Surface heating occurs over the streamline of the Antarctic Circumpolar Current (ACC) and balances the heat transport associated with the global meridional overturning circulation. With a combination ...of ocean assimilation model output, objectively analyzed products, and atmospheric reanalysis, this paper investigates the mechanism of climatological surface cooling in the Pacific sector with zonal asymmetry. The poleward shift of the ACC path in the Pacific with barotropic potential vorticity conservation was found to account for this cooling. The southward transport of warm/wet surface waters encounters relatively cold/dry air at high latitudes, causing strong turbulent heat fluxes. Sensible heat flux related to the sea‐air heat convection plays an equivalent role alongside the sea surface evaporative latent heat flux, both of which dominate the surface cooling in the Pacific sector. Solar radiation decreases with a poleward meandering of the ACC, which aggravates the cooling process. A significant seasonal cycle of the ensemble mean net surface heat flux (Qnet) is demonstrated, that is, approximately half‐year heating (cooling) during austral warm (cool) seasons. The estimated magnitude of Qnet over the ACC is approximately 20 W m−2 by averaging 10 heat flux climatologies and 4 W m−2 in an ocean state estimate model. However, efforts are still needed to reduce the excess heat flux over the sea surface in the Southern Ocean for the heat flux products.
Plain Language Summary
The Antarctic Circumpolar Current experiences surface heating that balances the global meridional heat transport associated with meridional overturning circulation, in which the waters in the North Atlantic subduct due to surface cooling and upwell to the surface in the Southern Ocean. In this paper, the author shows the zonal asymmetry of the climatological surface heat flux over the Antarctic Circumpolar Current. In the Pacific sector, the current meanders poleward as a result of topographic constraints. The solar radiation decreases with increasing latitude. The poleward shift brings warm waters to the higher latitudes, and the ocean releases extra heat under a colder atmosphere. Thus, the Antarctic Circumpolar Current is cooled in the Pacific sector, which is different from the other sectors around the circumpolar belt. How much heat flux enters the Antarctic Circumpolar Current? This paper also gives an ensemble mean estimate of the heat values based on a combination of ocean assimilation model output, objectively analyzed products, and atmospheric reanalysis. The magnitude of the net surface heat flux is approximately 20 W m−2 according to 10 heat flux climatologies and 4 W m−2 in an ocean state estimate model.
Key Points
The mechanism of zonal asymmetry in net air‐sea heat flux climatology over the Antarctic Circumpolar Current is investigated
Cooling processes occur in the Pacific sector with solar radiation less than the turbulent heat fluxes
The poleward shift in the warm/wet ocean encounters cold/dry air, which causes large turbulent heat fluxes and determines surface cooling
Agricultural water resources consumption and soil salinity interact with the distribution of radiation energy in arid salinized farmland. Understanding the temporal changes in energy distribution is ...necessary to enhance water resource use efficiency. Based on two years of monitoring the energy fluxes in a salinized sunflower field, it was found that field energy fluxes were dependent on available energy, and the temporal dynamics of energy distribution was strongly influenced by crop growth. As expected, soil moisture and meteorological conditions were the main factors limiting latent heat (LE) fluxes in the relatively dry year, with leaf area index showing a more significant positive correlation with LE under abundant soil moisture. Furthermore, path analysis revealed that soil moisture affected energy distribution at budding and flowering stages through the negative regulation of soil surface heat fluxes and the positive regulation of LE. The accumulation of soil salt decreased LE (with Pearson correlation coefficient of −0.59 and a total effect of −0.55), and positive regulated sensible heat (with Pearson correlation coefficient of 0.27 and a total effect of 0.31). Additionally, approximately 40% of actual evapotranspiration was contributed by groundwater, potentially influencing energy fluxes. Moreover, a negative correlation was observed between surface albedo and salinity, which might be another pathway influencing energy distribution. Our findings are important to understand energy distribution and water consumption during the crop growth period in salinized field in arid area.
•Meteorology and leaf area index control energy distribution under abundant soil moisture.•Soil salt decreases the proportion of latent heat with positive effect on sensible heat.•The negative correlation between salinity and surface albedo affects energy distribution.
