GPS based TEC measurements for a period August 2008– December 2009 near the northern crest of Indian equatorial ionospheric anomaly region

In recent years, measurements of total electron content (TEC) have gained importance with increasing demand for the GPS-based navigation applications in trans-ionospheric communications. To study the variation in ionospheric TEC, we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India (21.16°N, 72.78°E) located at the northern crest of equatorial anomaly region. The data collected (for the low sunspot activity period from August 2008–December 2009) were used to study the diurnal, monthly, seasonal semi-annual and annual variations of TEC at Surat. It was observed that the diurnal variation at the region reaches its maximum value between 13:00 and 16:00 IST. The monthly average diurnal variations showed that the TEC maximizes during the equinox months followed by the winter months, and are lowest during the summer months. The ionospheric range delay to TEC for the primary GPS signal is 0.162 m per TECU. The diurnal variation in TEC shows a minimum to maximum variation of about 5 to 50 TECU (in current low sunspot activity periods). These TEC values correspond to range delay variations of about 1 to 9 m at Surat. These variations in the range delay will certainly increase in high sunspot activity periods. Detected TEC variations are also closely related to space weather characterizing quantities such as solar wind and geomagnetic activity indices.     

Comparative study of scintillations at the magnetic equator and at the crest region of the equatorial anomaly in Indian zone

Using simultaneous long-term observations of ionospheric scintillation at equator and anomaly crest region in the same longitude (Indian) zone comparative features of scintillation occurrence are brought out. The salient features are: (a) predominantly pre-midnight occurrence of scintillation at equator during winter and equinox seasons, (b) increase of pre-midnight scintillation occurrence with solar activity (c) shifting of occurrence peak during summer from post-midnight in low to pre-midnight in high solar activity periods (d) similarity of scintillation behaviour at these locations during winter and equinoxes but dissimilarity during summer. The solar activity response and magnetic effects indicate that the scintillations at the anomaly crest region in winter and equinox, particularly during high solar activity periods, are of equatorial origin while the summer events may be of local or mid-latitude origin.     

Variation of the 0+ ion density during low and high solar activity as measured by the SR0SS-C2 satellite

The O⁺ ion density measured by the SROSS-C2 satellite during solar minima (year 1995, F_10.7 = 77) and maxima (year 2000, F_10.7 = 181) has been analyzed for studying diurnal, seasonal, latitudinal and geomagnetic variations. The study region covers an area encompassed between 5-3 5° N latitude and 65-95° E longitude over India at a ~500 km altitude (F2 region). The year 2000 shows significant enhancement in the annual average of O⁺ ion density and attainment of post sunset secondary enhancement compared to 1995. Attributed to photoionization, daytime shows a maximum ionization compared to nighttime. However, attainment of post sunset secondary maxima is attributed to the strong pre-reversal enhancement in the vertical E x B drift. The effect of geomagnetic activity Kp through the E x B drift dynamic movement on O⁺ ion density distribution studies indicates periodicities of seven and nine days in 1995 and 2000, respectively, and polynomial dependency of the O⁺ ion density on geomagnetic activity Kp. Further on, stratification of the O⁺ ion density according to latitude (5-35° N) indicates high density in mid-latitudes (12-24° N) compared to high and low latitudes, except in the winter of 1995, which shows a distinct trend (i.e., density decreases with increasing latitude).     

A comparison of winter and summer temperature variations in a shallow bar-built estuary

Bihourly water temperatures from two, 110-day study periods are compared for a study site in the Indian River Lagoon, along the Atlantic coast of South Florida. Results of a summer study include the annual maximum temperatures in July and August, and reveal low-frequency variations of ±1–2°C superimposed onto the annual curve. The winter study shows the annual minimum temperatures in late February and low-frequency variations of ±3–4°C superimposed onto the annual curve. At the very long and the very short periodicities, thermal activity is consistently higher during the winter study. At the diurnal period, however, the temperature range during the summer study is twice that recorded during the winter study, and the time of warmest water in the diurnal cycle is shifted back between two and three hours toward mid day in the summer months. This is attributed to the relative increase in importance of heating by insolation at that time of year. Sensible and latent heat fluxes appear to damp the diurnal cycle in both records.     

