Home About us Contact
|
Home About us Contact | ||
|
|
||
Observation Stations (observation + stations)
Selected AbstractsMoho undulations beneath Tibet from GRACE-integrated gravity dataGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007Young Hong Shin SUMMARY Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations, seismologic applications and geohistory reconstructions. We present a 3-D model of the Moho undulations over the entire Tibetan plateau derived from gravity inversion. The gravity field has been obtained by using the Gravity Recovery and Climate Experiment (GRACE) potential field development which has been integrated with terrestrial data, and is presently the best available in the studied area. For the effective use of the global geopotential model that has no height information of observation stations, upward continuation is applied. The Moho model is characterized by a sequence of troughs and ridges with a semi-regular pattern, which could reflect the continent,continent collision between the Indian and Eurasian plates. The three deep Moho belts (troughs) and shallow Moho belts (ridges) between them are clearly found to have an E,W directional trend parallel to the border of the plateau and tectonic lines, while variation of the directionality is observed in central to southeast Tibet. To describe the distinctive shape of the Moho troughs beneath Tibet, we introduce the term, ,Moho ranges'. The most interesting aspects of the Moho ranges are (1) that they run in parallel with the border and tectonic sutures of the plateau, (2) that the distances between ranges are found at regular distances of about 330 km except in northeast Tibet and (3) that the splitting of the ranges into two branches is found as the distance between them is increasing. From our study, we conclude that the distinctive undulations of the Tibetan Moho have been formed by buckling in a compressional environment, superimposed on the regional increase in crustal thickness. According to our analysis, the GRACE satellite-only data turns out to have good enough resolution for being used to determine the very deep Moho beneath Tibet. Our Moho model is the first one that covers the entire plateau. [source] Seasonal changes in radiation and evaporation implied from the diurnal distribution of rainfall in the Lower MekongHYDROLOGICAL PROCESSES, Issue 9 2008Kumiko Tsujimoto Abstract Solar radiation is an important input to many empirical equations for estimating evaporation, which in turn plays an important role in the hydrologic cycle in the Lower Mekong River Basin due to the high evaporation potential of the tropical monsoon climate. Few proper meteorological data exist for the Lower Mekong River Basin, however, and the region's meteorological conditions, including seasonal variation in radiation and evaporation, have not been clarified. In this study, ground-based hourly hydrometeorological data were collected at three observation stations located in different land-use types (urban district, paddy area, and lake) in the Lower Mekong River Basin. These data were analysed to investigate the seasonal variation in radiation and evaporation related to the diurnal distribution of rainfall. Contrary to common expectations, our results showed that rainy and dry seasons had nearly the same amount of solar radiation in the Lower Mekong River Basin because (1) rainy seasons had a relatively larger amount of extraterrestrial radiation; (2) no rain fell on nearly half of the days during rainy seasons; and (3) the amount of solar radiation on rainy days reached 88% of that on non-rainy days. The third factor was attributed to the high frequency of evening rainfall. Furthermore, this rainfall,radiation relationship meant that rainy seasons had a large amount of net radiation due to the low reduction ratio of solar radiation and an increase in long-wave incoming radiation. Accordingly, rainy seasons had a high evaporation potential. Moreover, for the rain-fed rice paddies that prevail in this region, sufficient radiation during the rainy season would be a great advantage for rice growing. Copyright © 2008 John Wiley & Sons, Ltd. [source] Responses of China's summer monsoon climate to snow anomaly over the Tibetan PlateauINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2003Prof. Y. F. Qian Abstract The climatological features of the winter snow depth over the Tibetan Plateau and the summer precipitation in China are diagnosed using datasets obtained from 78 snow observation stations and 160 rainfall stations during 1957 to 1998. The climatic effects of the snow anomaly over the Tibetan Plateau on the regional summer monsoon climate in China are diagnosed and numerically simulated by use of a regional climate model (RegCM2). The singular value decomposition technique is adopted to diagnose the relationships between the previous winter and spring plateau snow depth anomalies and the spring and summer regional precipitation in China. It is found that the snow depth anomaly, especially in winter, is one of the factors influencing precipitation in China; however, it is perhaps not the only one, and even not the most important one. Nevertheless, it is proved that the winter snow anomaly over the Tibetan Plateau is relatively more important than that in spring for the regional precipitation in China. Results of numerical simulations show that the snow anomaly over the plateau has effects that are evident on China's summer monsoon climate. The increase of both snow cover and snow depth can delay the onset and weaken the intensity of the summer monsoon obviously, resulting in a decrease in precipitation in southern China and an increase in the Yangtze and Huaihe River basins. The influence of the winter snow depth is more substantial than that of both the winter snow cover and the spring snow depth. The mechanism of how the plateau snow anomaly influences the regional monsoon climate is briefly analysed. It is found that snow anomalies over the Tibetan Plateau change the soil moisture and the surface temperature through the snowmelt process at first, and subsequently alter heat, moisture and radiation fluxes from the surface to the atmosphere. Abnormal circulation conditions induced by changes of surface fluxes may affect the underlying surface properties in turn. Such a long-term interaction between the wetland and the atmosphere is the key process resulting in later climatic changes. Copyright © 2003 Royal Meteorological Society [source] Recent variations in seasonality of temperature and precipitation in Canada, 1976,95INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2002Paul H. Whitfield Abstract A previously reported analysis of rehabilitated monthly temperature and precipitation time series for several hundred stations across Canada showed generally spatially coherent patterns of variation between two decades (1976,85 and 1986,95). The present work expands that analysis to finer time scales and a greater number of stations. We demonstrate how the finer temporal resolution, at 5 day or 11 day intervals, increases the separation between clusters of recent variations in seasonal patterns of temperature and precipitation. We also expand the analysis by increasing the number of stations from only rehabilitated monthly data sets to rehabilitated daily sets, then to approximately 1500 daily observation stations. This increases the spatial density of data and allows a finer spatial resolution of patterns between the two decades. We also examine the success of clustering partial records, i.e. sites where the data record is incomplete. The intent of this study was to be consistent with previous work and explore how greater temporal and spatial detail in the climate data affects the resolution of patterns of recent climate variations. The variations we report for temperature and precipitation are taking place at different temporal and spatial scales. Further, the spatial patterns are much broader than local climate regions and ecozones, indicating that the differences observed may be the result of variations in atmospheric circulation. Copyright © 2002 Environment Canada. Published by John Wiley & Sons, Ltd. [source] Spatial grouping of United States climate stations using a hybrid clustering approachINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2001Arthur T. DeGaetano Abstract The development of a hybrid clustering technique based on the geographic proximity of observing stations and some application-driven measure of statistical similarity (in this case rank correlation) is described. The procedure is then applied to temperature and precipitation data from the United States (US) Historical Climatology Network. The resulting station groups provide some insight into the number of observation stations that are necessary to monitor adequately the climate of the US. Based on temperature data alone, a 287-station subset of the original 1145 sites would be adequate to account for 80% of the spatial variability in seasonal temperature across the US. Geographically the distribution of these stations would be relatively sparse in the centre of the country with higher station density along the East Coast and from the Rocky Mountains to the West Coast. Generally, the temperature clusters match the existing US climate divisions to some extent. To monitor adequately the spatial variability of precipitation, a network of similar size could be used. However, such a network would only account for 65% of the spatial variability in precipitation. In this case, fairly uniform station density is indicated across the country with the highest station density in Florida and the Dakotas. A similar number of stations, but with slightly different geographic groupings would be adequate to monitor precipitation and temperature simultaneously. Copyright © 2001 Royal Meteorological Society [source] | ||||||||||