Decrease In Latent Heat Flux Research Articles

Potential effect of urbanization on extreme heat events in Metro Manila Philippines using WRF-UCM

This study aims to assess the performance of Weather Research and Forecasting coupled with the urban canopy model and anthropogenic heat (AH) on extreme heat events and determine the potential effect of urbanization on these extreme heat events in Metro Manila. Simulations with well-represented urban land use capture temperature (Mean Bias is -0.39 °C), especially during nighttime compared to simulations without urban land cover. The simulations with urban areas at night show an increase in sensible (∼75 W m−2) and ground heat fluxes (∼125 W m−2), while a decrease in latent heat flux (∼13 W m−2) compared to simulations without urban areas. Simulations with urban cover have temperatures more than 4 °C in central Metro Manila than simulations with no urban grids. Sensitivity tests with three different planetary boundary layer (PBL) and radiation schemes show that ACM2 performed best, while RRTMG captured distribution. During the heatwaves, the daytime and nocturnal urban heat island intensities (UHIIs) are estimated at 0.75 °C and 2.17 °C, respectively. The AH effect on UHII is more substantial during nighttime and contributes about 10 % to the UHII compared to the urbanization effect. This study may help policymakers identify hotspots in Metro Manila and develop adaptation/mitigation strategies for extreme heat events.

Effects of Surface Turbulence Flux Parameterizations on the MJO: The Role of Ocean Surface Waves

Abstract This study investigates the sensitivity of the Madden–Julian oscillation (MJO) to changes to the bulk flux parameterization and the role of ocean surface waves in air–sea coupling using a fully coupled ocean–atmosphere–wave model. The atmospheric and ocean model components of the Energy Exascale Earth System Model (E3SM) are coupled to a spectral wave model, WAVEWATCH III (WW3). Two experiments with wind speed–dependent bulk algorithms (NCAR and COARE3.0a) and one experiment with wave-state-dependent flux (COR3.0a-WAV) were conducted. We modify COARE3.0a to include surface roughness calculated within WW3 and also account for the buffering effect of waves on the relative difference between air-side and ocean-side momentum flux. Differences in surface fluxes, primarily caused by discrepancies in drag coefficients, result in significant differences in MJO’s properties. While COARE3.0a has better convection–circulation coupling than NCAR, it exhibits anomalous MJO convection east of the date line. The wave-state-dependent flux (COR3.0-WAV) improves the MJO representation over the default COARE3.0 algorithm. Strong easterlies over the Pacific Ocean in COARE3.0a enhance the latent heat flux (LHFLX). This is responsible for the anomalous MJO propagation after the date line. In COR3.0a-WAV, waves reduce the anomalous easterlies, leading to a decrease in LHFLX and MJO dissipation after the date line. These findings highlight the role of surface fluxes in MJO simulation fidelity. Most importantly, we show that the proper treatment of wave-induced effects in bulk flux parameterization improves the simulation of coupled climate variability.

Heat wave characterization and its impact on carbon and water vapour fluxes over sugarcane-based agroecosystem

Global climate change expected to exacerbate the temperature extremes and intensity of heat waves in recent decades. The terrestrial biosphere plays a crucial role in absorbing carbon from the atmosphere. Therefore, understanding how terrestrial ecosystems respond to extreme temperatures is essential for predicting land-surface feedbacks in a changing climate. In light of this, a study was conducted to assess the effects of 2022 heat wave [March-May (MAM)] on carbon and water vapour fluxes. This study utilized the measurements obtained from the eddy covariance tower mounted within the sugarcane agroecosystem. The study period (MAM) was characterized into three events: Heat wave event 1 (HE1), Heat wave event 2 (HE2), Non heat wave event (NHE). The variation in carbon and water vapour fluxes, along with meteorological variables, during these events in 2020 and 2022 was further analysed. Our findings indicate that the heat wave caused a decrease in net ecosystem exchange (NEE), leading to an increase in atmospheric CO2 concentration during HE1, HE2 compared to NHE. In HE1, maximum NEE in 2020 and 2022 was -19.15 µmol m-2 s-1 and -13.21 µmol m-2 s-1, respectively. Furthermore, the heat wave events led to a decrease in latent heat flux (LE) and sensible heat flux (H), with changes of up to 5% in LE and 57% in H compared to the same period in 2020. These results highlight the significant impact of the heatwave on both carbon and energy fluxes. Overall, the present study provides a valuable reference for further climate change analysis, specifically focusing on both carbon and energy fluxes within sugarcane ecosystem.

