Slope Winds Research Articles

Unraveling the martian water cycle with high-resolution global climate simulations

Global climate modeling of the Mars water cycle is usually performed at relatively coarse resolution (200−300km), which may not be sufficient to properly represent the impact of waves, fronts, topography effects on the detailed structure of clouds and surface ice deposits. Here, we present new numerical simulations of the annual water cycle performed at a resolution of 1° × 1° (∼ 60 km in latitude). The model includes the radiative effects of clouds, whose influence on the thermal structure and atmospheric dynamics is significant, thus we also examine simulations with inactive clouds to distinguish the direct impact of resolution on circulation and winds from the indirect impact of resolution via water ice clouds. To first order, we find that the high resolution does not dramatically change the behavior of the system, and that simulations performed at ∼ 200 km resolution capture well the behavior of the simulated water cycle and Mars climate. Nevertheless, a detailed comparison between high and low resolution simulations, with reference to observations, reveal several significant changes that impact our understanding of the water cycle active today on Mars. The key northern cap edge dynamics are affected by an increase in baroclinic wave strength, with a complication of northern summer dynamics. South polar frost deposition is modified, with a westward longitudinal shift, since southern dynamics are also influenced. Baroclinic wave mode transitions are observed. New transient phenomena appear, like spiral and streak clouds, already documented in the observations. Atmospheric circulation cells in the polar region exhibit a large variability and are fine structured, with slope winds. Most modeled phenomena affected by high resolution give a picture of a more turbulent planet, inducing further variability. This is challenging for long-period climate studies.

Analysis of wind-induced dynamic pressure fluctuations during one and a half Martian years at Gale Crater

The Rover Environmental Monitoring Station (REMS) instrument on-board the Mars Science Laboratory (MSL) has acquired unprecedented measurements of key environmental variables at the base of Gale Crater. The pressure measured by REMS shows modulations with a very structured pattern of short-time scale (of the order of seconds to several minutes) mild fluctuations (typically up to 0.2 Pa at daytime and 1 Pa at night-time). These dynamic pressure oscillations are consistent with wind, air and ground temperature modulations measured simultaneously by REMS. We detect the signals of a repetitive pattern of upslope/downslope winds, with maximal speeds of about 21 m/s, associated with thermal changes in the air and surface temperatures, that are initiated after sunset and finish with sunrise proving that Gale, a 4.5 km deep impact crater, is an active Aeolian environment. At nighttime topographic slope winds are intense with maximal activity from 17:00 through 23:00 Local Mean Solar Time, and simultaneous changes of surface temperature are detected. During the day, the wind modulations are related to convection of the planetary boundary layer, winds are softer with maximum wind speed of about 14 m/s. The ground temperature is modulated by the forced convection of winds, with amplitudes between 0.2 K and 0.5 K, and the air temperatures fluctuate with amplitudes of about 2 K. The analysis of more than one and a half Martian years indicates the year-to-year repeatability of these environmental phenomena. The wind pattern minimizes at the beginning of the south hemisphere winter (Ls 90) season and maximizes during late spring and early summer (Ls 270). The procedure that we present here is a useful tool to investigate in a semi-quantitative way the winds by: i) filling both seasonal and diurnal gaps where wind measurements do not exist, ii) providing an alternative way for comparisons through different measuring principia and, iii) filling the gap of observation of short-time wind variability, where the REMS wind sensor is blind.

