Variations of thermodynamical parameters in the atmospheric boundary layer over the Deccan plateau region,India

The thermodynamical structure of the atmospheric boundary layer over the Deccan plateau region has been studied with aerological data for 1980 and 1981.The temperatures in the sub-cloud layer were lower on active monsoon days than dose on weak monsoon days. An opposite trend was noticed in the layer above the 900 mbar level. The moisture content on active monsoon days was higher than that on weak monsoon days. The profile of relative humidity above the 850 mbar level showed large deviations between the active and weak monsoon conditions. On active monsoon days the values of dry static stability were higher than those on weak monsoon days. An opposite trend was noticed in the case of moist static stability. On active monsoon days the magnitudes of thev components of wind were small compared with those of theu components, and the latter showed a gradual decrease with height.     

大气的可预报性与大气模式的设计

本文首先提出了设计数值天气预报模式的基本原则——模式大气的可预报性和实际大气的可预报性相一致。然后依据此原则讨论了目前在设计各种数值预报模式时存在的问题。     

力模型误差对近地卫星定轨的影响分析

本文针对近地卫星所受摄动力的特点，详细分析了大气阻尼系数、大气模式、地球重力场模型、系统性误差等对定轨的影响。利用待估大气阻尼系数及其变率，可有效地消除大气模型差的影响，提高定轨精度。在得克萨斯大学空间研究中心编制的精密定轨软件ＵＴＯＰＩＡ８６的基础上，重新编制和调试出能有效处理近地卫星定轨的实用软件。     

Tschebyscheff 函数在大气模式垂直离散问题中的应用

文章就常用全球谱模式中的垂直离散问题进行了讨论，给出了用Tschebyscheff函数积分静力方程、连续方程，以及计算垂直平流、垂直扩散等的方法。还对某些气象要素在垂直方向微商呈现间断的问题进行了分析，指出了其中存在的问题和应采取的措施。     

The electric potential gradient in mist,haze, and fog

The variation of potential gradient in mist, haze, and fog has been studied. During the formation of these hydrometers the potential gradients were found to increase. Large positive potential gradients were observed during dense fog conditions. Possible charge generation mechanisms responsible for these potential gradients during fog formation are discussed.     

Structure and Dynamics of Katabatic Flow Jumps: Idealised Simulations

For the first time, results from a high-resolution numerical simulation (with horizontal grid spacing of 35m) were used to reveal the detailed structure near an atmospheric katabatic jump over an idealized slope. The simulation represents flow over the slopes of Coats Land, Antarctica for austral winter conditions. The katabatic jump is characterised by an updraft with vertical velocities of order 1ms⁻¹ and serves as a possible forcing mechanism for the gravity waves frequently observed over the ice shelves around the Antarctic. Results also indicate that strong turbulence is generally confined within a mixing zone near the top of the katabatic layer upstream of the jump and extends downstream through the top of the strong updraft associated with the jump. Detailed analyses of momentum and heat budgets across the katabatic jump indicate that, upstream of the jump, turbulent mixing is important in decelerating the upper part of the katabatic layer, while within the jump the upslope pressure gradient force associated with the pool of cold air plays a role in decelerating the flow near the surface. The heat budget near the jump reveals a simple two-term balance: the turbulent heat flux divergence is balanced by the advection. A comparison of model results with available theories indicates that mixing between layers of different potential temperature structure indeed plays some role in the development of katabatic flow jumps, especially for strong jumps. Theories used to study katabatic jumps should include this mixing process, of which the amount depends on the intensity of the jump. A conceptual model of a katabatic jump, including the main dynamical processes, is constructed from these detailed analyses.     

