Lake Breeze Circulation Research Articles

Influence of Lake Breezes on the Triggering of Moist Convection on the Tibetan Plateau: A Large-Eddy Simulation Study

Abstract Applying 1D surface heterogeneity and observed atmospheric vertical profiles as initial conditions, two sets of large-eddy simulation experiments provided insight into the influence of lake size and soil moisture (SM) on the development of lake breezes and moist convection over land beside the lake. When the lake diameter increased from 20 km to 50 and 70 km, the maximum precipitation increased by 71.4% and 1.29 times, respectively. There are two reasons for larger precipitation over land in large-lake simulations: 1) Stronger and broader updrafts were found near the lake-breeze front (LBF); 2) the air at 2–4 km was moister, probably because more water vapor below 2 km was advected by the lake breezes and transported upward through turbulent exchange. Moreover, when the lake diameter increased from 20 km to more than 50 km, the deep moist convection (DMC) occurred 20 min earlier. This may be related to broader shallow convective cloud and larger vertical velocity of cloud-initiating parcels in large-lake simulations. Shallow moist convection transitioned to DMC earlier with broader clouds under moderate and high soil moisture conditions. Notably, stronger and broader updrafts near the LBFs, along with the advection of moisture induced by the lake breezes, caused the shallow moist convection to reach its peak 1 h earlier in the driest soil moisture case. However, smaller evapotranspiration could not provide sufficient moisture for the development of DMC. Our simulation results show that lake-breeze circulations are essential for the development of moist convections in the lake region.

Measurement report: Observations of ground-level ozone concentration gradients perpendicular to the Lake Ontario shoreline

Abstract. Ground-level ozone (O3) is a secondary air pollutant that has harmful effects on human and ecosystem health. Close to larger bodies of water, the well-known sea-breeze (or lake-breeze) phenomenon plays a role in regulating ground-level ozone levels. An observed lake-edge removal effect, where ozone concentration decreases within the first 500 m to 1 km perpendicular to the lake, is thought to be related to the lake-breeze circulation as well as several dilution and removal pathways. A field campaign was conducted in summer 2022 and winter 2023 in two locations on the north shore of Lake Ontario: the urban centre of Toronto and suburban Oshawa, some 50 km east, to assess how the local environment and season affect the lake-edge removal effect. Ozone, wind speed, and wind direction were measured on 6–7 different days in each season and city along transects perpendicular to Lake Ontario's shoreline. A consistent negative linear relationship between ozone concentration and distance from shore over the first 500 m (i.e. a lake-edge removal effect) was observed in both cities and both seasons. The ozone gradient changed in Oshawa from −23.5 ± 8.5 (1 standard deviation) ppb km−1 in summer to −8.1 ± 5.1 ppb km−1 in winter. The slope remained consistent in Toronto at −15.4 ± 6.7 ppb km−1 in summer and −16.7 ± 7.3 ppb km−1 in winter. The year-round observation of an ozone gradient and lake-edge removal effect suggests that there is an inherent “baseline” ozone concentration gradient at the lake edge, caused by the dilution effect of the rapid increase of the boundary layer there. This gradient is seen to be enhanced in the summer and dependent on local effects such as lake-breeze circulation and increased deposition to vegetation.

The impact of lake shape and size on lake breezes and air-lake exchanges on Titan

Titan, the largest moon of Saturn, has many lakes on its surface, formed mainly of liquid methane. Like water lakes on Earth, these methane lakes on Titan likely profoundly affect the local climate. Previous studies (Rafkin and Soto, 2020; Chatain et al., 2022) showed that Titan's lakes create lake breeze circulations with characteristic dimensions similar to the ones observed on Earth. However, such studies used a model in two dimensions; this work investigates the consequences of the addition of a third dimension to the model. Our results show that 2D simulations tend to overestimate the extension of the lake breeze over the land, and underestimate the strength of the subsidence over the lake, due to divergence/convergence geometrical effects in the mass conservation equations. In addition, 3D simulations including a large scale background wind show the formation of a pocket of accelerated wind behind the lake, which did not form in 2D simulations. An investigation of the effect of shoreline concavity on the resulting air circulation shows the formation of wind currents over peninsulas. Simulations with several lakes can either result in the formation of several individual lake breeze cells (during the day), or the emergence of a large merged cell with internal wind currents between lakes (during the night). Simulations of several real-shaped lakes located at a latitude of 74°N on Titan at the autumn equinox show that larger lakes trigger stronger winds, and that some sections of lakes might accumulate enough methane vapor to form a thin fog. Additionally, we adapted the Turbulent Kinetic Energy closure scheme of the model to better represent the extremely low turbulence at the surface of Titan, of 2 10−4 m2.s−2 above the land, and inferior to 3 10−5 m2.s−2 above the lake. The addition of a third dimension, along with adjustments in the parametrizations of turbulence and subsurface land temperature, results in a reduction in the magnitude of the average lake evaporate rate, namely to ∼6 cm/Earth year.

