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1.
H. Linné B. Hennemuth J. Bösenberg K. Ertel 《Theoretical and Applied Climatology》2007,87(1-4):201-211
Summary Water vapour flux profiles in the atmospheric boundary layer have been derived from measurements of water vapour density fluctuations
by a ground-based Differential Absorption Lidar (DIAL) and of vertical wind fluctuations by a ground-based Doppler lidar.
The data were collected during the field experiment LITFASS-2003 in May/June 2003 in the area of Lindenberg, Germany. The
eddy-correlation method was applied, and error estimates of ±50 W/m2 for latent heat flux were found. Since the sampling error dominates the overall measurement accuracy, time intervals between
60 and 120 min were required for a reliable flux calculation, depending on wind speed. Rather large errors may occur with
low wind speed because the diurnal cycle restricts the useful interval length. In the lower height range, these measurements
are compared with DIAL/radar-RASS fluxes. The agreement is good when comparing covariance and error values. The lidar flux
profiles are well complemented by tower measurements at 50 and 90 m above ground and by area-averaged near surface fluxes
from a network of micrometeorological stations. Water vapour flux profiles in the convective boundary layer exhibit different
structures mainly depending on the magnitude of the entrainment flux. In situations with dry air above the boundary layer
a positive entrainment flux is observed which can even exceed the surface flux. Flux profiles which linearly increase from
the surface to the top of the boundary layer are observed as well as profiles which decrease in the lower part and increase
in the upper part of the boundary layer. In situations with humid air above the boundary layer the entrainment flux is about
zero in the upper part of the boundary layer and the profiles in most cases show a linear decrease. 相似文献
2.
Surface energy balance,parameterizations of boundary-layer heights and the application of resistance laws near an Antarctic Ice Shelf front 总被引：2，自引：0，他引：2
A study of the surface energy balance with turbulent fluxes obtained by the Monin-Obukhov similarity theory and a comparison with results for resistance laws are presented for the strong baroclinic conditions in the vicinity of the Filchner/Ronne Ice Shelf front. The data are taken from a field experiment in the Antarctic summer season 1983/84. For the first time in the coastal Antarctic region, this data set comprises synchronous energy balance measurements over the polynya and the ice shelf together with soundings of the boundary layer, yielding vertical profiles of the wind velocity and temperature over the ice shelf, at the ice shelf front and over the polynya.Over the ice shelf, the radiation balance is the largest component of the energy fluxes and is mainly compensated by the subsurface energy flux and the turbulent heat flux in the daily mean. Over the polynya, turbulent fluxes of sensible and latent heat lead to large energy losses of the water surface in the night-time and in situations of very low air temperatures.Different parameterizations for boundary-layer height are compared using tethered sonde and energy balance measurements. With the height of the inversion base over the polynya and the height of the critical bulk Richardson number over the ice shelf, external parameters for the application of resistance laws were determined. The comparison of turbulent surface fluxes obtained by the energy balance measurements and by the resistance laws shows good agreement for the convective conditions over the polynya. For the stably stratified boundary layer over the ice shelf with small amounts of the turbulent heat flux, the deviation is large for the case of a cold air outflow with a superposed inertial oscillation. 相似文献
3.
Large-Eddy Simulations of Surface Heterogeneity Effects on the Convective Boundary Layer During the LITFASS-2003 Experiment 总被引：3，自引：3，他引：0
We investigate the impact of observed surface heterogeneities during the LITFASS-2003 experiment on the convective boundary layer (CBL). Large-eddy simulations (LES), driven by observed near-surface sensible and latent heat fluxes, were performed for the diurnal cycle and compare well with observations. As in former studies of idealized one- and two-dimensional heterogeneities, secondary circulations developed that are superimposed on the turbulent field and that partly take over the vertical transport of heat and moisture. The secondary circulation patterns vary between local and roll-like structures, depending on the background wind conditions. For higher background wind speeds, the flow feels an effective surface heat-flux pattern that derives from the original pattern by streamwise averaging. This effective pattern generates a roll-like secondary circulation with roll axes along the mean boundary-layer wind direction. Mainly the upstream surface conditions control the secondary circulation pattern, where the fetch increases with increasing background wind speed. Unlike the entrainment flux that appears to be slightly decreased compared to the homogeneously-heated CBL, the vertical flux of sensible heat appears not to be modified in the mixed layer, while the vertical flux of latent heat shows different responses to secondary circulations. The study illustrates that sufficient time averaging and ensemble averaging is required to separate the heterogeneity-induced signals from the raw LES turbulence data. This might be an important reason why experiments over heterogeneous terrain in the past did not give any clear evidence of heterogeneity-induced effects. 相似文献
4.
