Intraseasonal variability in South America during the cold season   总被引：1，自引：1，他引：0  

Mariano S. Alvarez  C. S. Vera  G. N. Kiladis  B. Liebmann 《Climate Dynamics》2014,42(11-12):3253-3269

Intraseasonal (IS) variability in South America is analyzed during the cold season using 10–90 day bandpass filtered OLR anomalies (FOLR). IS variability explains a large percentage of variance with maximum values over Paraguay, northeastern Argentina, and southern Brazil. The leading pattern of FOLR, as isolated from an EOF analysis, (Cold Season IS pattern, CSIS), is characterized by a monopole centered over southeastern South America (SESA) with a northwest-southeast orientation. CSIS induces a large modulation on daily precipitation anomalies, especially on both wet spells and daily precipitation extremes, which are favored during positive (wet) CSIS phases. Large-Scale OLR anomalies over the tropical Indian and west Pacific Oceans associated with CSIS exhibit eastward propagation along tropical latitudes. In addition, circulation anomalies in the Southern Hemisphere reveal the presence of an anticyclonic anomaly over Antarctica with opposite-sign anomalies in middle latitudes 10 days before CSIS is maximum as well as evidence of Rossby wave-like patterns. Positive precipitation anomalies in SESA are favored during wet CSIS phases by the intensification of a cyclonic anomaly located further south, which is discernible over the southeastern Pacific for at least 14 days before CSIS peaks. The cyclonic anomaly evolution is accompanied by the intensification of an upstream anticyclonic anomaly, which remains quasi-stationary near the Antarctica Peninsula before the CSIS peak. We speculate that the stationary behavior of the anticyclonic center is favored by a hemispheric circulation anomaly pattern resembling that associated with a negative southern annular mode phase and a wavenumber 3–4 pattern at middle latitudes.  相似文献   

The origin of young mare basalts inferred from lunar meteorites Northwest Africa 4734, 032, and LaPaz Icefield 02205     

Stephen M. Elardo  Charles K. Shearer Jr.  Amy L. Fagan  Lars E. Borg  Amy M. Gaffney  Paul V. Burger  Clive R. Neal  Vera A. Fernandes  Francis M. McCubbin 《Meteoritics & planetary science》2014,49(2):261-291

Northwest Africa (NWA) 4734 is an unbrecciated basaltic lunar meteorite that is nearly identical in chemical composition to basaltic lunar meteorites NWA 032 and LaPaz Icefield (LAP) 02205. We have conducted a geochemical, petrologic, mineralogic, and Sm‐Nd, Rb‐Sr, and Ar‐Ar isotopic study of these meteorites to constrain their petrologic relationships and the origin of young mare basalts. NWA 4734 is a low‐Ti mare basalt with a low Mg* (36.5) and elevated abundances of incompatible trace elements (e.g., 2.00 ppm Th). The Sm‐Nd isotope system dates NWA 4734 with an isochron age of 3024 ± 27 Ma, an initial ε_Nd of +0.88 ± 0.20, and a source region ¹⁴⁷Sm/¹⁴⁴Nd of 0.201 ± 0.001. The crystallization age of NWA 4734 is concordant with those of LAP 02205 and NWA 032. NWA 4734 and LAP 02205 have very similar bulk compositions, mineral compositions, textures, and ages. Their source region ¹⁴⁷Sm/¹⁴⁴Nd values indicate that they are derived from similar, but distinct, source materials. They probably do not sample the same lava flow, but rather are similarly sourced, but isotopically distinct, lavas that probably originate from the same volcanic complex. They may have experienced slightly different assimilation histories in route to eruption, but can be source‐crater paired. NWA 032 remains enigmatic, as its source region ¹⁴⁷Sm/¹⁴⁴Nd definitively precludes a simple relationship with NWA 4734 and LAP 02205, despite a similar bulk composition. Their high Ti/Sm, low (La/Yb)_N, and Cl‐poor apatite compositions rule out the direct involvement of KREEP. Rather, they are consistent with low‐degree partial melting of late‐formed LMO cumulates, and indicate that the geochemical characteristics attributed to urKREEP are not unique to that reservoir. These and other basaltic meteorites indicate that the youngest mare basalts originate from multiple sources, and suggest that KREEP is not a prerequisite for the most recent known melting in the Moon.  相似文献   

Impact of projected SST changes on summer rainfall in southeastern South America   总被引：1，自引：1，他引：0  