Where and how to cool through blue infrastructure? Large lake groups to ameliorate urban overheating in a typical inland multi-lake megacity

Large lake groups have been recognized as important blue infrastructure to ameliorate urban overheating in inland megacities. Previous studies have evaluated climate regulation capabilities of large lakes on cities. However, how the specific location of lake groups affects thermal environments across extensive built-up areas through thermal and aerodynamic mechanisms remains unclear. Therefore, we conducted sensitivity experiments using the Weather Research and Forecasting (WRF) model to explore the intensity and spatial variation of air temperatures and wind fields influenced by lake groups—located in downtown areas, inner suburbs, and outer suburbs—under typical heatwave conditions in Wuhan. Results indicate that compared to similar-sized suburban lake groups, downtown lake groups exhibit higher and lower daytime lake-land differences in sensible and latent heat fluxes, respectively, resulting in greater lake cooling intensities (LCIs). Also, upwind lake groups cool more built-up areas since lake breeze circulations (LBCs) promote the spreading of lake cooling distances (LCDs). However, the development of LCIs, LCDs, and LBCs is asynchronous, with LCIs peaking around mid-morning before the generation of LBCs, and LCDs peaking in the afternoon once LBCs have developed vigorously. Moreover, we propose a planning framework integrating the cooling effects of lake groups to support cooler, healthier, and more sustainable cities.

Modeling Investigation of Thermal Circulations of a Large and Shallow Subtropical Lake

Lake Taihu, a typical shallow lake in eastern China, was selected for study in this paper. Methods: Considering that the accurate parameterization scheme is the key to a lake breeze simulation, then based on Lake Taihu’s characteristics, the setting of parameters of the lakes’ scheme was adjusted in the WRF (Weather Research and Forecasting Model) lake model. Results: By comparing the observed values of the mesoscale flux platform of Lake Taihu from June to August 2012, the results showed that the model significantly improved the simulation. The root-mean-square error of the simulated and observed comparison of the latent heat fluxes over the lake improved from 42.77 to 89.00. The adjusted WRF-Lake model better presents the characteristics of Lake Taihu’s lake wind. The different lake depth cases showed that the maximum difference in surface temperature between the shallow lake case and the deep lake case reached 9.9 °C, and the average was about 3 °C. Conclusion: Compared with the deep lake case, the shallow lake case stimulated less lake breeze circulation with a shorter time and smaller range in the horizontal and vertical directions. The lake breeze frequency, simulated by the shallow lake case, was 18.5%, while for the deep lake case, it reached 38%. These simulations of lake breeze contribute to understanding the influence of a lake’s depth on lake breeze characteristics and the accurate parameterization scheme of the inland shallow lakes.

How to use lake breeze circulations to improve urban natural ventilation: A case study in a typical inland multi-lake megacity

Utilizing lake breeze circulations (LBCs) to improve city breathability is one of the most promising nature-based solutions for inland cities under calm and stable weather conditions. Previous studies highlighted the LBC benefits from great-sized lakes to mitigate urban heat island effects at the regional scale. How cold air flows out from relatively small lakes to influence the heat transfer process within urban areas, however, remains unclear. Using the Weather Research and Forecasting (WRF) model, the temporal development of lake breezes (LBs) was simulated in Wuhan city on hot days with weak synoptic wind. We further explored the spatial structures of a single LBC and the interactions of multiple LBCs on a typical LB day. The results indicate that LBs occurred mostly in the morning, peaked around noon, and dissipated in the afternoon. The LB occurrence periods with high probability varied significantly with the lake size, shape, location, and distribution. Specifically, large lakes with simple shapes and aggregated distribution were more likely to develop and sustain LBs. There were distinct LBC flow regimes on different lakeshores, in which the perturbed LBC mainly on leeward lakeshores increased cool air penetrability compared with the strong LBC predominantly on windward lakeshores. In addition, chain flows of LBCs formed over lake groups parallel to the prevailing synoptic wind, as the upper-level outflows from one upwind LBC were connected to the lower-level inflows from the other downwind LBC. Based on these results, we propose a conceptual framework for planning urban blue space to enhance natural ventilation, which can support urban planners to create livable built environments with lake breezes entry.

