共查询到20条相似文献，搜索用时 515 毫秒
1.
Wayan Suparta Zainol Abidin Abdul Rashid Mohd. Alauddin Mohd. Ali Baharudin Yatim Grahame J. Fraser 《Journal of Atmospheric and Solar》2008,70(11-12):1419-1447
Predicting global climate change is a great challenge and must be based on a thorough understanding of how the climate system components behave. Precipitable water vapor (PWV) is one of the key components in determining and predicting the global climate system. It is well known that the local surface temperature and pressure have a direct influence on the production of PWV. However, the influence of solar activity on atmospheric dynamics and their physical mechanisms is still an open debate, where past studies are focused at mid-latitude regions. A new method of determining and quantifying the solar influence on PWV based on GPS observations to correlate the GPS PWV and total electron content (TEC) variations is proposed. Observed data from Scott Base (SBA) and McMurdo (MCM) stations from 2003 to 2005 have been used to study the response of PWV to solar activity. In the analysis, the effects of local conditions (wind speed and relative humidity) on the distribution of PWV are investigated. Results show significant correlation between PWV and solar activity for four geomagnetic storms, with correlation coefficients of 0.74, 0.77, 0.64 and 0.69, which are all significant at the 95% confidence level. There was no significant correlation between TEC and PWV changes during the absence of storms. On a monthly analysis, a strong relationship exists between PWV and TEC during storm-affected days, with correlation coefficients of 0.83 and 0.89 (99% confidence level) for SBA and MCM respectively. These indicate a statistically significant seasonal signal in the Antarctic region, which is very active (higher) during the summer and inactive (lower) for the winter periods. 相似文献
2.
Water vapor plays an important role in the global climate system. A clear relationship between water vapor and solar activity can explain some physical mechanisms of how solar activity influences terrestrial weather/climate changes. To gain insight of this possible relationship, the atmospheric precipitable water vapor (PWV) as the terrestrial climate response was observed by ground-based GPS receivers over the Antarctic stations. The PWV changes analyzed for the period from 2003 to 2008 coincided with the declining phase of solar cycle 23 exhibited following the solar variability trend. Their relationship showed moderate to strong correlation with 0.45 < R 2 < 0.93 (p < 0.01), on a monthly basis. This possible relationship suggests that when the solar-coupled geomagnetic activity is stronger, the Earth’s surface will be warmer, as indicated by electrical connection between ionosphere and troposphere. 相似文献
3.
Water vapor plays a crucial role in atmospheric processes that act over a wide range of temporal and spatial scales, from global climate to micrometeorology. The determination of water vapor distribution in the atmosphere and its changing pattern is very important. Although atmospheric scientists have developed a variety of means to measure precipitable water vapor(PWV) using remote sensing data that have been widely used, there are some limitations in using one kind satellite measurements for PWV retrieval over land. In this paper, a new algorithm is proposed for retrieving PWV over land by combining different kinds of remote sensing data and it would work well under the cloud weather conditions. The PWV retrieval algorithm based on near infrared data is more suitable to clear sky conditions with high precision. The 23.5 GHz microwave remote sensing data is sensitive to water vapor and powerful in cloud-covered areas because of its longer wavelengths that permit viewing into and through the atmosphere. Therefore, the PWV retrieval results from near infrared data and the indices combined by microwave bands remote sensing data which are sensitive to water vapor will be regressed to generate the equation for PWV retrieval under cloud covered areas. The algorithm developed in this paper has the potential to detect PWV under all weather conditions and makes an excellent complement to PWV retrieved by near infrared data. Different types of surface exert different depolarization effects on surface emissions, which would increase the complexity of the algorithm. In this paper, MODIS surface classification data was used to consider this influence. Compared with the GPS results, the root mean square error of our algorithm is 8 mm for cloud covered area. Regional consistency was found between the results from MODIS and our algorithm. Our algorithm can yield reasonable results on the surfaces covered by cloud where MODIS cannot be used to retrieve PWV. 相似文献
4.
