Spatial variations of incoming longwave radiationin Göteborg, Sweden

Summary  A measurement programme was conducted in G?teborg Sweden, to examine the spatial variations of incoming longwave irradiance on calm, cloudless nights. Both regional and local spatial variations were examined. Incoming longwave irradiance data was obtained from mobile car transects, and at a fixed site on a building roof at the city centre. Ancillary data included sky view factor at various transect locations, and balloon soundings of air temperature and humidity on one night. Measurements revealed that on average, incoming longwave irradiance at the fixed urban site was 11 W m ⁻² higher than at the rural station, with varying differences for intervening sites. Bulk apparent sky emissivity was higher at the most rural station compared to the fixed urban site, by about 0.03 on average. Nighttime balloon measurements and a sensitivity analysis with a radiative transfer model argue that the bulk apparent sky emissivity differences stem mainly from the temperature structure of the lower boundary layer which changes markedly from rural to urban areas. A good relationship was found between sky view factor and incoming longwave irradiance for a range of urban and park locations. The relationship applies to both individual nights and average data. Using a simple obstruction model, canyon wall temperatures are derived, and the relationship between sky view factor and wall temperature is examined. Received December 23, 1999 Revised May 5, 2000     

An intra-urban thermal breeze in Göteborg, Sweden

Summary ?The existence and character of an intra-urban thermal breeze (IUTB) in the city centre of G?teborg, Sweden was examined. The study was carried out in a 10 ha open area covered with gravel, asphalt and grass, surrounded by narrow street canyons. Measurements included an array of fixed wind and temperature sensors and smoke in the open area; temperature of the surrounding neighbourhood from mobile thermal mapping and fixed temperature sensors; standard climate measurements from four automatic weather stations in and around G?teborg. The results based on sixteen field surveys performed between December 1998 and March 2000 showed that the open urban area might generate a special type of IUTB under certain conditions. The IUTB was shown to be a rare nocturnal winter phenomenon developing during clear and calm weather conditions, with snow covered ground, strong ground based inversions and high stability (Ri _b  > 1). The most important driving forces for the generation of an IUTB were large intra-urban horizontal air temperature differences and strong atmospheric stability which led to decoupling of the canopy layer atmosphere from wind flow aloft. In order to estimate the physical principles underlying an IUTB of this type a simple 1.5-dimensional model was devised. Results indicated that the horizontal intra-urban air temperature difference recorded in G?teborg was enough to develop an IUTB. Received May 6, 2002; revised November 20, 2002; accepted January 7, 2003 Published online May 20, 2003     

Near surface climate in an urban vegetated park and its surroundings

Summary Near surface climate was observed through temperature profiling from the surface to 2.47 m height in an urban vegetated park and its surroundings in central Stockholm, Sweden. Measurements were conducted during three summer days by mobile traverses. Air temperature differences between the built-up area and the park were in the range of 0.5–0.8 °C during the day and reached a maximum of 2 °C at sunset. The thermal stratification of the air was mainly stable in the park and unstable in the built-up area. Inverse air temperature profiles in the park were less stable in open than in shady areas, and close to neutral at midday. The most unstable air was found in the north–south orientated canyons in the early afternoon. Possible heat advection from the surroundings, and thus uncoupling between the surface and the air, was identified through temperature gradients pointing at different directions within the 2.47 m profile. Examples at midday indicated that warm air advected as far as 150 m into the park.     

