共查询到20条相似文献，搜索用时 46 毫秒
1.
Buoy and satellite observations of mesoscale cellular convection (MCC) over the East China Sea in the vicinity of the Kuroshio current have been made during 14–18 February 1975, as a part of the Air Mass Transformation Experiment (AMTEX). Surface observations of solar radiation from spar buoys indicate the distinct passage of open and closed MCC that formed and continued for three consecutive days during an outbreak of cold polar air over the much warmer Kuroshio. A critical air-sea temperature of –5 °C for the occurrence of MCC has been substantiated. The time required for the passage of solar radiation peaks coupled with the buoy wind speed gave a computed closed cell diameter of 28 km, comparable to estimates from satellite photographs.The horizontal component of wind beneath the cloudy portion of a closed cell, due to convection, has been estimated as 0.6 m s–1. This represents the speed at which air near the sea surface moves from the edge toward the center of a closed cell. Also, the temperature difference obtained near the sea surface between the relatively cold descending branch and the warm ascending branch is 0.2°C. Similarly, the specific humidity difference of the less moist descending air near the edge and the moist ascending air near cell center is 9% (0.4 g/kg). Some indications were also found in the variation of horizontal wind direction with the passage of closed cells, since wind variations at the edge of passing cells exceeded the mean sequential variability (10.6 ° compared to 9.4 °).Sensible heat flux calculations associated with closed MCC suggest that strong surface heating can be associated with closed cells, previously reported by Hubert (1966) to be a characteristic of only open cells.Finally, the results of this study should remove any disclaimers that MCC appear in satellite photography simply because of a resolution bias and that the consideration of all visible clouds actually present would remove any periodicity one might expect to see in surface observations. 相似文献
2.
On the contribution of atmospheric moisture to dew formation 总被引：4，自引：0，他引：4
The relative contributions of dewfall (a flux of water vapour from air to surface) and distillation (a flux of water vapour from soil to canopy) to dew formation on closed canopy and bare soil surfaces are assessed, and the dependence of dew amount upon wind speed, absolute temperature, atmospheric stability, relative humidity, soil characteristics and cloudiness, all of which are significant factors, is evaluated. Some of these evaluations provide refinements to similar ones given in Monteith (1961). High dewfall rates are usually 0.06 mm hr–1 over canopy or bare soil, though upon a canopy under soil-saturated and air-saturated conditions, rates of dew formation may reach 0.07–0.09 mm hr–1 with contributions from distillation. Various sets of observations are reanalyzed to illustrate the importance of the horizontal advection of moisture in the nocturnal boundary layer (NBL) to observed high rates of dew formation arising from the atmospheric contribution of water vapour (dewfall). These locally observed high dewfall rates must be the result of small-scale or mesoscale horizontal advection of moisture in the NBL, since the humidity changes within the typically shallow NBL required to balance the loss of water at the surface are not observed. Over extensive areas of uniform surface (horizontal scales 10 km), such continuously high dewfall rates could only be balanced by a local supply of atmospheric moisture since advection of moisture would necessarily be small. 相似文献
3.
The optical refractive index fluctuation has been determined from measurements of turbulent temperature and humidity fluctuations in the atmospheric surface layer over the ocean. Probability density, spectral density and even- and odd-order structure functions of the refractive index fluctuation are presented. The spectral density exhibits a significant -5/3 inertial subrange as a result of the existence of a -5/3 subrange in the spectra of temperature and humidity fluctuations and in the temperature-humidity co-spectrum. The behaviour in the inertial subrange of fourth- and sixth-order structure functions of the refractive index is in reasonable agreement with that predicted by the analysis of Antonia and Van Atta (1975, 1978). The third-order structure functions of the refractive index exhibit an approximately linear dependence on separation in the inertial subrange, in agreement with a ramp model for the large coherent structure of the motion. 相似文献
4.