Global Positioning System (GPS) derived total electron content (TEC) measurements were analyzed to investigate the ionospheric
response during the X-class solar flare event that occurred on 5-6 December 2006 at geomagnetic conjugate stations: Syowa,
Antarctica (SYOG) (GC: 69.00°S, 39.58°E; CGM: 66.08°S, 71.65°E) and árholt, Iceland (ARHO) (GC: 66.19°N, 342.89°E; CGM: 66.37°N,
71.48°E). Bernese GPS software was used to derive the TEC maps for both stations. The focus of this study is to determine
the symmetry or asymmetry of TEC values which is an important parameter in the ionosphere at conjugate stations during these
solar flare events. The results showed that during the first flares on 5 December, effects were more pronounced at SYOG than
at ARHO. However, on 6 December, the TEC at ARHO showed a sudden spike during the flare with a different TEC variation at
SYOG. 相似文献
5.
Rajat Acharya Bijoy Roy M.R. Sivaraman Ashish Dasgupta 《Journal of Atmospheric and Solar》2011,73(7-8):779-784
The total electron content (TEC) of the equatorial ionosphere is controlled by photochemical processes as well as the transport of the ionospheric plasma near the magnetic equator. The transport phenomenon is initiated by the vertical drift driven by the eastward electric field, which also drives the Equatorial Electrojet. The empirical relation between the Equatorial Electrojet and the anomaly component of the equatorial TEC has already been established. Taking this relation as a reference, a simplified physical model of the anomaly component of equatorial TEC is obtained as a function of Equatorial Electrojet. Influence of other factors like the solar incidence angle and the solar flux are also considered here and the extent of their influence are also investigated. This has been done using TEC data obtained from dual frequency GPS receivers during the low solar activity period of 2005. The derived model is based on the physics of the underlying fountain effect and matches with the observed empirical relation to a fair extent. Obtained results are found to corroborate with previous findings and these physical model values are found to have improved correlation with the observed data than the reference empirical relation. This establishes the conformity between the EEJ based ionospheric model and the physical phenomenon of the fountain effect. 相似文献
6.
Space geodetic techniques (e.g., Global Positioning System, GPS and very long baseline interference, VLBI) have been widely used to determine the precipitable water vapor (PWV) for meteorology and climatology, which was verified by comparing with co-located independent technique observations. However, most of these comparisons have been conducted using only short-time spanning observations at several stations. The goal of this study is to identify and quantify the systematic errors between VLBI and GPS PWV estimates using a 5-year (2002–2007), PWV data set constructed from co-located measurements and radiosonde data as well. It has found systematic errors between VLBI and GPS PWV estimations from comparisons with long-term co-located GPS measurements. The total mean VLBI PWVs are systematically smaller than GPS estimates with 0.8–2.2 mm for all sites, but can be as much as 15–30%. The subdiurnal PWV variation magnitudes and long-term trends between VLBI and GPS are nearly similar, but the VLBI-derived PWV trends are systematically smaller than GPS estimates with about 0.1±0.02 mm/year. These systematic errors in PWV estimates between VLBI and GPS are probably due to technique own problems, different used elevation angles and co-location separation. 相似文献
7.
《Journal of Atmospheric and Solar》2007,69(15):1842-1850
Global positioning system (GPS) networks have provided an opportunity to study the dynamics and continuous changes in the ionosphere by supplementing ionospheric studies carried out using various techniques including ionosondes, incoherent scatter radars and satellites. Total electron content (TEC) is one of the physical quantities that can be derived from GPS data, and provides an indication of ionospheric variability. This paper presents a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. Three South African locations were identified and used in the development of an input space and NN architecture for the model. The input space included the day number (seasonal variation), hour (diurnal variation), Sunspot Number (measure of the solar activity), and magnetic index (measure of the magnetic activity). An analysis was done by comparing predicted NN TEC with TEC values from the IRI-2001 version of the International Reference Ionosphere (IRI), validating GPS TEC with ionosonde TEC (ITEC) and assessing the performance of the NN model during equinoxes and solstices. For this feasibility model, GPS TEC was derived for a limited number of years using an algorithm still in the early phases of validation. However, results show that NNs predict GPS TEC more accurately than the IRI at South African GPS locations, but that more good quality GPS data is required before a truly representative empirical GPS TEC model can be released. 相似文献
8.