Microclimatological characteristics of a miscanthus (Miscanthus cv. giganteus) stand during stable conditionsat night in the nonvegetative winter period

Summary ?Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during the cold and calm nights was relatively constant and about 20 W m⁻² less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed a mean air exchange rate of up to 22 m³ m⁻² h⁻¹, related to a stand volume of 1 m² area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties evidence of katabatic cold air flow is given. Received July 29, 1999; revised June 11, 2001; accepted March 14, 2002     

Vertical Interactions in a Nocturnal Multi-Scale Wind System Influenced by Atmospheric Stability in a Coastal Area

Summary  The winter wind regime of G?teborg, located on the West coast of Sweden, is composed of three different wind systems besides the ambient wind; a nocturnal low level jet (NLLJ), a winter land breeze (WLB) and an urban heat island circulation (UHIC). An inversion divides the air column into two layers, one between 10 – 50 m and one between 50 – 100 m. The UHIC is located in the lower layer, the WLB in the top layer and the NLLJ above the top layer. The intensity of the interacting processes depends on the stability of each layer as calculated from the bulk Richardson number (BRi_low and BRi_high) using continuous data collected during four years (1991 – 94) from two sites (one within and one outside the urban area) and sampled at three levels. In the evening the WLB develops from the ground level and increases in height until after midnight. At about the same time an UHIC develops in the urban area, below the WLB and causing an uplift of the latter. However, at both sites the WLB does not exceed the 100 m level. At this time BRi in both layers are below one resulting in continuous coupling between the WLB, the UHIC layers and the regional wind. Consequently, the exchange of momentum is still effective between all layers and this is highlighted by a change in the wind direction and a regulation of wind-speed to more constant levels. When BRi_high≥1, the layers become frictionally decoupled, as indicated by a return in the wind direction in the top level to the regional wind, and an acceleration of the top wind. The top level then becomes incorporated in to a nocturnal low-level jet (NLLJ) system. The normally acknowledged development of the NLLJ, with a start around sunset, is in this case delayed for several hours at the top level. The reason for this is that there are meso-scale/local wind systems present in layers beneath the jet causing an interaction between the layers. In the morning, when the layers are again coupled the top layer wind is once more influenced by the WLB and therefore changes direction and speed. The local and meso-scale wind systems thus delay the current nocturnal wind development. Received August 24, 1998 Revised March 17, 1999     

Evolution of the atmospheric boundary-layer structure of an arid Andes Valley

Summary The boundary-layer structure of the Elqui Valley is investigated, which is situated in the arid north of Chile and extends from the Pacific Ocean in the west to the Andes in the east. The climate is dominated by the south-eastern Pacific subtropical anticyclone and the cold Humboldt Current. This combination leads to considerable temperature and moisture gradients between the coast and the valley and results in the evolution of sea and valley wind systems. The contribution of these mesoscale wind systems to the heat and moisture budget of the valley atmosphere is estimated, based on radiosoundings performed near the coast and in the valley. Near the coast, a well-mixed cloud-topped boundary layer exists. Both, the temperature and the specific humidity do not change considerably during the day. In the stratus layer the potential temperature increases, while the specific humidity decreases slightly with height. The top of the thin stratus layer, about 300 m in depth, is marked by an inversion. Moderate sea breeze winds of 3–4 m s⁻¹ prevail in the sub-cloud and cloud layer during daytime, but no land breeze develops during the night. The nocturnal valley atmosphere is characterized by a strong and 900 m deep stably stratified boundary layer. During the day, no pronounced well-mixed layer with a capping inversion develops in the valley. Above a super-adiabatic surface layer of about 150 m depth, a stably stratified layer prevails throughout the day. However, heating can be observed within a layer above the surface 800 m deep. Heat and moisture budget estimations show that sensible heat flux convergence exceeds cold air advection in the morning, while both processes compensate each other around noon, such that the temperature evolution stagnates. In the afternoon, cold air advection predominates and leads to net cooling of the boundary layer. Furthermore, the advection of moist air results in the accumulation of moisture during the noon and afternoon period, while latent heat flux convergence is of minor relevance to the moisture budget of the boundary layer. Correspondence: Norbert Kalthoff, Institut für Meteorologie und Klimaforschung, Universit?t Karlsruhe/Forschungszentrum Karlsruhe, Postfach 3640, 76021 Karlsruhe, Germany     

