Sensible Heat Research Articles

Observations of aerosol–vapor pressure deficit–evaporative fraction coupling over India

Abstract. Northern India is a densely populated subtropical region with heavy aerosol loading (mean aerosol optical depth or AOD is ∼0.7), frequent heat waves, and strong atmosphere–biosphere coupling, making it ideal for studying the impacts of aerosols and the temperature variation in latent heat flux (LH) and evaporative fraction (EF). Here, using in situ observations during the onset of the summer monsoon over a semi-natural grassland site in this region, we confirm that strong co-variability exists among aerosols, LH, air temperature (Tair), and the vapor pressure deficit (VPD). Since the surface evapotranspiration is strongly controlled by both physical (available energy and moisture demand) and physiological (canopy and aerodynamic resistance) factors, we separately analyze our data for different combinations of aerosols and Tair/VPD changes. We find that aerosol loading and warmer conditions both reduce sensible heat (SH). Furthermore, we find that an increase in atmospheric VPD tends to decrease the gross primary production (GPP) and, thus, LH, most likely as a response to stomatal closure of the dominant grasses at this location. In contrast, under heavy aerosol loading, LH is enhanced partly due to the physiological control exerted by the diffuse radiation fertilization effect (thus increasing EF). Moreover, LH and EF increases with aerosol loading even under heat wave conditions, indicating a decoupling of the plant's response to the VPD enhancement (stomatal closure) in the presence of high aerosol conditions. Our results encourage detailed in situ experiments and mechanistic modeling of AOD–VPD–EF coupling for a better understanding of Indian monsoon dynamics and crop vulnerability in a heat stressed and heavily polluted future India.

The Effect of Anthropogenic Heat and Moisture on Local Weather at Industrial Heat Islands: A Numerical Experiment

The current study addresses the role of heat and moisture emitted from anthropogenic sources on the local weather with the aid of numerical weather prediction (NWP). The heat and moisture emitted by industries to the atmosphere are considered main sources in this study. In order to understand the effect of heat and moisture on local weather, the study is conducted to capture the impact of heat with no moisture change. The results are compared against a control run case without perturbation and also against the case where both heat and moisture are perturbed with temperature as a single parameter. The Angul district in Odisha that houses over 4000 industries is considered our study region. The numerical simulations are performed using the mesoscale Weather Research and Forecasting (WRF) model for two rain events, namely a light rain case and a heavy rain case, with different physics options available in the WRF model. The WRF simulated maximum rainfall rate using various microphysics schemes are compared with the Tropical rainfall measuring mission (TRMM) observations for validation purposes. Our study shows that the WDM6 double moment microphysics scheme is better in capturing rain events. The TRMM-validated WRF simulation is considered a reference state of the atmosphere against which comparisons for the perturbed case are made. The surface temperature is perturbed by increasing it by 10 K near the industrial site and exponentially decreasing it with height up to the atmospheric boundary layer. A numerical experiment represents heating without addition of moisture by recalculating the relative humidity (RH) corresponding to the perturbed temperature. The perturbed temperature affects sensible heat (SH) and latent heat (LH) parameters in the numerical experiment. From the results of the numerical investigation, it is found that the near-surface rainfall rate increases locally in a reasonable manner with the addition of sensible heat to the atmosphere. A comparison against the case where moisture is added shows that enhanced rainfall is more sensitive to sensible and latent heat than sensible heat alone.

Impact of urbanization on surface energy balance components over metropolitan cities of India during 2000–2018 winter seasons

The present study attempts to evaluate the urban energy balance components concerning increasing urbanization and artificial surfaces over Indian metropolitan cities during the 2000–2018 winter seasons by using Landsat 7 and 8 satellite imageries. The results indicate that the estimated ranges of the energy fluxes are in the typical values reported in the earlier literature over global cities. The sensible heat flux (SHF) increased considerably, and the latent heat flux (LHF) slightly decreased during the study period. The mean SHF over the built-up areas (BA) and the dry lands (DL) of Delhi record a maximum increase of 28.2 Wm−2and 39.7 Wm−2 during the study period. The inland cities have high values of SHF over DL than the coastal cities, and the LHF is high over all the land use classes for the west coast cities. The SHF (LHF) shows a positive (negative) correlation with the land surface temperature. The SHF (LHF) is about 19–33% (1.9–15%) of the net radiation flux, and the residual heat flux is about 60 to 80% of the net radiation flux. The present study advocates that the substantial changes of the surface energy balance parameters have a profound influence on the energy exchange mechanism and could affect regional climatic change.