Non-Linear, Microscale Modelling of the Flow Over Askervein Hill

The flow solver “3DWind” is used to explore new aspects of the Askervein hill flow case. Previous work has investigated sensitivities to the grid, the inflow boundary profile, the roughness and the turbulence model. Several different linear and non-linear numerical models have also been validated by means of the Askervein hill case. This analysis focuses on the flow sensitivity to the grid spacing, the incident wind direction and the vertical resolution of topographic data. The horizontal resolution is found to be fine enough to cause only minor differences compared to a grid where every second node is removed. The vertical resolution dependence is mainly attributed to the wall functions. Simulations are performed for wind directions 200°, 205°, 210° and 215° at the reference station. The smallest directional biases compared to experimental values along a line through the hilltop are found for the directions 200° and 205°. There are larger wind direction changes along this line through the hilltop in the 200° case than in the 215° case. Still the simulation results give less veering than found in the experimental results, and this is maybe caused by a slightly stable atmosphere. The sensitivity to the vertical resolution of the topographical data is found to be particularly high close to the ground at the top of the hill; this is where the speed-up is most important. Differences decrease with the height from the ground. At higher levels the speed-ups are smaller and caused by terrain formations with larger scales.     

Aeolian shear stress ratio measurements within mesquite-dominated landscapes of the Chihuahuan Desert, New Mexico, USA

A field study was conducted to ascertain the amount of protection that mesquite-dominated communities provide to the surface from wind erosion. The dynamics of the locally accelerated evolution of a mesquite/coppice dune landscape and the undetermined spatial dependence of potential erosion by wind from a shear stress partition model were investigated. Sediment transport and dust emission processes are governed by the amount of protection that can be provided by roughness elements. Although shear stress partition models exist that can describe this, their accuracy has only been tested against a limited dataset because instrumentation has previously been unable to provide the necessary measurements. This study combines the use of meteorological towers and surface shear stress measurements with Irwin sensors to measure the partition of shear stress in situ. The surface shear stress within preferentially aligned vegetation (within coppice dune development) exhibited highly skewed distributions, while a more homogenous surface stress was recorded at a site with less developed coppice dunes. Above the vegetation, the logarithmic velocity profile deduced roughness length (based on 10-min averages) exhibited a distinct correlation with compass direction for the site with vegetation preferentially aligned, while the site with more homogenously distributed vegetation showed very little variation in the roughness length. This distribution in roughness length within an area, defines a distribution of a resolved shear stress partitioning model based on these measurements, ultimately providing potential closure to a previously uncorrelated model parameter.     

Evidence for high-frequency late Glacial to mid-Holocene (16,800 to 5500 cal yr B.P.) climate variability from oxygen isotope values of Lough Inchiquin, Ireland

A 7.6-m core recovered from Lough Inchiquin, western Ireland provides evidence for rapid and long-term climate change from the Late Glacial period to the Mid-Holocene. We determined percentage of carbonate, total organic matter, mineralogy, and δ¹⁸O_calcite values to provide the first high-resolution record of climate variability for this period in Ireland. Following deglaciation, rapid climate amelioration preceded large increases in GISP2 δ¹⁸O_ice values by ∼2300 yr. The Oldest Dryas (15,100 to 14,500 cal yr B.P.) Late Glacial event is documented in this record as a decrease in δ¹⁸O_calcite values. Brief warming at ∼12,700 cal yr B.P. was followed by characteristic Younger Dryas cold and dry climate conditions. A rapid increase in δ¹⁸O_calcite values at ∼10,500 cal yr B.P. marked the onset of Boreal warming in western Ireland. The 8200 cal yr B.P. event is represented by a brief cooling in our record. Prior to general warming, a larger and previously undescribed climate anomaly between 7300 and 6700 cal yr B.P. is characterized by low δ¹⁸O_calcite values with high-frequency variability.     

大连地区主汛期多、少雨年同期大气环流场的差异

大连地区主汛期降水异常是该地区大气环流异常直接影响的结果,本文用1961~2000年各层大气环流场资料来分析对比多、少雨年同期大气环流的情况。揭示出大连地区主汛期多雨年和少雨年同期的海平面气压场、850 hPa大气环流场、500 hPa西风带槽脊和高度场都存在显著差异。多雨年较少雨年该地区低层的辐合上升运动加强,850 hPa盛行西南气流,水汽输送旺盛。同时,500 hPa西风带的槽脊波动加深,高空西风急流增强。