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1.
In mountainous lake areas, lake–land and mountain–valley breezes interact with each other, leading to an "extended lake breeze". These extended lake breezes can regulate and control energy and carbon cycles at different scales. Based on meteorological and turbulent fluxes data from an eddy covariance observation site at Erhai Lake in the Dali Basin,southwest China, characteristics of daytime and nighttime extended lake breezes and their impacts on energy and carbon dioxide exchange in 2015 are investigated. Lake breezes dominate during the daytime while, due to different prevailing circulations at night, there are two types of nighttime breezes. The mountain breeze from the Cangshan Mountain range leads to N1 type nighttime breeze events. When a cyclonic circulation forms and maintains in the southern part of Erhai Lake at night, its northern branch contributes to the formation of N2 type nighttime breeze events. The prevailing wind directions for daytime, N1, and N2 breeze events are southeast, west, and southeast, respectively. Daytime breeze events are more intense than N1 events and weaker than N2 events. During daytime breeze events, the lake breeze decreases the sensible heat flux(Hs) and carbon dioxide flux(FCO_2) and increases the latent heat flux(LE). During N1 breeze events, the mountain breeze decreases Hs and LE and increases FCO_2. For N2 breeze events, the southeast wind from the lake surface increases Hs and LE and decreases suppress carbon dioxide exchange.  相似文献   

2.
The sea-land breeze circulation （SLBC） occurs regularly at coastal locations and influences the local weather and climate significantly. In this study, based on the observed surface wind in 9 conventional meteorological stations of Hainan Island, the frequency of sea-land breeze （SLB） is studied to depict the diurnal and seasonal variations. The statistics indicated that there is a monthly average of 12.2 SLB days and an occurrence frequency of about 40%, with the maximum frequency （49%） in summer and the minimum frequency （29%） in autumn. SLB frequencies （41%） are comparable in winter and spring. A higher frequency of SLB is present in the southern and central mountains due to the enhancement effect of the mountain-valley breeze. Due to the synoptic wind the number of SLB days in the northern hilly area is less than in other areas. Moreover, the WRF model, adopted to simulate the SLBC over the island for all seasons, performs reasonably well reproducing the phenomenon, evolution and mechanism of SLBC. Chiefly affected by the difference of temperature between sea and land, the SLBC varies in coverage and intensity with the seasons and reaches the greatest intensity in summer. The typical depth is about 2.5 km for sea breeze circulation and about 1.5 km for land breeze circulation. A strong convergence zone with severe ascending motion appears on the line parallel to the major axis of the island, penetrating 60 to 100 km inland. This type of weak sea breeze convergence zone in winter is north-south oriented. The features of SLBC in spring are similar both to that in summer with southerly wind and to that in winter with easterly wind. The coverage and intensity of SLBC in autumn is the weakest and confined to the southwest edge of the central mountainous area. The land breeze is inherently very weak and easily affected by the topography and weather. The coverage and intensity of the land breeze convergence line is significantly less than those of the sea breeze. The orographic forcing of the cen  相似文献   

3.
To examine the correlation between the sizes of sea breeze fronts and pollutants under the influence of synoptic fields, a numerical simulation was conducted in the southeast coastal area of the Korean Peninsula, where relatively high concentrations of pollutants occur because of the presence of various kinds of industrial developments. Sea breeze and sea breeze front days during the period 2005-09 were identified using wind profiler data and, according to the results, the number of days were 72 and 53, respectively. When synoptic forcing was weak, sea breeze fronts moved fast both in horizontal fields and in terms of wind velocity, while in the case of strong synoptic forcing, sea breeze fronts remained at the coast or moved slowly due to strong opposing flows. In this case, the sea breeze front development function and horizontal potential temperature difference were larger than with weak synoptic forcing. The ozone concentration that moves together with sea breeze fronts was also formed along the frontal surfaces. Ozone advection and diffusion in the case of strong synoptic forcing was suppressed at the frontal surface and the concentration gradient was large. The vertical distribution of ozone was very low due to the Thermal Internal Boundary Layer (TIBL) being low.  相似文献   

4.
The evolution of a sea-breeze front(SBF)in parallel and offshore environmental flows was investigated by using high-resolution simulations of two SBF cases from the Bohai Bay region,China.The results show that the combination of a distinct vertical wind shear caused by the sea-breeze circulation with a neutral or slightly stable atmospheric stratification associated with the thermal inner boundary layer promoted the occurrence and maintenance of a Kelvin-Helmholtz billow(KHB).In a parallel environmental flow,the SBF evolved into a few connected segments because of the inhomogeneity of the sea-breeze direction and intensity as it penetrated inland.A significant upward vertical motion occurred at the two ends of the SBF segment owing to the sea-breeze convergence and was accelerated by the KHB.The KHB made a notable contribution to the intensity at the ends of the segment,whereas the intensity at the middle segment was primarily attributed to the convergence between the sea breeze and the parallel flow.In the offshore environmental flow,the clockwise rotation of the offshore flow varying with time increased the downstream convergence of the interface between the sea breeze and the offshore flow and pushed the downstream convergence zone to an orientation consistent with the offshore flow.The air parcels ascending from the downstream part of the SBF were continuously lifted by the downstream convergence zone during their advection,leading to a significant downstream development of the SBF.The significant upward vertical motion caused by the sea-breeze convergence behind the upstream end of the SBF was shifted to the upstream end of the SBF by the KHB,which enhanced the intensity of the upstream end of the SBF.  相似文献   

