turbulent heat fluxes
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MAUSAM ◽  
2022 ◽  
Vol 53 (1) ◽  
pp. 69-74
Author(s):  
MANOJ K. SRIVASTAVA ◽  
P. K. PASRICHA ◽  
H. N. DUTTA ◽  
R. SINGH

During the ninth Indian Scientific Expedition to Antarctica, in the year 1990, a micro-meteorological tower was installed at Maitri (70° S, 12° E) on the rocky terrain and on an experimental basis, on the nearby ice-shelf at the location of Dakshin Gangotri (70° 7¢ S, 11° 7¢ E). The synoptic features strongly influencing over the sites are the southeasterly  katabatic winds from the polar cap and/or northerly low level warm and humid winds from the sea. These flows are responsible for the formation of strong surface based inversion and strong convective conditions at the ice shelf and rocky terrain during the minimum and maximum insolation periods, respectively. This paper presents a study of surface layer structure over two contrasting surfaces on near-coastal Antarctica and deals with the significance of the energy exchange processes over the rocky Antarctic region and the parameterization of turbulent fluxes over surfaces having strong inversion/convection conditions. The paper makes use of turbulence structure functions  which are different from the conventional one given by Panofsky and Dutton (1984).


Atmosphere ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 90
Author(s):  
Yuting Han ◽  
Yuxin Liu ◽  
Xingwei Jiang ◽  
Mingsen Lin ◽  
Yangang Li ◽  
...  

Using bulk formulas, two-year platform (fastened to the seabed) hourly observations from 2016 to 2017 in the East China Sea (121.6° E, 32.4° N) are used to investigate the role of the tide-induced surface elevation in changing the fixed observational height and modifying the momentum and air-sea turbulent heat fluxes. The semidiurnal tide-dominated elevation anomalies ranging from −3.6 to 3.9 m change the fixed platform observational height. This change causes hourly differences in the wind stress and latent and sensible heat fluxes between estimates with and without considering surface elevation, with values ranging from −1.5 × 10−3 Nm−2, −10.2 Wm−2, and −3.6 Wm−2 to 2.2 × 10−3 Nm−2, 8.4 Wm−2, and 4.6 Wm−2, respectively. More significant differences occur during spring tides. The differences show weak dependence on the temperature, indicating weak seasonal variations. The mean (maximum) difference percentage relative to the mean magnitude is approximately 3.5% (7%), 1.5% (3%), and 1.5% (3%) for the wind stress and latent and sensible heat fluxes, respectively. The boundary layer stability (BLS) can convert from near-neutral conditions to stable and unstable states in response to tide-induced changes in the observational height, with a probability of occurrence of 2%. Wind anomalies play dominant roles in determining the hourly anomalies of the latent heat flux, regardless of the state of the BLS. Extreme cases, including the cold air outbreak in 2016, tropical cyclones Meranti in 2016, and Ampil in 2018, are also examined. This study will facilitate future observation-reanalysis comparisons in the studied coastal region where ocean–atmosphere-land interactive processes are significant.


MAUSAM ◽  
2021 ◽  
Vol 42 (4) ◽  
pp. 339-346
Author(s):  
S.C. Kar ◽  
N. Ramanathan

The air flow over the south Andaman island is simulated using a three dimensional numerical meso-scale model. Port Blair observations are used as initial data. The surface orography, soil moisture soil albedo variations and vegetations effects are included in the model. The combined effect of these factors on the development of sea/land breeze circulations is obtained quantitatively. The model simulated results are compared with the available observations. The principal results obtained are : (1) The meso-scale circulations induced by the differential heating of the island were intensified by topography. (2) The ground vegetative cover trans- port higher amount of turbulent heat fluxes: to the atmosphere and the meso-circulations appeared with higher intensities. (3) If we Include the lateral variations of flux with topographic and coastal asymmetries the induced meso-scale circulations appeared with different intensities along meridional direction and the inland penetration distances varied in y direction. The maximum Inland penetration of sea breeze was seen, where the inland was widest and terrain height was maximum. Stronger sea breeze was simulated over the central/northern parts of the island.


