On the Influence of Sea Surface Temperatures on the Development of Extratropical Cyclones

2020 ◽  
Author(s):  
Hai Bui ◽  
Thomas Spengler
Keyword(s):  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Extratropical Cyclones ◽  
Sensible Heat ◽  
Latent Heat Release ◽  
Surface Latent Heat Flux ◽  
A Minor ◽  
Sst Gradient

<p class="p1"><span class="s1">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 idealised channel simulations of moist baroclinic development under the influence of surface fluxes. The model is initialised with a zonal wind field resembling the midlatitude jet and a different SST distribution for each experiment, where both the strength and position of the SST gradient are varied.</span></p> <p class="p1"><span class="s1">The surface latent heat flux plays a key role in enhancing the moist baroclinic development, while the sensible heat fluxes play a minor and dampening role. 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 15 degrees Celsius, the additional latent heat is conducive to explosive cyclone development. A high absolute SST with a weak SST gradient, however, can lead to a delay of the deepening stage, because of unorganised convection at early stages. In addition, the cyclone can maintain its intensity for a longer period with an SST above 20 degrees Celsius, because there is a continuous and extensive moisture supply from the surface. The cyclone in this case has characteristics of a hybrid cyclone, where the latent heat release near the cyclone’s centre plays a major role in the development.</span></p>

scholarly journals On the Influence of Sea Surface Temperature distributions on the Development of Extratropical Cyclones

2021 ◽  
Author(s):  
Hai BUI ◽  
Thomas Spengler
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Minor Role ◽  
Extratropical Cyclones ◽  
The Absolute ◽  
Sst Gradient

AbstractThe 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.

Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

2013 ◽  
Vol 17 (14) ◽  
pp. 1-22 ◽  
Author(s):  
Allison L. Steiner ◽  
Dori Mermelstein ◽  
Susan J. Cheng ◽  
Tracy E. Twine ◽  
Andrew Oliphant
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Latent Heat ◽  
Atmospheric Aerosols ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Surface Energy Budget ◽  
Environmental Drivers ◽  
Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

scholarly journals Direct and Indirect Effects of Surface Fluxes on Moist Baroclinic Development in an Idealized Framework

2020 ◽  
Vol 77 (9) ◽  
pp. 3211-3225
Author(s):  
Kristine F. Haualand ◽  
Thomas Spengler
Keyword(s):  
Potential Energy ◽  
Latent Heat ◽  
Indirect Effects ◽  
Level Structure ◽  
Conveyor Belt ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Latent Heating ◽  
Sensible Heat ◽  
Available Potential Energy

Abstract The convoluted role of surface sensible and latent heat fluxes on moist baroclinic development demands a better understanding to disentangle their local and remote effects. Including diabatic effects in the Eady model, the direct effects of surface fluxes on the diabatic generation of eddy available potential energy as well as their indirect effects through modifications of the circulation and latent heating are investigated. It is shown that surface sensible heat fluxes have a minor impact, irrespective of their position and parameterization, while latent heating in the region equivalent to the warm conveyor belt is the dominant diabatic source for development. Downward surface sensible heat fluxes in proximity of the warm conveyor belt results in structural modifications that increase the conversion from basic-state available potential energy to eddy available potential energy, while concomitantly weakening the ascent and hence latent heating. The detrimental effects are easily compensated through provision of additional moisture into the warm conveyor belt. Upward surface heat fluxes in the cold sector, on the other hand, are detrimental to growth. When downward (upward) surface sensible heat fluxes are located below the equivalent of the warm conveyor belt, the diabatically induced PV anomaly at the bottom of the latent heating layer becomes dominant (less dominant). Shifting the downward surface sensible heat fluxes away from the warm conveyor belt results in substantial changes in the growth rate, latent heat release, low-level structure, and energetics, where the effect of surface sensible heat fluxes might even be beneficial.

scholarly journals Fetch Effect on Flux-Variance Estimations of Sensible and Latent Heat Fluxes of Camellia Sinensis