5.
The Florida peninsula in the USA has a frequent occurrence of sea breeze(SB)thunderstorms.In this study,the numerical simulation of a Florida SB and its associated convective initiation(CI)is simulated using the mesoscale community Weather Research and Forecasting(WRF)model in one-way nested domains at different horizontal resolutions.Results are compared with observations to examine the accuracy of model-simulated SB convection and factors that influence SB CI within the simulation.It is found that the WRF model can realistically reproduce the observed SB CI.Differences are found in the timing,location,and intensity of the convective cells at different domains with various spatial resolutions.With increasing spatial resolution,the simulation improvements are manifested mainly in the timing of CI and the orientation of the convection after the sea breeze front(SBF)merger into the squall line over the peninsula.Diagnoses indicate that accurate representation of geophysical variables(e.g.,coastline and bay shape,small lakes measuring 10-30 km2),better resolved by the high resolution,play a significant role in improving the simulations.The geophysical variables,together with the high resolution,impact the location and timing of SB CI due to changes in low-level atmospheric convergence and surface sensible heating.More importantly,they enable Florida lakes(30 km2 and larger)to produce noticeable lake breezes(LBs)that collide with the SBFs to produce CI.Furthermore,they also help the model reproduce a stronger convective squall line caused by merging SBs,leading to more accurate locations of postfrontal convective systems.  相似文献   

6.
By using the data set of light rain days and low cloud cover at 51 stations in South China (SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows: (1) The trends of light rain days and low cloud cover over SC are opposite (light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area. (2) The regression coefficients of light rain days and low cloud cover during 1960–2005 are 4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level. (3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter. (4) There are two regions with large values of aerosol optical depth (AOD), which distribute in central and southern Guangxi and Pearl River Delta (PRD) of Guangdong, and the value of AOD in PRD is up to 0.7. The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.  相似文献   

7.
A strong urban heat island (UHI) appeared in a hot weather episode in Suzhou City during the period from 25 July to 1 August 2007. This paper analyzes the urban heat island characteristics of Suzhou City under this hot weather episode. Both meteorological station observations and MODIS satellite observations show a strong urban heat island in this area. The maximum UHI intensity in this hot weather episode is 2.2℃, which is much greater than the summer average of 1.0℃ in this year and the 37-year (from 1970 to 2006) average of 0.35℃. The Weather Research and Forecasting (WRF) model simulation results demonstrate that the rapid urbanization processes in this area will enhance the UHI in intensity, horizontal distribution, and vertical extension. The UHI spatial distribution expands as the urban size increases. The vertical extension of UHI in the afternoon increases about 50 m higher under the year 2006 urban land cover than that under the 1986 urban land cover. The conversion from rural land use to urban land type also strengthens the local lake-land breeze circulations in this area and modifies the vertical wind speed field.  相似文献   

8.
In this paper,a simulation study is made on the sea breeze process over southwestern Bohai Gulf byuse of the Pielke mesoscale meteorological model.The simulated results show that when a south wind of 8m/s blows over the top of the model,a strong wind zone of 15—25 km wide with a maximum speed more than14 m/s,which is close and nearly parallel to the south shore,will appear at 160 m above the sea surface.When a strong sea breeze penetrates inland,there often appears a thermal internal boundary layer(TIBL)near shore.The inversion above the TIBL can damp the vertical dispersion of atmospheric pollution.Besides,it is also found that,for a three-dimensional sea/land breeze circulation,if the divergence centre inthe return flow departs vertically far from the correspondent convergence centre in the sea breeze,a centre ofstrong descending movement will be formed at the middle and upper levels of the return flow.The resultsin this paper is also applicable to the Laizhou Bay.  相似文献   

9.
In southern China,cold air is a common weather process during the winter season;it can cause strong wind,sharp temperature decreases,and even the snow or freezing rain events.However,the features of the atmospheric boundary layer during cold air passage are not clearly understood due to the lack of comprehensive observation data,especially regarding turbulence.In this study,four-layer gradient meteorological observation data and one-layer,10-Hz ultrasonic anemometer-thermometer monitoring data from the northern side of Poyang Lake were employed to study the main features of the surface boundary layer during a strong cold-air passage over southern China.The results show that,with the passage of a cold air front,the wind speed exhibits low-frequency variations and that the wind systematically descends.During the strong wind period,the wind speed increases with height in the surface layer.Regular gust packets are superimposed on the basic strong wind flow.Before the passage of cold air,the wind gusts exhibit a coherent structure.The wind and turbulent momentum fluxes are small,although the gusty wind momentum flux is slightly larger than the turbulent momentum flux.However,during the invasion of cold air,both the gusty wind and turbulent momentum fluxes increase rapidly with wind speed,and the turbulent momentum flux is larger than the gusty wind momentum flux during the strong wind period.After the cold air invasion,this structure almost disappears.  相似文献   

10.
Based on CAMP/Tibet [Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau] turbulent data collected at the Bujiao (BJ) site of the Nagqu area, the turbulent structure and transportation characteristics in the near surface layer during summer are analyzed. The main results show that the relationship between the normalized standard deviation of 3D wind speed and stability satisfies the similarity law under both unstable and stable stratifications. The relations of normalized standard deviation of temperature and specific humidity to stability only obey the “?1/3 power law” under unstable conditions. In the case of stable stratifications, their relations to stability are dispersing. The sensible heat dominates in the dry period, while in the wet period, the latent heat is larger than the sensible heat.  相似文献   

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