Diurnal and seasonal variation of planetary boundary layer height over East Asia and its climatic change as seen in the ERA-5 reanalysis data

The diurnal/seasonal structure of the boundary layer height (BLH) is investigated over East Asia by using the hourly synoptic monthly ERA5 reanalysis variables from 1979 to 2019. Sensible heat flux (SHF) is the major factor in the temporal and spatial variation of the BLH. Although BLH, in general, is positively correlated with SHF throughout the year, BLH-SHF relationship varies significantly based on the surface type, latitude and time of the year. Analysis also reveals that stability is an important parameter controlling the diurnal maximum BLH. The growth of BLH is strongly limited by the presence of a stable layer. On the other hand, BLH increases abruptly in the presence of a weakly stratified residual layer. In addition, regional warming tends to increase the BLH in the mid- to high-latitude continental area. In the low-latitude continental area, the sign of anomalous SHF varies seasonally and regionally. Stability plays only a minor role in the BLH change except over the Tibetan Plateau, where the increased stability at the top of boundary layer due to warming reduces BLH rather significantly.

Balanço de Energia no perímetro urbano de Campos dos Goytacazes, RJ: Um estudo de caso

De acordo com a ONU é crescente a tendência de urbanização sendo projetado um crescimento mundial em termos absolutos atingindo 665 em 2050. Utilizando imagens digitais orbitais e técnicas de sensoriamento remoto, este trabalho teve por objetivo avaliar o comportamento do balanço de energia da cidade de Campos dos Goytacazes, RJ contextualizando o estresse hídrico e correlacionando-o com a temperatura da superfície. Observou-se que o solo urbanizado em comparação com a área não construída apresentou os maiores fluxos de calor sensível e de calor no solo. Nas áreas urbanas foram encontrados os menores valores de saldo de radiação e fluxo de calor latente, gerando temperaturas mais elevadas no solo urbano e as áreas vegetadas apresentaram um maior fluxo de calor latente e menor fluxo de calor do solo. Observou-se ainda uma correlação de 96% entre o estresse hídrico e a temperatura, influenciando fortemente os fluxos da energia.Palavras-chaves: sensoriamento remoto, landsat 8, ilhas de calor, SEBAL Energy balance in the urban perimeter of Campos dos Goytacazes, RJ: A case study ABSTRACTAccording to the UN, the urbanization trend is growing, with a global growth projected in absolute terms reaching 665 in 2050. Using orbital digital images and remote sensing techniques, this work aimed to evaluate the behavior of the energy balance of the city of Campos dos Goytacazes, RJ contextualizing water stress and correlating it with surface temperature. It was observed that the urbanized land compared to the non-built-up area presented the highest fluxes of sensible heat and heat in the soil. In urban areas, the lowest values of radiation balance and latent heat flux were found, generating higher temperatures in the urban soil, and vegetated areas presented a greater latent heat flux and lower soil heat flux. There was also a correlation of 96% between water stress and temperature, strongly influencing energy flows, or for changes in the energy balance of the environment, further analyzes are proposed in different water conditions to compare with the results obtained with this work.Keywords: remote sensing, landsat 8, heat islands, SEBAL, temperature

Vegetation Impact on Atmospheric Moisture Transport Under Increasing Land-Ocean Temperature Contrasts

