Change detection in Sal forest in Dehradun Forest Division using remote sensing and geographical information system

The review of study site have revealed the change in vegetation cover of Sal Dense to Sal Medium and Sal Open in 6 forest Mosaics owing to biotic and abiotic conditions prevailing in the specific areas. Analysis carried out using thematic map derived from aerial photograph of 1976 and satellite data of IRS 1C LISS III False Colour Composite (FCC) of March 1999 revealed the cause for change in forest density classes. Deforestation, encroachment and agriculture have been identified as the underlying causes, which have affected some specific locations to a marked extent. There has been a progressive and remarkable change among vegetation classes from 1976 to 1999. It is evident from forest type and density map that Sal density has significantly reduced from Sal Dense 65.61 % in 1976 to Sal Dense 11.12% in the year 1999 followed by Sal Open 11.18 % and Sal Medium 18.24 %. The overall change has been estimated to be 42.11% of the total forested area.     

Estimation of recent glacial variations in baspa basin using remote sensing technique

The Himalayas has one of the largest concentrations of glaciers outside the Polar Regions. Various reports suggest that significant number of mountain glaciers is shrinking due to climatic variations. Monitoring of these glaciers is important to assess future availability of water resources in the Himalayan region. However, Himalayan glaciers are normally difficult to monitor due to the rugged, mountainous terrain. Therefore, images of Indian Remote Sensing Satellite were used to monitor glaciers in the Baspa basin. Investigations have shown the presence of 30 glaciers in the basin, with areal extent of 167 km2. Out of these, 19 glaciers, with areal extent of 140 km² were selected to estimate retreat. Investigation suggests that almost all glaciers are retreating in the study basin and overall 19% deglaciation has been observed from 1962 to 2001. In general, altitude distribution appears to have significant influence on glacial retreat. Glaciers located around 5000 m altitude range are showing 24% loss as compared to 14% by glaciers located in altitude range higher than 5400 m. In addition, mean altitude of glacier terminus is shifted upward by 88 m, i.e. from 4482 to 4570 m in last 39 years. The glacial volumes were estimated using regression relationship between area and depth. The investigations have suggested that 19.10 km³ of glacial water stored in the 19 glaciers in 1962, has been reduced to 14.71 km³ in 2001, respectively, an overall loss of 23 percent in a period between 1962 and 2001. These investigations suggest that all glaciers in the Baspa Basin are reducing and in long term, such reducing trend can create scarcity of water in the region.     

青藏高原上中尺度对流系统(MCSs)的个例分析及其比较

对1995年7月25—28日高原上连续数日出现MCSs的现象进行了红外云图特征及其演变、大尺度环境背景场和对流有效位能的分析。可以发现，所有这些MCSs有着相似的日变化演变过程；它们的初始对流在中午由于日射加热开始活跃，之后迅速发展，这些MCSs在后下午形成，在傍晚达到最强，之后逐渐减弱。其中26日MCS最为强大，它是在单一的强大的近于圆形的高原反气旋高压背景下受强的低层热力强迫和条件不稳定的驱动而发生的。这些发生条件都与高原本身的热力作用紧密相关，所以它的发生发展主要与高原特有的较为纯粹的热力因子相联系。28日MCS是另一个很强的MCS，它明显地受到中纬度西风槽的斜压区的影响，这二个很强的MCS有着不同的发展机制和显著不同的表现特征。     

GPS折射角资料的变分同化试验

越来越多的新型观测资料为数值天气预报水平的进一步提高提供了许多新的机会。在各种新型的观测资料中,GPS(全球定位卫星系统)折射角资料无疑是非常重要的。GPS折射角资料具有分辨率高、全天候探测、覆盖全球等优点,实现对GPS折射角资料的变分同化,将具有非常重要的意义。文中介绍了如何获得及同化GPS折射角资料的原理。对GPS折射角资料的变分同化可以分为两种:间接同化和直接同化,文中对这两种方法都作了具体介绍。在变分同化的最小化过程中,计算效率无疑是最重要的,而优化步长的计算又直接关系到算法效率的成败。根据最小化算法的特点,通过数学推导,得出一种适合于各种最小化算法的计算优化步长的自适应方法。最后,还利用1995年10月11日的GPS折射角资料进行了数值试验,结果表明了变分同化方法和计算优化步长方法的有效性。     

The Northward Shift of Climatic Belts in China During the Last 50 Years and the Corresponding Seasonal Responses

