Mantle sources of the Cenozoic volcanic rocks of the Lake Kizi region in the eastern Sikhote Alin     

S. V. Rasskazov  V. S. Prikhod’ko  T. A. Yasnygina  N. N. Fefelov  E. V. Saranina  I. P. Voinova  S. B. Brandt 《Russian Journal of Pacific Geology》2010,4(5):441-459

The Middle Cenozoic lava sequence of the Lake Kizi region was studied. It characterizes the activity of sources in the Northern zone of the eastern Sikhote Alin: a Middle Eocene pulse of slab-related magmatism and prolonged injection of magmas from the sublithospheric convecting mantle in the Late Oligocene. Low contents of high field strength elements (Nb and Ta) with low Nb/Ta, Ce/Pb, and Nb/La and high K/Nb ratios and a low (⁸⁷Sr/⁸⁶Sr)₀ of 0.703399 were determined in a Middle Eocene dacite with an age of ∼43.5 Ma. Three phases of Late Oligocene volcanic eruptions were distinguished: (1) basaltic andesites (29–27 Ma), (2) basaltic trachyandesites and trachyandesites (27–24 Ma), and (3) andesites (∼23 Ma). The lavas of the first and third phases showed low Ce/Pb, Nb/La, and Ba/La and high K/Nb ratios, which are also characteristic of supraslab processes. The lavas of the second phase are shifted with respect to these ratios toward ocean island basalt compositions. The entire Late Oligocene volcanic sequence falls within a narrow range of the initial strontium isotope ratios, (⁸⁷Sr/⁸⁶Sr)₀, from 0.703661 to 0.703853. Such ratios are characteristic of volcanic and subvolcanic rocks with ages of ∼37, 31–23, and ∼16 Ma over the whole region of the Tatar Strait coast.  相似文献   

Time-slice diagrams of solar granulation     

Müller  D.A.N.  Steiner  O.  Schlichenmaier  R.  Brandt  P.N. 《Solar physics》2001,203(2):211-232

From a series of 1400 white-light images of solar granulation spanning a time period of 8.2 hours, skeletal plots of time-slice diagrams are derived showing intergranular lane positions as a function of time. The diagrams permit to automatically track, classify, and relate 42 186 granules. Recurrently fragmenting granules are found that survive by means of their descendants for more than 3 hours. Such long-lived active granules tend to have a mean spatial distance along the slice of about 10 Mm. This distance decreases with decreasing minimal required lifetime. Since active granules are expected to generate a steadily divergent flow over a long period of time, it is suggested to identify them as a source of the mesogranular flow. Deficiencies of the time-slice analysis are discussed. The relative frequency of different types of granules and the granule decay time as derived from the time-slice diagrams are compared with corresponding results of previous works. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1013350505080  相似文献   

Commemoration of the 15th Anniversary of Atmospheric and Oceanic Science Letters          下载免费PDF全文

Huijun Wang  Ola M.Johannessen 《大气和海洋科学快报》2022,15(1):100151

First published in late 2008 and currently in Volume 15(2022), Atmospheric and Oceanic Science Letters(AOSL) is now 15 years old. Looking back on the journey, hardships and happiness, difficulties and hope coexist.AOSL is an international journal for providing a rapid communication channel between academic communities concerned with the interdisciplinary research areas of atmospheric science, oceanography.  相似文献   

Accumulation over the Greenland Ice Sheet as Represented in Reanalysis Data     

CHEN Linling  Ola M. JOHANNESSEN  WANG Huijun  Atsumu OHMURA 《大气科学进展》2011,28(5):1030-1038

Annual precipitation,evaporation,and calculated accumulation from reanalysis model outputs have been investigated for the Greenland Ice Sheet (GrIS),based on the common period of 1989-2001.The ERA-40 and ERA-interim reanalysis data showed better agreement with observations than do NCEP-1 and NCEP-2 reanalyses.Further,ERA-interim showed the closest spatial distribution of accumulation to the observation.Concerning temporal variations,ERA-interim showed the best correlation with precipitation observations at five synoptic stations,and the best correlation with in situ measurements of accumulation at nine ice core sites.The mean annual precipitation averaged over the whole GrIS from ERA-interim (363 mm yr 1) and mean annual accumulation (319 mm yr 1) are very close to the observations.The validation of accumulation calculated from reanalysis data against ice-core measurements suggests that further improvements to reanalysis models are needed.  相似文献   