Destabilization of the water cycle threatens human lives and livelihoods. Meanwhile our understanding of whether and how changes in vegetation cover could trigger abrupt transitions in moisture regimes remains incomplete. This challenge calls for better evidence as well as for the theoretical concepts to describe it. Here we briefly summarise the theoretical questions surrounding the role of vegetation cover in the dynamics of a moist atmosphere. We discuss the previously unrecognized sensitivity of local wind power to condensation rate as revealed by our analysis of the continuity equation for a gas mixture. Using the framework of condensation-induced atmospheric dynamics, we then show that with the temperature contrast between land and ocean increasing up to a critical threshold, ocean-to-land moisture transport reaches a tipping point where it can stop or even reverse. Land-ocean temperature contrasts are affected by both global and regional processes, in particular, by the surface fluxes of sensible and latent heat that are strongly influenced by vegetation. Our results clarify how a disturbance of natural vegetation cover, e.g., by deforestation, can disrupt large-scale atmospheric circulation and moisture transport. In view of the increasing pressure on natural ecosystems, successful strategies of mitigating climate change require taking into account the impact of vegetation on moist atmospheric dynamics. Our analysis provides a theoretical framework to assess this impact. The available data for Eurasia indicate that the observed climatological land-ocean temperature contrasts are close to the threshold. This can explain the increasing fluctuations in the continental water cycle including droughts and floods and signifies a yet greater potential importance for large-scale forest conservation.

Large-Eddy Simulations of Marine Boundary Layer Clouds Associated with Cold-Air Outbreaks during the ACTIVATE Campaign. Part I: Case Setup and Sensitivities to Large-Scale Forcings

Abstract Large-eddy simulation (LES) is able to capture key boundary layer (BL) turbulence and cloud processes. Yet, large-scale forcing and surface turbulent fluxes of sensible and latent heat are often poorly prescribed for LESs. We derive these quantities from measurements and reanalysis obtained for two cold-air outbreak (CAO) events during Phase I of the Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) in February–March 2020. We study the two contrasting CAO cases by performing LES and test the sensitivity of BL structure and clouds to large-scale forcings and turbulent heat fluxes. Profiles of atmospheric state and large-scale divergence and surface turbulent heat fluxes obtained from ERA5 data agree reasonably well with those derived from ACTIVATE field measurements for both cases at the sampling time and location. Therefore, we adopt the time-evolving heat fluxes, wind, and advective tendencies profiles from ERA5 data to drive the LES. We find that large-scale thermodynamic advective tendencies and wind relaxations are important for the LES to capture the evolving observed BL meteorological states characterized by the hourly ERA5 data and validated by the observations. We show that the divergence (or vertical velocity) is important in regulating the BL growth driven by surface heat fluxes in LESs. The evolution of liquid water path is largely affected by the evolution of surface heat fluxes. The liquid water path simulated in LES agrees reasonably well with the ACTIVATE measurements. This study paves the path to investigate aerosol–cloud–meteorology interactions using LES informed and evaluated by ACTIVATE field measurements.

Stable gap-filling for longer eddy covariance data gaps: A globally validated machine-learning approach for carbon dioxide, water, and energy fluxes

Continuous time-series of CO2, water, and energy fluxes are useful for evaluating the impacts of climate-change and management on ecosystems. The eddy covariance (EC) technique can provide continuous, direct measurements of ecosystem fluxes, but to achieve this gaps in data must be filled. Research-standard methods of gap-filling fluxes have tended to focus on CO2 fluxes in temperate forests and relatively short gaps of less than two weeks. A gap-filling method applicable to other fluxes and capable of filling longer gaps is needed.To address this challenge, we propose a novel gap-filling approach, Random Forest Robust (RFR). RFR can accommodate a wide range of data gap sizes, multiple flux types (i.e. CO2, water and energy fluxes). We configured RFR using either three (RFR3) or ten (RFR10) driving variables. RFR was tested globally on fluxes of CO2, latent heat (LE), and sensible heat (H) from 94 suitable FLUXNET2015 sites by using artificial gaps (from 1 to 30 days in length) and benchmarked against the standard marginal distribution sampling (MDS) method.In general, RFR improved on MDS's R2 by 15% (RFR3) and by 30% (RFR10) and reduced uncertainty by 70%. RFR's improvements in R2 for H and LE were more than twice the improvement observed for CO2 fluxes. Unlike MDS, RFR performed well for longer gaps; for example, the R2 of RFR methods in filling 30-day gaps dropped less than 4% relative to 1-day gaps, while the R2 of MDS dropped by 21%.Our results indicate that the RFR method can provide improved gap-filling of CO2, H and LE flux timeseries. Such improved continuous flux measurements, with low bias, can enhance our understanding of the impacts of climate-change and management on ecosystems globally.