The Gulf Stream plays an important role in North Atlantic climate variability on a range of timescales. The North Atlantic is notable for large decadal variability in sea surface temperatures (SST). ...Whether this variability is driven by atmospheric or oceanic influences is a disputed point. Long time series of atmospheric and ocean variables, in particular long time series of Gulf Stream position, reveal differing sources of SST variability on quasi‐decadal and multidecadal timescales. On quasi‐decadal timescales, an oscillatory signal identified in the North Atlantic Oscillation (NAO) controls SST evolution directly via air‐sea heat fluxes. However, on multidecadal timescales, this relationship between the NAO and SST changes, while the relationship between the NAO and Gulf Stream position remains consistent in phase and resonant in amplitude. Recent changes in the Gulf Stream Extension show a weakening and broadening of the current, consistent with increased instability. We consider these changes in the context of a weakening Atlantic overturning circulation.
Plain Language Summary
The North Atlantic Ocean is a region of remarkable variability in surface temperatures on timescales of decades and longer. Much debate surrounds whether this variability is driven by the atmosphere or by ocean currents, such as the Gulf Stream, moving heat around. In this study, we show that on timescales around 10 years, the atmosphere is the likely cause of Atlantic temperature variability but that this changes when multidecadal variability is considered. Changes ongoing in the Gulf Stream coincide with changes in the broader Atlantic—changes that imply a relatively cooler Atlantic in the coming decades.
Key Points
On quasi‐decadal timescales, NAO varies in phase with GSNW and in antiphase with Atlantic SSTs
On multidecadal timescales, NAO continues to vary in phase with GSNW, but the relationship to Atlantic SSTs has changed
The weakening and broadening of the Gulf Stream is consistent with increased instability since 2005 and not with a northward shift
•Optical-microwave scintillometers (OMS) are compared to eddy covariance systems (EC).•Surface hydrothermal conditions and different principles cause divergent measurements.•Irrigation, ...precipitation, and advection affect the divergent measurements.•OMS does not need to capture all-scale eddies and can improve energy balance closure.
The eddy-covariance (EC) method has been widely used to measure sensible (H) and latent (LE) heat fluxes, however, it has limited spatial representativeness (hundreds of meters’ scale). Optical-microwave scintillometers (OMS) can directly measure kilometer-scale H and LE, which can be used to validate satellite remote sensing products and model simulations. Therefore, quantitative comparisons and analyses between H and LE measured by OMS and EC are important. In this study, the H and LE values measured by OMS and EC were compared and analyzed over two different surfaces: alpine meadow (homogeneous underlying surface) and irrigated cropland (heterogeneous underlying surface). Results showed that the H (LE) difference between OMS and EC measurements was approximately 17% (18%) and 27% (37%) over the homogeneous and heterogeneous underlying surfaces during the vegetation growing season, respectively. Furthermore, the difference in measured LE from OMS and EC (ΔLEOMS−EC) is caused by the combination of the difference in land surface hydrothermal conditions (LSHCs) and the different principles of OMS and EC measurements. On the one hand, ΔLEOMS−EC varied with the changing LSHCs within the instruments’ source areas over the heterogeneous surface, and the value could be decreased by irrigation and precipitation events. On the other hand, OMS averages large-scale measurements over both space and time and does not need to capture all-scale eddies (e.g., large-scale eddies), so the occurrence of advection increases ΔLEOMS−EC. Finally, compared with that of EC system, the energy balance closure ratio of OMS system was similar over the homogeneous underlying surface but significantly increased by 26% over the heterogeneous underlying surface. These results indicate that OMS has a potential advantage in measuring sensible and latent heat fluxes, particularly over heterogeneous underlying surfaces.
It has been recently shown for two forests in France (Les Landes and Sologne) that summer cloud cover over the forest is increased relative to its surroundings. This study aims to contribute to the ...elucidation of the physical mechanisms responsible for this increased cloud cover, focusing on surface flux partitioning. This was done by performing a case study for a heatwave day on which enhanced cloud cover over the forest of Les Landes was observed. Two numerical experiments (large‐eddy simulations) with a homogeneous forest cover were performed, one in which the sensible heat flux was increased by approximately 5% of the total available energy and another one in which the same amount of energy was added to the latent heat flux. The addition of energy to the sensible heat flux led to a stronger increase in cloud cover than the same addition to the latent heat flux. The mean relative humidity at the boundary layer top showed only small differences, indicating it was not a sufficient indicator for cloud formation in this case. Important information, which immediately underlines the need for large‐eddy simulations, is contained in modifications of the shape of the probability density functions of temperature and humidity. With enhanced sensible heating, the higher peak values of relative humidity contribute to an increased cloud cover. A crucial reason for the differences in cloud cover between the experiments is conjectured to be a decrease in the required amount of energy for air parcels to reach the lifting condensation level, indirectly caused by the boundary layer and near‐surface warming associated with the stronger sensible heat flux. As forests in the region do have a higher sensible heat flux than their surroundings, we highlight one potential mechanism for enhanced cloud cover.
