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1.
We have studied the vertical structure of the planetary boundary layer (PBL) as well as the vertical exchanges between this layer and the free atmosphere, using average macroscopic temperature data obtained from radiosondes. For this study we have used, for seven months in 1972, twice-daily radiosondes (00 and 12 H) from Trappes (Paris area) and PointK (Atlantic Ocean). The vertical structure of the PBL is given in the first part of the present work in terms of monthly average statistical parameters (vertical temperature gradient, frequency and level of inversion layers, frequency and thickness of mixing layers). We have thus demonstrated for the continental station, the influence of the daily cycle on the vertical temperature gradient; we have determined the monthlyH M level above which the daily variation is not noticed. However, for the oceanic station, the absence of a daily cycle makes the temperature gradients at 00 and 12 H identical. The study of temperature inversion layers clearly indicates a high probability of their existence between 1500 and 2000 m; this probability is more than 80% both in summer at PointK, and in winter at Trappes. Similarly, we have demonstrated the annual evolution of the level of these elevated inversions at the two stations. An identical process has been performed in the case of the mixing layers. In the second part of our study, we have used a relationship between the vertical temperature gradient and the coefficients of matter exchange (K z ), obtained from natural radioactive tracers (Guedaliaet al., 1974). Statistics have thus been obtained on the values ofK z in the various layers above the two stations. These statistics prove that for the two stations and above 1500 m, values of the coefficients between 1 and 5 m2 s?1 are the most frequent; on the other hand, below 1500 m, the distribution of the coefficientsK z offers different characteristics according to the month and to the station considered. Finally, we have used the concept of ‘equivalent coefficient’ -K e - to characterize the exchanges between two levels considered as a whole. We have made a comparison of the values ofK e when in the 0–1000 m layer and when in the 0–2000 m layer. The equivalent coefficientK e allows us to compare the average exchanges above the two areas; thus, in summer, between the 0 and 1000 m level, the exchanges are more important above Trappes than they are above Point K. On the other hand, whatever may be the vertical structure of the PBL below, the value ofK e in the 0–2000 m-layer is always between 1 and 5 m2 s?1. A generalisation of such a study applied to better chosen continental and oceanic sites would allow a comprehensive view of the structure of the PBL as well as of the turbulent exchanges between the PBL and the free atmosphere.  相似文献   

2.
The seasonal cycle of water masses and sea ice in the Hudson Bay marine system is examined using a three-dimensional coastal ice-ocean model, with 10 km horizontal resolution and realistic tidal, atmospheric, hydrologic and oceanic forcing. The model includes a level 2.5 turbulent kinetic energy equation, multi-category elastic-viscous-plastic sea-ice rheology, and two layer sea ice with a single snow layer. Results from a two-year long model simulation between August 1996 and July 1998 are analyzed and compared with various observations. The results demonstrate a consistent seasonal cycle in atmosphere-ocean exchanges and the formation and circulation of water masses and sea ice. The model reproduces the summer and winter surface mixed layers, the general cyclonic circulation including the strong coastal current in eastern Hudson Bay, and the inflow of oceanic waters into Hudson Bay. The maximum sea-ice growth rates are found in western Foxe Basin, and in a relatively large and persistent polynya in northwestern Hudson Bay. Sea-ice advection and ridging are more important than local thermodynamic growth in the regions of maximum sea-ice cover concentration and thickness that are found in eastern Foxe Basin and southern Hudson Bay. The estimate of freshwater transport to the Labrador Sea confirms a broad maximum during wintertime that is associated with the previous summers freshwater moving through Hudson Strait from southern Hudson Bay. Tidally driven mixing is shown to have a strong effect on the modeled ice-ocean circulation.  相似文献   

3.
Summary Secular series of annual precipitation over Croatia have been studied at three stations representing the different climatic regions of Croatia: Osijek (continental precipitation climate), Zagreb-Gri (continental precipitation climate with maritime influence) and Crikvenica (maritime precipitation climate).The time series analysis has been deduced by using a quick test for stationarity according to Schönwiese and Malcher, moving average filters, the Mann-Kendall rank statistic, and a progressive test for trend according to Sneyers. From this analysis, the stationarity in time series of annual precipitation totals is stated over the entire interval at all locations except for a very short interval during the first decade of the twentieth century over the continental lowland (Osijek). A generally decreasing trend is present over the entire interval, but is statistically significant only in the continental lowland (Osijek).With 4 Figures  相似文献   