A Study of Orographic Blocking and Barrier Wind Development Upstream of the Southern Alps, New Zealand

Summary Upper level and surface wind data for 1994 are used to provide an initial identification of the orographic effect on regional airflow patterns upwind of the mountain barrier. A case study of the development of upstream blocking and barrier jets is also provided. The predominance of gradient airflow from between northwest and southwest through this region results in frequent trans-mountain winds. The mountains are seen to have a major effect on airflow in the lowest 2000 m above sea level, with clear evidence of orographic blocking and barrier wind development. Some variability in the extent of this blocking was noted during 1994, which appeared to be associated with changes in the synoptic circulation and air mass characteristics. The frequent occurrence of southwesterly winds between 300 m and 2000 m indicates significant deflection of the predominant winds to follow the southwest-northeast orientation of the mountains. These southwesterly barrier winds occur in opposition to the apparent pressure gradient. Northeasterly barrier winds occur mainly below 300 m, and represent a down-gradient, localised flow that is frequently separated from overlying northwesterly gradient winds by a transitional layer, within which the wind backs with height. The controls of the extent of orographic blocking are only assessed superficially, due to the lack of good thermodynamic data upstream of the mountains, although a combination of wind speed and atmospheric stability is obviously important. These initial results provide a useful insight into the extent of orographic effects on regional windfields, which will serve as the basis for future observational and modelling studies. Received June 11, 1998 Revised April 16, 1999     

Available potential energy of the daily coastal circulation at Zadar (Croatia)

Summary The aim of this study is the evaluation of the sea breeze speed on the basis of its energy. Energetics of the sea breeze can be studied by means of the available potential energy (APE). Part of this energy is transformed into the kinetic energy of the sea breeze. Some similarity exists between the large scale processes of the circulation and the small coastal air circulation due to the fact that both circulations are triggered by the same physics, i.e., solenoidal activity of the baroclinic atmosphere. To evaluate the sea breeze speed, APE was calculated by use of the Lorenz’s equation (1955), and which is possible if the coastal circulation is considered to be a closed system in a hydrostatic equilibrium. For calculations and verifications hourly sea-surface temperatures, near-ground air temperatures and wind speed measurements, as well as the radio-sounding measurements at 12 UTC were used at the Zadar station (ϕ = 44° 08′ N, λ = 15° 13′ E), which is situated in the central part of the eastern Adriatic coast. Two days with an undisturbed sea breeze circulation were extracted using the methods for minimizing other atmospheric influences. Calculated hourly near ground sea breeze speeds obtained in this way were higher than the measured ones. With the assumption that some of the APE is transformed into the kinetic energy it is possible to obtain characteristic speed of the developed sea breeze with small discrepancies to the near-ground measurements. If 6.6% of the mean daily near ground APE was taken to be transformed to the mean daily kinetic sea breeze energy on the 29th and 4.2% on the 30th September 2002, the best agreement was obtained with the mean daily measured near ground sea breeze speed. This range of values can be attributed to inability to extract precise values for the lapse-rate needed in the APE sea breeze calculations. Results show similarities to the general circulation of the atmosphere, since about 10% of the APE is transformed to the kinetic energy of the sea breeze. On the other hand calculated wind speed at the lower branch of the borderline coastal circulation was not dependent on the integral value of the APE over the land, but on its value at the near-ground level.     

Observing and modeling the nocturnal park cool island of an arid city: horizontal and vertical impacts