Effect of different land use land cover on surface heat budget – A case study from a tropical humid region of India

Surface energy balance largely depends on the state of atmospheric variables and a change in their interrelation propagates a change in the balance. Other than the meteorological factors, land use land cover (LULC) also plays a major role deciding the proportional participation of different heat fluxes in the heat balance of an area. Delineating the effects of LULC on energy budget is rather easy over extensive areas than doing it locally, especially over the regions where the influence of any certain climatic characteristics is pre-dominant. Burdwan district in the Indian state of West Bengal is located under tropical Gangetic type climate where the influence of monsoon is at large. Mann-Kendall test at 95% confidence interval showed significant trends of the atmospheric variables over three decades there and t-test at 5% confidence level found significant difference in variables over different LULCs. The Pearson’s correlation coefficients between LST and NDVI and NDBI are more than 0.81 and −0.74 respectively over different LULCs. Sensible heat flux (SHF) is found to be dominant in pre-monsoon and latent heat flux (LHF) in monsoon seasons, when an increase in minimum temperature about 1.2–2°C is also noticed. Albedo, net radiation, SHF and LULC are demarcated as the principal factors by PCA analysis. The screen temperature is related to the heat fluxes and LULC by the equations – ‘t = −57.0166 + 1.402SHF-0.203LHF+0.25vegetation cover+0.064 urban land’ in the western part and ‘t = 33.88–0.19SHF-0.047LHF-0.29 vegetation cover+0.76 settlement area’ in eastern part of the district. Based on the interrelationship of heat fluxes and LULC, LHF is predicted to decrease in near future by 0.17% whereas SHF can increase up to 1.58% with an increase of LST and screen temperature by 1.2% and 0.88% respectively if the present rate of change in LULC sustains.

Evaluation the WRF Model with Different Land Surface Schemes: Heat Wave Event Simulations and Its Relation to Pacific Variability over Coastal Region, Karachi, Pakistan

This study investigates the relative role of land surface schemes (LSS) in the Weather Research and Forecasting (WRF) model, Version 4, to simulate the heat wave events in Karachi, Pakistan during 16–23 May 2018. The efficiency of the WRF model was evaluated in forecasting heat wave events over Karachi using the three different LSS, namely NOAH, NOAH-MP, and RUC. In addition to this we have used the longwave (RRTM) and shortwave (Dudhia) in all schemes. Three simulating setups were designed with a combination of shortwave, longwave, and LSS: E1 (Dudhia, RRTM, and Noah), E2 (Dudhia, RRTM, and Noah-MP), and E3 (Dudhia, RRTM, and RUC). All setups were carried out with a finer resolution of 1 km × 1 km. Findings of current study depicted that E2 produces a more realistic simulation of daily maximum temperature T(max) at 2 m, sensible heat (SH), and latent heat (LH) because it has higher R2 and lower errors (BIAS, RMSE, MAE) compared to other schemes. Consequently, Noah-MP (LSS) accurately estimates T(max) and land surface heat fluxes (SH&LH) because uses multiple physics options for land atmosphere interaction processes. According to statistical analyses, E2 setup outperforms other setups in term of T(max) and (LH&SH) forecasting with the higher Nash-Sutcliffe efficiency (NSE) agreement is 0.84 (0.89). This research emphasizes that the selection of LSS is of vital importance in the best simulation of T(max) and SH (LH) over Karachi. Further, it is resulted that the SH flux is taking a higher part to trigger the heat wave event intensity during May 2018 due to dense urban canopy and less vegetated area. El Niño-Southern Oscillation (ENSO) event played role to prolong and strengthen the heat wave period by effecting the Indian Ocean Dipole (IOD) through walker circulation extension.