4.
The ECLATS experiment was conducted in order to investigate the influence of radiative processes on the dynamics of the atmospheric boundary layer during its diurnal evolution. This experiment was carried out over Niger, near Niamey, by measuring continuously the energy balance at ground level and by using an instrumented aircraft for turbulence, radiative fluxes and aerosol measurements in the boundary layer during dusty conditions (brumes sèches). This paper is restricted to an analysis of the turbulent structure in the homogeneous and stationary convective boundary layer. The turbulence moments for kinetic energy and the spectral characteristics of the vertical velocity are discussed. These results are compared with a set of data obtained for clear convective boundary layers. The differences observed are quite important and seem, at least in part, due to radiative processes (infrared radiative divergence in the surface layer and absorption of solar radiation in the boundary layer).  相似文献   

5.
Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm-3 in summer and a minimum of a few tens of particles per cm-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 m in winter to around 0.04 m in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.Department of Science, Antarctic Division  相似文献   

6.
For a ground-level continuous release of a trace substance like 222Rn, for which the vertical profile of concentrations is exponential, a quantity, equivalent mixing height h, is defined in this paper in the following way. If the substance were to be redistributed uniformly through a layer such that the concentration were to be equal to that at the surface, then the top of the layer would be h.Relative values of h can be obtained from surface measurements of Radon concentrations, but absolute values require estimates of the vertical fluxes of Radon. A comparison is given of the estimates of h obtained from surface measurements with estimates derived from the vertical profile of Radon from the surface to 100 m.Practical methods are proposed for estimating the surface flux of Rn.  相似文献   

7.
The effects of an air-temperature inversion in the atmosphere and a seawater density jump in the ocean on the structure of the atmospheric and oceanic boundary layers are studied by use of a coupled model. The numerical model consists of a closed system of equations for velocities, turbulent kinetic energy, turbulent exchange coefficient, local turbulent length scale, and stratification expressions for both air and sea boundary layers. The effects of the temperature inversion and the density jump are incorporated into the equations of turbulent kinetic energy of the atmosphere and ocean by a parameterization. A series of numerical experiments was conducted to determine the effects of various strengths of the inversion layer and surface heat fluxes in the atmosphere and of the density-jump layer in the ocean on the structure of the interacting boundary layers.The numerical results show that the temperature inversion in the atmosphere and density jump in the ocean have strong influences on turbulent structure [especially on the turbulent exchange coefficient (TEC) and turbulent kinetic energy (TKE)] and on air-sea interaction characteristics. Maxima of TKE and TEC strongly decrease with increasing strength of the inversion layer, and they disappear for strong inversions in the atmosphere. Certain strengths (density differences between the upper and the lower layers) of the density-jump layer in the ocean (2 0.1 g/cm3) produce double maxima in TEC-profiles and TKE-profiles in the ocean. The magnitudes of air-sea interaction characteristics such as geostrophic drag coefficient, and surface drift current increase with increasing strength of the density-jump layer in the ocean. The density-jump layer plays the role of a barrier that limits vertical mixing in the ocean. The numerical results agree well with available observed data and accepted quantitive understanding of the influences of a temperature inversion layer and a density-jump layer on the interacting atmospheric and oceanic boundary layers.  相似文献   

8.
Daily measurements of atmospheric sulfur dioxide (SO2) concentrations were performed from March 1989 to January 1991 at Amsterdam Island (37°50 S–77°30 E), a remote site located in the southern Indian Ocean. Long-range transport of continental air masses was studied using Radon (222Rn) as continental tracer. Average monthly SO2 concentrations range from less than 0.2 to 3.9 nmol m-3 (annual average = 0.7 nmol m-3) and present a seasonal cycle with a minimum in winter and a maximum in summer, similar to that described for atmospheric DMS concentrations measured during the same period. Clear diel correlation between atmospheric DMS and SO2 concentrations is also observed during summer. A photochemical box model using measured atmospheric DMS concentrations as input data reproduces the seasonal variations in the measured atmospheric SO2 concentrations within ±30%. Comparing between computed and measured SO2 concentrations allowed us to estimate a yield of SO2 from DMS oxidation of about 70%.  相似文献   