Water effects on urban heat islands in summer using WRF-UCM with gridded urban canopy parameters — A case study of Wuhan

Urbanization has rapidly occurred in China along with a significant reduction in ecological resources, greatly exacerbating urban heat island effect. In cities with abundant inland lake resources, it is valuable to study the use of climate regulation effects of water bodies to improve the urban climate environment. In this study, we built a single-layer urban canopy model with higher accuracy by importing gridded urban canopy parameters and studied the impact of water bodies distributed in different areas of Wuhan on the urban thermal environment using a weather research and forecasting model (WRF). Water bodies located in the upwind suburbs had the greatest cooling impact on the microclimate of downtown areas during the day. Furthermore, they promote the evacuation of heat inside the urban canopy to the upper air by enhancing the lake breeze circulation. Late morning temperatures drop above the ground when the breeze circulation fully develops, while the temperature rise in the upper air increases. However, the cooling effect of these water bodies on the downtown area was affected by construction intensity in the suburbs. When the building density increased from 20% to 40%, the cooling effect did not change significantly. However, a further increase from 40% to 60% increased the proportion of intense heat island areas downtown, and the cooling effect of water bodies was also severely weakened. Moreover, with an increase in building density in the suburbs, the intense heat island areas north of the city gradually expanded to the city center.

Observations of the Development and Vertical Structure of the Lake-Breeze Circulation during the 2017 Lake Michigan Ozone Study

Abstract Ground-based thermodynamic and kinematic profilers were placed adjacent to the western shore of Lake Michigan at two sites as part of the 2017 Lake Michigan Ozone Study. The southern site near Zion, Illinois, hosted a microwave radiometer (MWR) and a sodar wind profiler, while the northern site in Sheboygan, Wisconsin, featured an Atmospheric Emitted Radiance Interferometer (AERI), a Doppler lidar, and a High Spectral Resolution Lidar (HSRL). Each site experienced several lake-breeze events during the experiment. Composite time series and time–height cross sections were constructed relative to the lake-breeze arrival time so that commonalities across events could be explored. The composited surface observations indicate that the wind direction of the lake breeze was consistently southeasterly at both sites regardless of its direction before the arrival of the lake-breeze front. Surface relative humidity increased with the arriving lake breeze, though this was due to cooler air temperatures as absolute moisture content stayed the same or decreased. The profiler observations show that the lake breeze penetrated deeper when the local environment was unstable and preexisting flow was weak. The cold air associated with the lake breeze remained confined to the lowest 200 m of the troposphere even if the wind shift was observed at higher altitudes. The evolution of the lake breeze corresponded well to observed changes in baroclinicity and calculated changes in circulation. Collocated observations of aerosols showed increases in number and mass concentrations after the passage of the lake-breeze front.

Chemical Analysis of Surface-Level Ozone Exceedances during the 2015 Pan American Games

Surface-level ozone (O3) continues to be a significant health risk in the Greater Toronto Hamilton Area (GTHA) of Canada even though precursor emissions in the area have decreased significantly over the past two decades. In July 2015, Environment and Climate Change Canada (ECCC) led an intensive field study coincident with Toronto hosting the 2015 Pan American Games. During the field study, the daily 1-h maximum O3 standard (80 ppbv) was exceeded twice at a measurement site in North Toronto, once on July 12 and again on July 28. In this study, ECCC’s 2.5-km configuration of the Global Environmental Multi-scale (GEM) meteorological model was combined with the Modelling Air-quality and CHemistry (MACH) on-line atmospheric chemistry model and the Town Energy Balance (TEB) urban surface parameterization to create a new urban air quality modelling system. In general, the model results showed that the nested 2.5-km grid-spaced urban air quality model performed better in statistical scores compared to the piloting 10-km grid-spaced GEM-MACH model without TEB. Model analyses were performed with GEM-MACH-TEB for the two exceedance periods. The local meteorology for both cases consisted of light winds with the highest O3 predictions situated along lake-breeze fronts. For the July 28 case, O3 production sensitivity analysis along the trajectory of the lake-breeze circulation showed that the region of most efficient O3 production occurred in the updraft region of the lake-breeze front, as the precursors to O3 formation underwent vertical mixing. In this updraft region, the ozone production switches from volatile organic compound (VOC)-sensitive to NOx-sensitive, and the local net O3 production rate reaches a maximum. This transition in the chemical regime is a previously unidentified factor for why O3 surface-level mixing ratios maximize along the lake-breeze front. For the July 12 case, differences between the model and observed Lake Ontario water temperature and the strength of lake-breeze opposing wind flow play a role in differences in the timing of the lake-breeze, which impacts the predicted location of the O3 maximum north of Toronto.

