Annual Change Trend Research Articles

Correlation Between Space and Ground‐Based Observational Data in Their Near Direct Current Electric Field Background Characteristics

AbstractStudy of the characteristics of space‐ and ground‐based electromagnetic observational data, as well as the correlation between them, has important scientific significance for the combined application of both data to earthquake monitoring and research. In this paper, the near DC electromagnetic data recorded by the DEMETER satellite, vertical and horizontal geoelectric field data recorded at the Hongshawan station, and horizontal geoelectric field data recorded at the Chengdu station were comprehensively studied. The results show that observational data of the ULF electric field recorded directly by the DEMETER satellite do not indicate any significant annual change trends; the observational data from along the velocity vector direction on both the day and night sides present longer‐term cyclical characteristics, but no correlation or synchronization with the geoelectric field observational data. The magnitude of the electric field data in the ionosphere after removing the additional electric field values caused by the satellite cutting the magnetic line are consistent with the geoelectric field data, and concentrated at about 10−1∼ 10−2 mV/m. The concave annual seasonal change trends are displayed from the observation data along the normal to the orbit direction, and along the velocity vector direction on the night side, showing a relatively stable annual variation period, which is consistent with the trend of the annual variation of the horizontal geoelectric field. Therefore, it may be concluded that both the magnitude and annual trends have exhibited correlation and synchronization every year.

Modeling of Surface Runoff in Xitiaoxi Catchment, China

Xitiaoxi catchment is one of the most important catchments in the Taihu basin in China. Due to its significant contribution of surface runoff and associated nutrients input to Lake Taihu, understanding of the processes of surface runoff in this catchment is, therefore, of primary importance in quantifying water and nutrient balances for Lake Taihu. The generation of surface runoff in the catchment is mainly controlled by rainfall and land cover, so the variety of surface runoff in Xitiaoxi catchment is seasonal. Moreover, the annual change of surface runoff is distinct. Because of the diversity of land use and variety of hydrological characteristics, numerical simulation of the generation of surface runoff over this catchment is not straightforward. In this paper, attempts were made in applying the Large Scale Catchment Model (LASCAM) to Xitiaoxi catchment. The Xitiaoxi catchment is divided into 47 subcatchments connected via a river network based on topology. The model was first run in an optimization mode to calibrate the parameters against the observed runoff for the period of 1968-1977, and then was run in a prediction mode to try to reproduce the runoff for the next 10 years from 1978 to 1987. The model indicates that saturation excess runoff is probably the dominant process for the catchment. The modeling results indicate that water storage in shallow soils near the stream has a high correlation with daily rainfall, while the water storage changes in deep aquifers demonstrate an annual change trend, showing a rising level for wet seasons and a declining level for dry seasons. The success in modeling surface runoff leads to confidence in modeling nutrients transport as the next step of modeling work.

Vectors of tick-borne diseases and epidemiological situation in Latvia in 1993-2002.

During the period of 1993-2002 an increase and the remarkable changes in the incidence of tick-borne encephalitis (TBE) and Lyme borreliosis (LB) as well as annual activities of vector species were noticed. The highest increase of TBE morbidity in Latvia has been observed in 1994 and 1995, and less expressed also in 1998 which was followed by a significant decrease during subsequent years. Whereas the highest peak of LB morbidity has been noticed in 1998 with only a minor decrease during subsequent years. Two epidemiologically significant Ixodes tick species are common in Latvia. Ixodes ricinus L. spread in the western and central part of Latvia; but rarely and in small numbers also in the eastern part. Ixodes persulcatus P. Sch. seems to dominate only in the eastern part of the country. The changes of seasonal and annual activities of I. ricinus were observed in two types of monitoring sites--sylvatic and peridomestic, located in the central part of Latvia. Observations of I. persulcatus were made in the eastern districts. Comparing geographically the Tick-borne diseases (TBD) incidence data for three tick distribution regions (I. ricinus dominated, I. persulcatus dominated and mixed regions), it was observed that the trend of annual changes in LB incidence during the last decade is almost of the same kind for all regions. Whereas TBE incidence extremes in 1994 and 1995 were observed almost only in I. ricinus dominated region. The annual field-collected adult tick infection rate with TBE virus (TBEV) from 1993 to 2002 for I. ricinus adults varied between 1.7% and 26.6% and for I. persulcatus--between 0% and 37.3%. The infection level in ticks removed from humans was much higher and from 1998 to 2002 surpassed 30%. TBEV investigations of removed adults and nymphs in 2002 discovered a high TBEV prevalence also in I. ricinus nymphs (43%). Typing of TBE virus isolated from ticks and patient serum samples in collaboration with German and Swedish virologists revealed that all three TBEV subtypes were co-circulating in Latvia. The mean annual tick infection rate with Borrelia burgdorferi s.l. analysed by means of a nested polymerase chain reaction of OspA gene fragment during the period of 1999-2001 was 18%-38% for I. ricinus adults and 25%-51% for I. persulcatus adults. Typing of Borrelia-positive DNA samples indicated that B. afzelii was dominant in Borrelia-positive I. ricinus (64.9%) and I. persulcatus (81.2%) followed by B. garinii (I. ricinus: 24.3%; in I. persulcatus: 14.5%). Investigations of Ehrlichia phagocytophila genogroup (by nested PCR targeted the 16S rRNA gene) revealed the presence of Ehrlichia sp. in I. ricinus from the central part of Latvia. Obtained data on TBD vectors and the epidemiological situation during the last decade indicates the complex impact of different factors influencing TBE and LB morbidity in Latvia.