We examined the horizontal and vertical nocturnal cooling influence of a small park with irrigated lawn and xeric surfaces (??3?ha) within a university campus of a hot arid city. Temperature data from 0.01- to 3-m heights observed during a bicycle traverse of the campus were combined with modeled spatial temperature data simulated from a three-dimensional microclimate model (ENVI-met 3.1). A distinct park cool island, with mean observed magnitudes of 0.7?C3.6°C, was documented for both traverse and model data with larger cooling intensities measured closer to surface level. Modeled results possessed varying but generally reasonable accuracy in simulating both spatial and temporal temperature data, although some systematic errors exist. A combination of several factors, such as variations in surface thermal properties, urban geometry, building orientation, and soil moisture, was likely responsible for influencing differential urban and non-urban near-surface temperatures. A strong inversion layer up to 1?m over non-urban surfaces was detected, contrasting with near-neutral lapse rates over urban surfaces. A key factor in the spatial expansion of the park cool island was the advection of cooler park air to adjacent urban surfaces, although this effect was mostly concentrated from 0- to 1-m heights over urban surfaces that were more exposed to the atmosphere.     

Sea/land breeze climatological characteristics along the northern Croatian Adriatic coast

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.     

Numerical Simulation of a Sea Breeze Under Dominant Synoptic Conditions at Perth

Summary  The development and movement of sea breezes under the influence of a thermally induced synoptic coastal trough and coastal terrain are simulated. These simulations are analyzed in the context of an extensive observational data set. The synoptic trough acts to determine the presence and intensity of the sea breeze through the advection of warm air in the surface layer whereas local topography acts to enhance the breeze and turn the low-level flow. Interaction between the sea breeze circulation and the trough assists trough movement across the coastline. Received June 16, 1999/Revised November 3, 1999     

Objective method for classifying air masses: an application to the analysis of Buenos Aires’ (Argentina) urban heat island intensity

Summary ?During recent years, numerous studies have examined the Buenos Aires urban climate, but the relationship between large-scale weather conditions and the Buenos Aires urban heat island (UHI) intensity has not been studied. The goal of this paper is to apply an objective synoptic climatological method to identify homogeneous air masses or weather types affecting Buenos Aires during winter, and to relate the results to the UHI intensity. A K-means clustering method was used to define six different air masses considering the 03:00, 09:00, 15:00 and 21:00 LT surface observations of dry bulb temperature, dew point, cloud cover, atmospheric pressure and wind direction and velocity at Ezeiza, the most rural meteorological station of the Buenos Aires metropolitan area (Fig. 1). Results show that the mean UHI intensity is at its maximum (2.8 °C) a few hours before sunrise when conditions are dominated by cold air masses associated with cold-core anticyclones, weak winds and low cloud cover. Inverse heat islands are found during the afternoon for all air masses indicating that surface processes are not dominant at that time. The relatively infrequent and warmest air mass is the only one that presents a mean negative urban-rural temperature difference (−0.1 °C) during the afternoon with the smallest diurnal cycle of the UHI intensity probably due to the prevailing high humidity and cloudy sky conditions. The paper provides an insight into the Buenos Aires urban–rural temperature difference under a variety of winter weather types and results could be useful to improve local daily temperature forecasts for the metropolitan area of Buenos Aires on the basis of the routine forecasts of weather types. Received October 24, 2001; revised June 12, 2002; accepted October 10, 2002     

The Numerical Simulation on Atmospheric Transport and Dispersion of the Spray Atomized from Flood Discharging by Hydropower Station over Complex Terrain

Summary  A three-dimensional, nonhydrostatic numerical model with high spatial resolution, in which a simple energy closure scheme is employed, has been developed to simulate the spray dispersion over complex terrain. The evaporation, condensation, and dispersion of the spray and moisture are taken into account in model equations. The term of latent heat due to phase transformation is considered in detail to account for its effects on the temperature field and airflow. As an application of the model, the spray concentration and air relative humidity are calculated under neutral condition. The results indicate that under the neutral condition, the spray is transported to about 0.6 km downwind from the source, and its effects on the air humidity reach a further distance of 0.9 km downwind from the source. Attention is given to the dependence of the results upon the various factors influencing the simulation, such as the intensity of the source, the atmospheric stratification, and the dynamic factor of the terrain. Some numerical tests were carried out to provide extra insight to the effects of these factors. It has been demonstrated that the simulation results such as relative humidity and temperature are sensitive to these factors, especially to the thermal stratification. Under unstable conditions, the effects of the spray source increase significantly, and the variation extent of the temperature, relative humidity and flow field is larger than that under neutral condition. The effects of dynamic and thermal factors on the air flow field are discussed through the comparison of the modeling results over complex terrain and flat terrain. Received June 8, 1998 Revised April 17, 1999     

