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Radiative destabilization of the nocturnal stable atmospheric boundary layer (NSABL) over homogeneous desert terrain is predicted by an analytical model based on a modified diffusion equation. The model applies late at night under calm, dry conditions when long-wave radiative transfer dominates the NSABL evolution. A three-layer structure for the NSABL is proposed: a shear sub-layer closest to the surface, a radiative sub-layer which contains the inversion top, and a coupling sub-layer which matches the NSABL with the residual layer aloft. A sub-sub-layer called the nocturnal internal boundary layer (NIBL) is nested within the radiative sub-layer and comprises the temperature maximum. The model can explain: (1) maximum cooling in the NIBL, (2) deepening of the NIBL, (3) radiative destabilization of the NSABL, and (4) possible surface warming before sunrise. An example from the Mohave Desert, USA is presented, and the observed temperature profile compares favorably with the model solution. 相似文献
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Sea/land breeze climatological characteristics along the northern Croatian Adriatic coast 总被引：1，自引：0，他引：1
Summary Climatological characteristics along the northern Croatian Adriatic coast have been examined for nine meteorological stations
for the summertime sea/land breeze circulation. The stations considered are Pula-airport, Opatija, Rijeka, Senj, Malinska,
Rijeka-airport, Mali Lošinj, Rab and Zadar. The hourly surface measurements at each station from June to September for the
period 1991–2004 as well as the radiosoundings in Zadar (from 2002 to 2004) were used for the analysis. A dataset with the
sea/land breeze days was formed according to the several criteria.
The mean daily maxima of both air and sea surface temperatures were more influenced by the large scale disturbances toward
north (e.g. in Rijeka or Opatija) compared to the values for e.g. Zadar. Furthermore, the influence of the large scale disturbances
diminished toward the south concerning the sea–land temperature difference only at the stations placed at Rijeka Bay and Velebit
channel. The strongest sea breeze was found at Pula-airport and the most frequent ones at Opatija and Zadar. At Senj the rarest,
the weakest and the shortest sea breeze was observed. The climatological records of wind speed and air-sea temperature difference
(ΔT) showed for Opatija, Malinska and Zadar that the maximum measured wind speed is around 4.5 °C confirming the nonlinear relationship
between the sea breeze speeds and the ΔT during the day.
At most stations, the clockwise rotation of the hodographs prevails which is typical for the Northern hemisphere due to Coriolis
force, with the exception at Senj and Malinska. While the hodographs for Pula, Rijeka-airport and Mali Lošinj display a later
onset of the prevailing sea breeze because of the interaction among several sea breeze circulations, the results for Opatija,
Zadar and Senj show considerably distorted hodographs because of the nearby channeling of the air flow. 相似文献
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Ivan Güttler Čedo Branković Travis A. O’Brien Erika Coppola Branko Grisogono Filippo Giorgi 《Climate Dynamics》2014,43(7-8):1753-1772
This study investigates the performance of two planetary boundary layer (PBL) parameterisations in the regional climate model RegCM4.2 with specific focus on the recently implemented prognostic turbulent kinetic energy parameterisation scheme: the University of Washington (UW) scheme. When compared with the default Holtslag scheme, the UW scheme, in the 10-year experiments over the European domain, shows a substantial cooling. It reduces winter warm bias over the north-eastern Europe by 2 °C and reduces summer warm bias over central Europe by 3 °C. A part of the detected cooling is ascribed to a general reduction in lower tropospheric eddy heat diffusivity with the UW scheme. While differences in temperature tendency due to PBL schemes are mostly localized to the lower troposphere, the schemes show a much higher diversity in how vertical turbulent mixing of the water vapour mixing ratio is governed. Differences in the water vapour mixing ratio tendency due to the PBL scheme are present almost throughout the troposphere. However, they alone cannot explain the overall water vapour mixing ratio profiles, suggesting strong interaction between the PBL and other model parameterisations. An additional 18-member ensemble with the UW scheme is made, where two formulations of the master turbulent length scale in unstable conditions are tested and unconstrained parameters associated with (a) the evaporative enhancement of the cloud-top entrainment and (b) the formulation of the master turbulent length scale in stable conditions are systematically perturbed. These experiments suggest that the master turbulent length scale in the UW scheme could be further refined in the current implementation in the RegCM model. It was also found that the UW scheme is less sensitive to the variations of the other two selected unconstrained parameters, supporting the choice of these parameters in the default formulation of the UW scheme. 相似文献
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Thorsten?MauritsenEmail author Gunilla?Svensson Branko?Grisogono 《Boundary-Layer Meteorology》2005,117(2):259-273
We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised
conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons.