Boundary-layer heat and moisture budgets from fife 总被引：1，自引：0，他引：1
A. K. Betts R. L. Desjardins J. I. Macpherson R. D. Kelly 《Boundary-Layer Meteorology》1990,50(1-4):109-138
Aircraft stacks were flown upwind and downwind of the First ISLSCP Field Experiment (FIFE) site in Kansas to measure the heat and moisture budgets of the boundary layer under fairly clear skies for four daytime periods. In this paper, we evaluate the terms in the conservation equation. The vertical flux divergence and advection do not account for the difference between surface and low-level aircraft flux estimates. Budget estimates of the surface fluxes using the aircraft data agree well with surface flux measurements, but extrapolation of the aircraft fluxes gives surface fluxes that are too low. With the 5 km cutoff filter used, the aircraft underestimate for sensible heat flux is about 40%, and for the latent heat flux about 30%. Part of the underestimation is attributable to long-wavelength contributions (longer than the 5 km filter), but more investigation is needed. 相似文献
5.
We present aircraft measurements of boundary-layer structure and surface turbulent fluxes from a flight over the Larsen Ice Shelf, Antarctica. Warm advection, associated with föhn flow, led to the formation of a stable boundary layer over the ice shelf, with a well-defined low-level jet at the top of the surface inversion. The strong shear associated with the jet kept the gradient Richardson number small and maintained a turbulent boundary layer over a depth of at least 600 m. The net surface energy balance amounted to 52 Wm?2, equivalent to a melt rate of 13 mm water per day, with net radiation (48 Wm?2) making the largest contribution to melt. The contribution from the sensible heat flux (13 Wm?2) was largely balanced by an upwards latent heat flux (?9 Wm?2). These measurements provide insight into the processes that control surface melt rates in an area that has experienced recent rapid warming and deglaciation. 相似文献
6.
Steven K. Chai 《Atmospheric Research》1986,20(1)
This paper discusses the vapor-driven convection over snow and its limitations. It is shown on the basis of the moist convective plume model that vapor flux from the evaporating snow surface can drive convection, and maintain a super-cooled water cloud layer, without the assistance of heat flux from the surface, or entrainment or radiative cooling, at cloud top.Since the saturation vapor pressure over water is higher than that over ice, the base of the super-cooled water cloud has a lower limiting height. When the cloud base is lowered to this height, the air at the bottom of the convective layer is just saturated with respect to ice and the evaporation of snow stops, as does the vapor-driven convection. This limiting cloud base height varies with snow-surface temperature. The lower the snow temperature, the higher the cloud base height limit for continued convective transfer from the surface. 相似文献
7.
Burghard Brümmer 《Boundary-Layer Meteorology》1996,80(1-2):109-125
During the field experiment ARKTIS 1993 ten cases of boundary-layer modification in wintertime cold-air outbreaks from the Arctic sea ice in the Spitsbergen region were observed by aircraft over a distance ranging from about 50 km over the ice to about 300 km over the water. The modification depends decisively on the initial conditions over the ice, the boundary conditions at the bottom and top of the boundary layer and on the conditions of the large-scale flow. The modification of the bulk boundary-layer characteristics in relation to these conditions is presented.Besides the air-sea temperature contrast, the most important role for the boundary-layer modification is played by the stability on top of the boundary layer and by the divergence of the large-scale flow. According to the high variability of these conditions the observed boundary-layer modifications were very variable ranging from 100 to 300 m thick boundary layers with air temperatures between -32 and -22 °C over the ice to thicknesses between 900 and 2200 m and air temperatures between -15 and -5 °C after 300 km fetch over the open water. In most cases the large-scale flow was anticyclonic and divergent over the ice and changed to cyclonic and convergent over the water and an ice-sea breeze was superimposed on it.The sensible and latent heat fluxes are the dominant terms in the surface energy budget over the open water and ranged between 200 and 700 W m-2 whereas the net longwave radiation is the dominating term over the ice with the heat fluxes only about 10 W m-2. 相似文献
8.
