共查询到20条相似文献，搜索用时 500 毫秒
1.
N. C. Matalas 《水文科学杂志》2013,58(3):427-429
ABSTRACT Lake-sediment-based estimates of sediment yield are calculated from a 210Pb and 137Cs chronology for the period 1765–1983 for a small lake-catchment in the English Midlands. Based on a multiple coring exercise, synchronous sedimentation levels are identified on the basis of mineral magnetism because of the lack of a visual stratigraphy. The rates of sediment accumulation are adjusted for outflow losses, biogenic precipitation and atmospheric fallout and results are considered to reflect accurately sediment yields for the area. At best, these yields are averaged over 4–5 years in the recent past, and 50–60 years in previous centuries. It is suggested that analysis of sediment yields over the last 218 years provides data covering one of the most dramatic periods of change as a result of human activity and covers intermediate timescales often ignored in hydrological studies because they fall beyond the scope of direct process monitoring. 相似文献
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L. I. Abalkin 《Water Resources》2006,33(6):713-714
Chronicles
In memory of G.P. Kalinin (1916–1975) 相似文献3.
Agustín Udías 《Journal of Seismology》2015,19(3):807-808
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《Journal of Atmospheric and Solar》2002,64(3):367-376
Observations of winds in mesospheric airglow layers have been made at Mt. John (44°S,170°E), New Zealand for some years. We present a modelling study of airglow emissions which shows that the properties of wind detection based on airglow emission means that high-frequency gravity waves are effectively filtered from the wind spectrum observed. This filtering means that any waves with periods of the order of hours should be detectable in the record (as they will not be hidden in the noise of the higher-frequency waves ubiquitous at these heights). One example of such a wave is shown. As part of the analysis, we show that because the airglow layers differ in width, some waves might be observed in only one airglow layer, even when present in both. 相似文献
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《Journal of Atmospheric and Solar》2000,62(13):1177-1187
Continuous MF radar measurements of mesospheric mean winds are in progress at the observatories in Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E). The observations at Yamagawa and Wakkanai were started in August 1994 and September 1996, respectively. The real-time wind data are used for the study of major large scale dynamic features of the middle atmosphere such as mean winds, tides, planetary waves, and gravity waves, etc. In the present study of mean winds, we have utilized the data collected until June 1999, which include the simultaneous observation period of little more than two and a half years, for the two sites. The database permits us to draw conclusions on the characteristics of mean winds and to compare the mean wind structure over these sites. The mean prevailing zonal winds at both sites are dominated by westward/eastward motions in summer/winter seasons below 90 km. Meridional circulation at meteor heights is generally southward during most times of the year and it extends to lower mesospheric heights during summer also. The summer westward jet at Wakkanai is consistently stronger than those at Yamagawa. However, the winter eastward winds have identical strength at both locations. Meridional winds also show larger values at Wakkanai. The mean wind climatology has been examined and compared with the MU radar observations over Shigaraki (34.9°N, 136.1°E). The paper also presents the results of the comparison between the MF radar winds and the latest empirical model values (HWM93 model) proposed by Hedin et al. (1996. Journal of Atmospheric and Terrestrial Physics 58, 1421–1447). Hodograph analyses of mean winds conducted for the summer and winter seasons show interesting similarities and discrepancies. 相似文献
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Ocean Dynamics - In order to look for climatological changes on significant wave height and wind magnitude distributions, two decades of altimeter data were analyzed in a monthly 1° ×... 相似文献
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The July–August 2001 eruption of Mt. Etna stimulated widespread public and media interest, caused significant damage to tourist facilities, and for several days threatened the town of Nicolosi on the S flank of the volcano. Seven eruptive fissures were active, five on the S flank between 3,050 and 2,100 m altitude, and two on the NE flank between 3,080 and 2,600 m elevation. All produced lava flows over various periods during the eruption, the most voluminous of which reached a length of 6.9 km. Mineralogically, the 2001 lavas fall into two distinct groups, indicating that magma was supplied through two different and largely independent pathways, one extending laterally from the central conduit system through radial fissures, the other being a vertically ascending eccentric dike. Furthermore, one of the eccentric vents, at 2,570 m elevation, was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer, during both the initial and closing stages of the eruption. For 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer, permitting powerful explosive and effusive magmatic activity. While the eruption was characterized by a highly dynamic evolution, complex interactions between some of the eruptive fissures, and changing eruptive styles, its total volume (~25×10 6 m 3 of lava and 5–10×10 6 m 3 of pyroclastics) was relatively small in comparison with other recent eruptions of Etna. Effusion rates were calculated on a daily basis and reached peaks of 14–16 m 3 s -1, while the average effusion rate at all fissures was about 11 m 3 s -1, which is not exceptionally high. The eruption showed a number of peculiar features, but none of these (except the contemporaneous lateral and eccentric activity) represented a significant deviation from Etna's eruptive behavior in the long term. However, the 2001 eruption could be but the first in a series of flank eruptions, some of which might be more voluminous and hazardous. Placed in a long-term context, the eruption confirms a distinct trend, initiated during the past 50 years, toward higher production rates and more frequent eruptions, which might bring Etna back to similar levels of activity as during the early to mid seventeenth century. 相似文献
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《Journal of Atmospheric and Solar》1999,61(6):447-459