Cloud cover strongly depends on the distribution of the incoming solar and thermal energy between heating and evaporation, and therefore land use is crucial in determining cloud cover. We performed large‐eddy simulation experiments with various combinations of heating and evaporation. We found for our case study of a temperate forest that increases in the sensible heat flux are more important for cloud cover than increases in the latent heat flux, and have illustrated the mechanisms responsible for this.
Both sensible and latent heat fluxes are important components in the land surface energy budget, and accurately estimating them on kilometer-scale are important for understanding and modeling local ...hydro meteorological process. Scintillometry could provide kilometer-scale averaged turbulent heat fluxes, and has been used as ground-based remote sensing for estimating surface energy and water budget. This research compared heat fluxes obtained using an optical-microwave scintillometer (OMS) and an eddy covariance system (EC) over a typical temperate deciduous forest in hilly area, northern China. The observation period mainly represents growing season, from April to October 2018. We estimated the sensible and latent heat fluxes using both the two-wavelength method and the bichromatic correlation method, and the EC measurements were used as a benchmark. The results show the sensible heat fluxes from OMS showed 2% higher than EC, whilst the latent heat fluxes from OMS showed around 10% higher than EC. Changes in hydrological conditions or footprints have no significant effects on the measured turbulent fluxes from OMS. We also founded that there are slightly differences between fluxes derived by the two-wavelength method and the bichromatic correlation method due to assumed rTq value. Based on these results, we conclude that OMS can be a reliable approach to measure kilometer-scale surface turbulent heat fluxes over the hilly area, and its ability to estimate kilometer-area sensible and latent heat fluxes looks promising.
•This is a unique dataset of the two-wavelength method in calculated latent and sensible heat fluxes, which are lacking in the literature.•The microwave scintillometer (RPG-MWSC-160, Radiometer Physics GmbH, Germany) is a new commercialized microwave scintillometer device, and there is rare literature on its performance over a typical temperate deciduous forest in hilly area.•The result can provides much needed information about the performance of the OMS system and, more generally, two-wavelength scintillometry.
In most climate models, after an abrupt increase in radiative forcing the climate feedback parameter magnitude decreases with time. We demonstrate how the evolution of the pattern of ocean heat ...uptake—moving from a more homogeneous toward a heterogeneous and high‐latitude‐enhanced pattern—influences not only regional but also global climate feedbacks. We force a slab ocean model with scaled patterns of ocean heat uptake derived from a coupled ocean‐atmosphere general circulation model. Steady state results from the slab ocean approximate transient results from the dynamic ocean configuration. Our results indicate that cloud radiative effects play an important role in decreasing the magnitude of the climate feedback parameter. The ocean strongly affects atmospheric temperatures through both heat uptake and through influencing atmospheric feedbacks. This highlights the challenges associated with reliably predicting transient or equilibrated climate system states from shorter‐term climate simulations and observed climate variability.
Key Points
Ocean heat uptake patterns influence the magnitude of the global feedback parameter
We reproduce a coupled model's feedback parameter evolution with a series of slab ocean simulations
Local ocean heat uptake and release may have an important impact on global feedback magnitudes
Sensible heat fluxes control cloud trail strength Johnston, Michael C.; Holloway, Christopher E.; Plant, Robert S.
Quarterly journal of the Royal Meteorological Society,
April 2023 Part B, 2023-04-00, 20230401, Letnik:
149, Številka:
753
Journal Article
Recenzirano
Odprti dostop
Convective cloud bands known as “cloud trails” (CTs) are commonly found downwind of small islands (<O$$ \mathcal{O} $$(100) km2) throughout the world. They occur primarily in the afternoon, and are ...known to form in response to land–sea contrasts under the presence of background flow. A set of idealized numerical experiments with 100‐m horizontal grid spacing is performed to quantify the relationship between the surface forcing produced by an island and the strength of the resulting CT circulation. These experiments are based on observed environmental conditions for which a CT occurred off Bermuda, a small subtropical island. For these simulations, the CT circulation is found to be controlled by the strength of the integrated excess heating of the flow as it passes over the island. This excess heating is in turn controlled by the strength of the island heat fluxes when the wind speed and the island geometry are kept constant. Our experiments show, all else equal, a linear relationship between CT circulation strength and the island surface heat flux.