A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing     

Joseph Sedlar  Michael Tjernström  Thorsten Mauritsen  Matthew D. Shupe  Ian M. Brooks  P. Ola G. Persson  Cathryn E. Birch  Caroline Leck  Anders Sirevaag  Marcel Nicolaus 《Climate Dynamics》2011,37(7-8):1643-1660

Snow surface and sea-ice energy budgets were measured near 87.5°N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to ?7°C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between ?50 W m^?2 and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m^?2, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area.  相似文献   

Role of natural external forcing factors in modulating the Indian summer monsoon rainfall,the winter North Atlantic Oscillation and their relationship on inter-decadal timescale     

Xuedong Cui  Yongqi Gao  Jianqi Sun  Dong Guo  Shuanglin Li  Ola M. Johannessen 《Climate Dynamics》2014,43(7-8):2283-2295

We use reconstructed data and multi-centennial integrations performed with the Bergen Climate Model Version 2 to investigate the impact of natural external forcing factors on the Indian summer monsoon (ISM) rainfall, the winter North Atlantic Oscillation (NAO), and the potential relationship between the ISM rainfall and the winter NAO on decadal to inter-decadal timescales. The model simulations include a 600-year control integration (CTL600) and a 600-year integration with time-varied natural external forcing factors from 1400 to 1999 (EXT600). Both reconstructed data and the simulation showed increased ISM rainfall 2–3 years after strong volcanic eruptions. Strong volcanic eruptions decrease the Indian Ocean sea surface temperature (SST), which increases the strength of the southwesterly winds over the Arabian Sea. With negative externally-forced radiative anomaly, the lower stratospheric pole-to-equator winter temperature gradient is enhanced, leading to a positive winter NAO anomaly with a time lag of 1 year. There is no significant correlation between the winter NAO and ISM rainfall in CTL600. However, the ISM rainfall is significantly positively correlated with the winter NAO in EXT600, with the NAO leading by 2–4 years, which is consistent with the NAO–ISM rainfall relationship in the reconstructed data. We suggest that natural external forcing factors regulate the inter-decadal variability of both the winter NAO and the ISM rainfall and thus likely lead to an increased statistical but not causal relationship between them on the inter-decadal timescale over the past centuries.  相似文献   

Mean meridional currents in the central and eastern equatorial Atlantic     

Renellys C. Perez  Verena Hormann  Rick Lumpkin  Peter Brandt  William E. Johns  Fabrice Hernandez  Claudia Schmid  Bernard Bourlès 《Climate Dynamics》2014,43(11):2943-2962

Ship-based acoustic Doppler current profiler (ADCP) velocity measurements collected by several major field programs in the tropical Atlantic are averaged and combined with estimates of the mean near-surface velocity derived from drifters and Argo float surface drifts (ADCP+D) to describe the mean cross-equatorial and vertical structure of the meridional currents along 23°W and 10°W. Data from moored ADCPs and fixed-depth current meters, a satellite-derived velocity product, and a global ocean reanalysis were additionally used to evaluate the mean ADCP+D meridional velocity. The dominant circulation features in the long-term mean ADCP+D meridional velocity in the upper 100 m are the tropical cells (TCs) located approximately between 5°S and 5°N, with near-surface poleward flow and subsurface equatorward flow that is stronger and shallower in the northern cell compared to the southern cell. The thickness of the surface limb of the TCs decreases and the northern cell is found to shift further south of the equator from the central to eastern tropical Atlantic. Analysis of two-season means estimated from the ship-based ADCP, near-surface drift, and moored velocity data, as well as the simulated fields, indicates that the maximum poleward velocity in the surface limb of the TCs intensifies during December–May along 23°W largely due to seasonal compensation between the geostrophic and ageostrophic (or wind-driven) components of the meridional velocity, whereas the maximum equatorward flow in the subsurface limb of the northern cell intensifies during June–November along both 23°W and 10°W due to the seasonality of the geostrophic meridional velocity.  相似文献   

Oxygen variance and meridional oxygen supply in the Tropical North East Atlantic oxygen minimum zone     

