Spectral time method of identification of seismic events at distances of 15°–40°

The spectral time method is applied to the identification of underground nuclear explosions (UNEs) and earthquakes from P wave records obtained at stations at epicentral distances of 15°–40°. It is necessary to utilize data at such great distances because the density of stations of the International Monitoring System is small in several areas of the Earth. At such distances, it is difficult to detect S and surface LR waves and, therefore, the efficiency of the identification using the diagnostic parameters (discriminants) S/P and LR/P is drastically reduced. As a result, the role of spectral and spectral time methods in the identification of events from P waves becomes much more significant. An advantage of the spectral time method (STM) is that it is applicable in the region of interest, provided that data from one or two reference underground chemical explosions and a representative sample of earthquake records obtained at network stations of the region are available. Moreover, in the majority of cases, the STM identifies earthquakes that could not be recognized with the use of spectral diagnostic parameters. We used records of UNEs and earthquakes in Central Asia received from the archives of the Center of the Incorporated Research Institution for Seismology (IRIS) in Washington, the National Data Center in Dubna (Russian Federation), and the International Data Center (IDC) in Vienna. The effectiveness of earthquake record selection using the given method amounted to about 80%. Supposedly, the application of this method of identification can increase the percentage of filtration (screening) of regional events having a natural origin.     

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

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.     

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)

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.     

青藏高原东部全新世冬夏季风变化的高分辨率泥炭记录

在建立了全新世泥炭沉积物高分辨率冬夏季风代用指标时间序列的基础上, 发现青藏高原若尔盖地区全新世冬夏季风的变化具有此消彼长和同时消长两种基本的模式, 冬季风与夏季风在不同时间尺度上两种模式又相互嵌套. 由冬夏季风指标叠加效应合成的气候状况却有与全球同步的规律性, 表现出千年-百年尺度的不稳定性, 6.2 ka的季风突然减弱事件要比8.0 ka的事件更显著, 反映了亚洲季风的区域特点或它本身就是全球气候的一个窗口.     

The Enso-Fire Dynamic in Insular Southeast Asia

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.     

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

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.     

Estimation of monthly average solar radiation in Libya

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.     

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

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.