MONTBLEX tower observations: Instrumentation,data acquisition and data quality

Tower platforms, with instrumentation at six levels above the surface to a height of 30 m, were used to record various atmospheric parameters in the surface layer. Sensors for measuring both mean and fluctuating quantities were used, with the majority of them indigenously built. Soil temperature sensors up to a depth of 30 cm from the surface were among the variables connected to the mean data logger. A PC-based data acquisition system built at the Centre for Atmospheric Sciences, IISc, was used to acquire the data from fast response sensors. This paper reports the various components of a typical MONTBLEX tower observatory and describes the actual experiments carried out in the surface layer at four sites over the monsoon trough region as a part of the MONTBLEX programme. It also describes and discusses several checks made on randomly selected tower data sets acquired during the experiment. Checks made include visual inspection of time traces from various sensors, comparative plots of sensors measuring the same variable, wind and temperature profile plots, calculation of roughness lengths, statistical and stability parameters, diurnal variation of stability parameters, and plots of probability density and energy spectrum for the different sensors. Results from these checks are found to be very encouraging and reveal the potential for further detailed analysis to understand more about surface layer characteristics.     

Wind profiles in the boundary layer over Kharagpur associated with synoptic scale systems

Doppler sodar wind data for the boundary layer over Kharagpur obtained during MONTBLEX-1990 at a height interval of 30 m from surface up to 1500 m have been analysed for the periods when intense synoptic scale disturbances from north Bay of Bengal moved along the eastern end of the monsoon trough. The variation in the vertical wind profile in the lower boundary layer over Kharagpur during the passage of synoptic scale disturbances has been discussed in the paper. The analysis indicates that the mean winds over Kharagpur veered with height in the lower boundary layer near the surface suggesting divergence over Kharagpur when the system lay south/southwest of the station. No such veering has been noticed when the centre of the system lay very close to the station.     

Lidar Measurements of Aerosols in the Tropical Atmosphere

Measurements of atmospheric aerosols and trace gases using the Laser radar (lidar) techniques, have been in pro-gress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18o32’N, 73o51’E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal va-riation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected me-teorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles ob-tained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol lay-ers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.     

相关系数的变化形式和相关场揭示的大气波动及其物理本质

文中对相关系数公式的形式进行了变化,得到了以傅里叶谱系数表示的相关系数公式,完成了新形式的相关系数公式与大气动力学方程的直接连接,由此产生了由相关系数表示的动力学方程,从而指出用相关场研究大尺度动力过程是有意义的,相关场揭示的联系可通过相关系数表示的方程而得到动力学解释。     

卫星重力梯度测量与地球引力场的精度研究

本文根据地球引力位的球谐函数展开式,利用重力梯度张量各分量导出了位系数模型的精度估计公式.从三方面进行了研究:假定卫星重力梯度仪测量精度,探讨用重力梯度数据确定地球重力场模型的精度;求出位系数模型和大气阻力引起的重力梯度卫星的轨道误差;最后,反求轨道误差和位系数误差对重力梯度测量值的影响.数值计算表明,与地面技术和常规卫星方法相比,卫星梯度测量可使重力场模型的精度至少提高3-5倍;利用重力梯度张量全分量求得的重力值精度比单用径向分量V_rr的结果提高40％以上;若仅顾及位系数模型和大气阻力误差,则轨道误差对梯度测量值的影响△V_i3（i=3,2,1）至少可分别在1/4和1/3弧圈内达到△V_i3≤σ（仪器精度）.     

青藏高原地区的大气浑浊度特征

本文通过比较Angstrom大气浑浊度系数的各种计算方法,得出了适合青藏高原地区的大气浑浊度系数的计算方法。据此利用1982年8月至1983年7月青藏高原地区部分观测站的太阳直接辐射资料计算了大气浑浊度系数,分析了它的变化特征。同时利用常规气象要素拟合得出了计算大气浑浊度系数的经验公式,计算和分析了青藏高原地区大气浑浊度系数的时间和空间分布。     

航放数据图象复原技术研究

本文介绍一种独特的航放数据图象复原方法.该方法的主要技术关键是:提出航放数据图象复原原理和理论基础;建立航放数据图象复原处理流程;制定重建数据网格文件的途径;进行航放数据图象复原效果及误差评价.     

Measuring correlations between atmospheric oxygen and carbon dioxide mole fractions: A preliminary study in urban air

On 25 and 26 October 1986 the air in Cambridge, Massachusetts was monitored for O₂ and CO₂ mole fraction. O₂ concentrations were detected from changes in the relative refractivity of dried air between two lines of ¹⁹⁸Hg at 2537.269 and 4359.562 Å using dual-wavelength interferometry. Changes in oxygen mole fraction were resolved with two-minute time resolution to a precision of ±2.0 ppm. Changes in O₂ were shown to be strongly anticorrelated with changes in CO₂ as expected for combustion processes. The demonstrated instrumental capabilities are appropriate for measuring changes in O₂ mole fraction in background air which could be of importance to a broad range of biogeochemical studies.     

Effects of long-range transport on atmospheric trace constituents at the baseline station tenerife (Canary Islands)

First results of baseline observations from the new BAPMoN station Tenerife give information about the atmospheric background in this latitude of about 25° N in the North Atlantic. The influence of the meridional exchange with the northern part of the hemisphere as well as transport from the African continent is evident. Changes of air mass are strongly reflected in the concentration records of carbon dioxide, methane, and ozone depending on the seasonal and meridional distribution of these components. Transport of Sahara dust results in an increase of optical thickness and an ozone depletion. According to the seasonal frequency of characteristic transport conditions, these influences are reflected in the annual cycle of the records.