Lake Breeze Research Articles

The local climate impact of an African city during clear‐sky conditions—Implications of the recent urbanization in Kampala (Uganda)

AbstractThis study aims at assessing and understanding the impact of recent urbanization on the (surface) urban heat island ((S)UHI) under clear‐sky conditions in a tropical African city using different sources of remotely sensed data sets together with an urban climate model (UCM). The observed SUHI during clear sky conditions is found to be about 4°C on average over the capital city of Kampala, Uganda. The UCM, consisting of TERRA_URB embedded in COSMO‐CLM, represents the SUHI well during night but overestimates it by about 3°C in the mean during day. Moreover, a systematic warm land surface temperature bias of about 4°C is identified by night. Improved urban input parameters—derived from Local Climate Zones following the World Urban Database and Access Portal Tool (WUDAPT) framework—lead to a more realistic representation of spatial land surface temperatures patterns. In addition, this parameterization of the UCM can properly represent atmospheric variables such as air temperature, specific and relative humidity, as observed by the automated weather stations. A model sensitivity study furthermore demonstrates that the stronger urban heat island induced by the recent urbanization of Kampala over the past 15 years strongly interacts with the lake–land breeze circulation. Stronger daytime convection over the hotter city leads to areas of convergence that amplify the afternoon lake breeze in the Southern parts of the metropolis. Overall, this study demonstrates that the city of Kampala has a tangible effect on the regional climate that needs to be considered when studying present and future climate impacts.

Simulated effects of land immersion on regional arid climate: a case study of the pre-Saharan playa of Chott el-Jerid (south of Tunisia)

The potential effects on the regional climate induced by partially immersing the arid pre-Saharan playa basin of Chott el-Jerid (south of Tunisia) are investigated by comparing two multi-year (1991–2011) sets of numerical simulations each consisting of ten-member ensemble and performed using the WRF regional climate model. The first WRF ensemble is performed under current land use and land cover, while the second is carried out after introducing a virtual large and shallow surface water reservoir (a lake) in Chott el-Jerid. The most pronounced effects generated by the artificial lake are circumscribed over its surface and slightly spread downwind to the other parts of the Chott. The lake has a clear moderating effect on near-surface air temperatures by increasing (decreasing) the wintertime (summertime) air temperatures. Sensible heat fluxes are remarkably increased in winter and decreased in summer over the lake following the temperature gradient between the lake surface and the overlying atmosphere. Latent heat fluxes, moisture convergence, and water vapor mixing ratio are increased over the lake throughout the year, especially in winter. The lake also induces domain-wide decreased (increased) surface pressures and land (lake) breeze circulation in winter (summer). Simulated rainfall amounts are most increased over the lake in winter likely because of an enhanced atmospheric instability, while they slightly decrease in summer.

Enhanced NO2 and aerosol extinction observed in the tropospheric column behind lake-breeze fronts using MAX-DOAS

Abstract The lake breezes that frequently occur in Southern Ontario impact the levels of pollutants experienced by the populations in urban areas. The effects of lake breeze circulations on pollution transport and processing are not well understood. Few studies have measured the circulations’ impact on pollutants both at the surface and within the tropospheric column. In this study, pollutants in the tropospheric column (NO2 VCDs and AODs) were measured using MAX-DOAS concurrent with near-surface measurements of NOx, O3, and PM2.5 on lake breeze days in Toronto in September and October. The arrival of lake-breeze fronts (LBF) was identified using co-located meteorological data. The presence of lake breezes was confirmed using mesoscale analyses of radar, satellite and a network of meteorological stations. NO2 VCDs exhibited short-term increases of 0.8-3.4×1016 molecules cm-2 above the pre-LBF levels following the arrival of a LBF. These measurements are the first confirmation of the theorized presence of enhanced total burden of pollution within the total column behind the front within a lake-breeze circulation on multiple lake breeze days. Rapid decreases of O3 of up to 13 ppb at the arrival of the lake-breeze front were unexpected based on observed increases in O3 in other studies, but can be attributed to reduced photochemical O3 production during late summer and fall compared to mid-summer. AODs exhibited delayed enhancements compared to NO2 VCDs, appearing to be driven by enhanced humidity following the front, in addition to enhanced particle concentration. Our measurements highlight the complex 3-D structure of lake-breeze circulations.

Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa

Lake Victoria in East Africa supports the livelihood of thousands of fishermen and it is estimated that 3000–5000 human deaths occur per year over the lake. It is hypothesized that most of these fatalities are due to localized, severe winds produced by intense thunderstorms over the lake during the rainy season and larger scale, intense winds over the lake during the dry season. The intense winds produce a rough state of the lake (big wave heights) that cause fishing boats to capsize. In this region, weather radars have never been a primary tool for monitoring and nowcasting high impact weather. The Tanzania Meteorological Agency operates an S-band polarimetric radar in Mwanza, Tanzania, along the south shore of Lake Victoria. This radar collects high temporal and spatial resolution data that is now being used to detect and monitor the formation of deep convection over the lake and improve scientific understanding of storm dynamics and intensification. Nocturnal thunderstorms and convection initiation over the lake are well observed by the Mwanza radar and are strongly forced by lake and land breezes and gust fronts. Unexpected is the detection of clear air echo to ranges ≥100 km over the lake that makes it possible to observe low-level winds, gust fronts, and other convergence lines near the surface of the lake. The frequent observation of extensive clear air and low-level convergence lines opens up the opportunity to nowcast strong winds, convection initiation, and subsequent thunderstorm development and incorporate this information into a regional early warning system proposed for Lake Victoria Basin (LVB). Two weather events are presented illustrating distinctly different nocturnal convection initiation over the lake that evolve into intense morning thunderstorms. The evolution of these severe weather events was possible because of the Mwanza radar observations; satellite imagery alone was insufficient to provide prediction of storm initiation, growth, movement, and decay.

Sensitivity of Ozone Production to NOx and VOC Along the Lake Michigan Coastline

AbstractWe report on the sensitivity of enhanced ozone (O3) production, observed during lake breeze circulation along the coastline of Lake Michigan, to the concentrations of nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs). We assess the sensitivity of O3 production to NOx and VOC on a high O3 day during the Lake Michigan Ozone Study 2017 using an observationally constrained chemical box model that implements the Master Chemical Mechanism (MCM v3.3.1) and recent emission inventories for NOx and VOCs. The Master Chemical Mechanism model is coupled to a backward air mass trajectory analysis from a ground supersite in Zion, IL, where an extensive series of measurements of O3 precursors and their oxidation products, including hydrogen peroxide (H2O2), nitric acid (HNO3), and particulate nitrates (NO3−) serve as model constraints. We evaluate the chemical evolution of the Chicago‐Gary urban plume as it advects over Lake Michigan and demonstrate how modeled indicators of VOC‐ versus NOx‐sensitive regimes can be constrained by measurements at the trajectory endpoint. Using the modeled ratio of the instantaneous H2O2 and HNO3 production rates (PH2O2/PHNO3), we suggest that O3 production over the urban source region is strongly VOC sensitive and progresses towards a more NOx‐sensitive regime as the plume advects north along the Lake Michigan coastline on this day. We also demonstrate that ground‐based measurements of the mean concentration ratio of H2O2 to HNO3 describe the sensitivity of O3 production to VOC and NOx as the integral of chemical production along the plume path.

Improving Lake-Breeze Simulation with WRF Nested LES and Lake Model over a Large Shallow Lake