Variability of soil moisture and its relationship with surface albedo and soil thermal diffusivity at Astronomical Observatory,Thiruvananthapuram, south Kerala

Continuous observation data collected over the year 2008 at Astronomical Observatory, Thiruvananthapuram in south Kerala (76°59′E longitude and 8°30′N latitude) are used to study the diurnal, monthly and seasonal soil moisture variations. The effect of rainfall on diurnal and seasonal soil moisture is discussed. We have investigated relationships of soil moisture with surface albedo and soil thermal diffusivity. The diurnal variation of surface albedo appears as a U-shaped curve on sunny days. Surface albedo decreases with the increase of solar elevation angle, and it tends to be a constant when solar elevation angle is greater than 40°. So the daily average surface albedo was calculated using the data when solar elevation angle is greater than 40°. The results indicate that the mean daily surface albedo decreases with increases in soil moisture content, showing a typical exponential relation between the surface albedo and the soil moisture. Soil thermal diffusivity increases firstly and then decreases with the increase of soil moisture.     

Last glacial–interglacial sea-ice cover in the SW Atlantic and its potential role in global deglaciation

Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 10⁶ km² to a maximum of 19 × 10⁶ km² during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ～61°S to ～52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ～30 ka and 22 ka that extended to ～59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.     

SporadicE ionization associated with meteor events

Two meteor events which were sighted in the Gujarat skies of India, were accompained by the visibility of sporadicE ionization on the ionograms recorded at Ahmedabad (Geog. Lat. 23·2°N, long. 72·30°E). The first event was the Dhajala fireball which flashed into the geoatmosphere along an E-N to W-S trail at about 20·40 h IST on 28 January 1976; the closest distance of the ground projection of meteor trail from Ahmedabad was 50km. The other event was a possible meteor group sighted over Ahmedabad on 28 May 1978, at about 21·10 h IST. This work describes the nature of the sporadicE ionization observed on Ahmedabad ionograms during the two events. Features of theEs echo during the Dhajala event which indicate that it could be of meteoric origin are discussed. Meteor theory is used to relate the observed ionization with the physical dimensions of the Dhajala meteorite as obtained by other workers.     

Long-term variations in outgoing long-wave radiation (OLR), convective available potential energy (CAPE) and temperature in the tropopause region over India

Relationship of outgoing long-wave radiation (OLR) with convective available potential energy (CAPE) and temperature at the 100-hPa pressure level is examined using daily radiosonde data for a period 1980–2006 over Delhi (28.3°N, 77.1°E) and Kolkata (22.3°N, 88.2°E), and during 1989–2005 over Cochin (10°N, 77°E) and Trivandrum (8.5°N, 77.0°E), India. Correlation coefficient (R _xy) between monthly OLR and CAPE shows a significant (~???0.45) anti-correlation at Delhi and Kolkata suggesting low OLR associated with high convective activity during summer (seasonal variation). Though, no significant correlation was found between OLR and CAPE at Cochin and Trivandrum (low latitude region); analysis of OLR and temperature (at 100-hPa) association suggests that low OLR peaks appear corresponding to low temperature at Delhi (R _xy~ 0.30) and Kolkata (R _xy ~ 0.25) during summer. However, R _xy between OLR and temperature becomes opposite as we move towards low latitudes (~8°–10°N) due to strong solar cycle influence. Large scale components mainly ENSO and quasi-biennial oscillaton (QBO) that contributed to the 100-hPa temperature variability were also analyzed, which showed that ENSO variance is larger by a factor of two in comparison to QBO over Indian region. ENSO warm conditions cause warming at 100-hPa over Delhi and Darwin. However, due to strong QBO and solar signals in the equatorial region, ENSO signal seems less effective. QBO, ENSO, and solar cycle contribution in temperature are found location-dependent (latitudinal variability) responding in consonance with shifting in convective activity regime during El Niño, seasonal variability in the tropical easterly jet, and the solar irradiance.     

