Precipitation and evaporation budgets over the Baltic Proper: observations and modelling

Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgional-scale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of C_HN and C_EN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year^-1 and precipitation between 624 and 805 mm year^-1 for this particular 12 month period. Taking the results of model verification from the present study into account, the best estimate of P-E is about 100 ± 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year^-1 for the 12 month period studied here and 32 mm year^-1 as an average for 18 years.     

Study of the total lightning activity in a hailstorm

A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min^− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min^− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground.     

Modelling the Baltic Sea ocean climate on centennial time scale: temperature and sea ice

This study considers the possible use of different kinds of forcing datasets in Baltic Sea ocean climate modelling on centennial time scales, in particular for the past half millennium. We demonstrate that high-quality station data of the past century and gridded multi-proxy reconstructions for the past 500 years can be used with great success but with various levels of detail. We also demonstrate that output data from the state-of-the-art global climate model EcHo-G are not suitable for modelling the Baltic Sea ocean climate. Two climate properties were studied: the annual maximum ice extent (MIB) and the vertically and horizontally integrated annual water temperature. Centennial time scale results indicate that the seventeenth and nineteenth centuries were the coldest centuries, while the 1690s were the coldest decade and 1695 the coldest year in the last 500 years. The results also indicate that the twentieth century was the warmest century with the least MIB of the last 500 years. On a decadal time scale, the 1990s, 1930s and 1730s were the warmest decades and comparable in terms of both water temperature and MIB. The year 1989 had the minimum observed MIB of only 52,000 km², implying that the Baltic Sea has been partly ice covered in all winters of the past half millennium. Even though different climate forcing mechanisms may operate on the climate system today compared to over the last half millennium, this study cannot clearly state that the region is experiencing climate change outside the natural limits of the past 500 years.     

Moon and Earth : compositional differences inferred from siderophiles,volatiles, and alkalis in basalts

We have compared RNAA analyses of 18 trace elements in 25 low-Ti lunar and 10 terrestrial oceanic basalts. According to Ringwood and Kesson, the abundance ratio in basalts for most of these elements approximates the ratio in the two planets.Volatiles (Ag, Bi, Br, Cd, In, Sb, Sn, Tl, Zn) are depleted in lunar basalts by a nearly constant factor of 0.026 ± 0.013, relative to terrestrial basalts. Given the differences in volatility among these elements, this constancy is not consistent with models that derive the Moon's volatiles from partial recondensation of the Earth's mantle or from partial degassing of a captured body. It is consistent with models that derive planetary volatiles from a thin veneer (or a residuum) of C-chondrite material; apparently the Moon received only 2.6% of the Earth's endowment of such material per unit mass.Chalcogens (Se and Te) have virtually constant and identical abundances in lunar and terrestrial basalts, probably reflecting saturation with Fe(S, Se, Te) in the source regions.Siderophiles show diverse trends. Ni is relatively abundant in lunar basalts (4 × 10^?3 × Cl-chondrites), whereas Ir, Re, Ge, Au are depleted to 10^?4?10^?5× Cl. Except for Ir, these elements are consistently enriched in terrestrial basalts: Ni 3 × , Re 370 ×, Ge 330 × , Au 9 × . This difference apparently reflects the presence of nickel-iron phase in the lunar mantle, which sequesters these metals. On Earth, where such metal is absent, these elements partition into the crust to a greater degree. Though no lunar mantle rock is known, an analogue is provided by the siderophile-rich dunite 72417 (~0.1% metal) and the complementary, siderophile-poor troctolite 76535. The implied metal-siderophile distribution coefficients range from 10⁴ to 10⁶, and are consistent with available laboratory data.The evidence does not support the alternative explanation advanced by Ringwood—that Re was volatilized during the Moon's formation, and is an incompatible element (like La or W⁴⁺) in igneous processes. Re is much more depleted than elements of far greater volatility: (Re/U)_Cl～- 4 × 10^?6 vs (T1/U)_Cl = 1.3 × 10^?4, and Re does not correlate with La or other incompatibles.Heavy alkalis (K, Rb, Cs) show increasing depletion with atomic number. Cs/Rb ratios in lunar basalts, eucrites, and shergottites are 0.44, 0.36, and 0.65 × Cl, whereas the value for the bulk Earth is 0.15–0.26. These ratios fall within the range observed in LL and E6 chondrites. supporting the suggestion that the alkali depletion in planets, as in chondrites, was caused by localized remelting of nebular dust (= chondrule formation). Indeed, the small fractionation of K, Rb and Cs, despite their great differences in volatility, suggests that the planets, like the chondrites, formed from a mixture of depleted and undepleted material, not from a single, partially devolatilized material.     

Mobility and Transport of Nd Isotopes in the Vadose Zone During Weathering of Granitic Till in a Boreal Forest

There is a broad correlation between the ε_Nd values for rivers (including both the water and the particulate material it carries) and the age of the source terrain. This paper presents Nd isotope distribution data for soil, soil water, groundwater, and stream water samples gathered in a small catchment in northern Sweden. The results show that the release of Nd and Sm from boreal forests into streams and, eventually, into the oceans is more complicated than previously realized. The weathering of till causes changes in both the Nd isotopic composition and Sm/Nd ratios. Both the Sm/Nd ratio and ε_Nd were higher in strongly weathered soils horizons than in less weathered till, since minerals with high Sm/Nd ratios were, on average, more resistant to weathering than those with low Sm/Nd ratios. In contrast to the situation for the main minerals and the major elements, the weathering of rare earth elements (REE) was not restricted to the E-horizon: the measured REE concentrations continued to increase with depth in the C-horizon. In addition, REE released by weathering in the upper parts of the soil profile were partly secondarily retained at deeper levels. Therefore, the dissolved Nd released by weathering in the upper soil horizons was trapped and did not enter the groundwater directly. Rather, the Nd in the groundwater largely originated from weathering within the groundwater zone. However, this was not the only source of Nd in the stream water. The Nd isotope composition and Sm/Nd ratio were determined by the mixing between of Nd and Sm in the groundwater and REE-carrying organic material washed out of the soil profile. The groundwater close to the stream reaches the upper soil horizons during high discharge events such as snowmelts, and organic matter carrying Nd and Sm is washed out of the soils and thus released into the stream. Therefore, the Nd exported from catchment is derived from both the weathering within the groundwater zone, and the organic matter washed out from the soil. If longer timescales with more advanced weathering stages in the groundwater zone are considered, it cannot be ruled out that there will be a shift towards more radiogenic values in the exported Nd. Recorded shifts in the Nd isotopic composition in the ocean may thus not only reflect changed source regions, but also the weathering history of the same source region.     