Characterizing the indicator-based, day-and-night, and climate-based variations in response of surface urban heat island during heat wave across global 561 cities

Increasing surface urban heat island (SUHI) has been reported to be closely associated with a large number of environmental issues. The response of SUHI during heat wave was important for further mitigation proposal. However, it remained unknown whether the response of SUHI during heat wave varies with different SUHI indicators (intensity, frequency and maximum duration), day-and-night contrast, and climate zones, and how to characterize and explain these response variations. Therefore, this paper quantified and explained for these variations in response of SUHI during heat wave across global 561 cities. There were three major findings. (1) The average percentage of response in intensity, frequency and maximum duration at daytime was -20%, -12% and -47%, while it was 10%, 11% and -10% at nighttime. During heat wave, daytime SUHI decreased in the equatorial and arid climates, while nighttime SUHI increased. (2) The attenuated daytime SUHI during heat wave in the equatorial and arid climates resulted from a decrease in latent heat flux and vegetation cooling effect. (3) Increased solar radiation during heat wave contributed to intensified nighttime SUHI, of which energy sources were determined on surface solar absorption. Additionally, differences in evaporation, vegetation, and albedo during heat wave were discussed.

Contribution of future urbanization to summer regional warming in the Pearl River Delta

The impact of future urbanization on regional climate change in the Pearl River Delta (PRD), one of the largest urban agglomerations in China, has been a major concern. A new generation of future urban expansion projection data provides a guideline for exploring the above question. In this study, future urban expansion data are used with the Weather Research and Forecasting (WRF) model to explore and quantify future temperature change in the PRD in 2030 and 2050. The results show that the urban area will expand from 15.37% to 25.21% and 26.93% over the entire PRD in 2030 and 2050, respectively. The PRD urban agglomeration warms by 0.49 ± 0.14 °C in 2030 and 0.53 ± 0.12 °C in 2050, with warmer nights than days. The outgoing radiation rises by 10.28 ± 2.82 W·m−2 in 2030 and 11.18 ± 2.67 W·m−2 in 2050. The latent heat flux decreases by 39.81 ± 5.64 W·m−2 in 2030 and 44.71 ± 6.21 W·m−2 in 2050. The sensible heat flux increases by 38.45 ± 7.05 W·m−2 in 2030 and 42.43 ± 7.5 W·m−2 in 2050. Urbanization changes the physical properties of the urban surface, causing an increase in surface outgoing radiation and turbulent heat flux, eventually resulting in the warming of the PRD urban agglomeration.

Climate projections at a convection-permitting scale of extreme temperature indices for an archipelago with a complex microclimate structure

