTOS E PALEOCORRENTES SUBAQUOSAS DO SISTEMA DEPOSICIONAL PIRAMBÓIA NOS ESTADOS DE SÃO PAULO E PARANÁ, BACIA DO PARANÁ: ESTUDO BASEADO EM ANÁLISE ESTATÍSTICA DE DADOS AZIMUTAIS

Cross stratification dip directions data distributed along the outcrop area of the Piramboia eolian depositional system (Permian and/Triassic of Parana Basin), in the states of Sao Paulo and Parana, South Brazil, were grouped according to stratigraphic interval, geographic position and depositional facies criteria. Paleowinds and subaquous paleocurrents directions were estimated from eolian and subaqueous (coastal and/or fluvial) facies data, through statistical analysis. The geographic distribution of these paleocurrents and paleowinds directions, during the development of the Piramboia system, is discussed in terms of provenance and paleogeography, including aspects of atmospheric circulation and relief. The paleowind pattern shows a convergence zone, in the State of Parana, characterized by eolian influx from NW and NE, in the northern area, and from SW, in the southern area. During the development of Piramboia depositional system, this zone migrates from the central to the south-central portion of the Parana State. About the subaqueous facies for the lower Piramboia depositional system, the paleocurrents exhibit provenance from NE in the southwest of Sao Paulo State and north of Parana State. Bidirectional paleocurrents (NNE-SSW) are observed in the central-eastern area of Sao Paulo State. For the upper Piramboia depositional system, the paleocurrents found are from SE in the northern Sao Paulo State, and from NE and NNE in the central and southern areas of Parana State. Paleocurrents with high dispersion, without a main dip direction, were observed in the central-eastern portion of Sao Paulo and northern Parana. The observed paleowind pattern reflects air mass convergence, in global or regional scale of atmospheric circulation. In the regional scale, this convergence would be related to blockade exerted by a geographic barrier in Parana, which acted as an obstacle to the southern winds, in its north flank, and to the northern winds, in its southern flanks. The coincidence between the zone with reversal of paleowinds and subaquous paleocurrents and the area with concentration of rudaceous facies und with thinning of the stratigraphic unit are suggestive of the existence of structural highs internally to the basin during the development of the Piramboia depositional system.

GeoHostel: Geology of the Southern Wind River Range and Wind River Basin, Wyoming

GeoHostel: Geology of the Southern Wind River Range and Wind River Basin, Wyoming

Red Admirals <i>Vanessa atalanta</i> (Lepidoptera: Nymphalidae) select northern winds on southward migration

In the autumn periods of 1994–2001, the migrations of the Red Admiral Vanessa atalanta (L.) were recorded from the Porkkala Bird Tower, 35 km SW of Helsinki, Finland. By far the best year was 1998, when 1240 migrant V. atalanta were counted. Generalized to a 100-km strip, this would mean a minimum of half a million butterflies. Radar observations indicated that a large proportion may have migrated above the visible range. The migrations took place on sunny days with cool northern winds (down to +10–13 °C). On warmer days with southern winds, V. atalanta individuals were stationary in the terrain. Other species observed to migrate south in the same way, but in much lower numbers, included Vanessa cardui (L.), Pieris brassicae (L.) and Autographa gamma (L.). These records help to resolve the “evolutionary puzzle” of why migrant butterflies and moths travel to northern latitudes when their offspring have such limited possibilities of returning to the south. Until now, the only butterfly for which high-elevation return migrations in northern winds have been known has been the American Monarch Danaus plexippus (L.). The mechanics of the flights, the migratory behaviour and their evolutionary significance are discussed in light of the literature.

VARIABILITY OF CURRENTS IN BAYS OF TAGALAHT AND UUDEPANGA

The variability of the hydrodynamical fields in the sea around the Tagamoisa Cape, the north-western coast of the Saaremaa Island, has been investigated from August to November 2000 measuring currents and stratification. The time series of the forcing parameters, such as the sea level, wind, and currents are presented, and the primary relationships between them have been established. The horizontal fields and the progressive vector diagrams of the currents are constructed. The measured currents in the Tagalaht Bay are significantly dependent on the forcing factors and reveal predominantly a two-layer character. During the dominating southern winds the surface flow to the north, which carries water out from the bay, is compensated by the undercurrent, causing in such a way intensive ventilation of the bay. The two-layer shallow-water model was used to calculate the vertical structure of the currents by integrating the equation of motion through upper and lower layers and eliminating the local sea level forcing term. In the Uudepanga Bay the dominating southern winds cause anticlockwise circulation and the currents reveal predominantly the one-layer structure.