基于多期DEM和滑坡强度的滑坡风险评估

滑坡危险性定量评估是滑坡风险评估中的关键和难点,也是当前国际风险管理研究中的热点问题.以滑坡密集分布的黑方台南塬为研究区,以32处典型滑坡为研究对象,依据多期三维数字高程模型(DEM),提出了一种基于强度的滑坡危险性定量评估技术方法.根据多期三维地形信息的解译及野外调查,编制多期滑坡分布图,计算滑坡活动的频率.利用GIS技术,利用滑坡体积与速度的乘积计算滑坡强度.将滑坡危险性定义为滑坡频率和滑坡强度的乘积,同时调查和分析了黑方台地区各类承灾体的类型、价值及其在相应滑坡强度下的易损性,在此基础上开展了单体滑坡风险评估和黑方台南塬滑坡风险区划.     

基于ENVISAT/ASAR资料的土壤湿度反演方法

提出了利用ENVISAT/ASAR/AP模式VV极化的低入射角数据和黄土高原陆面过程试验资料对黄土高原平凉试验区表层土壤湿度进行反演的方法。结果表明:在相对平坦的混合地表类型区域,反演的土壤湿度与地面实测值平均误差<0.02 cm3.cm-3,绝对误差均在0.04 cm3.cm-3范围内,该结果能较好地对黄土高原塬区土壤湿度进行干旱监测;但在陡峭山坡及塬边等地形起伏较大的区域,结果较差。     

Redox cycling of iron and manganese in sediments of the Kalix River estuary, Northern Sweden

Iron and manganese redox cycling in the sediment — water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fe_total and 84% of Mn_total). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m^–2 d^–1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m^–2 d^–1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m^–2 d^–1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m^–2 d^–1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16–1.7 mol cm^–3 d^–1, respectively.     

Meteoritic material in a Boulder from the Apollo 17 Site: Implications for its origin

Sixteen samples of Boulder 1 from Station 2 at the Apollo 17 site were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, Ir, Ni, Rb, Re, Sb, Te, Tl, U, and Zn. Two clast samples contam no meteoritic material and appear to consist of relatively pristine igneous rocks: an unusual, KREEP-rich pigeonite basalt of very high Ge content, and an alkali-poor coarse norite. Nine grey or black breccia samples contain a unique, Group 3 meteoritic component of Ir/Au ratio 0.65–0.82, which appears to separate into subgroups 3H and 3L on the basis of Ni, Ge, and Re content. It is quite distinct from the Group 2 component (Ir/Au - 0.46–0.54) that dominates at the Apollo 17 site.The unique black-rimmed clasts from this boulder show striking compositional zoning. The cores of anorthositic breccia are very low in Rb, Cs, and U, and have a distinctive 5L meteoritic component (Ir/Au1.1). The black rinds are 5- to 10-fold richer in Rb, Cs, and U and have a Group 3 meteoritic component. The cores may represent breccias formed in an earlier impact that became coated with alkali-rich ejecta during the event that produced the boulder.Because of the rarity of the Group 3 meteoritic component at the Apollo 17 site, this boulder cannot represent ordinary Serenitatis ejecta, with their characteristic admixture of the Group 2 Serenitatis projectile. It may represent pre-Serenitatis material excavated from the fringes of the crater during late stages of the Serenitatis impact, but only lightly shocked and hence uncontaminated by the Serenitatis projectile.     

Further studies of trace elements in C3 chondrites

Five carbonaceous chondrites (Renazzo C2V, Allende C3V, Omans C3O, Warrenton C3O, and Orgueil Cl) were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs. Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U and Zn. These data, together with earlier measurements on seven additional C3 s, are interpreted in the light of pétrographie studies by MCSWEEN (1977a, b) and revised condensation temperatures (WAI and Wasson, 1977). Elements condensing between ~ 700 and 420 K (Se, Zn, S, Te, Br, In, Bi, Tl) are systematically more depleted than those condensing between 1000 and 900 K (Ge, Ag, Rb), by factors of 1.3 to 2, and the depletion correlates inversely with matrix content and directly with degree of metamorphism. The most plausible explanation appears to be a gas-dust fractionation during condensation, by settling of dust to the median plane of the nebula. In this model, gas/dust ratios relative to the cosmic ratio ranged from 0.7 at 1000 K to 0.5 at 700 K for those C3O s that accreted first (Ornans, Warrenton) and from 1.3 to 0.6 for the last (Kainsaz). There appears to have been no further gas/dust fractionation below 700 K.Abundances of Sb, Au and Cd follow earlier trends. Depletion of Sb and Au correlates with abundance of Fe-poor olivine and seems to reflect greater volatilization upon more prolonged or intense heating during chondrule formation. The 50–100-fold depletion of Cd in C3Os compared to C3Vs suggests condensation in a region where enough Fe was present to buffer the H₂S pressure.