In island systems with complex orography (e.g. Canary Islands), obtaining projections of climate extremes throughout the 21st century is necessary to evaluate the possible adverse effects of climate change. In this work, a dynamic downscaling methodology was applied to obtain the projections of temperature extremes indices. The WRF modeling system was properly configured with a spatial resolution of 3 km, for the periods: 2030–2059 (MID) and 2070–2099 (END), and for the RCPs 4.5 and 8.5 scenarios. This spatial-temporal resolution allows better modeling of the land-surface coupling processes (e.g., latent and sensible heat fluxes), which are one of the main sources of uncertainties in temperature extremes modeling. The initial and boundary conditions were defined by three CMIP5 Earth Systems Models: GFDL-ESM2M, MIROC-ESM, and IPSL-CM5. The future changes were calculated against the modeled reference period was 1980–2009 (HIS). The selected extremes indices were those defined by the Team of Experts on Climate Change Detection and Indices (ETCCDI) and were: monthly absolute maximum and minimum temperature respectively (TX and TN), monthly maximum of the diurnal temperature range (DTR), tropical nights (TR), warm days (TX90P), cold nights (TN10P), warm-spell duration index (WSDI) and cold-spell duration index (CSDI). Also, the return levels and return periods for annual maximum temperature were analyzed using the Generalized Extreme Value distribution (GEV).The modeled indices were compared with those obtained from observations at nine ground-based stations for the HIS period. Despite the high spatial and temporal resolution of the models a bias is still observed between the modeled and observational values for the absolute indices, even when the simulations are driven by reanalysis data. However, the comparison of these indices around their previously unbiased means yields values on average of 0.85 with a standard deviation of 0.06 on a Perkins-based skill score. Regarding the 20-year return levels for maximum temperature, differences between the average of the models and observations are below 2 °C for all sites, except for the highest stations IZO and TFN, which reach 2.9 and 4.2 °C, respectively.The analyses of the results indicate that the future projections of the indices obtained using any of the models remain constant from the mid-century to the end of the century for the RCP45 whereas they continue to increase if the RCP85 is considered. This finding shows that all models closely follow the variation in the CO2-equivalent concentrations used as input. Thus, TX and TN are expected to increase, with an average change for the END period and RCP8.5 of 4.0 ± 0.5 °C and 4.4 ± 0.4 °C for TN. TX90p increases considerably (30 percentage points), and the TN10p index will be close to zero. The increase in temperatures is mainly due to, in addition to the modification of the synoptic patterns, a decrease in total cloud cover and soil moisture.This decrease in soil moisture has a direct effect on the decrease in latent heat flux and an increase in sensible heat flux, associated with a projected increase of DTR. Also, the 20-year return levels for maximum temperature obtained for the HIS period will correspond to return periods between 1 and 6 years at the END period and RCP8.5.

Examining the characteristics of planetary boundary layer height and its relationship with atmospheric parameters over Indian sub-continent

Planetary boundary layer plays a critical role in the monsoon circulation studies at regional scales through exchange of land surface fluxes (heat and moisture) with atmosphere. The objective of the present study is to identify the spatial variability of long-term seasonal trends of planetary boundary layer height (PBLH) over Indian subcontinent and its association with atmospheri parameters. Monthly atmospheric boundary layer height data obtained from European centre for medium range weather forecast ERA-5 reanalysis has been used for the study during 1980–2018. Statistically robust non-parametric Mann Kendall test is used to investigate the significance of trend at 95% confidence interval. From the results it has been observed that decreasing trend for PBLH is noticed during pre-monsoon and monsoon seasons over Indian region. PBLH over central and north-west India is deeper (1600–1800 m) during pre-monsoon season whereas PBLH is shallow during other seasons. Seasonal variation of PBLH shows a strong negative association with the relative humidity (r more than −0.8) whereas it shows strong positive association with surface temperature (r > 0.7) and surface zonal winds (r > 0.5) over Indian subcontinent. Evaporative fraction which acts as a dominant controlling factor for the variation in PBLH is positively associated (r > 0.7) with the PBLH during monsoon season. Decreasing trend of PBLH during monsoon season may be attributed to the decrease in latent heat flux and increase in relative humidity that results in entrap of moisture at lower levels and may enhance the formation of extreme events. Inter annual variability of PBLH over Indian subcontinent demonstrates in-phase relationship with the deficit and excess monsoon years. Further to this, PBLH is found to be strongly negatively correlated with PM2.5 (r more than −0.5) during pre-monsoon and monsoon seasons suggesting an opposite phase relationship between the two parameters.

Skillful Subseasonal Prediction of United States Extreme Warm Days and Standardized Precipitation Index in Boreal Summer

AbstractSkillful subseasonal prediction of extreme heat and precipitation greatly benefits multiple sectors, including water management, public health, and agriculture, in mitigating the impact of extreme events. A statistical model is developed to predict the weekly frequency of extreme warm days and 14-day standardized precipitation index (SPI) during boreal summer in the United States (US). We use a leading principal component of US soil moisture and an index based on the North Pacific sea surface temperature (SST) as predictors. The model outperforms the NCEP’s Climate Forecast System version 2 (CFSv2) at weeks 3-4 in the eastern US. It is found that the North Pacific SST anomalies persist several weeks and are associated with a persistent wave train pattern (WTZ500), which leads to increased occurrences of blocking and extreme temperature over the eastern US. Extreme dry soil moisture conditions persist into week 4 and are associated with an increase in sensible heat flux and decrease in latent heat flux, which may help maintain the overlying anticyclone. The clear sky conditions associated with blocking anticyclones further decrease soil moisture conditions and increase the frequency of extreme warm days. This skillful statistical model has the potential to aid in irrigation scheduling, crop planning, reservoir operation, and provide mitigation of impacts from extreme heat events.