Along the meridian of 105°E, the Chinese region are divided into two parts, east and west. The results show that in the east part of China the temperate extratropical belt, the warm extratropical belt,and the northern subtropical belt shift northward significantly, whereas the middle subtropical belt and the southern subtropical belt have less or no change. As for the northern subtropical belt, the maximal northward shift can reach 3.7 degrees of latitude. As for the warm extratropical belt, along the meridian of 120°-125°E, the maximal northward shift can reach 3-4 degrees. In the west part of China, each climatic belt changes little. Only in the Xinjiang area are the significant northward shifts. Correspondingly, it is found that in the last 50 years the traditional seasons have changed. For Beijing, Hailar, and Lanzhou, in general, summer becomes longer and winter shorter over the last 50 years. Summer begins early and ends late with respect to early 1950s. Contrary to the summer, winter begins la     

Climate-Years in the True Prairie: Temporal Fluctuations of Ecologically Critical Climate Conditions

The True Prairie (TP) is a large area in the central U.S. which was a tall grass prairie for thousands of years prior to its conversion to crop land. An analysis of climatically controlling factors indicated that the tall grass prairie is favored by the ratio of warm season precipitation to potential evapotranspiration exceeding 0.75 (west boundary), cold season precipitation less than 38 cm (south boundary), high cold-season frequency of thunderstorms (north boundary), and high drought frequencies (entire region). A `climate-year' approach was used to assess the temporal and spatial variability of these conditions during the 20thcentury. This analysis did not reveal any long-term trends in most climate-year types, although there were significant decadal-scale fluctuations, most notably a high frequency of drought-type years in the 1930s and 1950s. However, the well-documented upward trend in precipitation is manifested in an increasing frequency of one climate-year type characterized by above normal cold season precipitation in the southern border area of the TP.     

In-situ Formation of Light-Absorbing Organic Matter in Cloud Water

Current climate models seem to underestimate the flux of solar energy absorbed by the global troposphere. All of these models are constrained with the assumption that cloud droplets consist of pure water. Here we demonstrate in a simple laboratory experiment that aromatic hydroxy-acids which are found in continental fine aerosol can react with hydroxyl radicals under typical conditions prevalent in cloud water influenced by biomass burning. The reactions yield colored organic species which do absorb solar radiation. We also suggest that the products of such reactions may be humic-like substances whose presence in continental aerosol has been confirmed but their source mechanisms are still much sought after. We also attempt to give a first order estimate of the enhancement of water absorption at a visible wavelength under atmospheric conditions.     

Modelling of the OASIS Energy Flux Measurements Using Two Canopy Concepts

Two land surface schemes, SCAM and CSIRO9, were used to model the measured energy fluxes during the OASIS (Observations At Several Interacting Scales) field program. The measurements were taken at six sites along a 100 km rainfall gradient. Two types of simulations were conducted: (1) offline simulations forced with measured atmospheric input data at each of the six sites, and (2) regional simulations with the two land surface schemes coupled to the regional climate model DARLAM.The two land surface schemes employ two different canopy modelling concepts: in SCAM the vegetation is conceptually above the ground surface, while CSIRO9 employs the more commonly used `horizontally tiled' approach in which the vegetation cover is modelled by conceptually placing it beside bare ground. Both schemes utilize the same below-ground components (soil hydrological and thermal models) to reduce the comparison to canopy processes only. However, the ground heat flux, soil evaporation and evapotranspiration are parameterised by the two canopy treatments somewhat differently.Both canopy concepts reproduce the measured energy fluxes. SCAM has a slightly higher root-mean standard error in the model-measurement comparison for the ground heat flux. The mean surface radiative temperature simulated by SCAM is approximately 1K lower than in the CSIRO9 simulations. However, the soil and vegetation temperatures (which contribute to the radiative temperature) varied more in the CSIRO9 simulations. These larger variations are due to the absence of a representation of the aerodynamic interactions between vegetation and ground.     

Closed-form solution of P4P or the three-dimensional resection problem in terms of Möbius barycentric coordinates

 The perspective 4 point (P4P) problem - also called the three-dimensional resection problem - is solved by means of a new algorithm: At first the unknown Cartesian coordinates of the perspective center are computed by means of M?bius barycentric coordinates. Secondly these coordinates are represented in terms of observables, namely space angles in the five-dimensional simplex generated by the unknown point and the four known points. Substitution of M?bius barycentric coordinates leads to the unknown Cartesian coordinates (2.8)–(2.10) of Box 2.2. The unknown distances within the five-dimensional simplex are determined by solving the Grunert equations, namely by forward reduction to one algebraic equation (3.8) of order four and backward linear substitution. Tables 1.–4. contain a numerical example. Finally we give a reference to the solution of the 3 point (P3P) problem, the two-dimensional resection problem, namely to the Ansermet barycentric coordinates initiated by C.F. Gau? (1842), A. Schreiber (1908) and A.␣Ansermet (1910). Received: 05 March 1996; Accepted: 15 October 1996