武汉基准台气压对重力潮汐观测的影响

武汉基准台超导重力仪观测重力残差和台站气压的相关分析结果表明,重力残差信号主要是由气压变化引起的。本文在频率和时间域内分别测定了大气重力导纳值,结果说明在时域内的导纳值为－０．３０７μＧａｌ／（１Ｇａｌ＝１ｃｍ／ｓ＾２）,而在频域内的大气重力导纳值变化范围在０．３￣０．５μＧａｌ／ｈＰａ之间,这一结果与理论模拟计算相符。对实测资料作气压改正的结果表明气压改正效果非常显著,各频段内的观测残差振幅均有     

Occurrence of polar stratospheric clouds at Kiruna

Polar stratospheric clouds (PSCs) are often observed in the Kiruna region in northern Sweden, east of the Scandinavian mountain range, during wintertime. PSC occurrence can be detected by ground-based optical instruments. Most of these require clear tropospheric weather. By applying the zenith-sky colour index technique, which works under most weather conditions, the data availability can be extended. The observations suggest that PSC events, especially of type II (water PSCs) may indeed more common than predicted by synoptic models, which is expected because of the frequent presence of mountain-induced leewaves. However, it will be of importance to increase the density of independent observations.     

An anomalous subauroral red arc on 4 August, 1972: comparison of ISIS-2 satellite data with numerical calculations

This study compares the Isis II satellite measurements of the electron density and temperature, the integral airglow intensity and volume emission rate at 630 nm in the SAR arc region, observed at dusk on 4 August, 1972, in the Southern Hemisphere, during the main phase of the geomagnetic storm. The model results were obtained using the time dependent one-dimensional mathematical model of the Earth’s ionosphere and plasmasphere (the IZMIRAN model). The major enhancement to the IZMIRAN model developed in this study to explain the two component 630 nm emission observed is the analytical yield spectrum approach to calculate the fluxes of precipitating electrons and the additional production rates of N⁺₂, O⁺₂, O⁺(⁴S), O⁺(²D), O⁻(²P), and O⁺(²P) ions, and O(¹D) in the SAR arc regions in the Northern and Southern Hemispheres. In order to bring the measured and modelled electron temperatures into agreement, the additional heating electron rate of 1.05 eV cm⁻³ s⁻¹ was added in the energy balance equation of electrons at altitudes above 5000 km during the main phase of the geomagnetic storm. This additional heating electron rate determines the thermally excited 630 nm emission observed. The IZMIRAN model calculates a 630 nm integral intensity above 350 km of 4.1 kR and a total 630 nm integral intensity of 8.1 kR, values which are slightly lower compared to the observed 4.7 kR and 10.6 kR. We conclude that the 630 nm emission observed can be explained considering both the soft energy electron excited component and the thermally excited component. It is found that the inclusion of N₂(v > 0) and O₂(v > 0) in the calculations of the O⁺(⁴S) loss rate improves the agreement between the calculated N_e and the data on 4 August, 1972. The N₂(v > 0) and O₂(v > 0) effects are enough to explain the electron density depression in the SAR arc F-region and above F2 peak altitude. Our calculations show that the increase in the O⁺ + N₂ rate factor due to the vibrationally excited nitrogen produces the 5–19% reductions in the calculated quiet daytime peak density and the 16–24% decrease in NmF2 in the SAR arc region. The increase in the O⁺ + N₂ loss rate due to vibrationally excited O₂ produces the 7–26% decrease in the calculated quiet daytime peak density and the 12–26% decrease in NmF2 in the SAR arc region. We evaluated the role of the electron cooling rates by low-lying electronic excitation of O₂(a¹δ_g) and O₂(b¹σ_g⁺), and rotational excitation of O₂, and found that the effect of these cooling rates on T_e can be considered negligible during the quiet and geomagnetic storm period 3–4 August, 1972. The energy exchange between electron and ion gases, the cooling rate in collisions of O(³P) with thermal electrons with excitation of O(¹D), and the electron cooling rates by vibrational excitation of O₂ and N₂ are the largest cooling rates above 200 km in the SAR arc region on 4 August, 1972. The enhanced IZMIRAN model calculates also number densities of N₂(B³π_g⁺), N₂(C³π_u), and N₂(A³σ_u⁺) at several vibrational levels, O(¹S), and the volume emission rate and integral intensity at 557.7 nm in the region between 120 and 1000 km. We found from the model that the integral integral intensity at 557.7 nm is much less than the integral intensity at 630 nm.     