The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism
for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature
and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between
the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of
the lead appear far downstream. 相似文献
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The influence of the main large-scale wind directions on thermally driven mesoscale circulations at the Baltic southwest coast, southeast of Sweden, is examined. The aim of the study is to highlight small-scale alterations in the coastal atmospheric boundary layer. A numerical three-dimensional mesoscale model is used in this study, which is focused on an overall behaviour of the coastal jets, drainage flows, sea breezes, and a low-level eddy-type flow in particular. It is shown that synoptic conditions, together with the moderate terrain of the southeast of Sweden (max. height h0 206 m), governs the coastal mesoscale dynamics triggered by the land-sea temperature difference T. The subtle nature of coastal low-level jets and sea breezes is revealed; their patterns are dictated by the interplay between synoptic airflow, coastline orientation, and T.The simulations show that coastal jets typically occur during nighttime and vary in height, intensity and position with respect to the coast; they interact with downslope flows and the background wind. For the assigned land surface temperature (varying ±8 K from the sea temperature) and the opposing constant geostrophic wind 8 m s-1, the drainage flow is more robust to the opposing ambient flow than the sea breeze later on. Depending on the part of the coast under consideration, and the prevailing ambient wind, the sea breeze can be suppressed or enhanced, stationary at the coast or rapidly penetrating inland, locked up in phase with another dynamic system or almost independently self-evolving. A low-level eddy structure is analyzed. It is governed by tilting, divergence and horizontal advection terms. The horizontal extent of the coastal effects agrees roughly with the Rossby radius of deformation. 相似文献
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The Ekman boundary-layer model is extended analytically for a gradually varying eddy diffusivity K(z) ≥ 0, z ≥ 0. A solution for the Ekman layer is provided having similar structure to the constant-K case; that is, exponentially decaying sine functions for the two horizontal wind components. The analytical asymptotic solution compares well with its numerical counterpart for various K(z). The result can be useful in theoretical studies such as Ekman pumping, for efficient estimation of the Ekman layer profiles in various analyses with near-neutral stratifications, or for a rapid initialization of mesoscale models. 相似文献
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The WKB method is used in conjunction with the variation of parameters technique to find an approximate analytical solution for Ekman layers with eddy viscosity and horizontal pressure gradient that are each variable with height from the surface. Behaviour of the solution is illustrated by comparing model output when several eddy viscosity and horizontal pressure gradient profiles are used. Cases where the pressure gradient decreases with height accentuate the super-geostrophic peak in the wind velocity profile, with decreasing eddy viscosity with height further enhancing this effect. Increasing pressure gradient with height reduces or eliminates the peak. The model output when using an eddy viscosity that has a low-level peak fits marine boundary-layer data taken during ASTEX better than the classic solution - the model giving greater low-level mixing which is seen in ASTEX data as well as in data from ERICA. 相似文献
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Golem Petar Toman Ivan Večenaj Željko Kozmar Hrvoje Grisogono Branko 《Boundary-Layer Meteorology》2022,183(3):495-504
Boundary-Layer Meteorology - Unique data from a 100-m meteorological mast located on the windward side of the Dinaric Alps, Croatia, are compared to high-resolution Weather Research and Forecasting... 相似文献
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A Note on the Pure Katabatic Wind Maximum over Gentle Slopes 总被引：2，自引：1，他引：1
The wind maximum of pure katabatic winds over moderate slopes, the inclination varying between 3 and 6°, is studied using large-eddy simulation (LES) and further discussed in the light of the classical Prandtl model. The LES results show that both the maximum katabatic wind speed and its height decrease with increasing slope angle, and vice versa. However, in the Prandtl analytical, i.e. linear classical, solution, only the wind maximum height is affected by the slope angle, not the maximum wind speed. For the given range of slope inclinations, a linear relation between the height and the magnitude of the wind maximum is found in our simulations, which is supported by a limited dataset obtained by other researchers; these results are further discussed. The inability of the analytical Prandtl solution to give the maximum wind-speed dependency on the slope angle is associated with the assumed constancy of (1) the background vertical potential temperature gradient ??, (2) the eddy diffusivity and (3) the Prandtl number. 相似文献