Statistics of gravity wave spectra in the troposphere and lower stratosphere over Beijing

We utilize the temperature profiles with a height resolution of 50-m obtained over the Beijing Observatory in the period between January of 2002 and December of 2002 to study vertical wavenumber spectra of normalized temperature fluctuations in the 1.67-8.02 km and 13.57-19.92 km altitude ranges and compare them with linear saturation model.Results indicate that individual vertical wavenumber spectra reveal a considerable variability in both slope and amplitude.The observed variability is not consistent wit...     

On the size distribution of ice-supersaturated regions in the upper troposphere and lowermost stratosphere

In order to determine typical sizes of ice-supersaturated regions (ISSRs) in the upper troposphere and lowermost stratosphere we set up the frequency distribution of path lengths flown by MOZAIC aircraft within ISSRs. The mean path length is about 150 km with a standard deviation of 250 km. We analyse the influence of a selection bias (viz. that large ISSRs are more often crossed by aircraft than small ones) on the obtained path length statistics and derive a mathematical equation that relates the path length distribution to the underlying size distribution of ISSRs, assuming that they have circular shape. We solve the equation (by trial and error) and test the result using numerical simulations. Surprisingly, we find that there may be many more very small ISSRs than apparent from the data such that the true mean diameter of the ISSRs may be of the order a few kilometres only. The relevance of the result is discussed and dedicated research flights to measure the true extension of ISSRs are recommended.     

Vertical distribution of chlorofluoromethanes in the upper troposphere and lower stratosphere

Vertical profiles of CCl₄, CFCl₃, and CF₂Cl₂ mixing ratios in the upper troposphere and lower stratosphere have been measured on four flights with chartered aircraft, type HS 125. The flights were carried out in November and December 1976 over Europe at latitudes between 50 and 60°N. At least eight air samples were taken during each ascent and descent of the aircraft at altitudes between 7 and 12.5 km. The samples were analysed in the laboratory using gaschromatographic procedures. The results indicate a decrease of the CCl₄, CFCl₃, and CF₂Cl₂ mixing ratios above the tropopause. The observed average gradients in the stratosphere are 14 pptv/km for CCl₄, 12 pptv/km for CFCl₃ and 27.8 pptv/km for CF₂Cl₂. With exception of CFCl₃ these gradients are higher than those predicted by model calculations. Apparently, further sink mechanisms for CCl₄ and CF₂Cl₂ exist in the lower stratosphere not yet included in the models.     

A distribution law for relative humidity in the upper troposphere and lower stratosphere derived from three years of MOZAIC measurements

Data from three years of MOZAIC measurements made it possible to determine a distribution law for the relative humidity in the upper troposphere and lower stratosphere. Data amounting to 13.5% of the total were obtained in regions with ice supersaturation. Troposphere and stratosphere are distinguished by an ozone concentration of 130 ppbv as threshold. The probability of measuring a certain amount of ice supersaturation in the troposphere decreases exponentially with the degree of ice supersaturation. The probability of measuring a certain relative humidity in the stratosphere (both with respect to water and ice) decreases exponentially with the relative humidity. A stochastic model that naturally leads to the exponential distribution is provided. Mean supersaturation in the troposphere is about 15%, whereas ice nucleation requires 30% supersaturation on the average. This explains the frequency of regions in which aircraft induce persistent contrails but which are otherwise free of clouds. Ice supersaturated regions are 3-4 K colder and contain more than 50% more vapour than other regions in the upper troposphere. The stratospheric air masses sampled are dry, as expected, having mean relative humidity over water of 12% and over ice of 23%, respectively. However, 2% of the stratospheric data indicate ice supersaturation. As the MOZAIC measurements have been obtained on commercial flights mainly between Europe and North America, the data do not provide a complete global picture, but the exponential character of the distribution laws found is probably valid globally. Since water vapour is the most important greenhouse gas and since it might enhance the anthropogenic greenhouse effects via positive feedback mechanisms, it is important to represent its distribution correctly in climate models. The discovery of the distribution law of the relative humidity makes possible simple tests to show whether the hydrological cycle in climate models is represented in an adequate way or not.     