C. Junquas  C. S. Vera  L. Li  H. Le Treut 《Climate Dynamics》2013,40(7-8):1569-1589

Recent studies have shown that global warming and associated sea-surface temperature (SST) changes may trigger an important rainfall increase in southeastern South America (SESA) during the austral summer (December–January–February, DJF). The goal of this paper is to provide some insight into processes which may link global and SESA changes. For this purpose, a “two-way nesting” system coupling interactively the regional and global versions of the LMDZ4 atmospheric model is used to study the response to prescribed SST changes. The regional model is a variable-grid version of the global model, with a zoom focused over South America. An ensemble of simulations forced by distinct patterns of DJF SST changes has been carried out using a decomposition of full SST changes into their longitudinal and latitudinal components. The full SST changes are based on projections for the end of the twenty-first century from a multi-model ensemble of WCRP/CMIP3. Results confirm the presence of a major rainfall dipole structure, characterized by an increase in SESA and a decrease in the South Atlantic Convergence Zone region. Rainfall changes found in the WCRP/CMIP3 models are largely explained as a response of this dipole structure to the zonally-asymmetric (or longitudinal) component of SST changes. The rainfall response to the zonal-mean (or latitudinal) SST changes (including the global warming signal itself) shows an opposite contribution. The processes explaining the role of zonally-asymmetric SST changes involve remote effects of SST warming over the equatorial Indian and Pacific oceans inducing an atmospheric wave-train extended across the South Pacific into South America.  相似文献   

Decadal predictability and prediction skill of sea surface temperatures in the South Pacific region     

Ramiro I. Saurral  Javier Garc&#;a-Serrano  Francisco J. Doblas-Reyes  Leandro B. D&#;az  Carolina S. Vera 《Climate Dynamics》2020,54(9):3945-3958

The South Pacific Ocean is a key driver of climate variability within the Southern Hemisphere at different time scales. Previous studies have characterized the main mode of interannual sea surface temperature (SST) variability in that region as a dipolar pattern of SST anomalies that cover subtropical and extratropical latitudes (the South Pacific Ocean Dipole, or SPOD), which is related to precipitation and temperature anomalies over several regions throughout the Southern Hemisphere. Using that relationship and the reported low predictive skill of precipitation anomalies over the Southern Hemisphere, this work explores the predictability and prediction skill of the SPOD in near-term climate hindcasts using a set of state-of-the-art forecast systems. Results show that predictability greatly benefits from initializing the hindcasts beyond the prescribed radiative forcing, and is modulated by known modes of climate variability, namely El Niño-Southern Oscillation and the Interdecadal Pacific Oscillation. Furthermore, the models are capable of simulating the spatial pattern of the observed SPOD even without initialization, which suggests that the key dynamical processes are properly represented. However, the hindcast of the actual phase of the mode is only achieved when the forecast systems are initialized, pointing at SPOD variability to not be radiatively forced but probably internally generated. The comparison with the performance of an empirical prediction based on persistence suggests that initialization may provide skillful information for SST anomalies, outperforming damping processes, up to 2–3 years into the future.  相似文献   

Risk occurrences of damaging frosts during the growing season of vegetables in the Elbe River lowland,the Czech Republic     

Vera Potop  Pavel Zahraniček  Luboš Türkott  Petr Štěpánek  Josef Soukup 《Natural Hazards》2014,71(1):1-19

This study has, for the first time, analysed in detail the risk occurrences of the last spring frost, first fall frost and the length of the frost-free period during the growing season of vegetable crops at a high horizontal resolution of 10 km in the Elbe River lowland in the Czech Republic. The daily minimum air temperature from 116 grid points throughout the studied area for the period 1961–2011 was used. The daily values of minimum air temperature ranges of 0 to ?1.1 °C, ?1.2 to ?2.2 °C and below ?2.2 °C were considered to constitute mild, moderate and severe frost intensities, respectively. Firstly, the spatiotemporal variability of the date of the last spring frost, the date of the first fall frost and the length of the frost-free period in the Elbe River lowland is provided. Secondly, the estimation of the probability of a later date in the spring and an earlier date in the fall for various severe frost events and the length of the frost-free period is determined. Third, the changes in the timing of the last and first frosts of the three severities, as well as the length of the frost-free period, are evaluated. From 1961 to 2011, the Elbe River lowland has experienced a decrease in the number of frost days, while the length of the frost-free period between the last spring frost and the first fall frost has increased. The temporal evolution of the frost-free period anomalies displays two distinct periods: a shortening of the frost-free period in the 1960s and an intensified lengthening of the frost-free period since the 1980s. Whereas the latest spring frost has ended on an earlier date across the Elbe River lowland, the first frost date in the fall has generally been delayed to a later date. The dates of the last spring frost have advanced by ?0.21 days per year on average. The fall dates are delayed up to 0.18 days per year, whereas the frost-free period is lengthening by up to 0.39 days per year on average. However, regional frost series suggests that the frost-free period exhibits a large amount of inter-annual variability. In terms of the growth of field vegetables, a late spring frost remains a risk factor, but the degree of risk has decreased. There is a 25 % chance of the occurrence of dangerous spring frosts during the planting of field vegetables after 3rd May, but after 15th May, the risk is only 10 %.  相似文献   

