•A novel ladder-shaped fin is proposed to accelerate melting process.•Compared to original straight fin, a maximal 52.2% of melting time can be saved.•Fin angle has a significant effect on reducing ...melting time of the whole PCM.•36.8% reduction in melting time is obtained if turning fins by 45° anticlockwise.•It is more profitable to add fins to mobile heat carrier than to have no fins.
Latent heat energy storage system provides an alternative solution to solving the imbalance problem of energy supply and demand. To improve the phase change efficiency, a novel ladder-shaped fin is proposed to accelerate melting process. Under the same mass of fin materials, two groups of fin shapes (totally eight cases) are innovatively designed. Upon being verified by experiments in literature, numerical models account for comprehensive descriptions on melting front propagation with emphasizing temperature development and free convection in the liquid phase. Results demonstrate that the ladder-shaped fins can better optimize the melting channel of phase change material than the straight fin. Compared to the original straight fin case, a maximal 52.2% of the total melting time can be saved. The angle change of fins has a significant effect on reducing the melting time of the whole PCM. In Group I where fins are arranged vertically and horizontally, the total melting time is much shorter than that of each corresponding case in Group II (45° from the vertical axis). For the original straight fin in Group II, a 36.8% reduction in total melting time is obtained if turning fins by 45°clockwise. To be conclusive, it is more beneficial to add fins to mobile heat accumulators than to have no fins, saving more energy charging time.
We provide observational evidence that land‐atmosphere coupling is underestimated by a conventional metric defined by the correlation between soil moisture and surface evaporative fraction (latent ...heat flux normalized by the sum of sensible and latent heat flux). Land‐atmosphere coupling is 3 times stronger when using leaf area index as a correlate of evaporative fraction instead of soil moisture, in the Southern Great Plains. The role of vegetation was confirmed using adjacent flux measurement sites having identical atmospheric forcing but different vegetation phenology. Transpiration makes the relationship between evaporative fraction and soil moisture nonlinear and gives the appearance of weak coupling when using linear soil moisture metrics. Regions of substantial coupling extend to semiarid and humid continental climates across the United States, in terms of correlations between vegetation metrics and evaporative fraction. The hydrological cycle is more tightly constrained by the land surface than previously inferred from soil moisture.
Key Points
Evaporative fraction is often better correlated with vegetation phenology than with soil moisture
Vegetation controls on evaporative fraction can be separated from atmospheric forcing
Vegetation metrics imply stronger land‐atmosphere coupling than soil moisture metrics
Understanding how different physical processes can shape the probability distribution function (PDF) of surface temperature, in particular the tails of the distribution, is essential for the ...attribution and projection of future extreme temperature events. In this study, the contribution of soil moisture–atmosphere interactions to surface temperature PDFs is investigated. Soil moisture represents a key variable in the coupling of the land and atmosphere, since it controls the partitioning of available energy between sensible and latent heat flux at the surface. Consequently, soil moisture variability driven by the atmosphere may feed back onto the near-surface climate—in particular, temperature. In this study, two simulations of the current-generation Geophysical Fluid Dynamics Laboratory (GFDL) Earth System Model, with and without interactive soil moisture, are analyzed in order to assess how soil moisture dynamics impact the simulated climate. Comparison of these simulations shows that soil moisture dynamics enhance both temperature mean and variance over regional “hotspots” of land–atmosphere coupling. Moreover, higher-order distribution moments, such as skewness and kurtosis, are also significantly impacted, suggesting an asymmetric impact on the positive and negative extremes of the temperature PDF. Such changes are interpreted in the context of altered distributions of the surface turbulent and radiative fluxes. That the moments of the temperature distribution may respond differentially to soil moisture dynamics underscores the importance of analyzing moments beyond the mean and variance to characterize fully the interplay of soil moisture and near-surface temperature. In addition, it is shown that soil moisture dynamics impacts daily temperature variability at different time scales over different regions in the model.
Using daily reanalysis data from 1979 to 2015, this paper examines the impact of winter Ural blocking (UB) on winter Arctic sea ice concentration (SIC) change over the Barents and Kara Seas (BKS). A ...case study of the sea ice variability in the BKS in the 2015/16 and 2016/17 winters is first presented to establish a link between the BKS sea ice variability and UB events. Then the UB events are classified into quasi-stationary (QUB), westward-shifting (WUB), and eastward-shifting (EUB) UB types. It is found that the frequency of the QUB events increases significantly during 1999–2015, whereas the WUB events show a decreasing frequency trend during 1979–2015.