Spatial Heating Monthly Degree-Day Features and ClimatologicPatterns in Turkey

Summary  Degree-days as a measure of accumulated temperature deviations from a base temperature have many practical applications in various human related activities such as home cooling, heating, plant growth in agriculture and power generation in addition to energy requirement. Long temperature records are necessary for their reliable estimations at given stations. In this paper, degree-day measure has been applied to monthly temperature records for systematically changed base temperature values from − 25 °C to + 35 °C with 5 °C increments at 255 meteorology stations in Turkey. The results are represented in the form of spatial degree-day distribution maps, which are then related to various climatic, meteorological and topographic features of Turkey. For instance, free surface water bodies in forms of surrounding seas, lakes and rivers insert retardation in the expansion of heating degree-days over large regions. On the other hand, cold air penetration from polar regions in the northeastern Turkey originating from Siberia appears at moderate base temperature heating degree-days. Received August 20, 1998 Revised June 21, 1999     

Local Winds In A Valley City

Local winds were studied around a valley city, by using a high resolution two-dimensional mesoscale model forced by surface temperatures from a measurement campaign around Lanzhou City, China, during stagnant conditions. In the simulations nighttime winds are purely katabatic downslope winds without urban effects, despite the fact that the city is 6–7°C warmer than its surroundings all night. In contrast, daytime near-surface winds result from upslope flow resisted by an opposing simultaneous urban heat-island circulation (UHIC). Hence winds remain weak and variable around a city in a narrow valley during daytime. These conditions may lead to severe air quality problems day and night.The local circulations are sensitive to the widths of the valley and/or city,and also latitude, as is demonstrated by model experiments. Interestingly, in a flat and calm environment an extratropical daytime UHIC cell may turn into a weak `anti-UHIC' by the morning, due to frictional decoupling after sunset and subsequent inertial oscillation during the night, analogously tothe land breeze and nocturnal low-level jet formation.     

Urban-suburban/rural vapour pressure and relative humidity differences at fixed hours over the area of Belgrade city

Summary  In the study, urban-suburban/rural vapour pressure and relative humidity differences at fixed hours in the Belgrade area were analysed and compared. The data from one urban, two suburban and one rural stations (0700, 1400 and 2100 hours LTC), for the period 1976–1980 were used. It has been found, on the basis of the vapour pressure differences that the atmosphere in urban areas is more humid than that in the suburban and rural areas at 0700 and 2100 hours, in the period from September to February, while from February to September the urban atmosphere is drier. At 1400 hours, urban atmosphere is drier throughout the year. However, relative humidity differences indicate that urban air is less humid than the air in suburban and rural areas throughout the year. Relationships between urban-suburban/rural vapour pressure differences and heat island intensity revealed that the local effects could be significant. Received December 23, 1999 Revised September 27, 2000     