Rayleigh lidar temperature measurements in the upper troposphere and lower stratosphere

A single-wavelength Rayleigh lidar system has been used to measure the temperatures in the upper troposphere and lower stratosphere in the night in the altitude range from about 8 to $\text{30}\text{km}$. The temperature derivation is based on an inversion algorithm of the pure Rayleigh backscatter. Calculations include the derivation of the air molecular concentration by an iterative method and the backscattered signals corrected by the background aerosol, which is now found to be low and stable. The uncertainties in estimating the temperature using this method are discussed in detail.The temperature profiles and the tropopause characteristics derived by using the lidar measurements are compared with the radiosonde data. Good agreement is found between these two measurements revealing the potential of this method. The comparison with radiosonde data shows that the lidar measured tropopause temperature is lower by $\text{0.8±1.5}\text{K}$ and the tropopause height is higher by $\text{0.45±0.8}\text{km}$ than the radiosonde measurements. The climatology of local tropopause (24.57°N,121.13°E) is briefly discussed in terms of a double tropopause formation and seasonal variations of the tropopause height and temperature.     

A note on the Aitken nuclei and ion flow measurements in the lower stratosphere

In the light of new measurements of small aerosol particles in the lower stratosphere, some of the old investigations—which were only published in part in scientific journals—are reviewed and compared. The discussion focuses on whether the Aitken nuclei (AN) size distribution up to 20 km can be described by Junge’s or log-normal density functions and under what circumstances one can find a bimodal distribution of these particles. The ion flow in correlated to the stratospheric pollution (intercept with the jet aircraft, volcanic activity) and is, in mean, directly proportional to the aircraft altitude in the undisturbed lower stratosphere. Note: The GCCPR, Univ. Missouri at Rolla, reports quoted in the article can be obtained from the author.     

Global distribution of gaseous mercury in the troposphere

Atmospheric mercury concentrations were measured during a nautical expedition on the Atlantic Ocean between Hamburg (54°N, 10°E) and Santo Domingo (20°N, 67°W). In addition, samples were taken during flights on a commerical aircraft in the upper and middle troposphere between 60°N and 55°S, mostly over the Pacific Ocean. The data obtained in the lower troposphere over the Northern Atlantic show considerable variation in the Hg concentrations, with values ranging between 1 and 11 ng/m³; the average concentration was found to be 2.8 ng/m³. The upper tropospheric data show an interhemispheric difference with average values of 1.45 ng/m³ and 1.08 ng/m³ in the Northern and Southern Hemisphere, respectively. This suggests that mercury production occurs predominantly over the continents both by natural and anthropogenic processes. The mercury content in aerosols was found to be 0.3 ng/m³, or one-tenth of the atmospheric concentration. The data indicate a mean residence time of mercury in the atmosphere of a few months to one year.     

Background concentrations of photochemically active trace constituents in the stratosphere and upper troposphere

Summary High resolution absorption spectroscopy can be used for obtaining very small background concentrations or very low upper limits of trace constituents, particularly from measurements inQ-branches of fundamental vibration-rotation bands. As examples, the results of a search for NH₃ and SO₂ in the Vermande and Dionne Mont-Louis solar spectra will be reported. The relative concentration of NH₃ is very much lower above the Pyrenees than the generally accepted minimum background concentrations near sea-level.     

Inertia-gravity waves in the troposphere and lower stratosphere associated with a jet stream exit region

Radar measurements at Aberystwyth (52.4°N, 4.1°W) of winds at tropospheric and lower stratospheric heights are shown for 12–13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation.     