Impact of recharge water temperature on bioclogging during managed aquifer recharge: a laboratory study

To investigate the effect of recharge water temperature on bioclogging processes and mechanisms during seasonal managed aquifer recharge (MAR), two groups of laboratory percolation experiments were conducted: a winter test and a summer test. The temperatures were controlled at ~5±2 and ~15±3 °C, and the tests involved bacterial inoculums acquired from well water during March 2014 and August 2015, for the winter and summer tests, respectively. The results indicated that the sand columns clogged ~10 times faster in the summer test due to a 10-fold larger bacterial growth rate. The maximum concentrations of total extracellular polymeric substances (EPS) in the winter test were approximately twice those in the summer test, primarily caused by a ~200 μg/g sand increase of both loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS). In the first half of the experimental period, the accumulation of bacteria cells and EPS production induced rapid bioclogging in both the winter and summer tests. Afterward, increasing bacterial growth dominated the bioclogging in the summer test, while the accumulation of LB-EPS led to further bioclogging in the winter test. The biological analysis determined that the dominant bacteria in experiments for both seasons were different and the bacterial community diversity was ~50% higher in the winter test than that for summer. The seasonal inoculums could lead to differences in the bacterial community structure and diversity, while recharge water temperature was considered to be a major factor influencing the bacterial growth rate and metabolism behavior during the seasonal bioclogging process.     

Fairweather atmospheric electricity at Antarctica during local summer as observed from Indian station,Maitri

Surface measurements of the atmospheric electrical parameters like Maxwell current, electric field and conductivity studied at the Indian station, Maitri (70.75° S, 11.75° E, 117 m above mean sea level), Antarctica, during austral summer have been analyzed for the years 2001 to 2004. A total of 69 days were selected which satisfied the ‘fairweather’ conditions, i.e., days with absence of high winds, drifting or falling snow, clouds, and fog effects. The diurnal variation curve of electric field and vertical current averaged for 69 fairweather days is a single periodic with a minimum at 03:00 UT and a maximum near 19:00 UT, which is very similar to the Carnegie curve. The correlation coefficient between these measured parameters has a high value (more than 0.9) for all the days. During fairweather days the measured current and field variations are similar and hence it is clear that the conductivity is more or less stable. During magnetically disturbed days, the dawn-dusk potential drop has clear influences on the diurnal variation and it modifies the conductivity. Apart from the day-to-day variation in low latitude thunderstorm activity, there are diurnal, seasonal, inter-annual variations in the electric potential and the currents, as well as solar influences on the measured parameters. This study will help us to examine the impact of solar and geophysical phenomena like solar flares, geomagnetic storms and substorms on the global electric circuit.     

藏北高原多年冻土区地表反照率时空变化特征

利用自动气象站数据和MODIS（MOD02）数据,对位于藏北高原多年冻土区的阿雅克气象站、卓乃湖气象站、唐古拉气象站和西大滩气象站四个观测站点的单点地表反照率的季节变化、日变化和站点所属区域（88°~95°E,32°~38°N）的区域地表反照率夏、冬季节的空间分布进行了分析研究,得出：2013年,四个研究站点地表反照率均是夏季最小,冬季最大,春季大于秋季,其他季节较夏季地表反照率峰值较多;当太阳高度角大于40°时各站点地表反照率日变化基本不变,地表冻融过程中地表反照率完全冻结阶段 ＞ 日冻融循环阶段 ＞ 完全融化阶段,且地表日冻融循环阶段地表反照率日变化的中间时刻有明显下降。研究区域夏、冬季地表反照率大部分在0.1~0.3范围内;冬季地表反照率大于0.3的区域明显多于夏季,夏季区域地表反照率自阿雅克到唐古拉呈带状递减。     

Comparison of temperature change between the westerly and monsoon influencing region in China from 1961 to 2006