AbstractThe Weather Research and Forecasting (WRF) Model is used in large-eddy simulation (LES) mode to investigate a lake-breeze case occurring on 12 June 2012 over the Lake Taihu region of China. Observational data from 15 locations, wind profiler radar, and the Moderate Resolution Imaging Spectroradiometer (MODIS) are used to evaluate the WRF nested-LES performance in simulating lake breezes. Results indicate that the simulated temporal and spatial variations of the lake breeze by WRF nested LES are consistent with observations. The simulations with high-resolution grid spacing and the LES scheme have a high correlation coefficient and low mean bias when evaluated against 2-m temperature, 10-m wind, and horizontal and vertical lake-breeze circulations. The atmospheric boundary layer (ABL) remains stable over the lake throughout the lake-breeze event, and the stability becomes even stronger as the lake breeze reaches its mature stage. The improved ABL simulation with LES at a grid spacing of 150 m indicates that the non-LES planetary boundary layer parameterization scheme does not adequately represent subgrid-scale turbulent motions. Running WRF fully coupled to a lake model improves lake-surface temperature and consequently the lake-breeze simulations. Allowing for additional model spinup results in a positive impact on lake-surface temperature prediction but is a heavy computational burden. Refinement of a water-property parameter used in the Community Land Model, version 4.5, within WRF and constraining the lake-surface temperature with observational data would further improve lake-breeze representation.

Observational Characterization of the Synoptic and Mesoscale Circulations in Relation to Crop Dynamics: Belg 2017 in the Gamo Highlands, Ethiopia

The Gamo Highlands in Ethiopia are characterized by complex topography and lakes. These modulate the mesoscale and synoptic scale weather systems. In this study, we analyzed the temporal and spatial variations in weather as function of topography and season and their impact on potato crop growth. To determine how crop growth varies with elevation, we installed a network of six automatic weather stations along two transects. It covers a 30-km radius and 1800-m elevation difference. We conducted a potato field experiment near the weather stations. We used the weather observations as input for a crop model, GECROS. Data analysis showed large differences between weather in February and May. February is more dominated by mesoscale circulations. The averaged February diurnal patter shows a strong east to southeast lake breezes and, at night, weak localized flows driven by mountain density flows. In contrast, in May, the synoptic flow dominates, interacting with the mesoscale flows. The GECROS model satisfactorily predicted the elevational gradient in crop yield. Model sensitivity experiments showed that belg-averaged precipitation distribution gave the highest yield, followed by exchanging May weather observations with April.

Effect of sea breeze propagation on the urban boundary layer of the metropolitan region of Sao Paulo, Brazil

Thermally driven circulations over urban areas, such as sea, lake, and land breezes and mountain-valley and urban heat island (UHI) circulations, strongly determine local weather and air quality conditions over highly populated areas. This study investigates the influence of sea breeze (SB) propagation on the development of the urban boundary layer (UBL) in the Metropolitan Region of Sao Paulo (MRSP), Brazil, an urban area with complex topography. This investigation is undertaken observationally by analyzing surface and upper air observations conducted in 2013 during the MCITY BRAZIL Project field campaigns and is conducted numerically by performing a set of Weather Research and Forecasting (WRF) simulations. The observational analysis highlights two SB events in the MRSP, one in February (austral summer) and the other in August (winter). In both seasons, the passage of the SB front disrupts the convective growth of the UBL and establishes a thermal internal boundary layer, thereby reducing the UBL height. The cooling also momentarily disrupts the UHI circulation. The results indicate that topography enhances SB propagation because it helps the marine air to go up the MRSP coastal escarpment and to reach the plateau while forcing adiabatic cooling of this air, intensifying the thermal gradient between the southern part of the plateau and the urban area. The UHI further increases the thermal gradient (from 0.5 K to 2 K in summer and 1 to 2.5 K in winter), accelerating the SB propagation. Synoptic conditions determine whether the SB front reaches the urban area and also may displace the convergence center of the UHI circulation.

Evaluation of Modeled Lake Breezes Using an Enhanced Observational Network in Southern Ontario: Case Studies