Mercury flux measurements in a naturally enriched area: Correlation with environmental conditions during the Nevada Study and Tests of the Release of Mercury From Soils (STORMS)

An international intercomparison of micrometerological techniques and dynamic flux chamber methods applied to measure mercury fluxes was conducted from September 1 to 4, 1997, during the Nevada Study and Tests of the Release of Mercury From Soils (STORMS) in Reno, Nevada. Nine research groups from four countries met in the Steamboat Springs, Nevada Geothermal Area, to participate in the first international flux intercomparison ever attempted for mercury. The highly heterogeneous soil Hg concentrations and complex landscape within the study area (4 ha) were unfavorable for spatial intercomparison of Hg fluxes between the research groups. However, reliable and correlated Hg fluxes were measured between our micrometerological technique and a dynamic flux chamber method (r2 = 0.29), run side by side (5 m). Hg fluxes and their relationships with environmental factors were complex. After ∼90 days of dry condition, a series of storm events impacted the site and increased the soil moisture from <0.5 to 6.6%. This appeared to promote strong Hg evasion during the transition period from dry to wet soil conditions. However, the subsequent relationship between soil moisture and Hg flux was significantly negatively correlated. Multivariate analysis was applied to extract the principal components (principal component analysis). Three principal components were extracted (explained up to 79% of the total variance) and discussed with respect to their environmental signification. Environmental conditions under southern wind sectors were optimal to promote Hg fluxes. Turbulence rather than Hg air concentrations seemed to be the main factor promoting the determined Hg fluxes during this study.

名古屋近郊域降水中に含まれるイオン濃度の季節変化

A continuous sampling at every 0.5mm of precipitation during rain (average sampling time of 19 minutes) and analyses of ions involved in the rainwater were carried out from April 1, 1993 to March 31, 1994 in Nagakute, 16km east of Nagoya, Japan, to understand temporal changes in ion concentrations in precipitation in detail. The average pH, nitrate (NO3-), and non-seasalt sulfate (nss-SO42-) in the collected rainwaters were 4.76, 14.5μeq l-1 and 18.0μeq l-1, respectively. The average concentrations of ions obtained in this study were about half of those obtained during 1984 and 1986 by the Japan Environmental Agency, which was thought to be caused by either the longer rainy season in 1993 or the reduction of sulfur dioxide emission in recent years.The seasonal changes in ion concentrations show that they were significantly influenced by Asian dust storms and typhoons. Asian dust storms and typhoons were found to play important role in characterizing the precipitation chemistry in Japan.A rapid change in ion concentrations during several minutes was frequently found in individual precipitation accompanied by weather change. Concentrations of NO3-, NH4+, and SO42- decreased with an increase in wind speed, while those of Na+ and Cl- increased, showing the differences in the production and the deposition processes of ions. Higher concentrations of NO3- and nss-SO42- in rain samples with southern wind direction were frequently observed, showing a clear relation to the industrial facilities of ion sources located in the southern direction. A greater amount of ammonium ion (NH4+) was observed to be transported from the suburbs of Nagoya rather than from the downtown area. This measurement (short period sampling and continuous observation) showed characteristics typical of a precipitation chemistry, especially for the seasonal concentration change in major cations and anions and ion transport processes, observed in suburbs in the eastern Asia region.

A numerical study of airflow over Taiwan island

Two-thirds of the land mass of Taiwan island is covered by mountains that affect precipitation systems over the island. Here, we tried to understand the distribution of precipitation associated with the interaction of the prevailing wind (a northern and southern wind direction, respectively) and terrain, if the synoptic forcing was relatively small. For a northern flow under stable conditions, near surface airflow with low Froude number diverted around the Taiwan island. The relatively higher amount of rainfall occurred in the higher mountains on the upstream side, due to topographic lifting of the airflow at similar height. Along the eastern and western side of the island, rainfall occurred over the confluence area of low-level airflow. If the prevailing flow with convectively unstable air and a low Froude number was from the south, the flow was diverted near southern Taiwan and converged near northern Taiwan. Surface heating could induce an upslope flow and enhance the convergence that occurred in northern Taiwan. The upward motion associated with an upslope wind and the convergence air could help precipitation systems form along sloped areas.