Long-Term Trend Comparison of Planetary Boundary Layer Height in Observations and CMIP6 Models over China

AbstractThe planetary boundary layer (PBL) plays an essential role in climate and air quality simulations. Nevertheless, large uncertainties remain in understanding the drivers for long-term trends of PBL height (PBLH) and its simulation. Here we combine the radiosonde data and reanalysis datasets to analyze PBLH long-term trends over China, and to further explore the performance of CMIP6 climate models in simulating these trends. Results show that the observed long-term “positive-to-negative” trend shift of PBLH is related to the variation in the surface upward sensible heat flux (SHFLX), and the SHFLX is further controlled by the synergistic effect of low cloud cover (LCC) and soil moisture (SM) changes. Variabilities in LCC and SM directly influence the energy balance via surface net downward shortwave flux (SWF) and the latent heat flux (LHFLX), respectively. The CMIP6 climate models, however, cannot reproduce the observed PBLH long-term trend shift over China. The CMIP6 results illustrate an overwhelming continuous downward PBLH trend during the 1979–2014 period, which is largely caused by the poor capability in simulating long-term variations of cloud radiative effect. Our results reveal that the long-term cloud radiative effect simulation is critical for CMIP6 models in reproducing the long-term trend of PBLH. This study highlights the importance of processes associated with LCC and SM in modulating PBLH long-term variations and calls attention to improve these processes in climate models in order to improve the PBLH long-term trend simulations.

Innovative cryogenic Phase Change Material (PCM) based cold thermal energy storage for Liquid Air Energy Storage (LAES) – Numerical dynamic modelling and experimental study of a packed bed unit

Electrical energy storage represents a necessary link between sustainability goals and the enhancement of intermittent renewable energy sources penetration in electricity grids. Liquid air energy storage (LAES) is a promising large scale thermo-mechanical energy storage system whose round trip efficiency is largely affected by the performance of the sub-thermal energy storages. The high grade cold storage (HGCS) is by far the most important due to the crucial thermodynamic recovery of the waste cold stream released by the liquid air regasification process. LAES pilot plant and pre-commercial demonstrator, as well as the vast majority of the theoretical and experimental analysis found in literature studies, currently design to store that exergetically valuable cold source in sensible heat (SH) thermal energy storage, economically efficient but low energy density solution. Conversely, phase change material (PCM) has the potential to store a larger amount of energy using the same amount of storage volume. The objective of the present work is to numerically and experimentally investigate the thermal behaviour of a novel cryogenic HGCS packed bed filled by PCM and determine how the novelty introduced affects the LAES thermodynamic and economic performance compared to the SH configuration. To this end, a simplified transient one-dimensional numerical model to simulate the charging and discharging phase of the HGCS system has been developed and successfully validated against experimental results provided by literature for SH medium and an experimental campaign carried out on a novel lab scale HGCS at TESLAB@NTU for PCM, representing a unicum in literature for both PCM and LAES applications. The numerical results have shown that the introduction of a PCM in the HGCS mitigates the thermocline effect shown in SH configuration ensuring: a) longer discharge phase by means of the thermal buffer phenomena triggered by the phase change process and b) lower specific consumption compared to SH configuration (0.272 vs 0.330 kWhe/kgLA) due to a lower time average outlet temperature of the heat transfer fluid during the HGCS discharge, corresponding to LAES charge phase. From an economic perspective, the decrease of the time average specific consumptions results in a notable payback period inferior to 3 years, making the economic investment considerably attractive.

Precipitation influence on and response to early and late Arctic sea ice melt onset during melt season