Characterizing the Relationship between Temperature and Soil Moisture Extremes and Their Role in the Exacerbation of Heat Waves over the Contiguous United States

AbstractIncreased heat-wave frequency across the United States has led to the need for improved predictability of heat-wave events. A detailed understanding of land–atmosphere interactions and the relationship between soil moisture and temperature extremes could provide useful information for prediction. This study identifies, for many locations, a threshold of soil moisture below which there is an increase in the sensitivity of atmospheric temperature to declining soil moisture. This shift to a hypersensitive regime causes the atmosphere to be more susceptible to atmospherically driven heat-wave conditions. The soil moisture breakpoint where the regime shift occurs is estimated using segmented regression applied to observations and reanalysis data. It is shown that as the soil gets drier, there is a concomitant change in the rate of decrease in latent heat flux and increase in sensible heat flux leading to a strong positive feedback of increased air temperature near the surface, which further dries out the soil. Central, southwestern, and southeastern parts of the United States seem to have regions of clear regime shifts, while the eastern part of the United States generally does not get dry enough to reveal significant breakpoints. Sensible heat flux is seen to be a primary driver of this increased temperature sensitivity aided by the drop in latent heat flux. An investigation of flux tower sites verifies the breakpoint–flux relationships found in reanalysis data. Accurate estimation of these breakpoints can contribute to improved heat-wave prediction.

Modeling of land-use and land-cover change impact on summertime near-surface temperature variability over the Delhi–Mumbai Industrial Corridor

This study explores the impact of land-use and land-cover (LULC) changes due to different urbanization scenarios in the Delhi–Mumbai Industrial Corridor (DMIC) region on surface air temperature by conducting sensitivity studies with the Weather Research and Forecasting (WRF) model. First, a sensitivity analysis conducted using the planetary boundary layer (PBL) and surface layer (SL) physical parameterizations available in WRF. Results show that the model performs better when a combination of the Mellor–Yamada–Janjic PBL and ETA SL schemes used. Then, numerical experiments performed using WRF with the above configuration and three different LULC scenarios to assess the possible impact of urbanization on near-surface temperature during May. A total of ten simulations were conducted for the May month of 2005–2014 to estimate the statistical and physical robustness of results. Each of these simulations considered as ensemble member while computing average values. The study shows that there is a significant effect of LULC change mainly on the minimum temperature (Tmin) with an increase of 2.9–3.7℃ over the DMIC region. The impact is less on maximum temperature, with a minor rise in 0.1–0.3℃. The probable reason for the increase in minimum temperature is likely due to a decrease in latent heat flux and an increase in sensible heat flux. The impact on air temperature was found to be prominent over existing urban clusters than the surrounding built environment; also, this effect is additive and more pronounced with the extreme LULC change scenario.

Impact of Wildfire on the Surface Energy Balance in Six California Case Studies

We investigate the impact of wildfires on surface energy exchange through the assessment of six California wildfires that occurred in the last 20 years. A burned–unburned binary mask was generated from the MODIS approximate date of burn product and implemented into the Simplified Simple Biosphere model for a series of simulations. Model performance was evaluated against the North American Land Data Assimilation System and is found to simulate surface temperature and net radiation accurately. Simulations show a decrease in latent heat flux in every case study except the Rush fire, which occurred in Lassen County in August 2012. Post-fire changes in net radiation and sensible heat followed similar trends, decreasing in each of the domains except for the Rush and Cedar fires. The greatest changes in temporally-averaged net radiation occurred in the Rim (− 41.7 W m−2), Basin Complex (− 31.6 W m−2), and Rush (26.5 W m−2) fires. Initial increases in sensible heat flux, caused by the decrease in albedo from ash deposition, are balanced by decreases in latent heat flux in the Zaca, Rim, and Basin Complex case studies. Results also indicate a relationship between decreases in average sensible heat flux and leaf-area-index change. Wildfires that burn in sparsely vegetated areas are associated with increases in sensible heat flux, an effect that is magnified by long ash-deposition periods (i.e., Rush fire), while wildfires that burn in densely vegetated areas are associated with large decreases in sensible and latent heat flux (i.e., Rim, Basin Complex fires).