Moreover, it is shown that the variation of the BKS-SIC is related to downward infrared radiation (IR) and surface sensible and latent heat flux changes due to different zonal movements of the UB. Calculations show that the downward IR is the main driver of the BKS-SIC decline for QUB events, while the downward IR and surface sensible heat flux make comparable contributions to the BKS-SIC variation for WUB and EUB events. The SIC decline peak lags the QUB and EUB peaks by about 3 days, though QUB and EUB require lesser prior SIC. The QUB gives rise to the largest SIC decline likely because of its longer persistence, whereas the BKS-SIC decline is relatively weak for the EUB. The WUB is found to cause a SIC decline during its growth phase and an increase during its decay phase. Thus, the zonal movement of the UB has an important impact on the SIC variability in BKS.
Abstract
The sea surface temperature (SST) distribution can modulate the development of extratropical cyclones through sensible and latent heat fluxes. However, the direct and indirect effects of ...these surface fluxes, and thus the SST, are still not well understood. This study tackles this problem using idealized channel simulations of moist baroclinic development under the influence of surface fluxes. The model is initialized with a zonal wind field resembling the midlatitude jet and a different SST distribution for each experiment, where the absolute SST, the SST gradient, and the meridional position of the SST front are varied. The surface latent heat flux associated with the absolute SST plays a key role in enhancing the moist baroclinic development, while the sensible heat fluxes associated with the SST gradient play a minor role that can be detrimental for the development of the cyclone. The additional moisture provided by the latent heat fluxes originates from about 1000 km ahead of the cyclone a day prior to the time of the most rapid deepening. When the SST in this region is higher than 16°C, the additional latent heat is conducive for explosive cyclone development. For SSTs above 20°C, the cyclones feature characteristics of hybrid cyclones with latent heat release close to their core, maintaining their intensity for a longer period due to continuous and extensive moisture supply from the surface. A high absolute SST with a weak SST gradient, however, can lead to a delay of the deepening stage, because of unorganized convection at early stages reducing environmental baroclinicity.
Non‐closure of the surface energy balance is a frequently observed phenomenon of hydrometeorological field measurements, when using the eddy‐covariance method, which can be ascribed to an ...underestimation of the turbulent fluxes. Several approaches have been proposed in order to adjust the measured fluxes for this apparent systematic error. However, there are uncertainties about partitioning of the energy balance residual between the sensible and latent heat flux and whether such a correction should be applied on 30‐min data or longer time scales. The data for this study originate from two grassland sites in southern Germany, where measurements from weighable lysimeters are available as reference. The adjusted evapotranspiration rates are also compared with joint energy and water balance simulations using a physically based distributed hydrological model. We evaluate two adjustment methods: the first one preserves the Bowen ratio and the correction factor is determined on a daily basis. The second one attributes a smaller portion of the residual energy to the latent heat flux than to the sensible heat flux for closing the energy balance for every 30‐min flux integration interval. Both methods lead to an improved agreement of the eddy‐covariance based fluxes with the independent lysimeter estimates and the physically based model simulations. The first method results in a better comparability of evapotranspiration rates, and the second method leads to a smaller overall bias. These results are similar between both sites despite considerable differences in terrain complexity and grassland management. Moreover, we found that a daily adjustment factor leads to less scatter than a complete partitioning of the residual for every half‐hour time interval. The vertical temperature gradient in the surface layer and friction velocity were identified as important predictors for a potential future parameterisation of the energy balance residual.
It was discovered several decades ago that eddy covariance measurements systematically underestimate sensible and latent heat fluxes, creating an imbalance in the surface energy budget. Since then, ...many studies have addressed this problem and proposed a variety of solutions to the problem, including improvements to instruments and correction methods applied during data postprocessing. However, none of these measures have led to the complete closure of the energy balance gap. The leading hypothesis is that not only surface-attached turbulent eddies but also sub-mesoscale atmospheric circulations contribute to the transport of energy in the atmospheric boundary layer, and the contribution from organized motions has been grossly neglected. The problem arises because the transport of energy through these secondary circulations cannot be captured by the standard eddy covariance method given the relatively short averaging periods of time (~30 minutes) used to compute statistics. There are various approaches to adjust the measured heat fluxes by attributing the missing energy to the sensible and latent heat flux in different proportions. However, few correction methods are based on the processes causing the energy balance gap. Several studies have shown that the magnitude of the energy balance gap depends on the atmospheric stability and the heterogeneity scale of the landscape around the measurement site. Based on this, the energy balance gap within the surface layer has already been modelled as a function of a nonlocal atmospheric stability parameter by performing a large-eddy simulation study with idealized homogeneous surfaces. We have further developed this approach by including thermal surface heterogeneity in addition to atmospheric stability in the parameterization. Specifically, we incorporated a thermal heterogeneity parameter that was shown to relate to the magnitude of the energy balance gap. For this purpose, we use a Large-Eddy Simulation dataset of 28 simulations with seven different atmospheric conditions and three heterogeneous surfaces with different heterogeneity scales as well as one homogeneous surface. The newly developed model captures very well the variability in the magnitude of the energy balance gap under different conditions. The model covers a wide range of both atmospheric stabilities and landscape heterogeneity scales and is well suited for application to eddy covariance measurements since all necessary information can be modelled or obtained from a few additional measurements.