AbstractThe region containing portions of the East Siberian Sea and Laptev Sea (73°–84°N, 90°–155°E) is the area of focus (AOF) for this study. The impacts of precipitation, latent heat (LH) and sensible heat (SH) fluxes on sea ice melt onset in the AOF are investigated. Four early melting years (1990, 2012, 2003, and 1991) and four late melting years (1982, 1983, 1984, and 1996) are compared to better identify the different responses to melt onset timing. A consistency check is performed between multiple Arctic precipitation products (including NASA MERRA‐2, ECMWF ERA‐Interim [ERA‐I], and ECMWF ERA5 reanalyses as well as GPCP V2.3 observations) since there is not yet a high‐quality ground‐truth Arctic precipitation data product. MERRA‐2 has the greatest monthly average precipitation, snowfall, evaporation, and net LH flux. ERA‐I suggests that liquid precipitation starts earlier in the year than MERRA‐2 and ERA5, while GPCP shows different seasonal precipitation variations from the reanalyses. MERRA‐2 has the clearest and most amplified seasonal trends for the parameters used in this study, so the daily time series and anomalies of MERRA‐2 variables before and after the first major melt event are investigated. ERA5 is used to check these results because ERA‐I and ERA5 display similar seasonal trends. According to MERRA‐2, during early melt years, surface SH flux loss and precipitation are above average in the days before and after the first major melt event. During late melt years, surface SH flux loss and precipitation are below average in the month leading up to the first major melt event.

Evaluation of CMIP6 Global Climate Models for Simulating Land Surface Energy and Water Fluxes During 1979–2014

AbstractThis study examined the overall performance of the climate models in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) in simulating the key energy and water fluxes over land. For this purpose, this study selected multiple land flux products as reference data sets and assessed the global spatial means, patterns, trends, seasonal cycles, and regional mean estimates of the sensible heat (SH), latent heat (LH), net radiation (RN), runoff (RF), and precipitation (PR) simulated by 32 CMIP6 models in recent decades. The global (Antarctica, Greenland, and hot deserts are not included) mean SH, LH, RN, RF, and PR simulated by the CMIP6 models are 37.55 ± 4.81 W m−2, 49.88 ± 5.31 W m−2, 89.10 ± 4.45 W m−2, 351.31 ± 95.28 mm yr−1, and 948.35 ± 88.77 mm yr−1, respectively. The ensemble median of CMIP6 simulations (CMIP6‐MED) can provide robust estimates of global and regional land fluxes, which are within the ranges given by the reference data sets, and highly consistent spatiotemporal patterns of these fluxes. The comparison of CMIP6‐MED with the first preferred reference data sets shows that CMIP6‐MED generally overestimates the water and energy fluxes over land, except for the simulated RF and PR in the Amazon region. The most disagreements between CMIP6‐MED and the reference data sets occur in South America (particularly the Amazon region) and the Tibetan Plateau. Finally, the sources of model biases are discussed. It is suggested that current land flux products should be widely used to optimize the structures and parameters of climate models in future work.

Contributions of vegetation restoration and climate change to spatiotemporal variation in the energy budget in the loess plateau of china

Quantifying the impacts of vegetation restoration (VR) on energy exchange is essential for exploring climate-vegetation interactions. Due to the complexity of land–atmosphere energy exchange and limited observation networks, the influence of VR on the energy balance remains unclear. To improve the understanding of the energy budget change associated with VR in the Loess Plateau (LP), we performed a series of sensitivity simulation experiments using the Community Land Model within the Community Earth System Model, and the spatiotemporal responses of energy exchange to VR and the roles of VR in the variations in energy budget under climate change were investigated. The results showed that the land cover changes from 2000 to 2015 exerted a positive effect on net radiation (NR) and sensible heat (SH), and evident increases in annual mean NR and SH were found in the southeastern LP where larger-scale cropland was converted to grassland or forestland, with increasing magnitudes exceeding 2 W/m2. Latent heat (LH) increased only during May–July, particularly on the southern edge of LP. The increasing magnitudes of NR and LH under Representative Concentration Pathway (RCP)8.5 were larger than those under RCP4.5, with the greatest differences being approximately 4 W/m2 and 5 W/m2 during 2081–2100 for NR and LH, respectively. SH remained nearly stable under RCP4.5 and showed a weak decrease under RCP8.5. Under the same RCP, only slight differences in the energy budget components were detected between the land cover condition in 2015 and 2000, with the largest difference of 0.8 W/m2 in SH during 2021–2040. These results suggested that although both VR and climate warming exerted positive effects on NR, the impact of climate change was larger than that of VR in the LP, and a shift in the local surface energy budget toward LH would occur with climate warming.