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 299
Author(s):  
Noman Ali Buttar ◽  
Hu Yongguang ◽  
Josef Tanny ◽  
M Waqar Akram ◽  
Abdul Shabbir
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Soil Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Effect Of Temperature ◽  
Sensible Heat ◽  
Fine Wire

Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.

scholarly journals Estimation of the Latent Heat Flux over Irrigated Short Fescue Grass for Different Fetches

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 322
Author(s):  
Francesc Castellví ◽  
Pedro Gavilán
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
The Other ◽  
Sensible Heat ◽  
Surface Renewal ◽  
Residual Method ◽  
Flux Footprints

Often in agrometeorology the instrumentation required to estimate turbulent surface fluxes must be installed at sites where fetch is not sufficient for a sector of wind directions. For different integrated flux-footprints (IFFP) thresholds and taking as a reference the half-hourly latent heat fluxes (LE) measured with a large weighing lysimeter (LELys), the eddy covariance (EC) method and two methods based on surface renewal (SR) analysis to estimate LE were tested over short fescue grass. One method combined SR with the flux-gradient (profile) relationship, SR-P method, and the other with the dissipation method, SR-D method. When LE was estimated using traces of air moisture, good performances were obtained using the EC and the SR-P methods for samples with IFFP higher than 85%. However, the closest LE estimates were obtained using the residual method. For IFFP higher than 50%, the residual method combined with the sensible heat flux estimates determined using the SR-P method performed close to LELys and using the SR-D method good estimates were obtained for accumulated LELys. To estimate the sensible heat flux, the SR-D method can be recommended for day-to-day use by farmers because it is friendly and affordable.

scholarly journals Roles of spatially varying vegetation on surface fluxes within a small mountainous catchment

2010 ◽  
Vol 7 (1) ◽  
pp. 593-619
Author(s):  
G. N. Flerchinger ◽  
D. Marks ◽  
M. L. Reba ◽  
Q. Yu ◽  
M. S. Seyfried
Keyword(s):  
Water Balance ◽  
Latent Heat ◽  
Populus Tremuloides ◽  
Sensible Heat Flux ◽  
Growing Season ◽  
Carbon Fluxes ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Area Index

Abstract. Understanding the role of ecosystems in modulating energy, water and carbon fluxes is critical to quantifying the variability in energy, carbon, and water balances across landscapes. This study compares and contrasts the seasonal surface fluxes of sensible heat, latent heat and carbon fluxes measured over different vegetation in a rangeland mountainous environment within the Reynolds Creek Experimental Watershed. Eddy covariance systems were used to measure surface fluxes over low sagebrush (Artemesia arbuscula), aspen (Populus tremuloides) and the understory of grasses and forbs beneath the aspen canopy. Peak leaf area index of the sagebrush, aspen, and aspen understory was 0.77, 1.35, and 1.20, respectively. The sagebrush and aspen canopies were subject to similar meteorological forces, while the understory of the aspen was sheltered from the wind. Estimated cumulative evapotranspiratation from the sagebrush, aspen understory, and aspen trees were 399 mm, 205 mm and 318 mm. A simple water balance of the catchment indicated that of the 700 mm of areal average precipitation, 442 mm was lost to evapotranspiration, and 254 mm of streamflow was measured from the catchment; water balance closure for the catchment was within 7 mm. Fluxes of latent heat and carbon for all sites were minimal through the winter. Growing season fluxes of latent heat and carbon were consistently higher above the aspen canopy than from the other sites. While growing season carbon fluxes were very similar for the sagebrush and aspen understory, latent heat fluxes for the sagebrush were consistently higher. Higher evapotranspiration from the sagebrush was likely because it is more exposed to the wind. Sensible heat flux from the aspen tended to be slightly less than the sagebrush site during the growing season when the leaves were actively transpiring, but exceeded that from the sagebrush in May, September and October when the net radiation was offset by evaporative cooling. Results from this study illustrate the influence of vegetation on the spatial variability of surface fluxes across mountainous rangeland landscapes.