Cloud trails are narrow bands of cloud which form downwind of islands and can extend hundreds of kilometers downwind such as the one shown in the image. Previous work using highly simplified and/or coarse‐resolution experiments for larger islands offers solutions for circulations at the expense of the representation of the clouds, while the smallest islands cannot be well described. Results presented here add detail to the conceptual model for the cloud trail system introduced in previous work.
The distinctive conditions present on the north and south slopes of Mount Qomolangma, along with the intricate variations in the underlying surfaces, result in notable variations in the surface ...energy flux patterns of the two slopes. In this paper, data from TESEBS (Topographical Enhanced Surface Energy Balance System), remote sensing data from eight cloud-free scenarios, and observational data from nine stations are utilized to examine the fluctuations in the surface heat flux on both slopes. The inclusion of MCD43A3 satellite data enhances the surface albedo, contributing to more accurate simulation outcomes. The model results are validated using observational data. The RMSEs of the net radiation, ground heat, sensible heat, and latent heat flux are 40.73, 17.09, 33.26, and 30.91 W m−2, respectively. The net radiation flux is greater on the south slope and exhibits a rapid decline from summer to autumn. Due to the influence of the monsoon, on the north slope, the maximum sensible heat flux occurs in the pre-monsoon period in summer and the maximum latent heat flux occurs during the monsoon. The south slope experiences the highest latent heat flux in summer. The dominant flux on the north slope is sensible heat, while it is latent heat on the south slope. The seasonal variations in the ground heat flux are more pronounced on the south slope than on the north slope. Except in summer, the ground heat flux on the north slope surpasses that on the south slope.
摘要: 珠穆朗玛峰南北坡独特的地形条件和复杂的下垫面, 导致了南北坡地表通量分布的显著差异.本文利用地形增强地表能量平衡模式 (Topographical Enhanced Surface Energy Balance System (TESEBS)),遥感数据和站点观测数据, 对季风和非季风期南北坡的地表热通量变化进行了研究.首先, 把MCD43A3卫星数据加入TESEBS, 改进了地表反照率, 使模拟结果更准确.受季风影响, 北坡季风期感热通量最大值出现在季风前期, 潜热通量最大值出现在季风期.南坡季风期潜热通量最大.全年北坡以感热交换为主, 南坡以潜热交换为主.土壤热通量的季节变化在南坡比北坡更明显.
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Abstract Plasmasphere plays an important role in the magnetospheric physics, defining many important inputs to the ionosphere from the middle to the auroral latitudes. Among them are electron thermal ...heat fluxes resulting from the Coulomb interaction of superthermal electrons (SE) and cold plasmaspheric electrons. These fluxes define the electron temperature at the upper ionospheric altitudes and are the input to the global ionospheric modeling networks. As was previously found from the calculation of lower energy SE and thermal heat fluxes, the knowledge of field‐aligned cold plasma distribution in the plasmasphere is a very sensitive parameter that introduces the most uncertainties in the calculation of these values. To verify the previously used SuperThermal Electron Transport code assumptions regarding plasmaspheric field‐aligned density structure ∼ B ( s )/ B o a , we used the latest version of 3D plasmaspheric model developed by Pierrard, Botek, and Darrouzet (2021, https://doi.org/10.3389/fspas.2021.681401 ). Such an assumption is found to be very reasonable in the calculations of electron thermal heat fluxes entering upper ionospheric altitudes and the associated electron temperature formation for the two selected dayside and nightside electron precipitation events driven by whistler‐mode wave activity.
Key Points The role of plasmaspheric field‐aligned density structure in the formation of electron thermal heat fluxes SuperThermal Electron Transport (STET) simulations of thermal heat fluxes using physics‐based 3D dynamic Belgian SWIFF Plasmasphere Model (BSPM) The BSPM simulation confirms the plasmaspheric field‐aligned density structure used in STET code and supports the heat flux calculations
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