Meteorología mesoescalar en Marte

The revitalizing of Mars exploration in the early 1990s combined with the maturation of terrestrial mesoscale modeling codes provided fertile ground for the application of suitably modified models to the atmosphere of Mars. The use of mesoscale models, particular for Mars, has become an integral part of interpreting the data returned from missions and providing constraints and bounds on environmental conditions in support of mission planning and operations. Mesoscale models are ideal tools for greatly minimize risk during entry, descent, and landing phases. Slope winds, dust injection processes and atmospheric volatiles transport are the main Mars mesoscale circulations that affect the atmospheric structure and dynamics. In this article is also included as an example the meteorological simulation of Gale Crater environment, in which the Mars Science Laboratory (MSL) Rover Curiosity landed in August 2012, with the spanish weather station Rover Environmental Monitoring Station (REMS) aboard. The observational data record provides sufficient means against which to evaluate mesoscale model. Meteorological interpretations show a dynamically complex environment. Local, regional and synoptic scales all interact in nonlinear ways to produce the observed weather. Two different atmospheric periods could be distinguished inside the crater: semi-isolated period during most of the martian year (Ls 0, 90 and 180) and mixing period during the summer (Ls 270). During the semi-isolated period, warm air from south overrides the crater creating a very stable boundary layer. Crater air mass is generally much colder than outside the crater forcing downslope flows, thermodynamically driven, to not scour crater and hence decreasing mixing level in this period. Ls 270 was shown to be an anomalous season when air within and outside the crater was well mixed by strong, flushing, northerly flow and large amplitude breaking mountain waves. At other seasons, the air in the crater was more isolated form the surrounding environment.

Evolution of Late Wintertime Thermally Driven Local Flows and Temperature Fields over Far-Western Nepal

Atmospheric processes over the Himalayan complex terrain are yet to be studied extensively. Only a few significant researches are reported from this region and the Far-Western Region (FWR) of Nepal still remains untouched. Thus, the present study was conceived to understand the meteorological flow characteristics and thermal environment over the region and associated areas during the late wintertime with the application of the state-of-the-art-of Weather Research and Forecasting (WRF) Modeling System. The study revealed that the northern mountainous region developed strong down slope wind during the night and morning times, which sweeps out the southern plain area of Nepal and may reach just beyond the border. The wind over the plain was very shallow whose depth was just about 100 m. The down slope winds over the southern slope of the Daijee and Nandhaur mountain ranges were significantly enhanced by the subsidence of the southerly wind that prevails above 1 km height above the mean sea level. Close to the noon time a very gentle southerly valley wind from the southern plain replaced the nighttime down slope. Very shallow but strong surface inversion builds up over the plain that breaks up in the late morning. The depth of the mixed layer and the valley wind may reach up to 1km in the afternoon. The thermal environment over the FWR of Nepal was fairly hot that may remain around 35°C in the afternoon around the Mahendranagar area whereas the temperature during the nighttime may go as low as 23°C. The study revealed that, contrary to the general perception, temperature over plain areas of Nepal was significantly higher than further southern areas belonging to India. The meteorological flow fields over the FWR of Nepal executed diurnal periodicity with little day-to-day variation during the late wintertime.Journal of Institute of Science and TechnologyVolume 21, Issue 1, August 2016, page: 35-47

Performance of WRF in simulating terrain induced flows and atmospheric boundary layer characteristics over the tropical station Gadanki

In this study the evolution of the topographic flows and boundary layer features over a tropical hilly station Gadanki in southern India were simulated using Advanced Research WRF (ARW) mesoscale model for fair weather days during southwest monsoon (20–22 July 2011) and winter (18–20 Jan. 2011). Turbulence measurements from an Ultra High Frequency (UHF) Wind Profiler, Ultra Sonic Anemometer, GPS Sonde and meteorological tower were used for comparison. Simulations revealed development of small-scale slope winds in the lower boundary layer (below 800m) at Gadanki which are more prevalent during nighttime. Stronger slope winds during winter and weaker flows in the monsoon season are simulated indicating the sensitivity of slope winds to the background synoptic flows and radiative heating/cooling. Higher upward surface fluxes (sensible, latent heat) and development of very deep convective boundary layer (~2500m) is simulated during summer monsoon relative to the winter season in good agreement with observations. Four PBL parameterizations (YSU, MYJ, MYNN and ACM) were evaluated to simulate the above characteristics. Large differences were noticed in the simulated boundary layer features using different PBL schemes in both the seasons. It is found that the TKE-closures (MYJ, MYNN) produced extremities in daytime PBL depth, surface fluxes, temperature, humidity and winds. The differences in the simulations are attributed to the eddy diffusivities, buoyancy and entrainment fluxes which were simulated differently in the respective schemes. The K-based YSU followed by MYNN best produced the slope winds as well as daytime boundary layer characteristics realistically in both the summer and winter synoptic conditions at Gadanki hilly site though with slight overestimation of nocturnal PBL height.