The Characteristics of Cold Air Outbreaks over the Eastern Highlands of Kenya

Summary Climatological statistics of extreme temperature events over Kenya are established from the analysis of daily and monthly maximum temperatures for a representative station (Nairobi Dagoretti Corner) over the period 1956–1997. The months of June to August were shown to be the coldest with a mean monthly maximum temperature of less than 22 °C. Seasonal (June to August) mean maximum temperature was 21.5 °C. Using this seasonal mean temperature for the period 1967–1997 delineated 1968 as the coldest year in this series and 1983 as the warmest year. Spectral analysis of the seasonal data, for both the coldest and the warmest years, revealed that the major periods were the quasi-biweekly (10 days) and the Intraseasonal Oscillations (23 days). Secondary peaks occurred at periods of 4–6 and 2.5–3.5 days. A temperature threshold of 16.7 °C during July was used to define cold air outbreaks over Nairobi. This threshold temperature of 16.7 °C was obtained from the mean July maximum temperature (20.9 °C) minus two standard deviations. Notable trends include a decrease in the frequency of station-days, between 1956 and 1997, with temperatures less than 16.7 °C during July. Surface pressure patterns indicate that the origin of the cold air is near latitude 25° S and to the east of mainland South Africa. The cold air near 25° S is advected northwards ahead of the surface pressure ridge. Received July 19, 1999 Revised January 11, 2000     

Scale Modelling of Nocturnal Cooling in Urban Parks

Scale modelling is used to determine the relative contribution of heat transfer processes to the nocturnal cooling of urban parks and the characteristic temporal and spatial variation of surface temperature. Validation is achieved using a hardware model-to-numerical model-to-field observation chain of comparisons. For the calm case, modelling shows that urban-park differences of sky view factor (_s) and thermal admittance () are the relevant properties governing the park cool island (PCI) effect. Reduction in sky view factor by buildings and trees decreases the drain of longwave radiation from the surface to the sky. Thus park areas near the perimeter where there may be a line of buildings or trees, or even sites within a park containing tree clumps or individual trees, generally cool less than open areas. The edge effect applies within distances of about 2.2 to 3.5 times the height of the border obstruction, i.e., to have any part of the park cooling at the maximum rate a square park must be at least twice these dimensions in width. Although the central areas of parks larger than this will experience greater cooling they will accumulate a larger volume of cold air that may make it possible for them to initiate a thermal circulation and extend the influence of the park into the surrounding city. Given real world values of _s and it seems likely that radiation and conduction play almost equal roles in nocturnal PCI development. Evaporation is not a significant cooling mechanism in the nocturnal calm case but by day it is probably critical in establishing a PCI by sunset. It is likely that conditions that favour PCI by day (tree shade, soil wetness) retard PCI growth at night. The present work, which only deals with PCI growth, cannot predict which type of park will be coolest at night. Complete specification of nocturnal PCI magnitude requires knowledge of the PCI at sunset, and this depends on daytime energetics.     

Synoptic patterns in relation to ozone concentrations in west-central Taiwan

Summary Recent studies have shown that regional orography and synoptic patterns greatly affect ozone concentrations. The orography of certain locations is unfavorable for pollutant dispersion, and specific synoptic patterns in these locations lead to serious air pollution episodes. Frequent ozone episodes (defined as hourly ozone ≥ 120 ppbv) in west-central Taiwan during recent years have generated much concern. High ozone days (defined as hourly ozone ≥ 80 ppbv) are also occurring more frequently. High ozone days occur mainly during autumn, but there has been no clear linear relationship demonstrated between any single meteorological variable and pollutant concentration. In this study, statistical data from 1997–1999 has shown that high ozone levels occur with two types of synoptic patterns. The first type consists of a continental anticyclone emanating from mainland China which is swept towards Taiwan. The second is a tropical low pressure system moving northwards closer to Taiwan. West-central Taiwan is located in the lee of the Central Ranges (altitude of 2500 ∼ 3500 m). These synoptic patterns are unfavorable for pollutant dispersion and cause high ozone days. Received October 14, 2000/Revised January 5, 2001     

2008年秋季从化山谷风观测研究

利用2008年10月15日—11月16日在广州从化获得的基线小球测风资料,分析研究了秋季从化山谷风的特征。研究表明:从化山谷风主要出现在系统风速小于1.5 m/s,谷风出现时间为10:00—18:00,山风强度比谷风强度大;山谷风厚度大致为300 m,回流出现高度在300～700 m;山谷风转换期间,静小风频率较高;系统风与山谷风方向相反时,山谷风高度内多为静小风。冷锋过境时不会出现山谷风。