scholarly journals The Impact of the Temperature Inversion Breakup on the Exchange of Heat and Mass in an Idealized Valley: Sensitivity to the Radiative Forcing

2015 ◽  
Vol 54 (11) ◽  
pp. 2199-2216 ◽  
Author(s):  
Daniel Leukauf ◽  
Alexander Gohm ◽  
Mathias W. Rotach ◽  
Johannes S. Wagner
Keyword(s):  
Radiative Forcing ◽  
Sensible Heat Flux ◽  
Temperature Inversion ◽  
Shortwave Radiation ◽  
Weather Research And Forecasting ◽  
Sensible Heat ◽  
Vertical Fluxes ◽  
Nocturnal Inversion ◽  
Surface Sensible Heat Flux ◽  
The Impact

Abstract The breakup of a nocturnal temperature inversion during daytime is studied in an idealized valley by means of high-resolution numerical simulations. Vertical fluxes of heat and mass are strongly reduced as long as an inversion is present; hence it is important to understand the mechanisms leading to its removal. In this study breakup times are determined as a function of the radiative forcing. Further, the effect of the nocturnal inversion on the vertical exchange of heat and mass is quantified. The Weather Research and Forecasting Model is applied to an idealized quasi-two-dimensional valley. The net shortwave radiation is specified by a sine function with amplitudes between 150 and 850 W m−2 during daytime and at zero during the night. The valley inversion is eroded within 5 h for the strongest forcing. A minimal amplitude of 450 W m−2 is required to reach the breakup, in which case the inversion is removed after 11 h. Depending on the forcing amplitude, between 10% and 57% of the energy provided by the surface sensible heat flux is exported out of the valley during the whole day. The ratio of exported energy to provided energy is approximately 1.6 times as large after the inversion is removed as before. More than 5 times the valley air mass is turned over in 12 h for the strongest forcing, whereas the mass is turned over only 1.3 times for 400 W m−2.

scholarly journals Energetics of Deep Alpine Valleys in Pooling and Draining Configurations

2017 ◽  
Vol 74 (7) ◽  
pp. 2105-2124 ◽  
Author(s):  
Gabriele Arduini ◽  
Charles Chemel ◽  
Chantal Staquet
Keyword(s):  
Boundary Layer ◽  
Temperature Difference ◽  
Heat Budget ◽  
Sensible Heat Flux ◽  
Volume Effect ◽  
Weather Research And Forecasting ◽  
Forecasting Model ◽  
Sensible Heat ◽  
Diabatic Processes ◽  
Surface Sensible Heat Flux

Abstract The Weather Research and Forecasting Model is used to investigate the nocturnal atmospheric boundary layer in a valley that opens either on a wider valley (draining configuration) or on a narrower valley (pooling configuration). One draining case and three weak to strong pooling cases are considered. Results show that the structure of the nocturnal boundary layer is substantially different for the draining and pooling configurations. Greater pooling corresponds with a deeper and colder boundary layer. Down-valley winds are weaker for pooling and draining configurations than in an equivalent valley opening directly on a plain. For the strong pooling case, an up-valley flow develops from the narrower to the wider valley during the evening transition, affecting the mass budget of the wider valley during that period. Considering the heat budget of the valley system, the contribution of the diabatic processes, when appropriately weighted, hardly varies along the valley axis. Conversely, the contribution of advection varies along the valley axis: it decreases for a pooling configuration and increases for a draining configuration. Consequently, for a pooling configuration, the heat transfer between the valley and the plain is reduced, thereby increasing the temperature difference between them. For the strong pooling case, this temperature difference can be explained by the valley-volume effect once the down-valley flow has developed. This occurs in a valley when the “extra” heat loss within the valley due to the surface sensible heat flux balances the heat input due to advection.

scholarly journals Toward Generalizing the Impact of Surface Heating, Stratification, and Terrain Geometry on the Daytime Heat Export from an Idealized Valley

2017 ◽  
Vol 56 (10) ◽  
pp. 2711-2727 ◽  
Author(s):  
Daniel Leukauf ◽  
Alexander Gohm ◽  
Mathias W. Rotach
Keyword(s):  
Sensible Heat Flux ◽  
Wrf Model ◽  
Total Export ◽  
Surface Heating ◽  
Sensible Heat ◽  
Initial Stability ◽  
Surface Sensible Heat Flux ◽  
The Impact ◽  
Breakup Parameter ◽  
Crest Height

AbstractThe convective export of heat from different types of idealized valleys for fair-weather daytime conditions is studied with the Weather Research and Forecasting (WRF) Model. The goal is to test the hypothesis that the total export of heat over the course of the day depends on a so-called breakup parameter B. The breakup parameter is the ratio between the energy required to neutralize the initially stably stratified valley atmosphere and the total energy provided by the surface sensible heat flux. To achieve this goal, simulations with different surface heating, initial stability, and terrain geometry are performed. The fraction of the sensible heat provided at the surface that is exported at crest height over the course of the day depends exponentially on B. The effects of variations of the valley width, crest height, forcing amplitude, and initial stratification on the total export of heat can be described by this function. The complete neutralization of the stratification in the valley is never reached if B exceeds a critical value of about 0.65 for an initially constant stratification. For a valley geometry with linear slopes and sharp crests, up to 60% of the provided heat is exported for the strongest forcing and the weakest stability (i.e., B ≈ 0.1), whereas less than 5% is exported for B > 0.65. The minimum heat export for larger B is higher for rounded crests (10%) and for a deep residual layer that extends to above crest height (17%).