Study of Urban Heat Islands Using Different Urban Canopy Models and Identification Methods

This work aims to compare the performance of the single‑(SLUCM) and multilayer (BEP-Building effect parameterization) urban canopy models (UCMs) coupled with the Weather Research and Forecasting model (WRF), along with the application of two urban heat island (UHI) identification methods. The identification methods are: (1) the “classic method”, based on the temperature difference between urban and rural areas; (2) the “local method” based on the temperature difference at each urban location when the model land use is considered urban, and when it is replaced by the dominant rural land use category of the urban surroundings. The study is performed as a case study for the city of Lisbon, Portugal, during the record-breaking August 2003 heatwave event. Two main differences were found in the UHI intensity (UHII) and spatial distribution between the identification methods: a reduction by half in the UHII during nighttime when using the local method; and a dipole signal in the daytime and nighttime UHI spatial pattern when using the classic method, associated with the sheltering effect provided by the high topography in the northern part of the city, that reduces the advective cooling in the lower areas under prevalent northern wind conditions. These results highlight the importance of using the local method in UHI modeling studies to fully isolate urban canopy and regional geographic contributions to the UHII and distribution. Considerable improvements were obtained in the near‑surface temperature representation by coupling WRF with the UCMs but better with SLUCM. The nighttime UHII over the most densely urbanized areas is lower in BEP, which can be linked to its larger nocturnal turbulent kinetic energy (TKE) near the surface and negative sensible heat (SH) fluxes. The latter may be associated with the lower surface skin temperature found in BEP, possibly owing to larger turbulent SH fluxes near the surface. Due to its higher urban TKE, BEP significantly overestimates the planetary boundary layer height compared with SLUCM and observations from soundings. The comparison with a previous study for the city of Lisbon shows that BEP model simulation results heavily rely on the number and distribution of vertical levels within the urban canopy.

Advection Fog over the Eastern Yellow Sea: WRF Simulation and Its Verification by Satellite and In Situ Observations

An observed sea fog event over the Eastern Yellow Sea on 15–16 April 2012 was reproduced in the Weather Research and Forecasting (WRF) simulation with high-resolution to investigate the roles of physical processes and synoptic-scale flows on advection fog with phase transition. First, it was verified by a satellite-based fog detection algorithm and in situ observation data. In the simulation, longwave (infrared) radiative cooling (LRC) with a downward turbulent sensible heat flux (SHF), due to the turbulence after sunset, triggered cloud formation over the surface when warm-moist air advection occurred. At night, warm air advection with continuous cooling due to longwave radiation and SHF near the surface modulated the change of the SHF from downward to upward, resulting in a drastic increase in the turbulent latent heat flux (LHF) that provided sufficient moisture at the lower atmosphere (self-moistening). This condition represents a transition from cold-sea fog to warm-sea fog. Enhanced turbulent mixing driven by a buoyancy force increased the depth of the sea fog and the marine atmospheric boundary layer (MABL) height, even at nighttime. In addition, cold air advection with a prevailing northerly wind at the top of the MABL led to a drastic increase in turbulent mixing and the MABL height and rapid growth of the height of sea fog. After sunrise, shortwave radiative warming in the fog layers offsetting the LRC near the surface weakened thermal instability, which contributed to the reduction in the MABL height, even during the daytime. In addition, dry advection of the northerly wind induced dissipation of the fog via evaporation. An additional sensitivity test of sea surface salinity showed weaker and shallower sea fog than the control due to the decrease in both the LHF and local self-moistening. Detailed findings from the simulated fog event can help to provide better guidance for fog detection using remote sensing.

The impact of sea waves on turbulent heat fluxes in the Barents Sea according to numerical modeling