アラスカ州プルドーベイの北極域ツンドラにおける盛夏期のＣＯ２収支に及ぼす微気象の影響

The characteristics of micrometeorology and the CO2 flux of the Arctic wet tundra ecosystem were measured during the mid-summer of 1994 at Prudhoe Bay, Alaska. CO2 flux was measured by the eddy correlation technique with a sonic anemometer and an open path IRGA.Over the coastal Arctic tundra, the micrometeorology of the surface boundary layer changed remarkably according to wind direction. Wind from the Polar Sea brought cold and moist air, and southern wind brought warm and dry air with higher water vapor deficit, which resulted different CO2 flux over the wet tundra ecosystem.A simple canopy resistance model was applied in order to analyze the relationship between the CO2 flux and the micrometeorology, in which parameters were determined using measured data. The ecosystem respiration increased with water temperature, and the rate was larger under higher wind speed. The photosynthesis rate decreased with water vapor deficit between leaves and the atmosphere, and its decrement was larger under higher wind speed conditions.The effects of micrometeorology on the CO2 flux were examined using the model, which showed that the level of ecosystem respiration due to high water temperature and that of photosynthetic decrease due to high water vapor deficit were the same orders as the potential of photosynthesis measured over the coastal Arctic tundra at Prudhou Bay, Alaska in mid summer. The magnitude of the ecosystem respiration and the decrement of photosynthesis were large enough to diminish the downward CO2 flux to zero. The CO2 budget over the coastal Arctic wet tundra was much affected by the ecosystem respiration and the contribution of water stress to plant photosynthesis caused by higher temperature and drying.

Directional analysis of extreme wind speeds in Poland

Abstract The paper deals with an analysis of extreme wind speeds for whole territory of Poland. Twenty-three meteorological stations having a complete, or near-complete records from the period 1966–1990 were selected from 60 existing stations for the directional analysis of strong winds. The majority of these stations were chosen for their geographical location and standard, open exposure. However, several stations with non-standard exposure were chosen to investigate the orographic effects on strong winds and exposure correction methods. The annual maxima of wind speeds from each of 12 sectors were abstracted from meteorological records and the analysis was performed to give estimates of the Gumbel probability distribution. Ten-minutes mean values and gust speeds were analysed. In the first phase, the raw data were analysed without any correction for anemometer height, terrain roughness and topography. Next the results will be corrected for each sector at each station. It has been found that western winds dominate for majority of territory of Poland. Wind velocity pressure for sectors from northern through eastern to southern may be reduced to 50% of western values. Only in mountains, where foehn winds occur, southern wind speeds are highest. Results will be used to the zoning of the country in wind loads zones. Intention is to harmonize these zones with all neighbouring countries.

Le Luirographe : étude de la crue du 22 Avril 1995 (réseau de la Luire, Vercors)

The Luirographe can record automatically parameters such as the water height in a karstic network. Placed at the beginning of April 1995, at -200 m, it recorded for the first time the Luire swelling, which lasted two days. The cave of the Luire is situated in the massif of Vercors, with an hydrogeolo-gical basin of 230 km2. The Vercors is a forest of middle mountain within the French Pre-Alps of the North. The Luire swelling only exits when there are very big nival spate accentued by important rainfalls and by a southern wind. Such event arrives only every other year on average. The difference between the high and low level of karst floods can reach the impressive height of 475 m, the most important known in the world. It is the difference between altitude of saturated zone where there is the continuous spring of Arbois and the temporary emergence of the Luire, known up to -451 m and are 20 km apart.

Suppression of dominant topographic overprints in gravity data by adaptive filtering: Southern Wyoming province

In areas of the world with a protracted tectonic history, the gravity field may be dominated by anomalies due to individual structural features developed during the latest tectonic event. These individual tectonic features often have a topographic expression. Adaptive filtering techniques can be used to suppress the gravity effects of such features. Iterative space domain techniques are particularly well suited to these types of problems. One such technique, the stochastic gradient algorithm, allows easy updating of filter coefficients at each spatial step through the data. This approach eliminates windowing and spectral estimation problems associated with cross‐spectral admittance schemes. In this study, adaptive filtering of Bouguer gravity and topography in the southern Wyoming Province was successful in suppressing gravity signatures of Laramide structural features. The regional gravity trends due to isostatic effects were significantly absent from the residual anomaly map. A large, continuous, positive gravity anomaly stretching from the southern Wind River Range to the northern end of the Laramie Range was another outstanding feature observed in the residual anomaly. This positive anomaly is about the same magnitude, size and shape as anomalies due to greenstone belts observed in other Archean cratonal areas. Scattered occurrences of greenstone lithologies are known throughout the area of the anomaly, but a continuous feature is absent in outcrop. Due to the unusual structural history of the area, it is possible that such a continuous belt does exist, but was buried at shallow crustal levels by Laramide thrusting, or later collapse of a Laramide uplift due to a change in the regional stress field.