AbstractCanadian Global Environmental Multiscale (GEM) numerical model output was compared with the meteorological data from an enhanced observational network to investigate the model’s ability to predict Lake Ontario lake breezes and their characteristics for two cases in the Greater Toronto Area—one in which the large-scale wind opposed the lake breeze and one in which it was in the same direction as the lake breeze. An enhanced observational network of surface meteorological stations, a C-band radar, and two Doppler wind lidars were deployed among other sensors during the 2015 Pan and Parapan American Games in Toronto. The GEM model was run for three nested domains with grid spacings of 2.5, 1, and 0.25 km. Comparisons between the model predictions and ground-based observations showed that the model successfully predicted lake breezes for the two events. The results indicated that using GEM 1 and 0.25 km increased the forecast accuracy of the lake-breeze location, updraft intensity, and depth. The accuracy of the modeled lake breeze timing was approximately ±135 min. The model underpredicted the surface cooling caused by the lake breeze. The GEM 0.25-km model significantly improved the temperature forecast accuracy during the lake-breeze circulations, reducing the bias by up to 72%, but it mainly underpredicted the moisture and overpredicted the surface wind speed. Root-mean-square errors of wind direction forecasts were generally high because of large biases and high variability of errors.

Increased nocturnal CO2 concentration during breeze circulation events in a tropical reservoir

The Balbina reservoir (59°28'50'' W, 1°53'25'' S), located near the city of Manaus, AM in central Amazonia, is the second largest hydroelectric reservoir in the Amazon basin. Carbon dioxide concentration measurements were performed at high frequency (10 Hz) at this reservoir with an IRGA Model LiCOR 7500A and meteorological variables were measured with a floating platform with sensors 2 meters above the surface of the lake. Maximum and minimum CO2 concentrations were observed during the night, related to forest breeze enriched with CO2 and the respiration or photosynthetic activity of the lake. Due to the dimensions of the lake, both land and lake breezes control the concentration of CO2. CO2 showed a strong correlation with the meteorological variables, temperature (- 0.76) and relative humidity (0.71). However, only the wind direction showed a statistically significant effect at 5% in the cross-correlation. Our results corroborate other studies in this lake and other Amazonian reservoirs.

Dead Sea evaporation by eddy covariance measurements vs. aerodynamic, energy budget, Priestley–Taylor, and Penman estimates

Abstract. The Dead Sea is a terminal lake, located in an arid environment. Evaporation is the key component of the Dead Sea water budget and accounts for the main loss of water. So far, lake evaporation has been determined by indirect methods only and not measured directly. Consequently, the governing factors of evaporation are unknown. For the first time, long-term eddy covariance measurements were performed at the western Dead Sea shore for a period of 1 year by implementing a new concept for onshore lake evaporation measurements. To account for lake evaporation during offshore wind conditions, a robust and reliable multiple regression model was developed using the identified governing factors wind velocity and water vapour pressure deficit. An overall regression coefficient of 0.8 is achieved. The measurements show that the diurnal evaporation cycle is governed by three local wind systems: a lake breeze during daytime, strong downslope winds in the evening, and strong northerly along-valley flows during the night. After sunset, the strong winds cause half-hourly evaporation rates which are up to 100 % higher than during daytime. The median daily evaporation is 4.3 mm d−1 in July and 1.1 mm d−1 in December. The annual evaporation of the water surface at the measurement location was 994±88 mm a−1 from March 2014 until March 2015. Furthermore, the performance of indirect evaporation approaches was tested and compared to the measurements. The aerodynamic approach is applicable for sub-daily and multi-day calculations and attains correlation coefficients between 0.85 and 0.99. For the application of the Bowen ratio energy budget method and the Priestley–Taylor method, measurements of the heat storage term are inevitable on timescales up to 1 month. Otherwise strong seasonal biases occur. The Penman equation was adapted to calculate realistic evaporation, by using an empirically gained linear function for the heat storage term, achieving correlation coefficients between 0.92 and 0.97. In summary, this study introduces a new approach to measure lake evaporation with a station located at the shoreline, which is also transferable to other lakes. It provides the first directly measured Dead Sea evaporation rates as well as applicable methods for evaporation calculation. The first one enables us to further close the Dead Sea water budget, and the latter one enables us to facilitate water management in the region.