9.
Shipboard measurements of atmospheric dimethyl sulfide were made during two transects along the east coast of the United States and at several stations in the Gulf of Maine. Limited measurements of carbon disulfide and hydrogen sulfide are also reported. The mean DMS mixing ratio was 29 pptv (=25, n=84, median 19 pptv) during the Atlantic transects, and 101 pptv (=67, n=77, median 79 pptv) in the Gulf of Maine. Distinct diurnal variations were found in the DMS data from the transects. The meteorology of the study area appears to control day-to-day differences in the magnitude of these diurnal variations, although rapid daytime oxidation is suggested in some cases. Diurnal variations were also evident in near-shore stations in the Gulf of Maine due to nocturnal boundary-layer inversion. Diurnal variation was not evident at other sites in the Gulf due to large scale changes in the atmospheric circulation pattern, which effectively masked any effects due to oxidation processes. Model simulations confirm that the DMS levels and diurnal variation found during the transects are not consistent with atmospheric oxidation processes alone. Atmospheric CS2 and H2S mixing ratios were less than 3 pptv during the transects, except for a single period of higher CS2 mixing ratios (reaching 11 pptv) during advection of continental air. Calculations of the flux of oceanic sulfur to the eastern United States show that the contribution of natural sulfur to the North American sulfur budget is small compared to anthropogenic sources.  相似文献   

10.
Summary The isentropic vertical coordinate model developed at UCLA is briefly reviewed. The review includes an outline of the approach used to overcome technical difficulties in handling model layers with small mass.The model's performance is demonstrated by simulating the evolution of a middle-latitude baroclinic disturbance. During the evolution of the disturbance, sharp frontal zones are generated in the upper and middle troposphere with realistic tropopause folding. The extent to which different dynamical processes contribute to frontogenesis is analyzed.While the model successfully simulates frontogenesis in the upper and middle troposphere, it has a difficulty in simulating surface fronts. The difficulty arises due to the lack of degrees of freedom in surface temperatures since an isentropic vertical coordinate model requires a large number ofvertical layers to obtain a highhorizontal resolution at the lower boundary. This suggests the potential of a hybrid vertical coordinate, which approaches at upper levels and at lower levels.With 12 Figures  相似文献   

11.
In 2005 the Study of Stable Boundary Layer Environment at Dome C (STABLEDC) experimental campaign was conducted at the plateau station of Concordia at Dome C, Antarctica. Temperature profiles measured with a microwave radiometer were used to study the characteristics of surface-based temperature inversions over the course of a year. Statistics of temperature profiles for every month are discussed; the difference between daytime and nocturnal cases observed during the summer months disappears during winter. Surface-based temperature inversions occurred in 70 % of the time during summer, and almost all of the time during winter. During winter the occurrence of warming events leads to a decrease in the temperature difference between the top and the base of the inversion (i.e. the inversion strength). The inversion strength maxima ranged between $3\,^{\circ }\mathrm{C}$ (December) and $35\,^{\circ }\mathrm{C}$ (August) corresponding to gradients of 0.1 and $0.3\,^{\circ }\mathrm{C}\, \mathrm{m}^{-1}$ , respectively. The average surface-based inversion height presents a daily cycle during the summer months with values up to 200 m in the morning hours, while it affects a layer always deeper than 100 m during the winter months. The relationships between inversion strength and the downward longwave radiative flux, absolute temperature, and wind speed are examined. The inversion strength decreases as the longwave radiation increases. A clear anti-correlation between inversion strength and near-surface temperature is evident throughout the year. During the winter, the largest inversion strength values were observed under low wind-speed conditions; in contrast, a clear dependence was not found during the summer.  相似文献   