Praveen Galav N. Dashora S. Sharma R. Pandey 《Journal of Atmospheric and Solar》2010,72(17):1309-1317
We present the mean diurnal, seasonal and annual variations in TEC during the lowest solar activity phase from low latitude Indian zone recorded at Udaipur (Geog. Lat. 24.6°N, Geog. Long.73.7°E, Geomag. Lat. 15.6°N) using a GPS receiver. Seasonal variations in daytime TEC show a semiannual periodicity, with a minimum in winter. Results of seasonal variations have been compared with that of the IRI-2007 model. Model calculations reveal significant seasonal as well as longitudinal differences in TEC. Seasonal variations in the nighttime TEC reveal an annual periodicity. Near the crest of the EIA, TEC shows a very good correlation with the solar flux. The results also point to weakening of the anomaly crest as well as its spatial and temporal contraction with declining solar activity. 相似文献
9.
《Journal of Atmospheric and Solar》2002,64(17):1833-1840
An empirical model of total electron content (TEC) for a low-latitude station, Palehua, has been developed using harmonic analysis of TEC data measured at this station during the period 1980–1990; the TEC data were obtained from Faraday rotation measurements of linearly polarised signals transmitted by geostationary satellites. The analysis reveals that monthly mean values of the daily mean and the first four harmonics vary in phase with solar activity and exhibit annual, semi-annual variations and equinoctial asymmetries. A set of 81 coefficients of zero and the first four orders were determined which were found to be sufficient to model the TEC. The model strongly depends on the sunspot number. The harmonic components derived from the 81 coefficients are scaled by this property. The modelled monthly mean TEC values agree quantitatively with the measured data, the maximum deviation being limited to ±15%. The model reasonably reproduces the features observed in the diurnal, seasonal and solar cycle variations of the measured data. The annual variation of observed TEC exhibits opposite equinoctial asymmetries at solar minimum and solar maximum. Also, the mean and first four harmonics show a saturation/decreasing effect when the sunspot number exceeds about 170. The observed features are discussed qualitatively. 相似文献
10.
This study analyzes the TEC data during 1998–2007, observed by the AREQ (16.5°S, 71.5°W) GPS station to investigate the equatorial ionospheric variations under geomagnetic quiet-conditions. The diurnal TEC values generally have a maximum value between 1330 and 1500 LT and a minimum around 0500 LT. For the seasonal variation, the semi-annual variation apparently exists in the daytime TEC with two peaks in equinoctial months. In contrast, this semi-annual variation is not found in the nighttime. Furthermore, the results of the annual variation show that the correlation between the daytime TEC value and the solar activity factor is highly positive. 相似文献
11.
本文尝试结合非相干散射雷达和GPS TEC观测数据提取等离子体层总电子含量(PTEC).我们首先描述所用的技术方法,然后具体利用了Millstone Hill台站的观测数据研究该地区上空等离子体层总电子含量(PTEC)的变化情况.我们采用变化标高的Chapman函数对非相干散射雷达测得的电子浓度剖面数据进行拟合,然后通过对剖面积分得到100 km到1000 km高度范围的电离层总电子含量.GPS提供的TEC数据为高度达20200 km的总电子含量,两者之差可近似看成等离子体层的电子含量.本文分别选取太阳活动高年(2000, 2002年)和太阳活动低年(2005,2008年)Millstone Hill台站的静日数据进行研究.结果表明,等离子体层电子含量及其所占GPS TEC的比例具有明显的周日变化.PTEC含量在白天高于夜间,而所占GPS TEC的百分比,夜间明显高于白天.太阳活动高年所选月份等离子体层电子含量在4~14 TECU (1TECU=1016el/m2) 范围内变化,夜间所占比例可达60%左右.太阳活动低年所选月份等离子体层电子含量在3~7 TECU范围内变化,所占比例夜间最高可达80%左右.我们所得到的结果与前人基于其它观测手段所得结果在变化趋势上一致,在量级上也大致相当.因此,这从一个侧面证明了我们所用方法的可靠性.非相干散射雷达能够探测包括F2层峰值以下及以上高度的电子浓度,利用这一设备所观测得到的资料来推算电离层电子含量将比前人基于电离层垂测仪观测资料进行的推算更具真实性,由此得到的等离子体层电子含量也将更为接近真实情况. 相似文献
12.