Prof. Dr. R. G. Fleagle Dr. N. A. Bond Dr. W. A. Nuss 《Meteorology and Atmospheric Physics》1988,38(1-2):50-63
Summary Surface fluxes of heat, latent heat, and momentum, and entrainment fluxes and vertical motion at the top of the boundary layer have been calculated for limited regions of several mid-latitude ocean storms. Results have been combined to describe distributions of boundary layer processes which are characteristic of such storms. Surface heat fluxes have important effects in the region west of cold or occluded fronts and are relatively unimportant within a band of about 200 km width east of fronts. Entrainment in pre-frontal regions is driven largely by vertical shear at the top of the boundary layer, while in post-frontal regions it is driven largely by surface heat flux. Boundary layers are well defined in regions more than roughly 200 km east or west of fronts; but closer to fronts boundary layers are not well defined due to the combined effects of entrainment, condensation, and vertical motion associated with the distribution of surface stress.With 12 Figures 相似文献
9.
Jens Bange Peter Zittel Thomas Spieß Jörg Uhlenbrock Frank Beyrich 《Boundary-Layer Meteorology》2006,119(3):527-561
The low-level flight method (LLF) has been combined with linear inverse models (IM) resulting in an LLF+IM method for the determination of area-averaged turbulent surface fluxes. With this combination, the vertical divergences of the turbulent latent and sensible heat fluxes were calculated from horizontal flights. The statistical errors of the derived turbulent surface fluxes were significantly reduced. The LLF+IM method was tested both in numerical and field experiments. Large-eddy simulations (LES) were performed to compare ‘true’ flux profiles with ‘measurements’ of simulated flights in an idealised convective boundary layer. Small differences between the ‘true’ and the ‘measured’ fluxes were found, but the vertical flux divergences were correctly calculated by the LLF+IM method. The LLF+IM method was then applied to data collected during two flights with the Helipod, a turbulence probe carried by a helicopter, and with the research aircraft Do 128 in the LITFASS-98 field campaign. The derived surface fluxes were compared with results from eddy-covariance surface stations and with large-aperture scintillometer data. The comparison showed that the LLF+IM method worked well for the sensible heat flux at 77 and 200 m flight levels, and also for the latent heat flux at the lowest level. The model quality control indicated failures for the latent heat flux at the 200 m level (and higher), which were probably due to large moisture fluctuations that could not be modelled using linear assumptions. Finally the LLF+IM method was applied to more than twenty low-level flights from the LITFASS-2003 experiment. Comparison with aggregated surface flux data revealed good agreement for the sensible heat flux but larger discrepancies and a higher statistical uncertainty for the latent heat flux 相似文献
10.
Buoyancy fluxes in the marine atmospheric boundary layer (MABL) for the cloud street regime, observed during the Genesis of Atlantic Lows Experiment (GALE), have been analyzed using the technique of joint frequency distribution. For the lower half of the MABL, the results suggest that the buoyancy flux is mainly generated by the rising thermals and the sinking compensating ambient air, and is mainly consumed by the entrainment and detrainment of thermals, penetrative convection, and the entrainment from the MABL top.The results are compared to those from previous studies of mesoscale cellular convection (Air-Mass Transformation Experiment, AMTEX), the dry convective boundary layer, and the trade-wind MABL. For the lower MABL, the quadrant buoyancy fluxes, fractional coverages, and flux intensities are in good agreement with those of mesoscale cellular convection (AMTEX) and the dry convective boundary layer. The results suggest that, if the buoyancy flux is primarily driven by the temperature flux, the physical processes for generating buoyancy flux mentioned above are about the same for the lower boundary layers over land and ocean, even with different convective regimes. For the trade-wind MABL, the buoyancy flux is mainly driven by the moisture flux; the quadrant flux intensities are stronger than those of the other three studies except for the buoyant updrafts (thermals). These results suggest that the entrainment and detrainment of thermals are more effective in the trade-wind MABL than in the boundary layers driven by the temperature flux.Scale analysis of the buoyancy flux is in good agreement with that of AMTEX. For the lower half of the MABL, the buoyancy flux is mainly generated by the intermediate scale (200 m to 2 km), which includes the dominant convective thermals in the surface layer and the mixed layer. The scale smaller than 200 m is important only in the surface layer. The scale larger than 2 km, which includes the roll vortices, increases its significance upward. While most of the positive and negative fluxes are associated with the updrafts for the intermediate scale, the downdrafts are as important as updrafts for the larger scale.ST Systems Corporation, Lanham, MD, 20706, U.S.A. 相似文献
11.
