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Cheng A.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Cheng A.,University of Chinese Academy of Sciences | Feng Q.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Fu G.,CSIRO | And 6 more authors.
Advances in Atmospheric Sciences | Year: 2015

Changes in rainfall extremes pose a serious and additional threat to water resources planning and management, natural and artificial oasis stability, and sustainable development in the fragile ecosystems of arid inland river basins. In this study, the trend and temporal variation of extreme precipitation are analyzed using daily precipitation datasets at 11 stations over the arid inland Heihe River basin in Northwest China from 1960 to 2011. Eight indices of extreme precipitation are studied. The results show statistically significant and large-magnitude increasing and decreasing trends for most indices, primarily in the Qilian Mountains and eastern Hexi Corridor. More frequent and intense rainfall extremes have occurred in the southern part of the desert area than in the northern portion. In general, the temporal variation in precipitation extremes has changed throughout the basin. Wet day precipitation and heavy precipitation days show statistically significant linear increasing trends and step changes in the Qilian Mountains and Hexi Corridor. Consecutive dry days have decreased obviously in the region in most years after approximately the late 1980s, but meanwhile very long dry spells have increased, especially in the Hexi Corridor. The probability density function indicates that very long wet spells have increased in the QilianMountains. The East Asian summer monsoon index and western Pacific subtropical high intensity index possess strong and significant negative and positive correlations with rainfall extremes, respectively. Changes in land surface characteristics and the increase in water vapor in the wet season have also contributed to the changes in precipitation extremes over the river basin. © 2015, Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg. Source

He Q.,Guangzhou Meteorological Satellite Ground Station | He Q.,CAS South China Sea Institute of Oceanology | He Q.,University of Chinese Academy of Sciences
International Journal of Remote Sensing | Year: 2013

Night-time cloud detection using satellite data is a challenging area of research. This article presents a night-time cloud detection algorithm based on multispectral thresholds for the Visible and Infrared Radiometer (VIRR). VIRR is one of the keystone instruments on board the Chinese Feng Yun 3 (FY-3) polar-orbiting meteorological satellite. In this algorithm, three thermal infrared channels and other ancillary data are used to test for the presence of clouds according to different underlying surface types, and the four levels of possible cloud confidence are used to report whether a pixel is cloudy or clear. This algorithm strengthens the ability of identification of low cloud using the brightness temperature difference between the 3.7 and 12 μm channels. The comparisons of a new cloud mask with the official VIRR cloud mask product and with the official Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask product are shown to illustrate and validate the effect of this new algorithm. In addition, this algorithm is applied to FY-3B/VIRR data to test the validity and accuracy of cloud detection. © 2013 Copyright Taylor and Francis Group, LLC. Source

Huang L.,Nanjing University of Information Science and Technology | Huang J.,Guangzhou Meteorological Satellite Ground Station | Wang J.,National Satellite Meteorological Center | Jiang Y.,Nanjing University of Information Science and Technology | And 3 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

The north-south asymmetry of the equatorial ionization anomaly (EIA) is studied using the total electron content (TEC) data measured by GPS observations from the network of International GNSS Service (IGS) in the 110°E longitude sector for more than a solar cycle term from 2000 to 2011. In this paper, we focus on the hemispheric asymmetry between the northern and southern crest regions of EIA during the geomagnetic quiet periods. The parameters of EIA crest obtained from the TEC profiles in daytime for different conditions of solar activity have been used to study the solar cycle variations of EIA in the Southeast Asian region. The season hereinafter referred to the northern hemisphere except stated otherwise. Results show that the strength, latitudinal and occurrence time position of EIA crest are found to be asymmetric about the magnetic equator. During high solar activity the strength of northern crest is generally greater than that of the southern crest all the months, especially in the winter months. It is also found that the latitude and occurrence time position of EIA crest show a hemispheric asymmetry because (a) During low solar activity the northern crest of EIA moves equatorward in winter and the southern crest moves equatorward in summer and poleward in winter, while during high solar activity the southern crest moves slightly equatorward in summer, and (b) During low solar activity the occurrence time of northern crest is ~1. h later in winter and ~2. h earlier in summer than that of southern crest; During high solar activity the northern crest appears ~1. h earlier only from June to August. The conditions of solar activity have a significantly effect on EIA crest and the north-south asymmetry. These phenomena can be explained by a combined theory of the transequatorial neutral wind, the subsolar point and the auroral equatorward wind. Meanwhile, the condition of the solar activity should be considered. © 2013. Source

Huang L.,Nanjing University of Information Science and Technology | Huang L.,National Center for Space Weather | Wang J.,National Center for Space Weather | Jiang Y.,Nanjing University of Information Science and Technology | And 4 more authors.
Advances in Space Research | Year: 2014

The diurnal variations in total electron content (TEC) in the equatorial ionisation anomaly (EIA) region are not always represented by two crests on both sides of the magnetic equator. Sometimes, only an obvious single crest is evident at equatorial and low latitudes. In this paper, we focus on analysis of the morphological features of the single crest phenomenon in TEC around 120°E longitude during geomagnetic quiet days (Kp < 4-). The variations in TEC are also compared with morphological parameters (foF2 and hmF2) derived from the International Reference Ionosphere extended to Plasmasphere (IRI-Plas) model. Our results show that the single crest phenomenon occurs mainly on days with extremely low solar activity, while the corresponding F2 layer critical frequency showed obvious asymmetry, or even only a single peak. © 2014 COSPAR. Published by Elsevier Ltd. Source

Quan H.-J.,South China University of Technology | Lin G.-G.,South China University of Technology | Deng B.-C.,South China University of Technology | Huang J.,Guangzhou Meteorological Satellite Ground Station
Huanan Ligong Daxue Xuebao/Journal of South China University of Technology (Natural Science) | Year: 2013

According to the data of ionospheric scintillation and total electron content (TEC) observed from January, 2011 to December, 2012 by a monitor set at Shenzhen Station as a part of Meridian Space Weather Monitoring Project in equatorial anomaly regions in South China, the relationship between the TEC depletion and the ionospheric scintillation at the nighttime in South China was analyzed. The results show that (1) there occurs frequent TEC depletion simultaneously with the scintillation; (2) the simultaneous occurrence of strong scintillation (S4>0.6) and TEC depletion is more frequent than that of weak scintillation (0.2 Source

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