Urban Heat Island Mitigation Effectiveness under Extreme Heat Conditions in the Suzhou–Wuxi–Changzhou Metropolitan Area, China

AbstractCool roofs and green roofs are two important methods used to mitigate the urban heat island (UHI) effect. The Weather Research and Forecasting Model was used to investigate the UHI effect and the effectiveness of cool and green roof mitigation strategies in the Suzhou–Wuxi–Changzhou metropolitan area during an extreme heat wave episode in the summer of 2013. Both urban land-cover change and anthropogenic heat releases exacerbated high temperatures in the urban area. Notably, urban land-cover change and anthropogenic heat release were responsible for 64% and 36% of the UHI intensity, respectively. Both cool and green roofs decreased near-surface air temperatures. The most dramatic decrease in near-surface air temperature occurred in the late morning; nocturnal air temperature decreased slightly because of the decrease in urban heat storage associated with the cool roof strategy. In addition, the UHI mitigation strategies affected the entire urban boundary layer. The decrease in the potential temperature and static stability created a stable urban boundary layer in which turbulent kinetic energy (TKE) decreased simultaneously. Analysis of an urban belt near a large water body showed that the decrease in the surface skin temperature difference between land and the water body weakened the daytime lake breeze. This effect was observed in both the inflow in the boundary layer and the return flow above the boundary layer, and it decreased the heat and moisture exchange between the lake and land boundary layers.

The Environment Canada Pan and Parapan American Science Showcase Project

AbstractThe Pan and Parapan American Games (PA15) are the third largest sporting event in the world and were held in Toronto in the summer of 2015 (10–26 July and 7–15 August). This was used as an opportunity to coordinate and showcase existing innovative research and development activities related to weather, air quality (AQ), and health at Environment and Climate Change Canada. New observational technologies included weather stations based on compact sensors that were augmented with black globe thermometers, two Doppler lidars, two wave buoys, a 3D lightning mapping array, two new AQ stations, and low-cost AQ and ultraviolet sensors. These were supplemented by observations from other agencies, four mobile vehicles, two mobile AQ laboratories, and two supersites with enhanced vertical profiling. High-resolution modeling for weather (250 m and 1 km), AQ (2.5 km), lake circulation (2 km), and wave models (250-m, 1-km, and 2.5-km ensembles) were run. The focus of the science, which guided the design of the observation network, was to characterize and investigate the lake breeze, which affects thunderstorm initiation, air pollutant transport, and heat stress. Experimental forecasts and nowcasts were provided by research support desks. Web portals provided access to the experimental products for other government departments, public health authorities, and PA15 decision-makers. The data have been released through the government of Canada’s Open Data Portal and as a World Meteorological Organization’s Global Atmospheric Watch Urban Research Meteorology and Environment dataset.

Observations of Lake-Breeze Events During the Toronto 2015 Pan-American Games

Enhanced meteorological observations were made during the 2015 Pan and Parapan American Games in Toronto in order to measure the vertical and horizontal structure of lake-breeze events. Two scanning Doppler lidars (one fixed and one mobile), a C-band radar, and a network including 53 surface meteorological stations (mesonet) provided pressure, temperature, humidity, and wind speed and direction measurements over Lake Ontario and urban areas. These observations captured the full evolution (prior, during, and after) of 27 lake-breeze events (73% of observation days) in order to characterize the convective and dynamic processes driving lake breezes at the local scale and mesoscale. The dominant signal of a passing lake-breeze front (LBF) was an increase in dew-point temperature of $$2.3 \pm 0.3 \,^{\circ }\hbox {C}$$ , coinciding with a $$180^{\circ }$$ shift in wind direction and a decrease in air temperature of $$2.1 \pm 0.2 \,^{\circ }\hbox {C}$$ . Doppler lidar observations over the lake detected lake breezes 1 hour (on average) before detection by radar and mesonet. On days with the synoptic flow in the offshore direction, the lidars observed wedge-shaped LBFs with shallow depths, which inhibited the radar’s ability to detect the lake breeze. The LBF’s ground speed and inland penetration distance were found to be well-correlated ( $$r = 0.78$$ ), with larger inland penetration distances occurring on days with non-opposing (non-offshore) synoptic flow. The observed enhanced vertical motion $$({>} 1\hbox { m s}^{-1})$$ at the LBF, observed by the lidar on 54% of lake-breeze days, was greater (at times $${>} 2.5\hbox { m s}^{-1}$$ ) than that observed in previous studies and longer-lasting over the lake than over land. The weaker and less pronounced lake-breeze structure over land is illustrated in two case studies highlighting the lifetime of the lake-breeze circulation and the impact of propagation distance on lake-breeze intensity.

