Geomagnetic factor of Dst variations in the selective generation of ionospheric characteristic waves     

V. P. Sivokon’  G. I. Druzhin 《Geomagnetism and Aeronomy》2006,46(4):492-495

HF Waves of rotating polarization have been experimentally studied on the Magadan-Petropavlovsk-Kamchatskii path. It has been obtained that the degree of suppression of one of the characteristic waves during the selective polarization generation depends on the Dst value and sign. It has been established that changes in the amplitude ratio of the signals received from the antennas of clockwise and counterclockwise polarization are maximal at a quiet geomagnetic field when Dst is positive. Under the conditions of medium disturbance of the geomagnetic field and small-scale negative Dst values, it has not been ruled out that the second characteristic wave can be observed at a receiving point in the case when one of the characteristic waves is generated. Selective polarization generation of one of the characteristic waves can be mainly masked by an increase in small-scale irregularities of ionospheric plasma.  相似文献   

Assessment of the natural resources of groundwater by using balance-hydrodynamic models     

V. A. Vsevolozhskii  S. O. Grinevskii 《Water Resources》2006,33(4):374-380

The specific features of formulation and implementation of balance-hydrodynamic simulation during different-scale studies of natural resources of groundwater. Are an example of detailed estimate of the resources and balance of groundwater in the Vologda River basin is given. It is noted that the use of balance-hydrodynamic models, in addition to an increase in the general reliability of estimates, allows the calculation of normal annual characteristics of groundwater resources with different occurrence (exceedance probability), which is impracticable when hydrodynamic methods in other formulations are used.  相似文献   

Cosmic ray flux variations, modulated by the solar and earth’s magnetic fields, and climate changes. 1. Time interval from the present to 10–12 ka ago (the Holocene Epoch)     

V. A. Dergachev  P. B. Dmitriev  O. M. Raspopov  H. Jungner 《Geomagnetism and Aeronomy》2006,46(1):118-128

Direct and indirect data on variations in cosmic rays, solar activity, geomagnetic dipole moment, and climate from the present to 10–12ka ago (the Holocene Epoch), registered in different natural archives (tree rings, ice layers, etc.), have been analyzed. The concentration of cosmogenic isotopes, generated in the Earth’s atmosphere under the action of cosmic ray fluxes and coming into the Earth archives, makes it possible to obtain valuable information about variations in a number of natural processes. The cosmogenic isotopes ¹⁴C in tree rings and ¹⁰Be in ice layers, as well as cosmic rays, are modulated by solar activity and geomagnetic field variations, and time variations in these concentrations gives information about past solar and geomagnetic activities. Since the characteristics of natural reservoirs with cosmogenic ¹⁴C and ¹⁰Be vary with climate changes, the concentrations of these isotopes also inform about climate changes in the past. A performed analysis indicates that cosmic ray flux variations are apparently the most effective natural factor of climate changes on a large time scale.  相似文献   

A nonstationary model of level variations in a drainless water body: The Caspian Sea     

V. A. Rumyantsev  A. O. Rumyantsev  Yu. A. Trapeznikov 《Water Resources》2006,33(4):396-401

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The Enso-Fire Dynamic in Insular Southeast Asia     

Douglas O. fuller  Kevin Murphy 《Climatic change》2006,74(4):435-455

We examined the spatiotemporal patterns of fire in insular Southeast Asia from July 1996 to December 2001 using a set of consistent, nighttime fire observations provided by the Along Track Scanning Radiometer (ATSR) sensor. Monthly ATSR fire counts were analyzed relative to georeferenced climatic and land-cover data from a variety of sources. We found that fires were strongly correlated with Southern Oscillation Index (SOI) (r = ?0.75) and Niño 3.4 index (r = 0.72) in forested land-cover types within the equatorial belt (5.5^°S–5.5^°N). Cross-correlation analysis revealed that detrended SOI was modestly correlated (r = 0.42) with detrended monthly fire count with a positive lag of four months. However, our analysis also revealed that fire counts reached their maximum 6 months before the absolute maximum of SOI. Annual sums of SOI (∑_SOI) and fire counts revealed linearity for ∑_SOI≤ 0. Overall, the results suggest that ENSO indices may have limited predictive utility at a monthly time scale, but that temporal aggregation and additional fire observations may enhance our capacity to forecast fires in different cover types based on ENSO data.  相似文献   

Characteristics of large-scale atmospheric circulation related to extreme monthly rainfall anomalies in the Pampa Region, Argentina, under non-ENSO conditions     

