Prediction of Snow Avalanches by Using Surface Layer Heat Fluxes

2012 ◽  
Vol 2 (6) ◽  
pp. 156-162
Author(s):  
Kireet Semwal
Keyword(s):  
Surface Layer ◽  
Heat Fluxes ◽  
Snow Avalanches

scholarly journals Evaluating the performance of two surface layer schemes for the momentum and heat exchange processes during severe haze pollution in Jing-Jin-Ji in eastern China

2018 ◽  
Vol 18 (23) ◽  
pp. 17421-17435 ◽  
Author(s):  
Yue Peng ◽  
Hong Wang ◽  
Yubin Li ◽  
Changwei Liu ◽  
Tianliang Zhao ◽  
...  
Keyword(s):  
Surface Layer ◽  
Roughness Length ◽  
Turbulent Flux ◽  
Eastern China ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Chemical Models ◽  
Atmospheric Stratification ◽  
Haze Pollution ◽  
Thermal Roughness Length

Abstract. The turbulent flux parameterization schemes in the surface layer are crucial for air pollution modeling. There have been some deficiencies in the prediction of air pollutants by atmosphere chemical models, which is closely related to the uncertainties of the momentum and sensible heat fluxes calculated in the surface layer. The differences between two surface layer schemes (Li and MM5 schemes) were discussed, and the performances of two schemes were mainly evaluated based on the observed momentum and sensible heat fluxes during a heavy haze episode in Jing-Jin-Ji in eastern China. The results showed that the aerodynamic roughness length z0m and the thermal roughness length z0h played major roles in the flux calculation. Compared with the Li scheme, ignoring the difference between z0m and z0h in the MM5 scheme induced a great error in the calculation of the sensible heat flux (e.g., the error was 54 % at Gucheng station). Besides the roughness length, the algorithm for the surface turbulent flux as well as the roughness sublayer also resulted in certain errors in the MM5 scheme. In addition, magnitudes of z0m and z0h have significant influence on the two schemes. The large z0m and z0m∕z0h in megacities with a rough surface (e.g., Beijing) resulted in much larger differences of momentum and sensible heat fluxes between Li and MM5, compared with the small z0m and z0m∕z0h in suburban areas with a smooth surface (e.g., Gucheng). The Li scheme could better characterize the evolution of atmospheric stratification than the MM5 scheme in general, especially for the transition stage from unstable to stable atmospheric stratification, corresponding to the PM2.5 accumulation. The biases of momentum and sensible heat fluxes from Li were lower, about 38 % and 43 %, respectively, than those from MM5 during this stage. This study indicates the superiority of the Li scheme in describing regional atmospheric stratification and an improved possibility of severe haze prediction in Jing-Jin-Ji in eastern China by coupling it into atmosphere chemical models.

Thermohaline structure and variability in the Terra Nova Bay polynya, Ross Sea

2000 ◽  
Vol 12 (4) ◽  
pp. 493-508 ◽  
Author(s):  
G. Budillon ◽  
G. Spezie
Keyword(s):  
Surface Layer ◽  
Cold Water ◽  
Ross Sea ◽  
Heat Budget ◽  
Salt Content ◽  
Heat Fluxes ◽  
Local Source ◽  
Near Surface ◽  
Terra Nova Bay ◽  
Terra Nova

Hydrological measurements from three cruises during the summers 1994/95, 1995/96 and 1997/98 in the western sector of the Ross Sea allow summer and year to year changes in heat and salt content in the Terra Nova Bay polynya to be analysed. Changes in the surface layer (upper pycnocline) followed the expected seasonal pattern of warming and freshening from the beginning to the end of the summer. These near-surface changes, expressed as net heating and salting rate, were about 11 W m−2 and -6 mg salt m−2 s−1. The heating changes were substantially lower than the estimated heat supplied by the atmosphere during the summer, which underlines the importance for this season of the advective component carried by the currents in the total heat budget. The year to year differences were about one or two orders of magnitude smaller than the seasonal changes in the surface layer. In the intermediate and deep layers, the summer heat and salt variability were of the same order as or one order higher than from one summer to the next. The differences in sign and magnitude for the heat change in the upper and in the lower pycnocline indicate a weak connection in the summer period between the surface heat fluxes and the deep waters. A local source of very cold water (with temperatures below the surface freezing point) of about 0.3 Sv has been detected close to the Terra Nova Bay coast. It arose out of the interaction of the shallow–intermediate layers of High Salinity Shelf Water with the coastal glaciers. The presence and the variability of this cold water point to the significant role of the thermohaline properties of Terra Nova Bay waters in controlling the floating glacier by governing the basal melting processes.