Palygorskite from cave sediments: case study from Wadi Haqil, United Arab Emirates

The x-ray powder diffraction identification of clay minerals both in bulk samples and in separated clay fraction confirmed the presence of palygorskite in samples of cave sediments from Wadi Haqil (the western slopes of Musandam Mountains; Ras Al-Khaimah Emirate, UAE). Samples contain quartz, gypsum, smectite, kaolinite, calcite, and palygorskite, some of them chlorite, illite, feldspars, and goethite. Calcite dominates in most samples; smectite prevails in clay fraction. After heating, the 001 reflection of chlorite shifts to higher diffraction angles and its intensity decreases; these features indicate that the chlorite represent a Fe-dominant species. Unit-cell dimensions of major phases as refined by the Rietveld method are in agreement with literature data. Chemical composition of palygorskite was derived from unit-cell dimensions as follows: MgO content is 11–14 wt% and Al2O3 10–13 wt%. Clay mineralogy is only hard to ascertain from the scanning electron microscope (SEM) images even after being combined with the energy-dispersive spectrometer data. The SEM was also used to characterize gypsum grains; they often display flow deformation features. Studied cave sediments represent palygorskite-bearing weathering products and desert soils re-deposited from the cave surroundings by slope processes and wind and/or surface runoff. The mixture with other clay minerals, quartz, feldspars, etc. supports this interpretation. Fine-grained quartz fraction is probably wind-blown. Gypsum and calcite are the precipitates (crusts and/or cements), although gypsum can also be re-deposited from omnipresent gypsum-cemented surface sediments.

Quantifying horizontal and vertical tracer mass fluxes in an idealized valley during daytime

Abstract. The transport and mixing of pollution during the daytime evolution of a valley boundary layer is studied in an idealized way. The goal is to quantify horizontal and vertical tracer mass fluxes between four different valley volumes: the convective boundary layer, the slope wind layer, the stable core, and the atmosphere above the valley. For this purpose, large eddy simulations (LES) are conducted with the Weather Research and Forecasting (WRF) model for a quasi-two-dimensional valley. The valley geometry consists of two slopes with constant slope angle and is homogeneous in the along-valley direction. The surface sensible heat flux is horizontally homogeneous and prescribed by a sine function. The initial sounding is characterized by an atmosphere at rest and a constant Brunt–Väisälä frequency. Various experiments are conducted for different combinations of surface heating amplitudes and initial stability conditions. A passive tracer is released with an arbitrary but constant rate at the valley floor and resulting tracer mass fluxes are evaluated between the aforementioned volumes.As a result of the surface heating, a convective boundary layer is established in the lower part of the valley with a stable layer on top – the so-called stable core. The height of the slope wind layer, as well as the wind speed within, decreases with height due to the vertically increasing stability. Hence, the mass flux within the slope wind layer decreases with height as well. Due to mass continuity, this along-slope mass flux convergence leads to a partial redirection of the flow from the slope wind layer towards the valley centre and the formation of a horizontal intrusion above the convective boundary layer. This intrusion is associated with a transport of tracer mass from the slope wind layer towards the valley centre. A strong static stability and/or weak forcing lead to large tracer mass fluxes associated with this phenomenon. The total export of tracer mass out of the valley atmosphere increases with decreasing stability and increasing forcing. The effects of initial stability and forcing can be combined to a single parameter, the breakup parameter B. An analytical function is presented that describes the exponential decrease of the percentage of exported tracer mass with increasing B. This study is limited by the idealization of the terrain shape, stratification, and forcing, but quantifies transport processes for a large range of forcing amplitudes and atmospheric stability.