利用COSMIC掩星资料研究对流层/下平流层大气比湿对ONI指数的响应

本文利用2006年6月至2014年6月COSMIC掩星观测的水汽廓线, 分析了对流层/下平流层(TLS)比湿信号对ENSO的响应.在数据处理中, 将COSMIC掩星水汽廓线计算得到的全球比湿数据内插为1000~30 hPa区间水平分辨率为5°×5°的三维格网, 在各等压面上求取各格网点去除年/月际信号后的比湿月异常值.然后在对比湿月异常时间序列低通滤波的基础上, 进行经验正交分解(EOF)得到比湿主成分, 并对该主成分信号进行二项式平滑; 接下来将平滑后的主成分信号与反映ENSO活动的ONI指数进行相关处理, 得到各等压面主成分信号相对于ONI指数的相关系数及对应的时间延迟.论文分析了包括Niño-3.4的5个代表性区域的TLS比湿异常主成分信号, 结果表明:在各区域, 采用本文先低通滤波再EOF分解的处理方法获得的TLS比湿异常主成分信号与ONI指数均有很强相关性, 对流层相关系数绝对值达0.8以上, 低平流层高于0.7, 在300~200 hPa的上对流层达到峰值; 各等压面上比湿异常主成分信号相对于ONI指数的时间延迟不尽相同, 在对流层中比湿异常主成分信号普遍滞后于ONI指数1~6个月; 在各区域, 比湿异常主成分与ONI指数相关系数绝对值达到最大的等压面都接近250 hPa, 最大相关系数绝对值均达到0.9以上.进一步对全球250 hPa等压面比湿异常主成分与ONI指数相关性的分析表明:两者强相关的区域主要集中在热带; 在这些强相关区域, 比湿异常主成分相对于ONI主要表现为滞后, 且相关系数越大, 相应的时间延迟越短.

     

Inertia gravity wave activity in the troposphere and lower stratosphere observed by Wuhan MST radar

The troposphere and lower stratosphere (TLS) is a region with active atmospheric fluctuations. The Wuhan Mesosphere-Stratosphere-Troposphere (MST) radar is the first MST radar to have become operational in Mainland China. It is dedicated to real-time atmospheric observations. In this paper, two case studies about inertia gravity waves (IGWs) derived from three-dimensional wind field data collected with the Wuhan MST radar are presented. The intrinsic frequencies, vertical wavelengths, horizontal wavelengths, vertical wavenumber spectra, and energy density are calculated and analyzed. In this paper, we also report on multiple waves existing in the lower stratosphere observed by the Wuhan MST radar. Lomb-Scargle spectral analysis and the hodograph method were used to derive the vertical wavenumber and propagation direction. Meanwhile, an identical IGW is observed by Wuhan MST radar both in troposphere and lower stratosphere regions. Combining the observations, the source of the latter IGW detected in the TLS would be the jet streams located in the tropopause region, which also produced wind shear above and below the tropopause.     

Spectral Aerosol Transmittance in the Ultraviolet and Visible Spectra in Athens,Greece

This work investigates the spectral atmospheric transmittance due to aerosols in the urban environment of Athens during a period of one year. The spectral transmittance due to aerosols is derived using measurements of spectral direct-beam solar irradiance in the 310–575 nm spectral band. This derivation is accomplished by using a radiative transfer model for estimating the partial spectral atmospheric transmittance functions due to Rayleigh scattering, and absorption by ozone, nitrogen dioxide and water vapor. The seasonal and diurnal variation of the aerosol transmittance is investigated and the results are discussed with a view to air pollution sources, meteorological factors and topographic characteristics of the Athens basin.     

A statistical study of pressure changes in the troposphere and lower stratosphere after strong solar flares

Summary The average change in height of several constant pressure levels in the troposphere and lower stratosphere after a strong solar flare is described. The analysis covers the northern hemisphere north of 10°N and is based on a sample of 81 carefully selected flares from the period July 1957 through December 1959.The statistical significance of the results is tested by drawing a comparison with the results obtained when one applies exactly the same analysis to three samples of 81 random key-dates selected from the same period.Properties of the reaction pattern are (1) it is pronounced at high as well as low latitudes, (2) it consists of alternating cells of positive and negative height change, (3) it is established within six hours after the flare, and (4) the maximum response occurs near the tropopause.It appears more likely that the atmospheric reaction pattern can be attributed to very energetic solar particles rather than to enhanced ultraviolet radiation.     