scholarly journals A theory for surface-layer scaling of thermally-driven slope flows

2021 ◽  
Author(s):  
Dino Zardi
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Sensible Heat Flux ◽  
Viscous Sublayer ◽  
Transport Processes ◽  
Heat Fluxes ◽  
Night Time ◽  
Slope Winds ◽  
Thermally Driven ◽  
Momentum And Heat Fluxes

<p>Sloping terrains of any inclination favour the development, under the daily cycle of day time surface heating and night time cooling, of thermally-driven organised flows, displaying peculiar boundary layer structures, and eventually triggering the development of atmospheric convection.</p><p>The ubiquitous occurrence over the Earth of variously tilted surfaces - from gently sloping plains to steep cliffs, or valley and basin sidewalls – makes the understanding of such flows of utmost importance in view of the appropriate forecasting of the associated boundary layer transport processes. Also, they display a highly conceptual relevance, as they represent a prototypal situations for many other thermally driven-flows over complex terrain.   </p><p>An appropriate surface-layer scaling for slope wind is derived extending the classical analysis for flat horizontal terrain situations to the cover inclines. In the former, momentum and heat fluxes at the surface are two independent quantities, and vertical profiles of velocity and temperature can only be connected to them by means  of similiarity relationships, as fluxes are nearly invariant with height.</p><p>Instead, equations governing slope winds show that the mean wind and temperature profiles are closely connected to the flux structure normal to the slope, as this is not constant. Also, surface values of momentum flux and sensible heat flux are shown to be proportional to each other.</p><p>Based on the above relationships, suitable expressions are derived for the slope-normal profiles of velocity and temperature, both in the viscous sublayer and in the fully turbulent surface layer, as well as for the appropriate scaling factors in the two regions.</p>

scholarly journals Sensible Heat Fluxes in the Nearly Neutral Boundary Layer: The Impact of Frictional Heating within the Surface Layer

2019 ◽  
Vol 76 (4) ◽  
pp. 1039-1053
Author(s):  
J. M. Edwards
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Frictional Heating ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Simple Modification ◽  
Neutral Boundary Layer ◽  
The Impact

Abstract The effect of frictional dissipative heating on the calculation of surface fluxes in the atmospheric boundary layer using bulk flux formulas is considered. Although the importance of frictional dissipation in intense storms has been widely recognized, it is suggested here that its impact is also to be seen at more moderate wind speeds in apparently enhanced heat transfer coefficients and countergradient fluxes in nearly neutral conditions. A simple modification to the bulk flux formula can be made to account for its impact within the surface layer. This modification is consistent with an interpretation of the surface layer as one across which the flux of total energy is constant. The effect of this modification on tropical cyclones is assessed in an idealized model, where it is shown to reduce the predicted maximum wind speed by about 4%. In numerical simulations of three individual storms, the impacts are more subtle but indicate a reduction of the sensible heat flux into the storm and a cooling of the surface layer.

scholarly journals An Extremum Solution of the Monin–Obukhov Similarity Equations

2010 ◽  
Vol 67 (2) ◽  
pp. 485-499 ◽  
Author(s):  
Jingfeng Wang ◽  
Rafael L. Bras
Keyword(s):  
Surface Layer ◽  
Atmospheric Surface Layer ◽  
Turbulent Transport ◽  
Asymptotic Properties ◽  
Field Measurements ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Obukhov Length ◽  
Surface Heat Fluxes ◽  
Momentum And Heat Fluxes

Abstract An extremum hypothesis of turbulent transport in the atmospheric surface layer is postulated. The hypothesis has led to a unique solution of Monin–Obukhov similarity equations in terms of simple expressions linking shear stress (momentum flux) and heat flux to mean wind shear and temperature gradient. The extremum solution is consistent with the well-known asymptotic properties of the surface layer. Validation of the extremum solution has been made by comparison to field measurements of momentum and heat fluxes. Furthermore, a modeling test of predicting surface heat fluxes using the results of this work is presented. A critical reexamination of the interpretation of the Obukhov length is given.

scholarly journals Estimation of Momentum and Heat Fluxes Using Dissipation and Flux-Variance Methods in the Unstable Surface Layer

1996 ◽  
Vol 32 (8) ◽  
pp. 2453-2462 ◽  
Author(s):  
Cheng-I Hsieh ◽  
Gabriel G. Katul ◽  
John Schieldge ◽  
John Sigmon ◽  
Kenneth R. Knoerr
Keyword(s):  
Surface Layer ◽  
Heat Fluxes ◽  
Unstable Surface ◽  
Momentum And Heat Fluxes
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