Distinguishing between early- and late-covering crops in the land surface model Noah-MP: impact on simulated surface energy fluxes and temperature

Abstract. Land surface models are essential parts of climate and weather models. The widely used Noah-MP land surface model requires information on the leaf area index (LAI) and green vegetation fraction (GVF) as key inputs of its evapotranspiration scheme. The model aggregates all agricultural areas into a land use class termed “cropland and pasture”. In a previous study we showed that, on a regional scale, the GVF has a bimodal distribution formed by two crop groups differing in phenology and growth dynamics: early-covering crops (ECC; e.g., winter wheat, winter rapeseed, winter barley) and late-covering crops (LCC; e.g., corn, silage maize, sugar beet). That result can be generalized for central Europe. The present study quantifies the effect of splitting the land use class cropland and pasture of Noah-MP into ECC and LCC on surface energy fluxes and temperature. We further studied the influence of increasing the LCC share, which in the study area (the Kraichgau region, southwest Germany) is mainly the result of heavily subsidized biomass production, on energy partitioning at the land surface. We used the GVF dynamics derived from high-resolution (5 m × 5 m) RapidEye satellite data and measured LAI data for the simulations. Our results confirm that the GVF and LAI strongly influence the partitioning of surface energy fluxes, resulting in pronounced differences between simulations of ECC and LCC. Splitting up the generic crop into ECC and LCC had the strongest effect on land surface exchange processes in July–August. During this period, ECC are at the senescence growth stage or already harvested, while LCC have a well-developed ground-covering canopy. The generic crop resulted in humid bias, i.e., an increase in evapotranspiration by +0.5 mm d−1 (latent heat flux is 1.3 MJ m−2 d−1), decrease in sensible heat flux (H) by 1.2 MJ m−2 d−1 and decrease in surface temperature by −1 ∘C. The bias increased as the shares of ECC and LCC became similar. The observed differences will impact the simulations of processes in the planetary boundary layer. Increasing the LCC share from 28 % to 38 % in the Kraichgau region led to a decrease in latent heat flux (LE) and a heating up of the land surface in the early growing season. Over the second part of the season, LE increased and the land surface cooled down by up to 1 ∘C.

Global lake evaporation accelerated by changes in surface energy allocation in a warmer climate

Lake evaporation is a sensitive indicator of the hydrological response to climate change. Variability in annual lake evaporation has been assumed to be controlled primarily by the incoming surface solar radiation. Here we report simulations with a numerical model of lake surface fluxes, with input data based on a high-emissions climate change scenario (Representative Concentration Pathway 8.5). In our simulations, the global annual lake evaporation increases by 16% by the end of the century, despite little change in incoming solar radiation at the surface. We attribute about half of this projected increase to two effects: periods of ice cover are shorter in a warmer climate and the ratio of sensible to latent heat flux decreases, thus channelling more energy into evaporation. At low latitudes, annual lake evaporation is further enhanced because the lake surface warms more slowly than the air, leading to more long-wave radiation energy available for evaporation. We suggest that an analogous change in the ratio of sensible to latent heat fluxes in the open ocean can help to explain some of the spread among climate models in terms of their sensitivity of precipitation to warming. We conclude that an accurate prediction of the energy balance at the Earth’s surface is crucial for evaluating the hydrological response to climate change.