J. Hahn  P. Brandt  R. J. Greatbatch  G. Krahmann  A. Körtzinger 《Climate Dynamics》2014,43(11):2999-3024

The distribution of the mean oceanic oxygen concentration results from a balance between ventilation and consumption. In the eastern tropical Pacific and Atlantic, this balance creates extended oxygen minimum zones (OMZ) at intermediate depth. Here, we analyze hydrographic and velocity data from shipboard and moored observations, which were taken along the 23°W meridian cutting through the Tropical North East Atlantic (TNEA) OMZ, to study the distribution and generation of oxygen variability. By applying the extended Osborn–Cox model, the respective role of mesoscale stirring and diapycnal mixing in producing enhanced oxygen variability, found at the southern and upper boundary of the OMZ, is quantified. From the well-ventilated equatorial region toward the OMZ core a northward eddy-driven oxygen flux is observed whose divergence corresponds to an oxygen supply of about 2.4 μmol kg^?1 year^?1 at the OMZ core depth. Above the OMZ core, mesoscale eddies act to redistribute low- and high-oxygen waters associated with westward and eastward currents, respectively. Here, absolute values of the local oxygen supply >10 μmol kg^?1 year^?1 are found, likely balanced by mean zonal advection. Combining our results with recent studies, a refined oxygen budget for the TNEA OMZ is derived. Eddy-driven meridional oxygen supply contributes more than 50 % of the supply required to balance the estimated oxygen consumption. The oxygen tendency in the OMZ, as given by the multidecadal oxygen decline, is maximum slightly above the OMZ core and represents a substantial imbalance of the oxygen budget reaching about 20 % of the magnitude of the eddy-driven oxygen supply.  相似文献   

Middle Mantle Seismic Structure of the African Superplume     

Martin B. C. Brandt 《Pure and Applied Geophysics》2013,170(5):845-861

I present the results of statistical hypothesis testing of Grand’s (2002) global tomography model of three-dimensional shear velocity variations for the middle mantle underneath eastern and southern Africa. I apply an F test to evaluate the validity of a model where a tilted, slow-velocity anomaly in the deepest mantle under southern Africa, known as the African superplume, is continuous with a slow-velocity anomaly in the upper mantle under eastern Africa. This null hypothesis is tested against alternative hypotheses, in which various “obstruction volumes” in the middle mantle are constrained to zero perturbation from the one-dimensional reference velocity during the tomographic inversion. I find that there is an equal probability of accepting an alternative hypothesis with a thin “obstruction volume” at 850–1,000 km depth, whereas volumes at other depths are rejected. But the alternative hypothesis, where a connection is forced at 850–1,000 km depth, is rejected. I conclude that the African superplume rises to at least 1,150 km depth, and that the upper mantle slow-velocity anomaly continues from the surface to below the mantle transition zone. I interpret the “obstruction volume” as a weakening of the superplume in the middle mantle.  相似文献   

Comparative analysis of Venus and Mars magnetotails     

A. Fedorov  C. Ferrier  S. Barabash  C. Mazelle  H. Gunell  K. Brinkfeldt  A. Grigoriev  M. Yamauchi  W. Baumjohann  A.J. Coates  D.R. Linder  K.C. Hsieh  J.-J. Thocaven  H. Koskinen  T. Sales  P. Riihela  N. Krupp  J. Luhmann  S. Orsini  A. Mura  M. Maggi  P. Brandt  K. Szego  R.A. Frahm  J.R. Sharber  P. Bochsler 《Planetary and Space Science》2008,56(6):812-817

We have an unique opportunity to compare the magnetospheres of two non-magnetic planets as Mars and Venus with identical instrument sets Aspera-3 and Aspera-4 on board of the Mars Express and Venus Express missions. We have performed both statistical and case studies of properties of the magnetosheath ion flows and the flows of planetary ions behind both planets. We have shown that the general morphology of both magnetotails is generally identical. In both cases the energy of the light (H⁺) and the heavy (O⁺, etc.) ions decreases from the tail periphery (several keV) down to few eV in the tail center. At the same time the wake center of both planets is occupied by plasma sheet coincident with the current sheet of the tail. Both plasma sheets are filled by accelerated (500-1000 eV) heavy planetary ions. We report also the discovery of a new feature never observed before in the tails of non-magnetic planets: the plasma sheet is enveloped by consecutive layers of He⁺ and H⁺ with decreasing energies.  相似文献