The boundary layer in the warm sector of a moderately deepening winter cyclone during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) is studied near the cold front. Data from the National Center for Atmospheric Research Electra research aircraft are used to examine mean and turbulence quantities. The aircraft data and supplemental data from ships, drifting buoys and moored buoys reveal an equivalent-barotropic pressure field. The area is found to be dominated by gradients in temperature and in turbulent fluxes, with changes occurring over 100 km horizontally being comparable to changes over 350 m vertically. The horizontal components of the gradients are found to be a maximum in a direction perpendicular to the front. Cross-sections perpendicular to the front are used to illustrate boundary-layer structure. Profiles of wind speed, stress, wind direction and stress direction are estimated from an Ekman model that is modified to take into account the equivalent-barotropic pressure field. Comparison of profiles from the model to the aircraft-measured data show reasonable agreement far from the front (100 km) when the model uses a constant eddy viscosity of approximately 6 kg m–1 s–1. Near the front there is less agreement with the model. Profiles of turbulent fluxes of momentum, heat and latent heat are divergent, with along-wind momentum flux negative and decreasing upward, cross-wind momentum flux positive and increasing upward, and heat flux and latent heat flux small, positive and decreasing upward. Far from the front, the turbulent kinetic energy budget shows that dissipation balances shear production. However, near-front behavior has an imbalance at low altitude, with shear production appearing as a TKE sink. 相似文献
12.
Summary An aircraft-based experimental investigation of the atmospheric boundary layer (ABL) structure and of the energy exchange
processes over heterogeneous land surfaces is presented. The measurements are used for the validation of the mesoscale atmospheric
model “Lokal-Modell” (LM) of the German Weather Service with 2.8 km resolution. In addition, high-resolution simulations using
the non-hydrostatic model FOOT3DK with 250 m resolution are performed in order to resolve detailed surface heterogeneities.
Two special observation periods in May 1999 show comparable convective boundary layer (CBL) conditions. For one case study
vertical profiles and area averages of meteorological quantities and energy fluxes are investigated in detail. The measured
net radiation is highly dependent on surface albedo, and the latent heat flux exhibits a strong temporal variability in the
investigation area. A reduction of this variability is possible by aggregation of multiple flight patterns. To calculate surface
fluxes from aircraft measurements at low altitude, turbulent energy fluxes were extrapolated to the ground by the budget method,
which turned out to be well applicable for the sensible heat flux, but not for the latent flux. The development of the ABL
is well captured by the LM simulation. The comparison of spatiotemporal averages shows an underestimation of the observed
net radiation, which is mainly caused by thin low-level clouds in the LM compared to observed scattered CBL clouds. The sensible
heat flux is reproduced very well, while the latent flux is highly overestimated especially above forests. The realistic representation
of surface heterogeneities in the investigation area in the FOOT3DK simulations leads to improvements for the energy fluxes,
but an overestimation of the latent heat flux still persists. A study of upscaling effects yields more structures than the
LM fields when averaged to the same scale, which are partly caused by the non-linear effects of parameter aggregation on the
LM scale. 相似文献
13.
A moderate cold air outbreak from the Arctic ice over the warm West-Spitsbergen current on 15 and 16 May 1988 during the field experiment ARKTIS '88 is analysed using data from four aircraft and one research vessel.The downstream development of cloud coverage appears to depend sensitively on the moisture content above the inversion. The cloud amount determines the energy balance at the sea surface. Under daytime conditions and little cloud cover, energy is added to the ocean in spite of sensible and latent heat losses.The downstream temperature increase in the boundary layer is controlled by sensible heat flux and by longwave radiation cooling. The entrainment sensible heat flux is the dominating term in the region near the ice edge. The downstream moisture increase is controlled by surface evaporation. Condensation processes play no significant role.On 16 May 1988 cloud streets near the ice edge changed to closed cloud meanders in the downstream direction. The aspect ratio increased from 3 to around 10 over a distance of 200 km. In the cloud street region, the dynamical generation of turbulent kinetic energy due to wind shear at the tilted inversion was larger than the thermal generation.Cloud droplet concentration, mean droplet radius and liquid water content increased linearly with height. The maximum liquid water content was only 0.1 g/kg near the top of a 400 m thick closed cloud and clearly below the adiabatic value. The net longwave radiation flux decreased by 50 W/m2 at cloud top and increased by 13 W/m2 at cloud base. 相似文献
14.