Application of an infrared carbon dioxide and humidity instrument to studies of turbulent transport 总被引：4，自引：0，他引：4
Eiji Ohtaki 《Boundary-Layer Meteorology》1984,29(1):85-107
A calibration equation and some results of the field performance of an infrared instrument, which is designed to measure simultaneous fluctuations of atmospheric carbon dioxide and water vapor, are described. Field observations show that the instrument is suitable for simultaneous measurement of turbulent fluxes of carbon dioxide and water vapor in conjunction with a sonic anemometer. Measured values of carbon dioxide and water vapor fluxes show diurnal variations characterized by crop activity with respect to assimilation, respiration and evapotranspiration. Carbon dioxide is transferred downward during the daytime and upward at night, while latent heat and sensible heat are transferred in the opposite sense. The non-dimensional gradient of carbon dioxide is expressed in the following form under weak unstable conditions:
c
= (1 – 16
v
)-1/2. Here,
v
is the Monin-Obukhov stability parameter including the humidity effect. This relation was originally proposed for temperature and humidity. Thus, the results indicate that the turbulent mechanisms of carbon dioxide fluctuations are similar to those of other scalar entities. This is strongly supported by the high correlation coefficient found between fluctuations of carbon dioxide and temperature or humidity in the air layer over crop fields. 相似文献
5.
Hiroshi Ishida 《Boundary-Layer Meteorology》1990,52(4):335-348
Seasonal variations of the spectra of wind speed and air temperature in the mesoscale frequency range from 1.3 × 10-4 to 1.5 × 10-3 Hz (10 min to 2 h periods) have been studied through observations over land for one year. Spectrographs [time series of isopleths of spectral densities, f · S(f) vs f] of wind speed and air temperature contain occasional peaks that are attributed to short-lived mesoscale atmospheric activity with narrow frequency bands. Significant spectral peaks of wind speed were found in 19% of the total observations in winter, and in 15–16% in the other seasons; for air temperature, they occured in 12% of observations in autumn, and in 16–19% in the other seasons. The peaks most often occurred in the period range from 30 min to 1 h; most had durations less than 24 h. Mesoscale fluctuations of wind speed and air temperature were highly correlated, and in most cases, phase differences were 90–180 ° with air temperature leading wind speed. Significant spectral peaks of wind speed often occurred during northerly seasonal cold winds in winter, and accompanied tropical and/or mid-latitude cyclones in the other seasons. When the peaks occurred, wind speed was usually relatively high and the atmospheric surface layer was unstable. 相似文献
6.
V. B. Titov 《Russian Meteorology and Hydrology》2009,34(5):316-320
Standard deviations of mesoscale, synoptic, seasonal, and interannual fluctuations of the air and water temperature are calculated from long-term measurements. The contributions of each type of fluctuation to the total temporal variability are estimated. The intraannual cycle of variability of monthly (long-term) means of mesoscale and synoptic fluctuations is considered. 相似文献
7.
Spectra of CO<Subscript>2</Subscript> and Water Vapour in the Marine Atmospheric Surface Layer 总被引：1，自引：1，他引：0
Erik Sahlée Ann-Sofi Smedman Anna Rutgersson Ulf Högström 《Boundary-Layer Meteorology》2008,126(2):279-295
Spectra of CO2 and water vapour fluctuations from measurements made in the marine atmospheric surface layer have been analyzed. A normalization
of spectra based on Monin–Obukhov similarity theory, originally developed for wind speed and temperature, has been successfully
extended also to CO2 and humidity spectra. The normalized CO2 spectra were observed to have somewhat larger contributions from low frequencies compared to humidity spectra during unstable
stratification. However, overall, the CO2 and humidity spectra showed good agreement as did the cospectra of vertical velocity with water vapour and CO2 respectively. During stable stratification the spectra and cospectra displayed a well-defined spectral gap separating the
mesoscale and small-scale turbulent fluctuations. Two-dimensional turbulence was suggested as a possible source for the mesoscale
fluctuations, which in combination with wave activity in the vertical wind is likely to explain the increase in the cospectral
energy for the corresponding frequency range. Prior to the analysis the turbulence time series of the density measurements
were converted to time series of mixing ratios relative to dry air. Some differences were observed when the spectra based
on the original density measurements were compared to the spectra based on the mixing ratio time series. It is thus recommended
to always convert the density time series to mixing ratio before performing spectral analysis. 相似文献
8.