A simple method to model the reduced environment of lake bottom sapropel formation     

Gaskova  Olga L.  Strakhovenko  Vera D.  Ermolaeva  Nadezhda I.  Zarubina  Eugene Yu.  Ovdina  Ekaterina A. 《中国海洋湖沼学报》2017,35(4):956-966

The Kambala and Barchin brackish lakes(Baraba steppe,southern West Siberia) contain an organic-rich sapropel layer that was formed in oxygen-depleted waters.We measured the bulk sediment elemental composition,the water chemistry and determined the mineralogical composition and predominant biota species(Diatoms and Cyanobacteria in phytoplankton community respectively) in the lakes.The result indicates that the first lake has a siliceous type of sapropel and the second a carbonaceous one.A computer thermodynamic model was developed for chemical interaction in water-bottom sediment systems of the Kambala and Barchin Lakes.The surface sodium bicarbonate waters are supersaturated with respect to calcite,magnesite(or low Mg-calcite),quartz and chlorite with minor strontianite,apatite and goethite(pH8.9-9.3,Eh 0.3 V).Nevertheless,it is shown that during sapropel deposition,deep silt waters should be anoxic(Eh0 V).The virtual component CH_2O has been used to create an anoxic environment suitable for pyrite formation due to the biotic community impact and abiotic reduction.Thermodynamic calculation has shown that silt water is not necessarily euxinic(anoxic and sulfidic).Depending on Eh,sulfate sulfur can dominate in solution,causing the formation of gypsum together with pyrite.An attempt was made to find a reason for solution supersaturation with respect to Ca and Mg ions due to their complexation with humic acids.  相似文献   

On the possibility of systematizing classical novae by light curve type. I. Type criteria     

A. E. Rosenbush 《Astrophysics》1999,42(1):43-53

Nova light curves, plotted on “outburst amplitude-logarithm of main shell radius” axes, have differences that can be systematized. As a result of a survey of over 90 novae, nova groups that are typical in light curve shape have been distinguished: DQ Her, CP Pup, RR Pic, PU Vul, V1974 Cyg, CP Lac, and GQ Mus. The light curve criterion is supplemented by other characteristics. The DQ Her group includes only novae having dust formation in the ejected shell. The GQ Mus group combines certain novae with smooth light curves that are separated into several subgroups with respect to outburst amplitude and the duration of the light curve section before the transitional stage, but for which the linear section of the light curve has the same slope. Translated from Astrofizika, Vol. 42, No. 1, pp. 61–74, January–March, 1999.  相似文献   

Are Sakurai’s object and Nova Aquilae 1919 recurrent outbursts of classical novae?     

A. é. Rosenbush 《Astrophysics》1999,42(4):425-430

It is proposed to interpret the outbursts of Nova Aquilae 1919 (V605 Aql) and the nova-like outburst of Sakurai’s object in 1996 as recurrent outbursts of classical novae of the DQ Her and RR Pic types with recurrence periods of about 1100 and 50,000 years, respectively, and some characteristics of these stars are derived on that basis. Only now has V605 Aql returned to the quiet state, and it has an absolute visual magnitude no fainter than 8^m−9^m. The orbital inclination of the prenova’s binary system is about 90°. The absolute visual magnitude of the prenova of V4334 Sgr is no brighter than 3^m. It is quite possible that the orbital inclination of the prenova’s binary system is close to 0°. The expansion velocities of the shells are 30–40 km/sec in both cases. The structure of the ejection is conserved in the recurrent outbursts. Translated from Astrofizika, Vol. 42, No. 4, pp. 563–570, October–December, 1999.  相似文献   

Advancements in hydrochemistry mapping: methods and application to groundwater arsenic and iron concentrations in Varanasi,Uttar Pradesh,India     

Ricardo?A.?OleaEmail author  N.?Janardhana?Raju  Juan?José?Egozcue  Vera?Pawlowsky-Glahn  Shubhra?Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(1):241-259

The area east of Varanasi is one of numerous places along the watershed of the Ganges River with groundwater concentrations of arsenic surpassing the maximum value of 10 parts per billion (ppb) recommended by the World Health Organization in drinking water. Here we apply geostatistics and compositional data analysis for the mapping of arsenic and iron to help in understanding the conditions leading to the occurrence of elevated level of arsenic in groundwater. The methodology allows for displaying concentrations of arsenic and iron as maps consistent with the limited information from 95 water wells across an area of approximately 210 km²; visualization of the uncertainty associated with the sampling; and summary of the findings in the form of probability maps. For thousands of years, Varanasi has been on the erosional side in a meander of the river that is free of arsenic values above 10 ppb. Maps reveal two anomalies of high arsenic concentrations on the depositional side of the valley, which has started seeing urban development. The methodology using geostatistics combined with compositional data analysis is completely general, so this study could be used as a prototype for hydrochemistry mapping in other areas.  相似文献