Author(s):  
Е.А. Averyanova ◽  

The features of the spatial distribution of climate values and the coefficients of linear trends of total tur-bulent heat fluxes are revealed, based on NCEP/NCAR reanalysis data for 1950–2020 for the Atlantic Ocean. Variability of total turbulent heat fluxes is investigated on scales of more than 10 and more than 30 years. It is shown that the trends of average annual total heat fluxes significant at 95% level in most part of the Atlantic Ocean area are negative (except for the western parts of anticyclonic gyres and area of arctic sea ice edge). It is confirmed that the maxima of the low-frequency variability of the total heat fluxes correspond to important energy-active zones of the Atlantic, they are North Atlantic deep-water mass formation region, ice edge zone in the north of the North Atlantic and the Atlantic sector of the Arc-tic Ocean.


Author(s):  
Xiang-Yu Li ◽  
Hailong Wang ◽  
Jingyi Chen ◽  
Satoshi Endo ◽  
Geet George ◽  
...  

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 LES simulations. 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 the reanalysis data ERA5 agree reasonablywell with those derived fromACTIVATE 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 reanalysis 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 reanalysis 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 LES simulations. 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.


2021 ◽  
Vol 22 (10) ◽  
pp. 2547-2564
Author(s):  
Georg Lackner ◽  
Daniel F. Nadeau ◽  
Florent Domine ◽  
Annie-Claude Parent ◽  
Gonzalo Leonardini ◽  
...  

AbstractRising temperatures in the southern Arctic region are leading to shrub expansion and permafrost degradation. The objective of this study is to analyze the surface energy budget (SEB) of a subarctic shrub tundra site that is subject to these changes, on the east coast of Hudson Bay in eastern Canada. We focus on the turbulent heat fluxes, as they have been poorly quantified in this region. This study is based on data collected by a flux tower using the eddy covariance approach and focused on snow-free periods. Furthermore, we compare our results with those from six Fluxnet sites in the Arctic region and analyze the performance of two land surface models, SVS and ISBA, in simulating soil moisture and turbulent heat fluxes. We found that 23% of the net radiation was converted into latent heat flux at our site, 35% was used for sensible heat flux, and about 15% for ground heat flux. These results were surprising considering our site was by far the wettest site among those studied, and most of the net radiation at the other Arctic sites was consumed by the latent heat flux. We attribute this behavior to the high hydraulic conductivity of the soil (littoral and intertidal sediments), typical of what is found in the coastal regions of the eastern Canadian Arctic. Land surface models overestimated the surface water content of those soils but were able to accurately simulate the turbulent heat flux, particularly the sensible heat flux and, to a lesser extent, the latent heat flux.


2021 ◽  
Author(s):  
Axel Kleidon ◽  
Maik Renner ◽  
Annu Panwar ◽  
Sarosh Alam Ghausi

<p>Land-atmosphere interactions are typically evaluated using numerical simulation models of increasingly greater complexity.  But what are the key, major constraints that determine the first-order controls of the land-atmosphere system?  Here, we present an alternative approach that is solely based on energetic and thermodynamic constraints of the coupled land-atmosphere system and show that this approach can reproduce observations at the diurnal scale very well.  The key concept we use is that turbulent heat fluxes are predominantly the result of an atmospheric heat engine that is driven by the heat input from the surface and that operates at the thermodynamic limit of maximum power.  This provides a closure for the magnitude of turbulent fluxes in the surface energy balance.  Interactions enter this approach mainly in two ways: First, the cooling effect of turbulent heat fluxes on surface temperature lowers the engine's efficiency, thereby setting the maximum power limit, and second, by heat storage changes in the lower atmosphere, which represent an entropy term inside the heat engine and alter the thermodynamic limit for power output.  Both effects are, however, well constrained by energy balances, yielding analytical solutions for energy balance partitioning during the day without the need for empirical parameters. The further partitioning into sensible and latent heat fluxes is obtained from the assumption of thermodynamic equilibrium at the surface where heat and moisture is added to the atmosphere (if sufficient soil water is accessible).  We then show that this approach works remarkably well in reproducing FluxNet observations over the diurnal cycle.  What this implies is that these physical constraints determine the first-order dynamics of the land-atmosphere system, enabling us to derive simple, physics-based estimates of climate, the dominant effects of vegetation, and the response of the coupled system to global climate change.</p>


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