Hiroshi Ishida 《Boundary-Layer Meteorology》1989,47(1-4):71-84
Based on the data from an array of buoys during the JASIN-1978 field experiment made in an area northwest of Scotland, power spectra of surface wind speed and air temperature over the ocean in the mesoscale frequency range were studied. The averaged composite spectrum of wind speed for the whole period shows the existence of a spectral gap in the frequency range from 10–4 to 5 × 10–3 Hz. However, significant peaks in this range are often seen in particular spectra under certain weather conditions. Mesoscale spectral peaks of wind speed occur in 14 segments of the data record, approximately 10% of the total duration of the observations. In 4 of these segments, the mesoscale spectral peaks of both wind speed and air temperature occurred simultaneously. Several wave patterns of mesoscale atmospheric disturbances when mesoscale spectral peaks were seen are derived from phase differences between buoys. Significant mesoscale peaks in spectra appear in relatively strong winds and unstable or near-neutral atmospheric conditions, and none in stable atmospheric conditions. A criterion of wind speed and atmospheric stability is found for the mesoscale spectral peak appearance. 相似文献
9.
Abstract The effects of marine fronts on the local atmospheric surface layer and air‐sea interaction were studied. Several mesoscale fronts were crossed by a research vessel in the Greenland Sea. Air temperature, humidity and stability conditions, and the fluxes of momentum, as well as sensible and latent heat, were investigated. For relatively calm conditions, close air‐sea coupling was observed in the temperature whereas for stronger winds, the air temperature of the surface layer was not markedly modified by the front below. Changes in the moisture content in the frontal area were observed and, in one case, evaporation was observed on the warm water side and condensation on the cold water side of the front. Frontal differences in heating from the sea were assumed to affect the surface‐layer wind field. 相似文献
10.
文章推导出了改进的大气声散射截面σ(θ)表达式，确定了大气声散射系数αs的解析表达式，并得出改进的大气声折射指数脉动结构系数c2n表达式。实测结果表明，在潮湿大气中，湿度脉动和温湿相关脉动与温度脉动一样是影响声散射衰减的重要因子，而在干燥大气中，湿度脉动的影响可以忽略。 相似文献
11.
Masaru Yamamoto 《Meteorology and Atmospheric Physics》2012,115(3-4):89-112
Two types of cold-air outbreaks over the Yellow and East China Seas are investigated using a regional mesoscale model. Distinct patterns of surface turbulent heat fluxes and precipitation are identified between the two cases. The sea surface heat flux and frictional velocity are strongly influenced by mesoscale differences between high- and low-resolution datasets of sea surface temperature (SST). The influence of the SST difference on atmospheric water is spread to the downstream area of the outbreak with the phase transition of water. The air mass transformation around 800?hPa over the Kuroshio is partly influenced by the upstream SST difference. In particular, the SST difference near the mouth of the Yanzi River strongly modifies the air mass around Taiwan. Thus, in addition to the Kuroshio front, the mesoscale Chinese coastal SST structure is also important in the air mass transformation over the East China Sea. 相似文献
12.
C. J. Moore 《Boundary-Layer Meteorology》1983,25(3):245-269
The single-beam infrared hygrometer (Hyson and Hicks, 1975) is increasingly popular as a device capable of measuring atmospheric humidity fluctuation for use in eddy correlation studies. However, it is generally applied without recognition of the effect of temperature on its performance. Calibration data from a number of such instruments indicate that the resulting calibration coefficients vary with mean temperature as a direct consequence of temperature dependence in photodetector response. Fluctuations in atmospheric and instrumental temperatures can also introduce significant errors in the measurement of humidity fluctuations.This paper draws attention to the problem of temperature dependence in the calibration of these devices and provides a framework for investigating the magnitude of other errors involved in their use. 相似文献
13.