Interaction between soil hydrology and boundary-layer development 总被引：14，自引：1，他引：14
A two-layer model of soil hydrology and thermodynamics is combined with a one-dimensional model of the planetary boundary layer to study various interactions between evolution of the boundary layer and soil moisture transport. Boundary-layer moistening through surface evaporation reduces the potential and actual surface evaporation as well as the boundary-layer growth. With more advanced stages of soil drying, the restricted surface evaporation allows greater sensible heat flux which enhances boundary-layer growth and entrainment drying.Special individual cases are studied where the wind speed is strong, solar radiation is reduced, transpiration is important, the soil is thin, or the soil is covered with organic debris. 相似文献
15.
The Moist Boundary Layer under a Mid-latitude Weather System 总被引：1，自引：1，他引：0
I. A. Boutle R. J. Beare S. E. Belcher A. R. Brown R. S. Plant 《Boundary-Layer Meteorology》2010,134(3):367-386
Mid-latitude weather systems are key contributors to the transport of atmospheric water vapour, but less is known about the
role of the boundary layer in this transport. We expand a conceptual model of dry boundary-layer structure under synoptic
systems to include moist processes, using idealised simulations of cyclone waves to investigate the three-way interaction
between the boundary layer, atmospheric moisture and large-scale dynamics. Forced by large-scale thermal advection, boundary-layer
structures develop over large areas, analogous to the daytime convective boundary layer, the nocturnal stable boundary layer
and transitional regimes between these extremes. A budgeting technique demonstrates the key role of boundary-layer processes
in the transport of moisture. Moisture is evaporated from the ocean behind the cold front and in the high-pressure part of
the wave, and transported large distances within the boundary layer into the footprint of the warm-conveyor belt. The warm-conveyor
belt forms one of the two main processes of boundary-layer ventilation, with shallow cumulus convection being of similar importance. 相似文献
16.
南海季风建立前后珠江三角洲的陆气热量交换与热力边界层结构特征 总被引：4，自引：0，他引：4
根据动力与热力指标,2004和2005年南海季风建立前后可分成明显的4个阶段——季风建立前的雨期、非雨期;季风建立后的活跃期与非活跃期。对2004和2005年南海季风建立前后的广州番禺综合外场观测资料进行分析,得到了这4个阶段陆气热量交换与热力边界层的主要特征:净辐射与净短波辐射的变化趋势基本一致,净短波辐射与净长波辐射之比为3.49—4.81,净短波辐射是净辐射的主要贡献项,云量与降水是控制净短波辐射与净辐射的直接因素;季风活跃期间午间对流云系对太阳辐射衰减显著,造成了辐射各分量以及热通量的峰值区变窄,量值急剧变小;季风建立前后感热与潜热均是净辐射的主要消耗项,占净辐射的90%以上,潜热明显大于感热,2005年较2004年潜热的分配额有明显的增加,其原因可能与近地层的风速较大,总是维持向上的湿度梯度有关;季风建立前后除季风活跃期外边界层位温结构均具有明显的日变化特征,午间混合层可发展至1070m,而季风活跃期间午间混合层发展受到对流云释放潜热的抑制,导致季风活跃期混合层消失的现象,分析还发现季风建立前后各阶段夜间残余混合层均不明显。分析表明引起陆气能量过程及边界层热力结构差异的关键因素之一是云系与降水,加强边界层过程与降水宏微观过程相互作用的研究是深入认识陆气过程与边界层结构特征的关键。 相似文献
17.
为了研究湍涡对中尺度绿洲灌溉的响应,利用WRF模式大涡模拟模块（WRF-LES）在西北半干旱区绿洲区开展灌溉前和灌溉后两个大涡模拟试验（分别简称为BI和AI）,其中灌溉可能会改变绿洲非均匀强度。利用面积平均的办法计算湍流热通量并利用小波分析将湍流热通量模态分解到不同的尺度。结果表明灌溉增加了土壤湿度,引起绿洲内部非均匀强度增加,灌溉对垂直热通量以及通量频散都有较大影响。AI中的湍涡为网状,与BI中一致。AI与BI中的感热通量的频散高度都随着感热通量的减小而减小。AI与BI中感热通量小波能量谱尺度一致,但是BI中强度比AI小。潜热通量的频散高度依赖于感热通量,且潜热通量能量谱随高度减小。空间滞后相关系数的结果表明由于灌溉前地表加热较强,感热通量对地表热通量的响应高度在灌溉之前（BI）比灌溉后（AI）更高。灌溉后的通量模态的飘移距离小于灌溉前的。 相似文献
18.