Long-term changes of temperature and wind data have been investigated using U.S. rocketsondes at six selected sites at northern tropical and subtropical locations (from 8°S to 34°N). The analysis method used here is based on a multi-function regression analysis that allows for a continuous linear trend, for natural variability, and for sudden changes of the mean due to successive instrumental improvements. Results show that while sensor replacement does not seem to induce major measurement bias, successive correction procedures have produced significant mean temperature shifts, mostly above 55 km. Changes in the local time of measurement may have an impact on trend estimates because of tidal effects. This effect is probably enhanced by the direct solar radiative heating on the sensor. Selecting data according to the time of measurement has sometimes reduced the amplitude of the observed cooling.Using a detailed statistical model and error analysis, significant temperature trends are detected in the upper stratosphere with amplitudes slightly increasing with height. As the trend profiles from the selected sites are very similar in patterns and magnitudes, a mean annual temperature trend profile is composed using these six data sets. A significant cooling of 1.1±0.6 K per decade is estimated for 25 km height, increasing with height up to 1.7±0.7 K per decade in the altitude range of 35 to 50 km, and to 3.3±0.9 K per decade near 60 km. Previous published simulations of stratospheric changes induced by greenhouse gas increases and stratospheric ozone depletion, using numerical models, predict smaller cooling than that estimated here by a factor of around two. A similar analysis for zonal wind data reveals no significant changes larger than 5 m · s−1 per decade. 相似文献
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K. Pavlou G. Drakatos V. Kouskouna K. Makropoulos H. Kranis 《Journal of Seismology》2016,20(2):701-710
The spatial-temporal evolution of seismicity is examined, during the initial impoundment of Pournari reservoir located on Arachthos River (Western Greece), as well as for the next 30 years. The results show that, despite the relatively moderate-to-high seismicity from west to east, there is no remarkable earthquake in the vicinity before the first reservoir impoundment. Immediately after the impoundment (January 1981), and during the first 4 months, a considerable number of low-magnitude seismic events were recorded in the broader area of the dam. Moreover, two independent major events occurred on March 10, 1981 (M L ?=?5.6) and April 10, 1981 (M L ?=?4.7) with focal depths 13 and 10 km, respectively. The detailed analysis of the two corresponding aftershock sequences shows that they present different behaviors (e.g., larger b-value and lower magnitude of the main aftershock) than that of other aftershock sequences in Greece. This seismicity is probably due to triggering, via the water loading mechanism and the undrained response due to a flysch appearance on the reservoir basement. The activation of the thrust fault may be attributed to the bulging of evaporites that characterize the disordered structure of W. Greece, via possible water intake. The detailed processing of the recorded seismicity during the period 1982–2010, in comparison with the variations of Pournari Dam water level, shows an increase of shallow seismicity (h?≤?5 km) in the vicinity of the reservoir up to a 10-km distance—in contrast to the initial period, characterized by a number of deeper events due to the background response change from undrained to drained status. 相似文献
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N. Gopalswamy S. Akiyama S. Yashiro G. Michalek R.P. Lepping 《Journal of Atmospheric and Solar》2009,71(8-9):1005-1009
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Irina V. Medvedeva Anatoly I. Semenov Vladimir I. Perminov Alexander B. Beletsky Andrey V. Tatarnikov 《Acta Geophysica》2014,62(2):340-349
Data about the variations of mesopause temperature (～87 km) obtained from ground-based spectrographic measurements of the OH emission (834.0 nm, band (6-2)) at Irkutsk and Zvenigorod observatories were compared with satellite data on vertical temperature distribution in the atmosphere from Aura MLS v3.3. We analyzed MLS data for two geopotential height levels: 0.005 hPa (～84 km) and 0.002 hPa (～88 km) as the closest to OH height (～87 km). We revealed that Aura MLS temperature data have lower values than ground-based (cold bias). In summer periods, that difference increases. Aura cold biases compared with OH(6-2) at Irkutsk and Zvenigorod were calculated. For the 0.002 hPa height level, the biases are 10.1 and 9.4 K, and for 0.005 hPa they are 10.5 and 10.2 K at Irkutsk and Zvenigorod, respectively. When the bias is accounted for, an agreement between Aura MLS and OH(6-2) data obtained at both Irkutsk and Zvenigorod is remarkable. 相似文献
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Averaged seasonal variations of wind perturbation intensities and vertical flux of horizontal momentum produced by internal gravity waves (IGWs) with periods 0.2/1 h and 1/6 h are studied at the altitudes 65/80 km using the MU radar measurement data from the middle and upper atmosphere during 1986/1997 at Shigaraki, Japan (35°N, 136°E). IGW intensity has maxima in winter and summer, winter values having substantial interannual variations. Mean wave momentum flux is directed to the west in winter and to the east in summer, opposite to the mean wind in the middle atmosphere. Major IGW momentum fluxes come to the mesosphere over Shigaraki from the Pacific direction in winter and continental Asia in summer. 相似文献
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M. A. BENSON 《水文科学杂志》2013,58(3):5-6
Abstract This study was made to define the relation between floods in a humid region and the causative factors that account for their variability. The study covered the basic relationships between peak discharges and hydrologic factors as well as the practical working methods for generalizing the results on a regional basis. Statistical multiple-correlation techniques were applied to hydrologic data in New England. A field and library investigation of historical flood data extended the period of flood knowledge to as much as 300 years. The relation of many topographic and climatic factors to flood peaks was tested. Flood peaks with recurrence intervals at 9 levels, from 1.2 to 300 years, were related to 6 independent variables, 3 of which are topographic, 2 climatic, and 1 orographic. 相似文献