12.
Summary Statistical tests were used to detect the variations of winter (December to February), summer (June to August), and annual mean temperatures of 160 representative stations in China during the period from 1951 to 2000. Changes of temperature in the observed time series that exceed the confidence level of 0.01 were classified as significant temperature rises or drops. The stations with significant temperature rises were classified into several temperature rise types, by the use of a clustering method. A search was made for sudden, or abrupt, temperature changes at each of the 160 stations. Possible reasons for the observed temperature variations are discussed. The statistical analysis reveals that for the 160 stations, significant rises occur in 53.1% of their annual mean temperatures, 51.9% of their winter temperatures, and 13.8% of their summer temperatures. Temperature rises increase with latitude. In contrast, significant drops occur in annual mean temperatures at 1 station, winter temperatures at 3 stations, and summer temperatures at 5 stations. Approximately 50% of stations with significant temperature variations are in the form of abrupt changes. The abrupt temperature changes all occurred in the 1970s, most often in 1979 and 1980. The abrupt changes are shown to be related to the subtropical high in South China Sea. The temperature rises in winter are shown to be linked to the presence of an anomalously strong zonal circulation in Eurasia, and a weak polar vortex, since the 1980s. The summer temperature rise in South China also has a link with the increase in size and intensity of the subtropical high, over the same period. Some of the station temperature drops in summer were related to a weaker summer monsoon. The annual mean temperature rise at 71.8% of the stations was influenced mainly by their winter temperature rises. For 8.2% of the stations, the annual mean temperature rise was connected to their summer temperature rise, and for 12.9% of the stations it was related to both the summer and winter temperature rises.  相似文献   

13.
A study of the temperature field for the Baltimore-Washington region reveals that since 1950 there has been the development of an urban heat corridor. Trend surface analysis shows that there has been an inversion of the thermal topography in the region as a saddle of rising temperatures has emerged, replacing a trough of lowered temperatures through three decades. Steady population growth throughout the area is seen to be the most important contributor. The strengthening of the heat corridor is best expressed in the summer months and weakest during the winter months. As population continues to grow in this region, the thermal topography is sure to be modified even further.It is recommended that further study be devoted to temperature and precipitation changes in regions experiencing urban growth.  相似文献   

14.
Periodicity of annual precipitation in different climate regions of Croatia   总被引：1，自引：1，他引：0  
Summary The periodicity of a 100-year series of annual precipitation over Croatia has been studied by means of power spectrum analysis at 3 stations representing the different climatic regions of Croatia. The annual precipitation variance spectra in the continental lowland (Osijek) and at the north East Adriatic coast (Crikvenica) can be fitted by Markov white noise continuum, but in the transitional region between the Dinaric Alps and the Pannonian lowland (Zagreb-Gri) a non-white noise continuum is necessary. Quasi-periodic oscillations appear in two spectra ranges: short (2.2 and 4.7 years) and medium (25.0 and 33.3 years). These results are compared with those of other authors for other parts of the Europe.With 2 Figures  相似文献   

15.
Summary Composite time series combining the results of total ozone measurements taken at Dobson stations located within the latitude band 30°N–60°N, in Europe, and North America, have been examined in order to detect any trends. Various regression trend models were used to identify any trend variations over the regions during the period 1970–1990. The results of fitting the models to the data imply that the model which assumes a linear trend provides precise information about the long-term ozone trends (trends during the period 1970–1990). The study identifies short-term summer trends in the 1980s that are evidently more strongly negative than trends that occur in the 1970s (the differences are statistically significant at the 2 level). The year-round loss (in all analyzed regions) and the winter loss in total ozone (the belt 30°N–60°N) N. America, during the 1980s are about 2–3 times higher than the losses during the 1970s (the differences are statistically significant at the 1 level).With 1 Figure  相似文献   

16.
基于L波段雷达探空资料的重庆市区低空逆温特征分析   总被引：2，自引：0，他引：2  
唐家萍  谭桂容  谭畅 《气象科技》2012,40(5):789-793
利用重庆市沙坪坝气象站2005- 2009年L波段雷达探空观测资料,研究重庆市区接地逆温和悬浮逆温的出现频率、逆温厚度、垂直分布特征和强度状况,对本地低空大气的逆温分布特征进行了详细分析.分析结果表明:重庆市区低空大气全年均不同程度存在逆温层,低空逆温出现频率为93％,夏季发生的频率最高,冬季最低;逆温强度总体不大,07:00 和19:00接地逆温多年平均强度分别为0.53℃/hm和0.6℃/hm,为同时段悬浮逆温强度的2倍;从垂直分布特征来看,低空逆温呈现厚度薄且层次多的特点,层次最多时达6层.  相似文献   