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.

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.

Spatiotemporal variation in summer ground-level ozone in the Sandbanks Provincial Park, Ontario

Ground-level ozone (O3) is an atmospheric pollutant of concern owing to its impacts on both human and environmental health. In southern Ontario, Canada, air pollutants (including O3) are continuously monitored through a network of active monitoring stations; however, these stations are largely located in urban areas. Passive samplers for O3 and NO2 were deployed at 24 sites throughout the Sandbanks Provincial Park, on the shore of Lake Ontario during the summer of 2016 to assess the influence of lake-breeze circulation on air quality. Average O3 measured at the park (39.4 ppb) was higher than inland sites at Belleville (32.6 ppb) and Peterborough (30.0 ppb). A negative-linear relationship (R2 = 0.71) was observed between O3 concentration and distance from shore (<500 m from Lake Ontario). While a positive-linear relationship was observed between exposure wind speed and O3 (R2 = 0.84) when the predominant wind direction was W–SW. The results suggest that the Sandbanks was influenced by lake-breeze circulation, resulting in elevated summertime O3. Similarly, average NO2 concentrations (4.3 ppb) were higher than the inland site at Peterborough (2.9 ppb), suggesting that lake-breeze circulation transported NO2 onshore from Lake Ontario. Elevated levels of O3 at the Sandbanks may be a potential concern for human health; moreover, estimated three-month AOT40 suggest that O3 may also damage vegetation.

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.

Impact of the Increase of Greenhouse Gas Concentration on the Lake-Breeze Circulation in the Neighborhood of Tucuri Hydroelectric Dam, Brazil

Impact of the Increase of Greenhouse Gas Concentration on the Lake-Breeze Circulation in the Neighborhood of Tucuri Hydroelectric Dam, Brazil

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.

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.

High Resolution Deterministic Prediction System (HRDPS) Simulations of Manitoba Lake Breezes

ABSTRACTThe Effects of Lake Breezes On Weather–Manitoba (ELBOW-MB) field project, conducted around Lakes Manitoba and Winnipeg in July 2013, was the first in-depth field study of lake breezes in Manitoba, Canada. Using observational data collected during ELBOW-MB and output from the 2.5 km Canadian High Resolution Deterministic Prediction System (HRDPS), comparisons were made between HRDPS output and observational data to determine whether the HRDPS can simulate Manitoba lake breezes. The model comparisons considered various lake-breeze characteristics, such as depth, inland penetration distance, and initiation and dissipation time. In addition, cross-sections of lake-breeze circulations were analyzed. The results show that the HRDPS was able to correctly simulate lake breezes, or lack thereof, in 78% of cases on Lake Winnipeg and 68% of cases on Lake Manitoba. Modelled lake-breeze initiation and dissipation times were found to be too early in some cases and too late in others when compared with observations. Overall, it was found that the HRDPS was able to simulate most aspects of lake breezes, although inland penetration distance was one characteristic that the HRDPS was not able to simulate realistically.

Chicago’s Heat Island and Climate Change: Bridging the Scales via Dynamical Downscaling

AbstractThe interaction of global climate change and urban heat islands (UHI) is expected to have far-reaching impacts on the sustainability of the world’s rapidly growing urban population centers. Given that a wide range of spatiotemporal scales contributed by meteorological forcing and complex surface heterogeneity complicates UHI, a multimodel nested approach is used in this paper to study climate-change impacts on the Chicago, Illinois, UHI, covering a range of relevant scales. One-way dynamical downscaling is used with a model chain consisting of global climate (Community Atmosphere Model), regional climate (Weather Research and Forecasting Model), and microscale (“ENVI-met”) models. Nested mesoscale and microscale models are evaluated against the present-day observations (including a dedicated urban miniature field study), and the results favorably demonstrate the fidelity of the downscaling techniques that were used. A simple building-energy model is developed and used in conjunction with microscale-model output to calculate future energy demands for a building, and a substantial increase (as much as 26% during daytime) is noted for future (~2080) climate. Although winds and lake-breeze circulation for future climate are favorable for reducing energy usage by 7%, the benefits are outweighed by such factors as exacerbated UHI and air temperature. An adverse change in human-comfort indicators is also noted in the future climate, with 92% of the population experiencing thermal discomfort. The model chain that was used has general applicability for evaluating climate-change impacts on city centers and, hence, for urban-sustainability studies.