Incorporating Autonomous Sensors and Climate Modeling to Gain Insight into Seasonal Hydrometeorological Processes within a Tropical Glacierized Valley

Peru is facing imminent water resource issues as glaciers retreat and demand for water increases, yet limited observations and model resolution hamper understanding of hydrometerological processes on local to regional scales. Much of current global and regional climate studies neglect the meteorological forcing of lapse rates (LRs) and valley and slope wind dynamics on critical components of the Peruvian Andes' water cycle, and herein we emphasize the wet season. In 2004 and 2005 we installed an autonomous sensor network (ASN) within the glacierized Llanganuco Valley, Cordillera Blanca (9° S), consisting of discrete, cost-effective, automatic temperature loggers located along the valley axis and anchored by two automatic weather stations. Comparisons of these embedded hydrometeorological measurements from the ASN and climate modeling by dynamical downscaling using the Weather Research and Forecasting model elucidate distinct diurnal and seasonal characteristics of the mountain wind regime and LRs. Wind, temperature, humidity, and cloud simulations suggest that thermally driven up-valley and slope winds converging with easterly flow aloft enhance late afternoon and evening cloud development, which helps explain nocturnal wet season precipitation maxima measured by the ASN. Furthermore, the extreme diurnal variability of along-valley-axis LR and valley wind detected from ground observations and confirmed by dynamical downscaling demonstrate the importance of realistic scale parameterizations of the atmospheric boundary layer to improve regional climate model projections in mountainous regions.

A study of local turbulence and anisotropy during the afternoon and evening transition with an unmanned aerial system and mesoscale simulation

Abstract. Observations of turbulence are analysed for the afternoon and evening transition (AET) during the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) experimental field campaign that took place in Lannemezan (foothills of the Pyrenees) in summer 2011. The case of 2 July is further studied because the turbulence properties of the lower atmosphere (up to 300 m above ground level) were sampled with the Meteorological Mini Aerial Vehicle (M2AV) from turbulently mixed to stably stratified atmospheric conditions. Additionally, data from radiosoundings, 60 m tower and UHF wind profiler were taken together with the model results from a high-resolution mesoscale simulation of this case. Weak large-scale winds and clear-sky conditions were present on the studied AET case favouring the development of slope winds and mountain–plain circulations. It is found that during the AET the anisotropy of the turbulent eddies increases as the vertical motions are damped due to the stably stratified conditions. This effect is enhanced by the formation of a low-level jet after sunset. Finally, the comparison of the anisotropy ratio computed from the different sources of observations allow us to determine the most relevant scales of the motion during the AET in such a complex terrain region.

Theoretical calculations of interactions between urban breezes and mountain slope winds in the presence of basic-state wind

Many big cities around the world are located near mountains. In city-mountain regions, thermally and topographically forced local winds are produced and they affect the transport of pollutants emitted into the urban atmosphere. A better understanding of the dynamics of thermally and topographically forced local winds is necessary to improve the prediction of local winds and to cope with environmental problems. In this study, we theoretically examine the interactions of urban breezes with mountain slope winds in the presence of basic-state wind within the context of the response of a stably stratified atmosphere to prescribed thermal and mechanical forcing. The interactions between urban breezes and mountain slope winds are viewed through the linear superposition of individual analytical solutions for urban thermal forcing, mountain thermal forcing, and mountain mechanical forcing. A setting is considered in which a city is located downwind of a mountain. In the nighttime, in the mountain-side urban area, surface/near-surface horizontal flows induced by mountain cooling and mountain mechanical forcing cooperatively interact with urban breezes, resulting in strengthened winds. In the daytime, in the urban area, surface/near-surface horizontal flows induced by mountain heating are opposed to urban breezes, giving rise to weakened winds. It is shown that the degree of interactions between urban breezes and mountain slope winds is sensitive to mountain height and basic-state wind speed. Particularly, a change in basic-state wind speed affects not only the strength of thermally and mechanically induced flows (internal gravity waves) but also their vertical wavelength and decaying rate. The examination of a case in a setting in which a city is located upwind of a mountain reveals that basic-state wind direction is an important factor that significantly affects the interactions of urban breezes with mountain slope winds.