基于GNSS(Global Navigation Satellite Systems)的发展,我们利用具有北斗、GLONASS和GPS三系统信号接收功能的接收机观测的数据,结合电离层总电子含量(Total Electron Content, TEC)的反演算法,提取出GNSS三系统观测的电离层TEC;同时,将GNSS三系统获取的TEC应用到电离层TEC地图、行进式扰动、不规则体结构和电离层的太阳耀斑响应等方面的研究中,这也是首次使用三种GNSS系统数据对电离层进行联合探测研究.研究结果表明,增加了北斗系统的GNSS三系统在研究中国地区电离层TEC地图、周日变化、逐日变化,行进式扰动以及电离层的实时监测等方面较单系统的GPS具有明显的优势. 相似文献
13.
14.
The relation of the long-period variations in the midnight and noon values of the critical frequency of the ionospheric F 2 layer at three midlatitude stations (Irkutsk, Moscow, and Boulder) to the daily mean index of geomagnetic activity in years of different solar activity has been studied. It has been found that the correlation coefficients between the above parameters depend on time of day, season, and solar activity level. The correlation coefficients are higher at night than in the daytime, especially at low solar activity. The highest absolute values of the correlation coefficient most often appear during equinoxes: April–May and September–October. It has been shown that the variability of the critical frequencies of the midlatitude ionospheric F 2 layer depends not only on geomagnetic activity but also (to a considerable degree) on the effect of the lower atmosphere. 相似文献
15.
电离层TEC是描述电离层特性的一个重要参量,利用GPS观测数据（包括广州站接收的GPS-TEC数据和国际GNSS提供的IGS-TEC数据）与IRI-2007模型计算的TEC预测值对太阳活动低年2008年的广州地区TEC周日和季节变化以及年变化特征等进行了多方面的对比分析。结果表明：TEC观测值白天较高且变化迅速,夜间较低且变化缓慢,同时表现出明显的季节依赖性和半年变化特性,全年在春秋分季节出现两次峰值,IRI-TEC预测值能较好地反映GPS观测值,但局部上也存在着一些偏差,并对其中的物理机制和产生差异的原因给出了合理的分析和解释。 相似文献
16.
利用GPS计算TEC的方法及其对电离层扰动的观测 总被引：36，自引：8，他引：28
在总结用ＧＰＳ研究电离层电子总量ＴＥＣ的数据处理方法基础上,分析了利用伪距观测量和载波相位观测量计算电离层ＴＥＣ的特点及误差来源．在处理过程中考虑了卫星的硬件延迟偏差,分析了应用ＩＲＩ模型进行接收机硬件延迟偏差修正的可能性,发现利用少量ＧＰＳ数据和ＩＲＩ模型修正接收机硬件延迟偏差有一定的困难．最后,利用一些ＧＰＳ观测数据有针对性地研究了电离层对若干次扰动事件的响应．包括一次大的太阳耀斑期间的电离层ＴＥＣ变化、一次较典型的电离层行扰以及日食期间的电离层ＴＥＣ的相对变化等电离层物理问题．结果表明,利用该方法计算ＴＥＣ的精度可满足电离层扰动现象的研究． 相似文献
17.
SONG Dong-mei XIANG Liang SHAN Xin-jian YIN Jing-yuan WANG Bin CUI Jian-yong 《地震地质》2019,41(6):1511-1528
There are many factors related to the variations of TEC, and the changes of TEC caused by earthquake only occupy a small portion. Therefore, it is vital how to exclude the ionospheric interference of non-seismic factors accurately in the process of seismic ionospheric anomaly extraction. This study constructed a TEC non-seismic dynamic background field considering the influence of solar and geomagnetic activities. Firstly, the TEC components of half-year cycle and annual cycle are extracted by wavelet decomposition. Then, it establishes a regression model between TEC in which periodic factors are removed and solar activity index, geomagnetic activity index with SVR method(support vector regression)in non-seismic period. Finally, based on the constructed model, the solar activity index and geomagnetic activity index is used to reconstruct aperiodic components of TEC in earthquake's period. From the reconstructed aperiodic components of TEC plus the half-year periodic components and annual periodic components of TEC in the same period, the non-seismic dynamic background field is obtained. Comparing the residuals relative to original TEC values in non-seismic dynamic background field and traditional sliding window background, there are apparent monthly periodic change and semi-annual periodic change in the residuals of sliding window background, which can have obvious impacts on the subsequent seismic ionospheric anomaly detection. In order to test the validity of seismic TEC anomaly detection based on the background field construction method, this paper investigated the long time series TEC anomalies near Wenchuan city(30°N, 100°E)from March 1 to September 26 in 2008. It is found that under the condition of non-seismic disturbance such as solar activity and geomagnetic activity, TEC abnormal disturbance is rarely detected by non-seismic dynamic background field method, when compared with the traditional sliding time-window method. And before the earthquake, more TEC anomalies were detected based on the proposed method, also, they were more intense than those extracted by sliding window method. Therefore, the TEC background field construction method based on SVR(support vector regression)has superiorities in both system errors elimination, which are caused by solar, geomagnetism, the non-seismic ionospheric disturbance events and periodic fluctuations of TEC, and in reducing the false alarm rate of seismic TEC anomaly. Moreover, it can also improve the seismic TEC anomaly detection ability. In addition, this paper analyzed the time-spatial distribution of TEC anomaly before three earthquakes on May 12, August 21 and August 30, 2008. They were mainly negative abnormal perturbations and often distributed on the equatorial side of epicenter. 相似文献
18.