Effects of the Lake Sobradinho Reservoir (Northeastern Brazil) on the Regional Climate

This study investigates the effects of Lake Sobradinho, a large reservoir in Northeastern Brazil, on the local near-surface atmospheric and boundary layer conditions. For this purpose, simulations with the regional climate model COSMO-CLM are compared for two different scenarios: (1) with the lake being replaced by the average normal native vegetation cover and (2) with the lake as it exists today, for two different two-month periods reflecting average and very dry conditions, respectively. The performance of the simulation is evaluated against data from surface meteorological stations as well as satellite data in order to ensure the model’s ability to capture atmospheric conditions in the vicinity of Lake Sobradinho. The obtained results demonstrate that the lake affects the near-surface air temperature of the surrounding area as well as its humidity and wind patterns. Specifically, Lake Sobradinho cools down the air during the day and warms it up during the night by up to several ∘ C depending on the large-scale meteorological conditions. Moreover, the humidity is significantly increased as a result of the lake’s presence and causes a lake breeze. The observed effects on humidity and air temperature also extend over areas relatively far away from the lake.

Spatiotemporal Characteristics of Lake Breezes over Lake Taihu, China

AbstractLake Taihu is a shallow lake located in the Yangtze River delta region in eastern China. Lake breezes and their interactions with urban heat islands are of great importance to air quality and weather forecasting. In this study, surface observations at a dense network and Wind Profile Radar measurements were utilized to characterize the lake breezes at Lake Taihu and assess the impact of geophysical factors on the development and intensity of the lake breezes. The lake breezes were characterized by a low occurrence frequency of 12%–17% (defined as the percentage of days with lake breezes in a given month), weak speed (annual mean ranging from 1.5 to 3.3 m s−1), late onset [average onset around 1110 local standard time (LST), with a range of 0900–1300 LST], short duration (annual mean 3.5 h), and low circulation depth (average depth of 400 m from 1200 to 1400 LST). The lake breezes were greatly suppressed when the geostrophic winds were higher than 4.1 m s−1. The low heat capacity of shallow water (mean depth 2.0 m) led to small temperature differences between the land and the lake, which was the main factor responsible for the low occurrence frequency along Lake Taihu. All of the characteristic parameters showed distinct seasonal variations. Increased frequencies, earlier onset times, and longer durations on the northern lakeshore were indicative of the impact of the urban heat island on the lake breezes.

A novel approach for monitoring vertical profiles of boundary-layer pollutants: Utilizing routine news helicopter flights

Air quality varies greatly in space and time across urban locales. However, criteria pollutants are typically monitored routinely at a relatively small number of surface sites within each metropolitan area, and routine vertical profiles of pollution are typically unavailable. We illustrate that a news helicopter provides an effective sensor platform to provide spatiotemporal analyses and vertical profiles of pollutant concentrations. We are unaware of any other air quality study that has utilized routine helicopter flights, despite the ubiquity of helicopters in urban environments across the world. Particulate and ozone concentration profiles have been collected since 2015 from sensors installed on a news helicopter that travels primarily over the metropolitan areas of northern Utah. The air quality data are retrieved in real time, archived, combined with surface-based observations, and disseminated in terms of time series and maps on a website for research, forecasting, and public awareness. Large vertical variations in particulate pollution concentrations were observed during the 2015–2016 winter associated with meteorological cold-air pool episodes. During the 2015 and 2016 summer seasons, ozone concentrations frequently exhibited complex spatial and temporal variations arising from many interrelated factors, including local terrain-forced circulations, lake breezes, and distant wildfires.