17.
The seasonality of the vertical air temperature profile in an urban area in the vicinity of the coast was studied. The vertical air temperature profile showed the characteristic seasonality. In the summer, the atmosphere was thermally stratified in the 60–100 m layer, while the 20–60 m layer was unstable or weakly stable throughout the day due to the strong solar radiation. On the other hand, no temperature inversion layer was observed in the winter presumably due to the heat supply from the sea as well as the strong wind speed in the vicinity of the coast. The vertical air temperature profiles at nighttime in the spring and autumn were transitional between the summer and the winter. In contrast, the vertical air temperature profile in the daytime in the spring was similar to that in the summer, while that in the autumn was comparable to that in the winter. Characteristic findings in the study due to the site location, i.e., in the vicinity of the coast, can be summarized as follows: (1) the elevated temperature inversion layer at noon was observed in the summer, and (2) no temperature inversion layer was observed in the winter.  相似文献   

18.
Summary Spatial and temporal patterns of trends in the diurnal temperature ranges (DTRs) of the 70 stations and the role of maximum and minimum temperatures on the year-to-year variability and the long-term trends of the DTRs in Turkey have been investigated for the period 1929–1999. The principal results of the study are as follows:(i) The daytime maximum temperatures have shown weak warming and cooling in comparison with significant warming of the night-time minimum temperatures in many regions of Turkey and in most seasons. (ii) The DTRs have significantly decreased at most of the urbanised and rapidly urbanising stations throughout the seasons except partly in winter, without showing an apparent north/south (west–east) and land/sea gradient. (iii) Annual and seasonal DTRs of some stations have shown significant increasing trends. Nevertheless, the spatial distribution of significant increasing trends in the DTR series is geographically incoherent across the country in all seasons and annually, as compared with significantly decreased DTRs. (iv) Autumn and summer DTRs have decreased generally at a higher rate than in winter and spring. (v) Changes in the temperature regime of Turkey towards the more temperate and/or warmer climate conditions are most strongly related with the significant night-time warming in spring and summer. (vi) Magnitudes and signs of correlation coefficients and correlation patterns between the DTRs and the maximum and minimum temperatures have revealed that there is an opposite physical control mechanism on the year-to-year variability and the long-term variations and trends in the DTRs, particularly for the annual, spring and summer series. (vii) Significant increases of the night-time temperatures have most likely led to strong decreasing trends in the DTRs of most stations during the spring and summer seasons and annually and of some stations during winter and autumn. (viii) The asymmetric trends and the symmetric, but with different magnitude, trends in the maximum and minimum temperatures resulted in a significant decrease in the DTRs of many stations and are a considerable signal of ongoing changes in the climatic variability of Turkey.  相似文献   

19.
Free tropospheric measurements of ozone, peroxyacetylnitrate andprecursors (CO, NMHC) that were made within the framework of the EUROTRACsub-project TOR (Tropospheric Ozone Research) between 1990 and 1995 at theGAW station Izana, Tenerife (28°18N, 16°30W) arediscussed. The average annual cycles reveal the importance of transport fromnorthern mid-latitudes and the role of photo-chemistry. According toair-mass trajectories, which were supplied to us from AEROCE(Atmosphere/Ocean Chemistry Experiment), transport from northernmid-latitudes is associated with high precursor concentrations in winter,whereas ozone concentrations in winter are not much influenced by transportpatterns, suggesting a rather uniform distribution over the northern part ofthe Northern Hemisphere around mean value of 43 ± 5 ppb. In summer,high ozone concentrations of up to 90 ppb are often encountered duringtransport from north, while the levels of precursors are much lower than inwinter, because of photochemical destruction. Trajectories from southerlylatitudes and the Sahara usually have the lowest ozone concentrationsassociated with them.  相似文献   

20.
The nocturnal structure of the lower troposphere is studied using aerosol profile data (50–2800 m AGL) obtained with a bistatic, continuous wave, Argon ion lidar system during October 1986–September 1989 at Pune (18°32 N, 73°51 E, 559m AMSL), India. The top of the nocturnal groundbased inversion is taken as the height above ground where the negative vertical gradient in aerosol concentration first reaches a maximum. During the post-sunset period over this station, this height is as low as 160m and frequently lies around 550m. Greater heights are observed in pre-monsoon months and smaller ones during the southwest monsoon season. Positive vertical gradients in aerosol concentration, indicative of stable/elevated layers, appear frequently around 750m. Temporal variations of aerosol concentration gradients in two adjacent air layers, 920–1000m and 100–1100m, provide evidence that stability increases downward in the early night hours.  相似文献   

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