scholarly journals Energy balance closure and advective fluxes at ADVEX sites

2020 ◽  
Vol 143 (1-2) ◽  
pp. 761-779
Author(s):  
Uta Moderow ◽  
Thomas Grünwald ◽  
Ronald Queck ◽  
Uwe Spank ◽  
Christian Bernhofer
Keyword(s):  
Energy Balance ◽  
Latent Heat ◽  
Heat Budget ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Energy Balance Closure ◽  
Sensible Heat ◽  
Large Scatter ◽  
Additional Energy ◽  
Parallel Measurement

AbstractWhen measuring the energy balance at the earth’s surface using the Eddy covariance technique, the obtained budgets seldom produce a closed energy balance. The measurements often miss some of the energy fluxes. A possible reason is the neglect of non-turbulent surface fluxes of latent heat and sensible heat, i.e. advective fluxes of these quantities. We present estimates of advective latent and sensible heat fluxes for three different sites across Europe based on the ADVEX dataset. The obtained horizontal and vertical advective fluxes were site-specific and characterized by large scatter. In relative terms, the data indicated that the sensible heat budget was less affected by advection than the latent heat budget during nighttime; this is because vertical turbulent latent heat fluxes were very small or close to zero during the night. The results further showed that the additional energy gain by sensible heat advection might have triggered enhanced evaporation for two sites during nighttime. Accounting for advective fluxes improved the energy balance closure for one of the three ADVEX sites. However, the energy balance closure of the other two sites did not improve overall. A comparison with energy balance residuals (energy missed by the measurements without accounting for advection) indicated a large influence of systematic errors. An inspection of the energy balance for the sloped site of the ADVEX dataset underlined the necessity of slope-parallel measurement of radiation.

scholarly journals Energy fluxes and surface characteristics over a cultivated area in Benin: daily and seasonal dynamics

2014 ◽  
Vol 18 (3) ◽  
pp. 893-914 ◽  
Author(s):  
O. Mamadou ◽  
J. M. Cohard ◽  
S. Galle ◽  
C. N. Awanou ◽  
A. Diedhiou ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Latent Heat ◽  
Bare Soil ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Evaporative Fraction ◽  
Surface Conditions ◽  
African Monsoon

Abstract. Latent and sensible heat surface fluxes are key factors of the western African monsoon dynamics. However, few long-term observations of these land surface fluxes are available; these are needed to increase understanding of the underlying processes and assess their impacts on the energy and water cycles at the surface–atmosphere interface. This study analyzes turbulent fluxes of one full year, measured with the eddy covariance technique, over a cultivated area in northern Benin (western Africa). The study site is part of the long-term AMMA–CATCH (African Monsoon Multidisciplinary Analysis–Coupling of the Tropical Atmosphere and Hydrological Cycle) hydrological observatory. The flux partitioning was investigated through the evaporative fraction (EF) and the Bowen ratio (β) at both seasonal and daily scales. Finally, the surface conductance (Gs) and the decoupling coefficient (Ω) were calculated and compared with specific bare soil or canopy models. Four contrasting seasons were identified and characterized by their typical daily energy cycles. The results pointed out the contrasting seasonal variations of sensible and latent heat fluxes due to changing atmospheric and surface conditions. In the dry season, the sensible heat fluxes were largely dominant (β ~ 10) and a low but significant evapotranspiration was measured (EF = 0.08); this was attributed to a few neighboring bushes, possibly fed by the water table. During the wet season, after the monsoon onset, surface conditions barely affected the evaporative fraction (EF), which remained steady (EF = 0.75); the latent heat flux was dominant and the Bowen ration (β) was about 0.4. During the dry-to-wet and wet-to-dry transition seasons, both EF and β were highly variable, as they depended on the atmospheric forcing or the response to isolated rains. A complete surface–atmosphere decoupling was never observed in 2008 (0 < Ω < 0.6), which suggests a systematic mixing of the air within the canopy with the atmospheric surface layer, irrespective of the atmospheric conditions and the vegetation height. Modeling approaches showed a good agreement of soil resistance with the Sakaguchi bare soil model. Canopy conductance was also well reproduced with the Ball–Berry stomata model. We showed that the skin surface temperature had a large seasonal and daily amplitude, and played a major role in all the surface processes. Consequently, an accurate modeling of the surface temperature is crucial to represent correctly the energy and water budgets for this region.