Surface air temperature is one of the main factors that can be used to denote climate change. Its variation in the westerly and monsoon-influenced part of China (i.e., North-West and East China) were analyzed by using monthly data during 1961–2006 from 139 and 375 meteorological stations over these two regions, respectively. The method of trend coefficient and variability was utilized to study the consistency and discrepancy of temperature change over North-West and East China. The results suggest that whether for the annual or the seasonal mean variations of temperature, there were consistent striking warming trends based on the background of global warming over North-West and East China. The most obvious warming trends all appeared in winter over the two regions. Except for the period in spring, the annual and seasonal mean warming trends in North-West China are more obvious than those in East China. The annual mean temperature warming rates are 0.34°C per decade and 0.22°C per decade over North-West and East China, respectively. The average seasonal increasing rates in spring, summer, autumn, and winter are 0.22°C per decade, 0.24°C per decade, 0.35°C per decade, and 0.55°C per decade in North-West China, respectively. At the same time, they are 0.25°C per decade, 0.11°C per decade, 0.22°C per decade, and 0.39°C per decade in East China, respectively. The temperature discrepancies of two adjacent decades are positive over the westerlies and monsoonal region, and they are bigger in the westerlies region than those in the monsoonal region. The most significant warming rate is from the North-East Xinjiang Uygur Autonomous Region of China to West Qinghai Province of China in all seasons and annually over the westerlies region. The North and North-East China are the main prominent warming areas over the monsoonal region. The warming rate increases with latitude in the monsoonal region, but this is not the case in the westerlies region.     

Solar zenith angle and frequency dependence of ionosphericD-region absorption

In this paper, the results of a series of extensive measurements of multifrequency radio wave absorption in theD-region of the ionosphere during the epoch of the minium period of the solar cycle are presented. Experimental results for Udaipur, a low latitude station (24°35′N) are compared with the theoretically expected results. It is found that the experimental values of frequency indexm and cos χ indexn agree well with those obtained theoretically. The mean values ofm andn for the whole period of observation are found to be 1·76 and 1·4 respectively. The seasonal variation of the values ofm andn is also discussed.     

Variability in the surface wind direction at a coastal site of complex terrain

Variability in the standard deviation of surface wind direction (σ_θ), under different Pasquill stability regimes on diurnal, seasonal and interannual scales has been investigated making use of a 10-year data set collected at Visakhapatnam (17°42′ N., 82° 18′ E) during January, April, August and October for winter, pre-monsoon, monsoon and post-monsoon seasons respectively. The diurnal scale variability in σ_θ is more pronounced during day time than in night. The seasonal variability in σ_θ is only moderate around noon while relatively large fluctuations are noticed on inter-annual scale only during day time in January and August. The seasonal dispersion in σ_θ decreased from most unstable regime to most stable regime.     

中纬度海气相互作用研究进展

回顾了中纬度海气相互作用的研究现状,分析了长期以来该项研究进展缓慢的原因和近十几年来的研究成果,结果指出:中纬度海洋在全球气候变化中有着重要的作用;冬季中纬度海气相互作用的强信号是冷空气强度;中纬度海洋强暖流区海气能量交换异常对同期和后期(半年至一年)北半球范围内的大气环流型有重要影响;当冬季黑潮和湾流海域海洋对大气同时异常多或异常少加热时,易形成夏季长江中下游偏旱或偏涝的环流形势。最后还提出,深入研究中纬度海气能量系统异常对大气环流影响及其物理机制,是今后海气相互作用研究的重要内容,其结果将为短期气候预测提供理论依据。     

天山南坡科其喀尔冰川表碛区小气候特征研究

利用天山南坡科其喀尔冰川3号观测站2009年全年的气象观测资料,分析研究了科其喀尔冰川表碛区的小气候特征. 结果表明：总辐射和净辐射夏秋季较高、冬春季较低;反射辐射和地表反照率反之. 与其他地区不同,该区主要受积雪物理性质和下垫面状况的影响,冬春季地表反照率日变化表现为由大到小的变化过程,夏秋季表现为倒U型. 温度年变化表现为夏秋季高、冬春季低,最高月均值出现在8月,为9.4℃,最低月均值出现在1月,为-9.6℃. 受山谷风和冰川风的影响,全年的风向以西北风和西北偏西风为主,风向的日变化以11：00为界发生转向. 受降水和冰川消融等的影响,比湿夏秋季月均值较大,冬春季月均值较小.     