The impact of embedded valleys on daytime pollution transport over a mountain range

Abstract. Idealized large-eddy simulations were performed to investigate the impact of different mountain geometries on daytime pollution transport by thermally driven winds. The main objective was to determine interactions between plain-to-mountain and slope wind systems, and their influence on the pollution distribution over complex terrain. For this purpose, tracer analyses were conducted over a quasi-two-dimensional mountain range with embedded valleys bordered by ridges with different crest heights and a flat foreland in cross-mountain direction. The valley depth was varied systematically. It was found that different flow regimes develop dependent on the valley floor height. In the case of elevated valley floors, the plain-to-mountain wind descends into the potentially warmer valley and replaces the opposing upslope wind. This superimposed plain-to-mountain wind increases the pollution transport towards the main ridge by an additional 20 % compared to the regime with a deep valley. Due to mountain and advective venting, the vertical exchange is 3.6 times higher over complex terrain than over a flat plain. However, the calculated vertical exchange is strongly sensitive to the definition of the convective boundary layer height. In summary, the impact of the terrain geometry on the mechanisms of pollution transport confirms the necessity to account for topographic effects in future boundary layer parameterization schemes.

Modeling the thermal and physical evolution of Mount Sharp's sedimentary rocks, Gale Crater, Mars: Implications for diagenesis on the MSL Curiosity rover traverse

AbstractGale Crater, the Mars Science Laboratory (MSL) landing site, contains a central mound, named Aeolis Mons (informally Mount Sharp) that preserves 5 km of sedimentary stratigraphy. Formation scenarios include (1) complete filling of Gale Crater followed by partial sediment removal or (2) building of a central deposit with morphology controlled by slope winds and only incomplete sedimentary fill. Here we model temperature‐time paths for both scenarios, compare results with analyses provided by MSL Curiosity, and provide scenario‐dependent predictions of temperatures of diagenesis along Curiosity's future traverse. The effects of variable sediment thermal conductivity and historical heat flows are also discussed. Modeled erosion and deposition rates are 5–37 µm/yr, consistent with previously published estimates from other Mars locations. The occurrence and spatial patterns of diagenesis depend on sedimentation scenario and surface paleotemperature. For (1) temperatures experienced by sediments decrease monotonically along the traverse and up Mount Sharp stratigraphy, whereas for (2) temperatures increase along the traverse reaching maximum temperatures higher up in Mount Sharp's lower units. If early Mars surface temperatures were similar to modern Mars (mean: −50°C), only select locations under select scenarios permit diagenetic fluids. In contrast, if early Mars surface temperatures averaged 0°C or brines had lowered freezing points, diagenesis is predicted in most locations with temperatures < 225°C. Comparing our predictions with future MSL results on diagenetic textures, secondary mineral assemblages, and their spatial variability will constrain past heat flow, Mount Sharp's formation processes, the availability of liquid water on early Mars, and sediment organic preservation potential.

Numerical and Obserbational study of the thermal belt and down slope wind on Mt.Tsukuba

Numerical and Obserbational study of the thermal belt and down slope wind on Mt.Tsukuba

Local circulations in and around the Ulaanbaatar, Mongolia, metropolitan area

Many cities around the world are located in mountainous areas. Understanding local circulations in mountainous urban areas is important for improving local weather and air quality prediction as well as understanding thermally forced mesoscale flow dynamics. In this study, we examine local circulations in and around the Ulaanbaatar, Mongolia, metropolitan area using the Weather Research and Forecasting model coupled with the Seoul National University Urban Canopy Model. Ulaanbaatar lies in an east–west-oriented valley between the northern base of Mt. Bogd Khan and the southern base of branches of the Khentiin Nuruu mountain range. Idealized summertime fair-weather conditions with no synoptic winds are considered. In the daytime, mountain upslope winds, up-valley winds, and urban breeze circulation form and interact with each other. Mountain upslope winds precede up-valley winds. It is found that the transition of upslope winds to downslope winds on the urban-side slope of Mt. Bogd Khan occurs and the downslope winds in the afternoon strengthen due to urban breezes. In the nighttime, mountain downslope winds and down-valley winds are prominent and strong channeling flows form over the city. The sensitivities of local circulations to urban fraction, atmospheric stability, and soil water content are examined. As urban fraction increases, daytime up-valley winds over the city and daytime downslope winds on the urban-side slope of Mt. Bogd Khan strengthen. Daytime near-surface up-valley winds in the city strengthen with increasing atmospheric stability. As soil water content decreases, daytime near-surface up-valley winds in the city weaken. The daytime urban atmospheric boundary-layer height is found to be sensitive to atmospheric stability and soil water content. This study is a first attempt to examine local circulations in and around the Ulaanbaatar metropolitan area and demonstrates that the city alters mountain slope winds and up-/down-valley winds.