《中国科学:地球科学(英文版)》2015,(8)
The importance of water vapor in research of global climate change and weather forecast cannot be over emphasized; therefore substantial efforts have been made in exploring the optimal methods to measure water vapor. It is well-established that with a conversion factor, zenith wet delays can be mapped onto precipitable water vapor(PWV). However, the determination of the exact conversion factor depends heavily on the accurate calculation of a key variable, weighted mean temperature of the troposphere(T_m). As a critical parameter in Global Positioning System(GPS) meteorology, T_m has recently been modeled into a global grid known as GWMT. The GWMT_model only requires the location and the day of year to calculate T_m. Despite the advantages that the GWMT_model offers, anomalies still exist in oceanic areas due to low sampling resolution. In this study, we refine the GWMT_model by incorporating the global T_m grid from Global Geodetic Observing System(GGOS) and obtain an improved model, GWMT-G. The results indicate that the GWMT-G model successfully addresses the anomaly in oceanic areas in the GWMT_model and significantly improves the accuracy of T_m in other regions. 相似文献
19.
人类活动引起全球变暖,衡量全球气候变化的指标有陆地、大气和海洋温度,水汽含量等等.研究对流层底层大气温度和水汽含量变化的传统方法是用数值天气预报模型和微波声纳,尚未实现用全球均匀覆盖的数据来做精确的定量研究.和GNSS系列卫星计划比较,最近发射的COSMIC卫星气象探测数据的空间、时间以及垂直分辨率都大大提高.采用COSMIC数据可以改进和量化南极洲的大气压力模型,并综合GNSS系列卫星测量的水汽和温度剖面研究全球气候变化.用一维协方差算法估计南极洲及附近海洋的大气压、温度和湿度剖面.把COSMIC卫星密集测量期间演算得到的大气折射率和GNSS系列卫星的结果进行比较.再和独立测量数据进行比较,包括南极洲自动气象观测站资料,数值天气预报模型资料,多种测高卫星水汽资料和海洋表面温度资料以及区域GPS水汽图.上述工作将改进发展中的气象遥感技术并应用于天气预报和空间天气预报及全球气候变化研究. 相似文献
20.
C. Jacobi 《Annales Geophysicae》1998,16(12):1534-1543
At the Collm Observatory of the University of Leipzig LF D1 low-frequency total reflection nighttime wind measurements have been carried out continuously for more than two decades. Using a multiple regression analysis to derive prevailing winds, tides and the quasi-2-day wave from the half-hourly mean values of the horizontal wind components, monthly mean values of mesopause wind parameters are obtained that can be analysed with respect to long-term trends and influences of solar variability. The response of the prevailing wind to the 11-year solar cycle differs throughout the year. While in winter no significant correlation between the zonal prevailing wind and solar activity is found, in spring and summer a negative correlation between the TWC can be seen from the measurements. This is connected with stronger vertical gradients of the zonal prevailing wind during solar maximum than during solar minimum. Since the amplitude of the quasi-2-day wave is dependent on the zonal mean wind vertical gradient, this is connected with a positive correlation between solar activity and quasi-two-day wave activity.Paper Presented at the Second IAGA/ICMA (IAMAS) Workshop on Solar Activity Forcing of the Middle Atmosphere, Prague, August 1997 相似文献