Modeling the Warming Impact of Urban Land Expansion on Hot Weather Using the Weather Research and Forecasting Model: A Case Study of Beijing, China

The impacts of three periods of urban land expansion during 1990–2010 on near-surface air temperature in summer in Beijing were simulated in this study, and then the interrelation between heat waves and urban warming was assessed. We ran the sensitivity tests using the mesoscaleWeather Research and Forecasting model coupled with a single urban canopy model, as well as high-resolution land cover data. The warming area expanded approximately at the same scale as the urban land expansion. The average regional warming induced by urban expansion increased but the warming speed declined slightly during 2000–2010. The smallest warming occurred at noon and then increased gradually in the afternoon before peaking at around 2000 LST—the time of sunset. In the daytime, urban warming was primarily caused by the decrease in latent heat flux at the urban surface. Urbanization led to more ground heat flux during the day and then more release at night, which resulted in nocturnal warming. Urban warming at night was higher than that in the day, although the nighttime increment in sensible heat flux was smaller. This was because the shallower planetary boundary layer at night reduced the release efficiency of near-surface heat. The simulated results also suggested that heat waves or high temperature weather enhanced urban warming intensity at night. Heat waves caused more heat to be stored in the surface during the day, greater heat released at night, and thus higher nighttime warming. Our results demonstrate a positive feedback effect between urban warming and heat waves in urban areas.

Impact of highway construction on land surface energy balance and local climate derived from LANDSAT satellite data

Extensive construction of highways has a major impact on the landscape and its structure. They can also influence local climate and heat fluxes in the surrounding area. After the removal of vegetation due to highway construction, the amount of solar radiation energy used for plant evapotranspiration (latent heat flux) decreases, bringing about an increase in landscape surface temperature, changing the local climate and increasing surface run-off. In this study, we evaluated the impact of the D8 highway construction (Central Bohemia, Czech Republic) on the distribution of solar radiation energy into the various heat fluxes (latent, sensible and ground heat flux) and related surface functional parameters (surface temperature and surface wetness). The aim was to describe the severity of the impact and the distance from the actual highway in which it can be observed. LANDSAT multispectral satellite images and field meteorological measurements were used to calculate surface functional parameters and heat balance before and during the highway construction. Construction of a four-lane highway can influence the heat balance of the landscape surface as far as 90m in the perpendicular direction from the highway axis, i.e. up to 75m perpendicular from its edge. During a summer day, the decrease in evapotranspired water can reach up to 43.7m3 per highway kilometre. This means a reduced cooling effect, expressed as the decrease in latent heat flux, by an average of 29.7MWh per day per highway kilometre and its surroundings. The loss of the cooling ability of the land surface by evaporation can lead to a rise in surface temperature by as much as 7°C. Thus, the results indicate the impact of extensive line constructions on the local climate.

WRF-UCM을 활용한 수도권 지역의 열환경 변화 연구: 2000년과 2009년의 비교

This study examined the impact of change of land-use and meteorological condition due to urbanization on heat environment in Seoul metropolitan area over a decade (2000 and 2009) using Weather Research and Forecasting (WRF)-Urban Canopy Model (UCM). The numerical simulations consist of three sets: meteorological conditions of (1) October 2000 with land-use data in 2000 (base simulation), (2) October 2009 with land-use data in 2000 (meteorological condition change effect) and (3) October 2009 with land-use data in 2009 (both the effects of land-use and meteorological condition change). According to the experiment results, the change of land-use and meteorological condition by urbanization over a decade showed different contribution to the change of heat environment in Seoul metropolitan area. There was about <TEX>$1^{\circ}C$</TEX> increase in near-surface (2 m) temperature over all of the analyzed stations due to meteorological condition change. In stations where the land-use type changed into urban, large temperature increase at nighttime was observed by combined effects of meteorological condition and land-use changes (maximum <TEX>$4.23^{\circ}C$</TEX>). Urban heat island (UHI) over <TEX>$3^{\circ}C$</TEX> (temperature difference between Seoul and Okcheon) increased 5.24% due to the meteorological condition change and 26.61% due to the land-use change. That is, land-use change turned out to be contributing to the strengthening of UHI more than the meteorological condition change. Moreover, the land-use change plays a major role in the increase of sensible heat flux and decrease of latent heat flux.