Abstract. This paper investigates the impact of sea waves on turbulent heat fluxes in the Barents Sea. The Coupled Ocean–Atmosphere Response Experiment (COARE) algorithm, meteorological data from reanalysis and wave data from the WAVEWATCH III wave model results were used. The turbulent heat fluxes were calculated using the modified Charnock parameterization for the roughness length and several parameterizations that explicitly account for the sea wave parameters. A catalog of storm wave events and a catalog of extreme cold-air outbreaks over the Barents Sea were created and used to calculate heat fluxes during extreme events. The important role of cold-air outbreaks in the energy exchange between the Barents Sea and the atmosphere is demonstrated. A high correlation was found between the number of cold-air outbreak days and turbulent fluxes of sensible and latent heat, as well as with the net flux of longwave radiation averaged over the ice-free surface of the Barents Sea during a cold season. The differences in the long-term mean values of heat fluxes calculated using different parameterizations for the roughness length are small and are on average 1 %–3 % of the flux magnitude. The parameterizations of Taylor and Yelland (2001) and Oost et al. (2002) lead to an increase in the magnitude of the fluxes on average, and the parameterization of Drennan et al. (2003) leads to a decrease in the magnitude of the fluxes over the entire sea compared with the Charnock parameterization. The magnitude of heat fluxes and their differences during the storm wave events exceed the mean values by a factor of 2. However, the effect of explicitly accounting for the wave parameters is, on average, small and multidirectional, depending on the parameterization used for the roughness length. With respect to the climatic aspect, it can be argued that explicitly accounting for sea waves in the calculations of heat fluxes can be neglected. However, during the simultaneously observed storm wave events and cold-air outbreaks, the sensitivity of the calculated values of fluxes to the parameterizations used increases along with the turbulent heat transfer increase. In some extreme cases, during storms and cold-air outbreaks, the difference exceeds 700 W m−2.

Sampling error in aircraft flux measurements based on a high-resolution large eddy simulation of the marine boundary layer

Abstract. A high-resolution (1.25 m) large eddy simulation (LES) of the nocturnal cloud-topped marine boundary layer is used to evaluate random error as a function of continuous track length L for virtual aircraft measurements of turbulent fluxes of sensible heat, latent heat, and horizontal momentum. Results are compared with the widely used formula of Lenschow and Stankov (1986). In support of these comparisons, the relevant integral length scales and correlations are evaluated and documented. It is shown that for heights up to approximately 100 m (z/zi=0.12), the length scales are accurately predicted by empirical expressions of the form If=Azb. The Lenschow and Stankov expression is found to be remarkably accurate at predicting the random error for shorter (7–10 km) flight tracks, but the empirically determined errors decay more rapidly with L than the L-1/2 relationship predicted from theory. Consistent with earlier findings, required track lengths to obtain useful precision increase sharply with altitude. In addition, an examination is undertaken of the role of uncertainties in empirically determined integral length scales and correlations in flux uncertainties as well as of the flux errors associated with crosswind and along-wind flight tracks. It is found that for 7.2 km flight tracks, flux errors are improved by factor of approximately 1.5 to 2 for most variables by making measurements in the crosswind direction.

Evapotranspiration and energy exchange in a temperate forest in Mexico

En los ecosistemas forestales el balance de energía, el ciclo del agua y el ciclo del carbono se encuentran vinculados a través del proceso de evapotranspiración. La evapotranspiración es altamente variable en espacio y tiempo y está controlada por numerosos factores biofísicos. El objetivo de este estudio fue analizar la variabilidad estacional de la evapotranspiración e identificar los principales factores que influyen en dicho proceso. El método de eddy covariance se utilizó para medir los flujos de calor sensible y calor latente (equivalente a evapotranspiración) en un bosque bajo manejo forestal, ubicado en la región forestal de Zacualtipán, Hidalgo. Simultáneamente se midió la radiación neta, el flujo de calor del suelo, el contenido de agua en el suelo y otros parámetros meteorológicos. A lo largo del periodo analizado, la proporción de la radiación neta con los flujos de calor latente y calor sensible fue similar la mayor parte del tiempo. La evapotranspiración total anual observada fue de 980 mm. Ésta fue menor en el periodo de “nortes" y no se encontraron diferencias significativas entre el periodo de lluvias y el de secas. La temperatura, humedad del suelo, radiación neta y déficit de presión de vapor explicaron la mayor parte de la variabilidad de la evapotranspiración. Se recomienda realizar estudios posteriores que involucren el análisis de la productividad del ecosistema y eficiencia en el uso del agua, para comprender mejor los procesos del ecosistema e identificar prácticas apropiadas para el manejo forestal sostenible.