利用自动站观测资料、FY-2G卫星资料和多普勒雷达等资料,对发生在副热带高压影响下的重庆局地强风暴过程进行了观测和数值模拟分析,探讨了其中尺度对流系统(MCS)演变,抬升触发和维持机制。结果表明:(1)在副热带高压影响下,重庆处于高温、高湿气团中,大气层结极不稳定;(2)此次局地风暴抬升触发的关键因子是地面附近浅薄边界层中尺度辐合线,辐合线由川渝盆地中西部MCS的雷暴高压与重庆地面热低压共同作用形成;(3)中尺度辐合线触发的对流风暴形成小范围冷池出流与环境风场形成新的辐合线,加强对流风暴发展,并再次触发新的对流单体。承载层平均风为偏南风,使得对流单体向北缓慢移动,冷池出流和边界层辐合线共同作用使得风暴单体向西向北传播和长时间维持。 相似文献
14.
The spatial and temporal distributions of marine cold air outbreaks (MCAOs) over the northern North Atlantic have been investigated using re-analysis data for the period from 1958 to 2007. MCAOs are large-scale outbreaks of cold air over a relatively warm ocean surface. Such conditions are known to increase the severity of particular types of hazardous mesoscale weather phenomena. We used a simple index for identifying MCAOs: the vertical potential temperature gradient between the sea surface and 700 hPa. It was found that atmospheric temperature variability is considerably more important than the sea surface temperature variability in governing both the seasonal and the inter-annual variability of MCAOs. Furthermore, a composite analysis revealed that a few well-defined and robust synoptic patterns are evident during MCAOs in winter. Over the Labrador and Irminger Seas the MCAO index was found to have a correlation of 0.70 with the North Atlantic Oscillation index, while over the Barents Sea a negative correlation of 0.42 was found. 相似文献
15.
M. V. Kurgansky A. V. Chernokulsky I. I. Mokhov 《Russian Meteorology and Hydrology》2013,38(8):539-546
Analyzed are large- and mesoscale atmospheric processes which preceded and accompanied the tornado formation on June 12, 2012 near Khanty-Mansiysk city (61° N) in West Siberia. After the record-breaking hot weather observed in the region during the first half of June 2012, the tornado formation was favored by the passage of the cold front (cold advection at low altitudes), by the wind rotation with height in the lower atmospheric layer of 1.5 km (by more than 180°), and by very high air humidity in the surface layer with the cloud base of about 200 m. Estimated are the possible trends in the nature of the atmospheric circulation over West Siberia at the global warming observed in the 21st century which may contribute to a more regular tornado formation in high-latitudinal regions due to the physiographic peculiarities of the region. 相似文献
16.
《大气与海洋》2013,51(2):171-185
Abstract The exceptional sea‐ice retreat and advance that occurred in the Bellingshausen Sea, Antarctica during August 1993 was the largest such winter event in this sector of the Antarctic during the satellite era. The reasons for this fluctuation of ice are investigated using passive microwave satellite imagery, ice motion vectors derived from the satellite data, in‐situ meteorological reports and near‐surface winds and temperatures from the European Centre for Medium‐range Weather Forecasts (ECMWF) numerical weather prediction model. The ice edge retreat of more than 400 km took place near 80°W from approximately 1–15 August, although the southward migration of the ice edge was not continuous and short periods of advance were also recorded. Between 16 August and 2 September there was almost continuous sea‐ice recovery. The rate of change of the ice edge location during both the retreat and advance phases significantly exceeded the southward and northward velocity components of ice within the pack, pointing to the importance of ice production and melting during this event. During the month, markedly different air masses affected the area, resulting in temperature changes from +2°C to ‐21°C at the nearby Rothera station. ‘Bulk’ movement of the pack, and compaction and divergence of the sea ice, made a secondary, but still significant, contribution to the observed advance and retreat. The ice extent fluctuations were so extreme because strong meridional atmospheric flow was experienced in a sector of the Southern Ocean where relatively low ice concentrations were occurring. The very rapid ice retreat/advance was associated with pronounced low‐high surface pressure anomaly couplets on either side of the Antarctic Peninsula. 相似文献
17.