B. Scian  J. C. Labraga  W. Reimers  O. Frumento 《Theoretical and Applied Climatology》2006,85(1-2):89-106

Summary There is a widely held view that the Pampa region (PR) dry and wet periods are predominantly a consecuence of the El Ni?o-Southern oscillation (ENSO) phenomenom. The current paper focuses on non-ENSO rainfall anomalies for the period 1948–2000, the more recent of which have had catastrophic consequences throughout the region. We analyze horizontal water vapor transport, pressure and circulation anomalies occurring in Southern South America (SSA) during this type of event. Positive and negative (wet and dry) extreme events during the rainy and dry seasons in the region were registered. Based on NCEP reanalysis data it was established that under rainfall deficit, anomalies of similar intensity occurred simultaneously in the PR and in central Chile, whereas under excess rainfall the anomalies were mostly confined to the PR. The existence of a cyclone-anticyclone pair in the anomalous circulation pattern over mid latitudes of the Atlantic and Pacific oceans and straddling the southern portion of the continent maintains an intense and extense meridional circulation over the continental plains, which leads to the abnormal values in moisture transport and rainfall rate. The atmospheric water balance equation calculated for the PR indicates that anomalous water vapor is carried in from the continental equatorial region and from the subtropical Atlantic, its magnitude varying in accordance with the season and the sign of the anomaly. Furthermore, evidence of the important role of transient terms corroborates their contribution to the anomalous total moisture flux divergence under rainfall deficit during the dry season. The mean sea-level pressure anomaly fields of the extreme cases were further examined by principal component analysis to discern those circulation features directly linked to rainfall deviations.  相似文献   

Uncertainties in modelling future hydrological change over West Africa     

T. d’Orgeval  J. Polcher  L. Li 《Climate Dynamics》2006,26(1):93-108

The aim of this paper is to evaluate current knowledge and uncertainties associated with the impact of increasing greenhouse gas and aerosol concentrations on the West African monsoon. For this purpose, coupled and time-slice simulations are used. A global measure of the monsoon changes is defined in order to avoid regional biases and to try and obtain significant results. The position and width of the monsoon in latitude are the main focuses. There is almost no agreement between the Coupled General Circulation models from the Coupled models Inter-Comparison project—Phase II in regard to the impact of climate change on the monsoon. Moreover, very simple discriminations between the models seem inappropriate to get a better signal. The role of the different forcings in time-slice simulations is then investigated. The sea surface temperature (SST) and particularly the pattern of the SST are shown to be the most important forcing. This accounts for the diversity of the results either from the coupled or the forced simulations with different SST changes. With a fixed SST, but of a smaller magnitude in AMJ, there are still uncertainties, coming first from the Atmospheric General Circulation models and the way they balance greenhouse gas and global SST increase. Finally the uncertainty due to the Land Surface models (LSMs) is not negligible. The greenhouse gas and the LSMs are shown to have more impact in August, when the monsoon is at its highest latitude on the continent.  相似文献   

Estimation of monthly average solar radiation in Libya     

F. K. Bannani  T. A. Sharif  A. O. R. Ben-Khalifa 《Theoretical and Applied Climatology》2006,83(1-4):211-215

Summary In order to estimate the monthly average global radiation, regression equations for eleven stations in Libya are fitted, using monthly average hours of sunshine duration as predictors. Since only eight years of monthly average global radiation are available for each station, a reliable model for estimating solar radiation for each single month could not be obtained. The monthly data were merged together to produce a single regression equation for each station rather than twelve monthly regression equations. The results indicate that the regression equations for ten stations out of eleven hold very well.  相似文献   

Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints   总被引：1，自引：0，他引：1  

V. Masson-Delmotte  M. Kageyama  P. Braconnot  S. Charbit  G. Krinner  C. Ritz  E. Guilyardi  J. Jouzel  A. Abe-Ouchi  M. Crucifix  R. M. Gladstone  C. D. Hewitt  A. Kitoh  A. N. LeGrande  O. Marti  U. Merkel  T. Motoi  R. Ohgaito  B. Otto-Bliesner  W. R. Peltier  I. Ross  P. J. Valdes  G. Vettoretti  S. L. Weber  F. Wolk  Y. Yu 《Climate Dynamics》2006,27(4):437-440

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Determining rainy season onset and retreat over Nigeria from precipitation amount and number of rainy days     

T. O. Odekunle 《Theoretical and Applied Climatology》2006,83(1-4):193-201

Summary This study assesses the relative efficiency of the use of rainfall amount and rainy days in the determination of rainfall onset and retreat dates in Nigeria based on rainfall data for the period 1961 to 2000. Daily rainfall data were sourced from the archives of the Nigerian Meteorological Services, Oshodi Lagos. The specific locations for which data were collected are: Ibadan, Ilorin, Kaduna and Kano. The method of percentage cumulative mean rainfall values was employed in the determination of the rainfall onset and retreat dates. The results obtained show that both rainfall amount and rainy days are equally effective in the determination of the mean rainfall onset and retreat dates in Nigeria. With regards to the rainfall onset and retreat dates of the individual years however, the method based on the rainy days is more effective than that based on rainfall amount, as the former yielded more realistic dates than the latter. It is thus recommended that studies investigating rainfall onset and retreat dates within a series of individual years in Nigeria, should be based on rainy days rather than rainfall amount.  相似文献