Wind Regimes above and below a Temperate Deciduous Forest Canopy in Complex Terrain: Interactions between Slope and Valley Winds

The thermally driven wind over mountainous terrains challenges the estimation of CO2 exchange between forests and the atmosphere when using the eddy covariance technique. In this study, the wind regimes were investigated in a temperate deciduous forested valley at the Maoershan site, Northeast China. The wind direction above the canopy was preferentially up-valley in the daytime and down-valley in the nighttime, corresponding to the diurnal patterns of above-canopy temperature gradient and stability parameter. In both leaf-on and -off nighttime, a down-valley flow with a maximum velocity of 1~3 m∙s−1 was often developed at 42 m above the ground (2.3-fold of the canopy height). However, the below-canopy prevailing wind was down-slope in the night, contrast to the below-canopy temperature lapse and unstable conditions. This substantial directional shear illustrated shallow slope winds were superimposed on larger-scale valley winds. As a consequence, the valley-wind component becomes stronger with increasing height, indicating a clear confluence of drainage flow to the valley center. In the daytime, the below-canopy wind was predominated down-slope due to the temperature inversion and stable conditions in the leaf-on season, and was mainly up-valley or down-slope in the leaf-off season. The isolation of momentum flux and radiation by the dense canopy played a key role in the formation of the below-canopy unaligned wind and inverse stability. Significant lateral kinematic momentum fluxes were detected due to the directional shear. These findings suggested a significant interaction between slope and valley winds at this site. The frequent vertical convergence / divergence above the canopy and horizontal divergence/convergence below the canopy in the nighttime / daytime is likely to induce significant advections of trace gases and energy flux.

Pollutant Dispersion in a Developing Valley Cold-Air Pool

Pollutants are trapped and accumulate within cold-air pools, thereby affecting air quality. A numerical model is used to quantify the role of cold-air-pooling processes in the dispersion of air pollution in a developing region of enhanced cooling within an Alpine valley under decoupled stable conditions. Results indicate that the negatively buoyant downslope flows transport and mix pollutants into the valley to depths that depend on the temperature deficit of the flow and the ambient temperature structure inside the valley. Along the slopes, pollutants are generally entrained above the region of enhanced cooling and detrained within the region of enhanced cooling largely above the ground-based inversion layer. The ability of the region of enhanced cooling to dilute pollutants is quantified. The analysis shows that the downslope flows fill the valley with air from above, which is then largely trapped within the region of enhanced cooling and that dilution depends on where the pollutants are emitted with respect to the positions of the top of the ground-based inversion layer and region of enhanced cooling, and on the slope wind speeds. Over the lower part of the slopes, the concentrations averaged across the region of enhanced cooling are proportional to the slope wind speeds where the pollutants are emitted, and diminish as the region of enhanced cooling deepens. Pollutants emitted within the ground-based inversion layer are largely trapped there. Pollutants emitted farther up the slopes detrain within the region of enhanced cooling above the ground-based inversion layer, although some fraction, increasing with distance from the top of the slopes, penetrates into the ground-based inversion layer.