Summary The seasonal and diurnal variations in the vertical component of the atmospheric electric field, air temperature, relative humidity and horizontal wind speed were studied using the surface data for the two periods (1936–40) and (1962–66) recorded at the tropical urban station, Colaba, Bombay (18°51N, 72°49E, 11 m ASL), located on the west coast of India.The atmospheric electric field during the latter period (1962–66) is significantly higher (up to 42.3%) than the earlier period (1936–40). This has been attributed to the enhanced particulate concentrations in the atmosphere. The increase noticed in the atmospheric electric field is a maximum during winter and minimum during the monsoon. The atmospheric electric field exhibited a marked semi-diurnal oscillation with peaks at 0900 LST and 2200 LST during winter, premonsoon and post-monsoon seasons of both the periods. During the monsoon season the double oscillation is not marked.The variations noticed in the surface air temperature and the relative humidity are in agreement with those observed in the atmospheric electric field. The horizontal wind speed showed a decrease which has been attributed to the surface roughness resulting from urbanization.With 7 Figures 相似文献
18.
Twentieth century variability of surface humidity as the climate change indicator in Kraków (Southern Poland) 总被引：1，自引：0，他引：1
Agnieszka Wypych 《Theoretical and Applied Climatology》2010,101(3-4):475-482
Air humidity is an element that plays an important role among meteorological processes within the atmosphere; however, the variety of humidity indices makes the global view of air moisture changes difficult. Long-term variability of air humidity in Kraków was examined by time-series (1901–2000) analysis of vapour pressure and saturation deficit values and their characteristic days with the background of temperature and saturated vapour pressure changes. Long-term variability of air humidity in Kraków has been visible above all in variations of saturation deficit. It should be connected with the contemporary temperature growth and the city development as the atmospheric water vapour content (described by vapour pressure) becomes relatively stable (with no significant tendencies). The parameter showed well-marked trends over the examined period. The growth of saturation deficit values predominated in the warm half of a year (above all in August: an increase in SD value by 3.0 hPa per century). Apart from atmospheric circulation variability, gradual rise in the number of inhabitants and higher development density contributed to the decline in the city’s air humidity; however, the causes of changes in air humidity should be also attributed to natural factors, mainly to variation of air circulation reinforced by the operation of anthropogenic factors. Using air humidity as the indicator, the results that confirm climatic fluctuations in central Europe in the twentieth century obtained earlier were verified and some new aspects of present climate change were given. 相似文献
19.
A computational scheme is developed for estimating turbulent surface stress, sensible heat flux and humidity flux from mean velocity, temperature and humidity at a single height in the atmospheric surface layer; conditions at this reference level are presumed known from observations or from a numerical atmospheric circulation model. The method is based on coupling a Monin-Obukhov similarity profile to a force-restore formulation for the evolution of surface soil temperature to yield the local values of shear stress, heat flux and surface temperature. A self-contained formulation is presented including parameterizations for solar and infrared radiant flux at the surface.In addition to reference-level mean flow properties, the parameters needed to implement the scheme are thermal heat capacity of the soil, surface aerodynamic roughness, latitude, solar declination, surface albedo, surface emissivity and atmospheric transmissivity.Sample calculations are presented for (a), constant atmospheric forcing at the reference level, and (b) variable atmospheric forcing corresponding to Kahle's (1977) measurements of windspeed, air temperature and radiometer soil surface temperature under dry vegetatively sparse conditions in the Mohave Desert in California. The latter case simulated the observed diurnal variations resonably well for the parameters used.Consultant, Atmospheric Sciences Division, Department of Energy and Environment, Brookhaven National Laboratory, Upton, N.Y., pc11973, U.S.A. 相似文献
20.
The variations of the statistics of wind,temperature and humidity fluctuations with stability 总被引：1，自引：0，他引：1
G. A. McBean 《Boundary-Layer Meteorology》1971,1(4):438-457
Measurements of the turbulent fluctuations of wind, temperature and humidity were made in the atmospheric surface layer. The statistics of the fluctuations were investigated in both the time and frequency domains. The vertical wind, temperature and smaller-scale horizontal wind fluctuations appear to obey the Monin-Obukhov similarity hypothesis. The humidity fluctuations were found to be governed by a humidity flux stability parameter rather than the normal Monin-Obukhov length. 相似文献