scholarly journals The impact of broadleaved woodland on water resources in lowland UK: II. Evaporation estimates from sensible heat flux measurements over beech woodland and grass on chalk sites in Hampshire

2005 ◽  
Vol 9 (6) ◽  
pp. 607-613 ◽  
Author(s):  
J. Roberts ◽  
P. Rosier ◽  
D. M. Smith
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Excellent Agreement ◽  
Sensible Heat Flux ◽  
Late Summer ◽  
Eddy Correlation ◽  
Sensible Heat ◽  
Flux Measurements ◽  
Shallow Soils ◽  
The Impact

Abstract. The impact on recharge to the Chalk aquifer of substitution of broadleaved woodland for pasture is a matter of concern in the UK. Hence, measurements of energy balance components were made above beech woodland and above pasture, both growing on shallow soils over chalk in Hampshire. Latent heat flux (evaporation) was calculated as the residual from these measurements of energy balances in which sensible heat flux was measured with an eddy correlation instrument that determined fast response vertical wind speeds and associated temperature changes. Assessment of wind turbulence statistics confirmed that the eddy correlation device performed satisfactorily in both wet and dry conditions. There was excellent agreement between forest transpiration measurements made by eddy correlation and stand level tree transpiration measured with sap flow devices. Over the period of the measurements, from March 1999 to late summer 2000, changes in soil water content were small and grassland evaporation and transpiration estimated from energy balance-eddy flux measurements were in excellent agreement with Penman estimates of potential evaporation. Over the 18-month measurement period, the cumulative difference between broadleaved woodland and grassland was small but evaporation from the grassland was 3% higher than that from the woodland. In the springs of 1999 and 2000, evaporation from the grassland was greater than that from the woodland. However, following leaf emergence in the woodland, the difference in cumulative evaporation diminished until the following spring.

scholarly journals Atmospheric Dynamics Triggered by an Oceanic SST Front in a Moist Quasigeostrophic Model

2012 ◽  
Vol 69 (5) ◽  
pp. 1617-1632 ◽  
Author(s):  
Bruno Deremble ◽  
Guillaume Lapeyre ◽  
Michael Ghil
Keyword(s):  
Heat Flux ◽  
Heat Release ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Latent Heat Release ◽  
Sst Front ◽  
Moist Processes ◽  
Surface Sensible Heat Flux ◽  
Sst Fronts

Abstract To understand the atmospheric response to a midlatitude oceanic front, this paper uses a quasigeostrophic (QG) model with moist processes. A well-known, three-level QG model on the sphere has been modified to include such processes in an aquaplanet setting. Its response is analyzed in terms of the upper-level atmospheric jet for sea surface temperature (SST) fronts of different profiles and located at different latitudes. When the SST front is sufficiently strong, it tends to anchor the mean atmospheric jet, suggesting that the jet’s spatial location and pattern are mainly affected by the latitude of the SST front. Changes in the jet’s pattern are studied, focusing on surface sensible heat flux and on moisture effects through latent heat release. It is found that latent heat release due to moist processes is modified when the SST front is changed, and this is responsible for the meridional displacement of the jet. Moreover, both latent heat release and surface sensible heat flux contribute to the jet’s strengthening. These results highlight the role of SST fronts and moist processes in affecting the characteristics of the midlatitude jet stream and of its associated storm track, particularly their positions.

scholarly journals Parameterization of Urban Sensible Heat Flux from Remotely Sensed Surface Temperature: Effects of Surface Structure

2019 ◽  
Vol 11 (11) ◽  
pp. 1347 ◽  
Author(s):  
Jinxin Yang ◽  
Massimo Menenti ◽  
E. Scott Krayenhoff ◽  
Zhifeng Wu ◽  
Qian Shi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Sensible Heat Flux ◽  
Effective Resistance ◽  
Three Dimensions ◽  
Sensible Heat ◽  
Wall Surface ◽  
Surface Temperatures ◽  
Flux Parameterization ◽  
The Impact

Sensible heat exchange has important consequences for urban meteorology and related applications. Directional radiometric surface temperatures of urban canopies observed by remote sensing platforms have the potential to inform estimations of urban sensible heat flux. An imaging radiometer viewing the surface from nadir cannot capture the complete urban surface temperature, which is defined as the mean surface temperature over all urban facets in three dimensions, which includes building wall surface temperatures and requires an estimation of urban sensible heat flux. In this study, a numerical microclimate model, Temperatures of Urban Facets in 3-D (TUF-3D), was used to model sensible heat flux as well as radiometric and complete surface temperatures. Model data were applied to parameterize an effective resistance for the calculation of urban sensible heat flux from the radiometric (nadir view) surface temperature. The results showed that sensible heat flux was overestimated during daytime when the radiometric surface temperature was used without the effective resistance that accounts for the impact of wall surface temperature on heat flux. Parameterization of this additional resistance enabled reasonably accurate estimates of urban sensible heat flux from the radiometric surface temperature.