Spatial Variation of Surface Energy Fluxes Due to Land Use Changes across China

We estimate the heat flux changes caused by the projected land transformation over the next 40 years across China to improve the understanding of the impacts of land dynamics on regional climate. We use the Weather Research and Forecasting (WRF) model to investigate these impacts in four representative land transformation zones, where reclamation, overgrazing, afforestation, and urbanization dominates the land use and land cover changes in each zone respectively. As indicated by the significant variance of albedo due to different land use and cover changes, different surface properties cause great spatial variance of the surface flux. From the simulation results, latent heat flux increases by 2 and 21 W/m2 in the reclamation and afforestation regions respectively. On the contrary, overgrazing and urban expansion results in decrease of latent heat flux by 5 and 36 W/m2 correspondingly. Urban expansion leads to an average increase of 40 W/m2 of sensible heat flux in the future 40 years, while reclamation, afforestation, as well as overgrazing result in the decrease of sensible heat flux. Results also show that reclamation and overgrazing lead to net radiation decrease by approximately 4 and 7 W/m2 respectively, however, afforestation and urbanization lead to net radiation increase by 6 and 3 W/m2 respectively. The simulated impacts of projected HLCCs on surface energy fluxes will inform sustainable land management and climate change mitigation.

Modeling Land Surface Processes and Heavy Rainfall in Urban Environments: Sensitivity to Urban Surface Representations

Abstract High-resolution simulations with the Weather Research and Forecasting Model (WRF) are used in conjunction with observational analyses to investigate land surface processes and heavy rainfall over the Baltimore–Washington metropolitan area. Analyses focus on a 6-day period, 21–26 July 2008, which includes a major convective rain event (23–24 July), a prestorm period (21–22 July), and a dry-down period (25–26 July). The performance of WRF in capturing land–atmosphere interactions, the bulk structure of the atmospheric boundary layer, and the rainfall pattern in urban environments is explored. Results indicate that WRF captures the incoming radiative fluxes and surface meteorological conditions. Mean profiles of potential temperature and humidity in the atmosphere are also relatively well reproduced, both preceding and following the heavy rainfall period. However, wind features in the lower atmosphere, including low-level jets, are not accurately reproduced by WRF. The biases in the wind fields play a central role in determining errors in WRF-simulated rainfall fields. The study also investigates the sensitivity of WRF simulations to different urban surface representations. It is found that urban surface representations have a significant impact on the surface energy balance and the rainfall distribution. As the impervious fraction increases, the sensible heat flux and the ground heat flux increase, while the latent heat flux decreases. The impact of urban surface representations on precipitation is as significant as that of microphysical parameterizations. The fact that changing urban surface representations can significantly alter the rainfall field suggests that urbanization plays an important role in modifying the regional precipitation pattern.

Response of extratropical cyclone activity to the Kuroshio large meander in northern winter

We examined possible responses of cyclone activities to the bimodal path states of the Kuroshio Current [i.e., large meander (LM) and non‐LM (NLM)] by using the long‐term reanalysis data and the 20th century hindcast experiment of a high‐resolution atmosphere‐ocean coupled model. Compared with a seasonal mean cyclone track frequency for the LM and NLM periods, a primary cyclone track shifts southward in association with the meander of Kuroshio Current. Composite analyses of the hindcast experiment showed remarkable atmospheric responses accompanying the Kuroshio LM. The Kuroshio LM causes a decrease in latent heat flux in the south of Japan and a southward shift of the near‐surface baroclinic zone. Distinctive decreases in thermodynamic fluxes inhibit the rapid development of cyclones in the meander region, eventually inducing positive sea level pressure anomalies downstream from that region.

Variations of latent heat flux during tropical cyclones over the South China Sea

Latent heat flux exchanges at the air–sea interface play important roles in the formation and development of tropical cyclones (TCs). Usually, the latent heat flux transferred from oceans to atmosphere increases during the intensification stages of the TCs. However, through analysing a number of TC cases over the South China Sea, it is found that the changes of latent heat flux exhibit different behaviours during the intensification stage of the TCs, depending upon their travelling pathways. The air–sea latent heat flux increases while the TCs are intensifying in open sea areas of the South China Sea. However, the latent heat flux decreases while the TCs are travelling over the narrow area between the Indo-China Peninsula and Hainan Island, even though the TCs are in their intensification stage. For the latter case, the decrease in latent heat flux F is accompanied by the decrease in surface winds due to the terrain frictions even though the upper troposphere winds are still increasing. Copyright © 2013 Royal Meteorological Society