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Central American cold surge outbreaks, known as Nortes, are standard features of the Gulf of Mexico (GoM) climate, having significant oceanic and atmospheric impacts over the region that are ...essential for the marine ecosystem. Fifteen years of analysis of weather reports showed that Nortes occur within a 9 months window (September to May), with a total number of 24 ± 5 episodes per season. On average, there were 2.5 ± 1 events per month, lasting between 1 and 3 days with a maximum duration of 13 consecutive days. A Principal Component Analysis of 15 years of in situ observations identified the air temperature (41.6% of the explained variance) and the wave height (36.3%) as the two main drivers of these events impacts. Cluster Analysis to these same data categorized the Nortes into three types: Moderate, Strong, and Severe, based on the environmental impact caused in the GoM. These events tend to transit between categories as they lose strength while travelling to southern latitudes. Severe events are more frequent in the northwestern coast, occurring from January to March, whereas moderate events are more common in the middle of the GoM during September–December. Our results showed that Nortes increase the wind stress over the sea surface, rising the height and period of the waves over the southwestern and central GoM. Nortes also disturb the sea‐level and the surface currents, provoking high amplitude oscillations along the coasts, and accelerating and shifting the currents towards the southwest. Nortes bring cold, dry air that cools the ocean surface and the lower atmosphere and diminishes its relative humidity, which, together with the wind velocity increments, promote a positive sensible and latent heat flux maximized on the northwestern and western coasts.
Central American cold surge outbreaks, or Nortes, are standard features of the Gulf of Mexico (GoM) climate, having significant oceanic, and atmospheric impacts over the region, that are essential for the marine ecosystem. Principal Component Analysis identified the air temperature (41.6% of the explained variance) and the wave height (36.3%) as the two main drivers of these events. Cluster Analysis, categorized them into three types: Moderate, Strong, and Severe, based on the environmental impact caused in the GoM.
This paper aims to evaluate the effects of fin arrangement in a vertical finned double-pipe latent heat storage system based on the locations, thickness and diameter of the fins in melting and ...solidification mechanisms. The PCM is placed in the outer tube while water is passed through the inner tube. The fins are circularly placed around the inner pipe in the PCM zone considering a constant fins number. The results show significant advantages of fins addition in reducing the melting time along with a lower advantage on the solidification time. For the uniform fin array compared with the non-fined case, the melting and solidification times reduces by 41.4% and 9.7%, respectively. For the best fin array compared with the uniform case, the melting time reduces by 23.9%. For the solidification process, the best case is the uniform distribution of the fins when the rate of heat recovery increases by 11.4% compared with the non-finned case. Furthermore, the melting time reduces by decreasing the thickness of the fins. The evaluation of fins’ diameter shows that after a certain diameter, increasing the diameter of the fins shows an adverse effect due to suppressing the natural convection effect.
•Evaluate the thermal performance of a vertical finned double-pipe LHS system.•Evaluate the fins array to have a higher heat storage/recovery rate.•41.4/9.7% reduction in melting/solidification time using a uniform fins array.•54% reduction in melting time in the best distribution of the fins.•Higher effect of fins array on natural convection for higher fins’ diameters.
The present review is an extensive overview of the research progress obtained in the field of Phase Change Material (PCM) integrated with solar thermal applications. Solar energy has become an ...attractive method of using clean energy to eliminate the shortage and environmental drawbacks of fossil fuels but it needs energy storage to bridge the mismatch between times of energy demand and energy supply. Latent Heat Storage (LHS) in PCMs is the most suitable solution for thermal energy storage due to their high latent heat. In this review, special attention is given to recent publications in the field of PCM integrated with solar thermal applications along with the material problems and possible solutions. Finally, future directions on possible studies and applications are proposed.
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