Boundary-layer measurements made from the Swedish icebreaker Oden during the Arctic Ocean Experiment 2001 (AOE-2001) are analysed. They refer mainly to ice drift in the central Arctic during
the period 2–21 August 2001. On board Oden a remote sensing array with a wind profiler, cloud radar and a scanning microwave radiometer, and a regular weather station
operated continuously; soundings were also released during research stations. Turbulence and profile measurements on an 18-m
mast were deployed on the ice, along with two sodar systems, a microbarograph array and a tethered sounding system. Surface
flux and meteorological stations were also deployed on nearby ice floes. There is a clear diurnal cycle in radiation and also
in wind speed, cloud base and visibility. It is absent in temperature and humidity, probably due to the very strong control
by melting/ freezing ice and snow. In the advection of warm air, latent heat of melting maintains the surface temperature
at 0 °C, while with a negative energy balance the latent heat of freezing of the salty ocean water acts to maintain the surface
temperature > −2 °C. The constant presence of water at the surface maintains a relative humidity close to 100%, and this is
also often facilitated by an increasing specific humidity through the capping inversion, making entrainment a moisture source.
This ensures cloudy conditions, with low cloud and fog prevailing most of the time. Intrusions of warm and moist air from
beyond the ice edge are frequent, but the local Arctic boundary layer remains at a relatively constant temperature, and is
shallow and well mixed with strong capping inversions. Power spectra of surface-layer wind speed sometimes show large variance
at low frequency. A scanning radiometer provides a monitoring of the vertical thermal structure with a spatial and temporal
resolution not seen before in the Arctic. There are often two inversions, an elevated main inversion and a weak surface inversion,
and occasionally additional inversions occur. Enhanced entrainment across the main inversion appears to occur during frontal
passages. Variance of the scanning radiometer temperatures occurs in large pulses rather than varying smoothly, and the height
to the maximum variance appears to be a reasonable proxy for the boundary-layer depth. 相似文献
19.
Regional turbulent statistics over contrasting natural surfaces 总被引：1，自引：0，他引：1
T. J. Lyons Li Fuqin J. M. Hacker Wan-Li Cheng Huang Xinmei 《Meteorology and Atmospheric Physics》2001,78(3-4):183-194
Summary
Regional turbulent fluxes of momentum, sensible and latent heat collected over both agricultural and native vegetation in
the south west of Australia are presented. Analysis of the energy spectrum illustrates that the most energetic eddies are
between scales of 20 metres to 5 kilometres and highlights the spatial distance required to obtain representative regional
fluxes. For the sensible heat flux, this distance is a function of measurement height whereas the latent flux is also influenced
by surface variability. Statistics of these fluxes highlight that for the unstable surface layer, despite marked differences
in the underlying vegetation and the corresponding sources of heat and moisture, heat is transported more efficiently than
water vapour from the ground surface.
Received October 9, 2000/Revised April 23, 2001 相似文献
20.
Chris K. Wendt Jason Beringer Nigel J. Tapper Lindsay B. Hutley 《Boundary-Layer Meteorology》2007,124(2):291-304
Fire scars have the ability to radically alter the surface energy budget within a tropical savanna by reducing surface albedo,
increasing available energy for partitioning into sensible and latent heat fluxes and increasing substrate heat flux. These
changes have the potential to alter boundary-layer conditions and ultimately feedback to local and regional climate. We measured
radiative and energy fluxes over burnt and unburnt tropical savanna near Howard Springs, Darwin, Australia. At the burnt site
a low to moderate intensity fire, ranging between 1,000 and 3,500 kW m−1, initially affected the land surface by removing all understorey vegetation, charring and blackening the ground surface,
scorching the overstorey canopy and reducing the albedo. A reduction in latent heat fluxes to almost zero was seen immediately
after the fire when the canopy was scorched. This was then followed by an increase in the sensible heat flux and a large increase
in the ground heat flux over the burnt surface. Tethered balloon measurements showed that, despite the presence of pre-monsoonal
rain events occurring during the measurement period, the lower boundary layer over the burnt site was up to 2°C warmer than that over the unburnt site. This increase in boundary-layer heating when applied to fire scars at the landscape
scale can have the ability to form or alter local mesoscale circulations and ultimately create a feedback to regional heating
and precipitation patterns that may affect larger-scale processes such as the Australian monsoon. 相似文献