Impact of Lake Breezes on Summer Ozone Concentrations in the Salt Lake Valley

AbstractDuring the late afternoon of 18 June 2015, ozone concentrations in advance of a strong lake-breeze front arising from the Great Salt Lake in northern Utah were ~20 ppb lower than those in its wake. The lake-breeze progression and ozone concentrations in the valley were monitored by an enhanced observation network that included automated weather stations, a nearby Terminal Doppler Weather Radar, state air quality measurement sites, and mobile platforms, including a news helicopter. Southerly flow opposing the lake breeze increased convergent frontogenesis and delayed the onset of its passage through the Salt Lake valley. Ozone concentrations were exceptionally high aloft at the lake-breeze frontal boundary. The progression of this lake breeze was simulated using the Weather Research and Forecasting Model at 1-km horizontal grid spacing over northern Utah. The model was initialized using hourly analyses from the High Resolution Rapid Refresh model. Errors in the underlying surface initialization were improved by adjusting the areal extent and surface temperature of the lake to observed lake conditions. An urban canopy parameterization is also included. The opposing southerly flow was weaker in the simulation than that observed such that the simulated lake-breeze front occurred too early. Continuous passive tracers initialized within and ahead of the lake breeze highlight the dispersion and transport of pollutants arising from the lake-breeze front. Tracers within the lake breeze are confined near the surface while tracers in advance of the front are lofted over it.

Atmospheric electrical field measurements near a fresh water reservoir and the formation of the lake breeze

In order to access the effect of the lakes in the atmospheric electrical field, measurements have been carried out near a large man-made lake in southern Portugal, the Alqueva reservoir, during the ALqueva hydro-meteorological EXperiment 2014. The purpose of these conjoint experiments was to study the impact of the Alqueva reservoir on the atmosphere, in particular on the local atmospheric electric environment by comparing measurements taken in the proximity of the lake. Two stations 10 km apart were used, as they were located up- and down-wind of the lake (Amieira and Parque Solar, respectively), in reference to the dominant northwestern wind direction. The up-wind station shows lower atmospheric electric potential gradient (PG) values than the ones observed in the down-wind station between 12 and 20 UTC. The difference in the atmospheric electric PG between the up-wind and the down-wind station is ~30 V/m during the day. This differential occurs mainly during the development of a lake breeze, between 10 and 18 UTC, as a consequence of the surface temperature gradient between the surrounding land and the lake water. In the analysis presented, a correlation is found between the atmospheric electric PG differences and both wind speed and temperature gradients over the lake, thus supporting the influence of the lake breeze over the observed PG variation in the two stations. Two hypotheses are provided to explain this observation: (1) The air that flows from the lake into the land station is likely to increase the local electric conductivity through the removal of ground dust and the transport of cleaner air from higher altitudes with significant light ion concentrations. With such an increase in conductivity, it is expected to see a reduction of the atmospheric electric PG; (2) the resulting air flow over the land station carries negative ions formed by wave splashing in the lake's water surface, as a result of the so-called balloelectric effect. These negative ions will form a space-charge density (SCD) that can reduce the atmospheric electric PG. A formulation is derived here in order to estimate the local SCD.

Ground-Based Observations of the Thermodynamic and Kinematic Properties of Lake-Breeze Fronts in Southern Manitoba, Canada

The “Effects of Lake Breezes on Weather in Manitoba” project was conducted during 6–24 July 2013 to better understand local lake-breeze characteristics. Data were collected using a variety of platforms including Doppler wind lidar, rawinsondes, Doppler radar, surface meteorological stations, and a mobile weather station. The spatial and temporal variability of thermodynamic and kinematic characteristics of lake-breeze fronts are presented for three cases. Lake-breeze frontal passages were characterized by an average increase in dew point of 2.5 $$^{\circ }$$ C and decrease in temperature of 0.5 $$^{\circ }$$ C. The lake-breeze front width varied significantly over multiple measurements and cases, ranging between 50 and 800 m. The depth of the lake-breeze circulation varied between 100 and 700 m. Vertical velocities were measured at the lake-breeze front using lidar, with upward velocities of 2–3 m s $$^{-1}$$ and small downward velocities of magnitude 0.5 m s $$^{-1}$$ behind the front. These observations of lake-breeze fronts in southern Manitoba contribute both to the local and broader understanding of the variability (temporally and spatially) of inland shallow lake breezes.