On the diurnal ranges of Sea Surface Temperature (SST) in the north Indian Ocean

This paper describes the variability in the diurnal range of SST in the north Indian Ocean using in situ measurements and tests the suitability of simple regression models in estimating the diurnal range. SST measurements obtained from 1556 drifting and 25 moored buoys were used to determine the diurnal range of SSTs. The magnitude of diurnal range of SST was highest in spring and lowest in summer monsoon. Except in spring, nearly 75–80% of the observations reported diurnal range below 0.5°C. The distributions of the magnitudes of diurnal warming across the three basins of north Indian Ocean (Arabian Sea, Bay of Bengal and Equatorial Indian Ocean) were similar except for the differences between the Arabian Sea and the other two basins during November–February (winter monsoon) and May. The magnitude of diurnal warming that depended on the location of temperature sensor below the water level varied with seasons. In spring, the magnitude of diurnal warming diminished drastically with the increase in the depth of temperature sensor. The diurnal range estimated using the drifting buoy data was higher than the diurnal range estimated using moored buoys fitted with temperature sensors at greater depths. A simple regression model based on the peak solar radiation and average wind speed was good enough to estimate the diurnal range of SST at ∼1.0 m in the north Indian Ocean during most of the seasons except under low wind-high solar radiation conditions that occur mostly during spring. The additional information on the rate of precipitation is found to be redundant for the estimation of the magnitude of diurnal warming at those depths.     

东海冷涡中心位置及季节性变化的初步研究

使用1958—2001年SODA温度场资料,较为系统地对东海冷涡附近海域具代表性剖面温度场进行逐月分析,对冷涡中心提取方法进行了总结完善。结果表明,35 m深处冷涡44年的平均中心位于(32.0°N,125.7°E);冷涡的中心位置存在较显著的季节性变化:经向变化方面,由夏季、秋季至冬季,冷涡中心位置自北向南逐渐移动;从冬季、春季至夏季自南向北移动。纬向变化方面,冬季冷涡中心明显偏西,其他季节冷涡中心偏东且中心经度变化不大。以上变化主要是由冷涡周边流场的季节性变化引起的。冷涡中心在冬末春初和秋初表现不明显,这应是由环流场季节性转换导致。     

The interannual variability of mid-latitude meridional circulation and its teleconnection with Indian monsoon activity

The statistical relationship between the summer monsoon rainfall over all India, northwest India and peninsular India, onset dates of monsoon and the index of mid latitude, (35° to 70°N) meridional circulation at 500 hPa level over different sectors and hemisphere based on 19 years (1971–1989) data, have been examined. The results indicate that (i) the summer monsoon rainfalls over all India, northwest India and peninsular India show a significant inverse relationship with the strength of meridional index during previous January over sector 45°W to 90°E. (ii) The summer monsoon rainfalls over all India and peninsular India show a significant inverse relationship with the strength of meridional index during previous December over sector 90°E to 160°E, (iii) The summer monsoon rainfall over northwest India shows a significant direct relationship with the meridional index during previous May over sector 160°E to 45°W. Significant negative relationships are also observed between the meridional circulation indices of previous October (sector 3 and 4), previous December (sectors 1, 3 and 4), previous winter season (sector 3 and 4) and the onset dates of summer monsoon over India. The meridional circulation index thus can have some possible use for long range forecasting of monsoon rainfall over all India, northwest India and peninsular India, as well as the onset dates of monsoon.     

北京上空大气臭氧垂直分布的特征

利用我国自行研制的探空仪和地面接收设备首次较系统地获得了北京地区连续一年（2001年 3月至2002年 2月）的大气臭氧垂直分布资料。结果分析表明：①北京地区上空臭氧浓度极大值的季节均值的变化范围为15．1～16．7 mPa,其高度位于20．7～25．1km之间,极小值的季节均值的变化范围为 2．0～2．8 mPa,其高度在对流层顶附近。②边界层和平流层下部是臭氧浓度变化的活跃区域,并具有明显的季节变化,在边界层内夏季臭氧积分浓度高于冬季相应值的 1．7倍之多,而在平流层下部,冬季臭氧积分浓度则高于夏季的相应值。夏季边界层中臭氧浓度偏高,表明臭氧是北京地区夏季重要的污染气体之一。③北京上空臭氧垂直廓线的形态呈多样性,夏秋季节以单峰为主,冬春季节经常出现双峰和多峰结构;次峰出现的区域一般在10～18km高度范围内。