The production and distribution of nitrogen oxides in the lower stratosphere

Pure and Applied Geophysics -     

新疆库尔勒地区秋季下平流层重力波特性

利用2011年秋季无线电探空数据,采用矢端曲线法首次分析了新疆库尔勒地区下平流层重力波特征参量,得到36组准单色重力波的结果.结果统计显示：库尔勒秋季下平流层重力波垂直波长、水平波长平均值分别为2.8 km和580 km,固有频率平均值为1.74f.垂直传播方向以上传为主,约占78%,其中下传重力波水平波长较短,固有频率较高.水平传播方向以西北和东南为主,各占1/3,其中上传（下传）重力波水平传播方向以西北（东南）居多,这与热带低纬站点和其他中纬站点观测结果不同.与其他站点比较,库尔勒地区最小,中高纬地区水平波长、垂直波长随纬度增加大致有减小的趋势,库尔勒地区偏离这一趋势,波长偏大.     

Aerosol retrieval over land by exploiting the synergy of TERRA and AQUA MODIS DATA

Aerosol particles over land mainly come from man- made source such as biomass burning, industrial de-bris and natural source such as soil dust, sea salt parti-cles, etc. More and more research results show that, aerosols impact global and regional energy radiative budget; aerosol particles also modify the cloud mi-crophysics, as a result, aerosol particles may change the cloud radiative properties. Aerosol particles also play an important role in many biogeochemical cycles. All the above-menti…     

Internal gravity wave selection in the upper troposphere and lower stratosphere observed by the MU radar: Preliminary results

Marked wavelike variations of the lower stratospheric wind observed on 7–10 May, 1985 by an MST radar in Japan (by the MU radar) are analyzed assuming that they are induced by monochromatic internal inertio-gravity waves. These variations are mainly composed of two modes (periods: 22 and 24 hours), both of which have zonal phase velocities (C _X ) slower than the mean westerly wind (). A statistical analysis of the zonal phase velocity shows thatC _X above andC _X below the tropopause jet stream, which is considered to be a vivid proof of wave selection due to the tropospheric mean flow and upward wave emission from the tropopause jet. A comparison between the MU radar results and routine meteorological observations leads to the conclusion that the marked waves appear when the jet stream takes a maximum wind speed.     

Spatial variability of the aspect sensitivity of VHF radar echoes in the troposphere and lower stratosphere during jet stream passages

The aspect sensitivity of SOUSY-VHF-radar oblique-beam echoes from the troposphere and lower stratosphere has been examined for a number of jet stream passages during the years 1990 - 1992. When the core of the jet is overhead or nearly so, vertical profiles of the aspect sensitivity display two notable features. First, the distinction between mainly isotropic and strongly aspect-sensitive echoes in the troposphere and the lower stratosphere, respectively, often reported for measurements made during calm conditions, does not necessarily prevail in the vicinity of the jet stream. Second, echoes obtained at altitudes near the height of the horizontal wind maximum are found to be more aspect sensitive for beams directed parallel to the horizontal flow or nearly so, than for other beam directions. It is demonstrated that time-averaged horizontal wind speeds estimated from the radar data, taking into account the reduced effective oblique-beam zenith angle resulting from aspect sensitivity, may exceed uncorrected wind speeds by as much as 10 m s⁻¹ in these circumstances. Implications for wind profiling and for describing the backscattering process are discussed. Doppler spectral widths examined for one jet stream passage are found to be narrower in a beam aligned with the horizontal wind at heights near the wind speed maximum than corresponding widths measured in a beam projected at right angles to the jet. The narrowest spectra thus coincide with the most aspect-sensitive echoes, consistent with the hypothesis that such returns result from specular backscattering processes.     

Effects of the imf sector structure in the midlatitude troposphere and stratosphere

Summary The data on geopotential heights and temperatures at 7 pressure levels between 1000-10 hPa above Berlin(52.5 °N, 13.4 °E) are analysed for the winters of 1963–1973. No demonstrable effect of the interplanetary magnetic field sector boundary crossing (IMF SBC) is found in the lower and middle stratosphere, but there is a demonstrable effect in the middle troposphere at the 500 hPa level. This effect is less important than the IMF SBC effect in the tropospheric vorticity area index and seems to be of a different type.

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