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.     

Late spring ultraviolet levels over the United Kingdom and the link to ozone

Erythemally-weighted ultraviolet (UV_ery) levels measured over southern England, during anticyclonic weather between 30 April and 2 May, 1997, were almost 50 higher than normally expected for clear skies and were similar to mid-summer values for the first time since measurements began in 1990. Investigation of this episode suggests that a combination of both meteorological and chemical effects were responsible for generating record low ozone amounts for the time of year. Further, comparisons between the A band ultraviolet (315 to 400 nm wavelength) amounts, and radiative calculations confirm that the high UV_ery was primarily due to the reduction in total ozone. These results are contrasted with a similar period for 1998, in which near climatological ozone amounts were measured. The prospects for enhanced UV_ery levels in future years are briefly reviewed in the light of expected increases in stratospheric halogen levels and greenhouse gases.     

Vertical circulation and thermospheric composition: a modelling study

The coupled thermosphere-ionosphere-plasmasphere model CTIP is used to study the global three-dimensional circulation and its effect on neutral composition in the midlatitude F-layer. At equinox, the vertical air motion is basically up by day, down by night, and the atomic oxygen/molecular nitrogen [O/N₂] concentration ratio is symmetrical about the equator. At solstice there is a summer-to-winter flow of air, with downwelling at subauroral latitudes in winter that produces regions of large [O/N₂] ratio. Because the thermospheric circulation is influenced by the high-latitude energy inputs, which are related to the geometry of the Earth’s magnetic field, the latitude of the downwelling regions varies with longitude. The downwelling regions give rise to large F2-layer electron densities when they are sunlit, but not when they are in darkness, with implications for the distribution of seasonal and semiannual variations of the F2-layer. It is also found that the vertical distributions of O and N₂ may depart appreciably from diffusive equilibrium at heights up to about 160 km, especially in the summer hemisphere where there is strong upwelling.     

大气电场异常判别及预报效能的统计检验

依据郝建国等提出的异常判别规则对大气电场的原始观测资料重新进行了异常判别和分组, 并依据朱成熹等提出的效率值法,分别对监测到的异常及实际上报的异常与地震预报的相关进行了统计检验及评分,信度在 15% 以下,该方法通过了假设检验。 结果表明,这一方法用于地震预报是有统计依据的。     

The IAG approach to the atmospheric geoid correction in Stokes' formula and a new strategy

The well-known International Association of Geodesy (IAG) approach to the atmospheric geoid correction in connection with Stokes' integral formula leads to a very significant bias, of the order of 3.2 m, if Stokes' integral is truncated to a limited region around the computation point. The derived truncation error can be used to correct old results. For future applications a new strategy is recommended, where the total atmospheric geoid correction is estimated as the sum of the direct and indirect effects. This strategy implies computational gains as it avoids the correction of direct effect for each gravity observation, and it does not suffer from the truncation bias mentioned above. It can also easily be used to add the atmospheric correction to old geoid estimates, where this correction was omitted. In contrast to the terrain correction, it is shown that the atmospheric geoid correction is mainly of order H of terrain elevation, while the term of order H ² is within a few millimetres. Received: 20 May 1998 / Accepted: 19 April 1999     

用蒙特-卡罗方法计算大气点扩散函数

大气效应的纠正是一个仍未被彻底解决的定量遥感问题,随着遥感器空间分辨率的不断提高,各种斜视星勒遥感不断涌现,寻找交叉辐射项的修正方法日显迫切,该文应用蒙特－卡罗（Ｍ－Ｃ）方法求得不同大气条件下的点扩散函数图形,结果显示：（１）大气状况对点扩散函数的形状、目标像元的贡献率有不可忽略的影响;（２）一次散射的假定将导致背景像元的贡献率,其绝对误差最大可达７％,其相对误差最大可达４０％;（３）斜视条件下与     

青藏高原能量收支观测实验的新进展

通过对１９９３年９月－１９７年３月在五道梁所取的观测资料的分析,简述了在青藏高原地区能量收支观测中所取得的新认识和新进展。