scholarly journals Influence of a New Turbulence Regime on the Global Air–Sea Heat Fluxes

2008 ◽  
Vol 21 (22) ◽  
pp. 5925-5941 ◽  
Author(s):  
Erik Sahlée ◽  
Ann-Sofi Smedman ◽  
Anna Rutgersson ◽  
Ulf Högström
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensible Heat Flux ◽  
Sensitivity Study ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Turbulence Structure ◽  
Sensible Heat ◽  
Monsoon Period

Abstract Recent research has found that boundary layer turbulence changes its organization as the stratification approaches neutral from the unstable side. When the thermal forcing weakens in combination with wind speed above approximately 10 m s−1, detached eddies are formed in the upper part of the surface layer. These eddies effectively transport drier and colder air from aloft to the surface as they move downward, thereby enhancing the surface fluxes of sensible and latent heat. This effect has been observed over both land and sea; that is, it is not dependent on the nature of the underlying surface. Here the authors perform a sensitivity study of how this reorganization of the turbulence structure influences the global air–sea heat fluxes. Using modified bulk formulations incorporating this effect, the magnitude of the enhancement in a climatic sense was estimated by the use of 40-yr ECMWF Re-Analysis (ERA-40) data in the bulk formulas. It is found that for the 1979–2001 period, the global increase of the latent and sensible heat fluxes over the ice-free oceans is 3.6 and 1.2 W m−2, respectively. These numbers suggest that this effect is of some significance. The results also indicate that the regional and seasonal variability may be large. The largest annual increases are found over the southern oceans between 30° and 60°S where the sensible heat flux increases by 2.3 W m−2 and the latent heat flux by 6.5 W m−2. Ocean areas close to the equator experience almost no increase, whereas the latent heat flux from the Arabian Sea during the monsoon period is enhanced by 11.5 W m−2.

Subcloud and Cloud-Base Latent Heat Fluxes during Shallow Cumulus Convection

2019 ◽  
Vol 77 (3) ◽  
pp. 1081-1100 ◽  
Author(s):  
Neil P. Lareau
Keyword(s):  
Boundary Layer ◽  
Water Vapor ◽  
Latent Heat ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Cloud Base ◽  
Cumulus Convection ◽  
Mixing Ratio ◽  
Convective Boundary ◽  
Water Vapor Mixing Ratio

Abstract Doppler and Raman lidar observations of vertical velocity and water vapor mixing ratio are used to probe the physics and statistics of subcloud and cloud-base latent heat fluxes during cumulus convection at the ARM Southern Great Plains (SGP) site in Oklahoma, United States. The statistical results show that latent heat fluxes increase with height from the surface up to ~0.8Zi (where Zi is the convective boundary layer depth) and then decrease to ~0 at Zi. Peak fluxes aloft exceeding 500 W m−2 are associated with periods of increased cumulus cloud cover and stronger jumps in the mean humidity profile. These entrainment fluxes are much larger than the surface fluxes, indicating substantial drying over the 0–0.8Zi layer accompanied by moistening aloft as the CBL deepens over the diurnal cycle. We also show that the boundary layer humidity budget is approximately closed by computing the flux divergence across the 0–0.8Zi layer. Composite subcloud velocity and water vapor anomalies show that clouds are linked to coherent updraft and moisture plumes. The moisture anomaly is Gaussian, most pronounced above 0.8Zi and systematically wider than the velocity anomaly, which has a narrow central updraft flanked by downdrafts. This size and shape disparity results in downdrafts characterized by a high water vapor mixing ratio and thus a broad joint probability density function (JPDF) of velocity and mixing ratio in the upper CBL. We also show that cloud-base latent heat fluxes can be both positive and negative and that the instantaneous positive fluxes can be very large (~10 000 W m−2). However, since cloud fraction tends to be small, the net impact of these fluxes remains modest.

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