A theoretical study of the interactions of urban breeze circulation with mountain slope winds

A theoretical study of the interactions of urban breeze circulation with mountain slope winds

A numerical study of the interactions of urban breeze circulation with mountain slope winds

The two-dimensional interactions of urban breeze circulation with mountain slope winds are investigated using the Weather Research and Forecasting (WRF) model coupled with the Seoul National University Urban Canopy Model (SNUUCM). A city is located near an isolated mountain, and there is no basic-state wind. Circulation over the urban area is asymmetric and characterized by the weakened mountain-side urban wind due to the opposing upslope wind and the strengthened plain-side urban wind in the daytime. The transition from upslope wind to downslope wind on the urban-side mountain slope occurs earlier than that on the mountain slope in a simulation that includes only an isolated mountain. A hydraulic jump occurs in the late afternoon, when the strong downslope wind merges with weaker mountain-side urban wind and stagnates until late evening. The sensitivities of the interactions of urban breeze circulation with mountain slope winds and urban heat island intensity to mountain height and urban fraction are also examined. As mountain height decreases and urban fraction increases, the transition from urban-side upslope wind to downslope wind occurs earlier and the urban-side downslope wind persists longer. This change in transition time from urban-side upslope wind to downslope wind affects the interactions between urban breeze circulation and mountain slope winds. Urban heat island intensity is more sensitive to urban fraction than to mountain height. Each urban fraction increase of 0.1 results in an average increase of 0.17 °C (1.27 °C) in the daytime (nighttime) urban heat island intensity. A simulation in which a city is located in a basin shows that the urban-side downslope wind develops earlier, persists longer, and is stronger than in the simulation that includes a city and an isolated mountain.

Modeling the Impacts of a Man-Made Lake on the Meteorological Conditions of the Surrounding Areas

AbstractThe possible modifications of the surface meteorological conditions due to construction of a small, man-made lake in midlatitudes (surface area of 11.55 km2 and maximum fetch distance L ≈ 5 km) were investigated using the Weather Research and Forecasting (WRF) model (version 3.3). The model was applied to four real typical synoptic situations for which the area of interest was under the influence of a wintertime anticyclone (WA), a wintertime cyclone (WC), a summertime anticyclone (SA), and a summertime cyclone (SC). Each of these four typical synoptic setups was simulated twice—once assuming the present state (“NO-LAKE” experiment) and again assuming the existence of the new lake (“LAKE” experiment). The differences between 36-h average LAKE and NO-LAKE simulation results show noticeable mean changes in the surface temperature and relative humidity as well as a small increase of the mean surface wind speeds in the air above the newly constructed lake. At other portions of the investigated area (distances up to ~4L–6L downstream of the new lake), the 36-h mean differences produced by the new lake are below the order of magnitude of accuracy of operational meteorological measurement instruments. In individual hours, however, these differences are occasionally very high, particularly for cyclonic episodes. In addition, results obtained for SA suggest an existence of a lake circulation cell associated with small differences between the lake and land temperatures (at most up to ~3°–5°C) and consequently, a slight enhancement of slope winds in future (LAKE) conditions.

Effects of Urbanization on the Temperature Inversion Breakup in a Mountain Valley with Implications for Air Quality

AbstractMany cities located in valleys with limited ventilation experience serious air pollution problems. The ventilation of an urban valley can be limited not only by orographic barriers, but also by urban heat island–induced circulations and/or the capping effect of temperature inversions. Furthermore, land-use/-cover changes caused by urbanization alter the dynamics of temperature inversions and urban heat islands, thereby affecting air quality in an urban valley. By means of idealized numerical simulations, it is shown that in a mountain valley subject to temperature inversions urbanization can have an important influence on air quality through effects on the inversion breakup. Depending on the urban area fraction in the simulations, the breakup time changes, the cross-valley wind system can evolve from a confined to an open system during the daytime, the slope winds can be reversed by the interplay between the urban heat island and the temperature inversion, and the breakup pattern can migrate from one dominated by the growth of the convective boundary layer to one also involving the removal of mass from the valley floor by the upslope winds. The analysis suggests that the influence of urbanization on the air quality of an urban valley may lead to contrasting and possibly counterintuitive effects when considering temperature inversions. More urban land does not necessarily imply worse air quality, even when considering that the amount of pollutants emitted grows with increased urbanization.