A long-term Climatology of Planetary Boundary Layer Height over the Tibetan Plateau revealed by ERA5

2020 ◽  
Author(s):  
Nils Slättberg ◽  
Deliang Chen
Keyword(s):  
Heat Flux ◽  
Monsoon Season ◽  
Sensible Heat Flux ◽  
Dry Season ◽  
The Tibetan Plateau ◽  
Climate Variables ◽  
Sensible Heat ◽  
Boundary Layer Height ◽  
Surface Sensible Heat Flux

<p>The Planetary Boundary Layer Height (PBLH) is important for the exchange of energy, water, and momentum between the surface and the free atmosphere, making it a significant factor in studies of surface climate and atmospheric circulation. Over the Tibetan Plateau (TP) - a vast elevated heat source exerting significant influence on the Asian monsoon systems - the climate is changing rapidly. Among the many climate variables expected to change as global temperatures rise is the PBLH which, in addition to temperature profile, mechanical turbulence production, vertical velocity, and horizontal advection, is highly dependent on the surface sensible heat  fluxes. Our understanding of PBLH over the TP is very limited, although scattered estimates has indicated that it sometimes reach unusual heights – up to the vicinity of the tropopause. Long-term assessment of PBLH covering the whole TP is hampered by the fact that observations are scarce in time and space. This study takes advantage of a recently available high-resolution reanalysis (ERA5) for 1979-2018 to create a multi-decadal climatology of PBLH over the TP, and assess the seasonality, interannual variation and long-term trend of PBLH in relation to other climate variables such as tropopause height and surface sensible heat flux as well as large-scale atmospheric circulation. </p><p>The results show that the most prominent feature of the PBLH trend is a large region of decline in the central TP during the monsoon season. Notably, this is a region where the temperature increase is smaller than in the rest of the region, and the precipitation shows a statistically significant increasing trend. Increased cloudiness may therefore have decreased the surface heating and thus the sensible heat flux and PBLH. Assessing the spatially averaged trends for the first and second halves of the period separately reveals that the monsoon season PBLH does in fact increase during the first half of the period. In the dry season in contrast, the spatially averaged PBLH decreases by almost 30 meter per decade during the first half of the period and increases slightly in the second. Although none of the spatially averaged PBLH trends are statistically significant at the 95% level, it can be noted that the shift from decreasing to increasing PBLH for the dry season is in accordance with a recent study of spring sensible heat flux over the TP. The aforementioned study found that although the sensible heat flux has been declining because of wind speed decreases, it has recently started to recover in response to an increased difference between the ground surface temperature and the air temperature. Given that the PBLH is highly dependent on the surface sensible heat flux, this decline and recovery may very well have produced the PBLH trends for the dry season. In the monsoon season, with cloudy conditions and less solar radiation reaching the ground, other factors are likely of greater importance for the PBLH.</p>

scholarly journals The Extratropical Tropopause Inversion Layer: Global Observations with GPS Data, and a Radiative Forcing Mechanism

2007 ◽  
Vol 64 (12) ◽  
pp. 4489-4496 ◽  
Author(s):  
William J. Randel ◽  
Fei Wu ◽  
Piers Forster
Keyword(s):  
Water Vapor ◽  
Radiative Forcing ◽  
Inversion Layer ◽  
Temperature Inversion ◽  
Shortwave Radiation ◽  
Gps Data ◽  
Circulation Types ◽  
High Vertical Resolution ◽  
Extratropical Tropopause ◽  
Balanced Dynamics

Abstract Global characteristics of the extratropical tropopause inversion layer identified in radiosonde observations by Birner are studied using high vertical resolution temperature profiles from GPS radio occultation measurements. The GPS data are organized according to the height of the thermal tropopause in each profile, and a temperature inversion layer above the tropopause (with an average magnitude of 3–5 K) is found to be a ubiquitous, climatological feature. The GPS data show that the inversion layer is present for all seasons in both hemispheres, spanning the subtropics to the pole, and there is not strong longitudinal structure. Dependence of the inversion layer on upper-troposphere vorticity is studied; while anticyclones exhibit a substantially stronger inversion than cyclones (as expected from balanced dynamics), the inversion is evident for all circulation types. Radiative transfer calculations indicate that strong gradients in both ozone and water vapor near the tropopause contribute to the inversion. Significant absorption of both longwave and shortwave radiation by ozone occurs, warming the region above the tropopause. Water vapor near and immediately above the tropopause contributes to cooling, effectively enhancing the inversion.

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