Circulation Of Earth Research Articles

Deep Meteoric Water Circulation in Earth's Crust

AbstractDeep meteoric waters comprise a key component of the hydrologic cycle, transferring water, energy, and life between the Earth's surface and deeper crustal environments, yet little is known about the nature and extent of meteoric water circulation. Using water stable isotopes, we show that maximum circulation depths of meteoric waters across North America vary considerably from <1 to 5 km, with the deepest circulation in Western North America in areas of greater topographic relief. Shallower circulation occurs in sedimentary and shield‐type environments with subdued topography. The amount of topographic relief available to drive regional groundwater flow and flush saline fluids is an important control on the extent of meteoric water circulation, in addition to permeability. The presence of an active flow system in the upper few kilometers of the Earth's crust and stagnant brines trapped by negative buoyancy offers a new framework for understanding deep groundwater systems.

From Super-Earths to Mini-Neptunes: Implications of a Surface on Atmospheric Circulation

Abstract It is well known that planets with radii between that of Earth and Neptune have been the most commonly detected to date. To classify these planets as either terrestrial or gaseous, typically we turn to mass–radius relations and composition curves to determine the likelihood of such a planet being rocky or gaseous. While these methods have set a likely transition radius of approximately 1.5 R ⊕, we cannot expect that any change between terrestrial and gaseous compositions will be a sharp cutoff, and composition curve predictions result in ambiguous designations for planets right near this transition radius. In this work, we present 3D general circulation models (GCMs) of transition planets, wherein we study the effects of a surface on observable quantities such as the latitudinal variations and eclipse depths. We present our updated GCM, validated on the circulation of Earth, before discussing our modeling choices for this transition planet. Finally, we discuss the results of this study and explore the prospects of detecting the presence of a surface through observations of secondary eclipses in the future.

Recent geomagnetic variations and the force balance in Earth’s core

SUMMARY The nature of the force balance that governs the geodynamo is debated. Recent theoretical analyses and numerical simulations support a quasigeotrophic (QG), magneto-Archimedes-Coriolis (MAC) balance in Earth’s core, where the Coriolis and pressure forces equilibrate at leading order in amplitude, and where the buoyancy, Lorentz and ageostrophic Coriolis forces equilibrate at the next order. In contrast, earlier theoretical expectations have favoured a magnetostrophic regime where the Lorentz force would reach leading order at the system scale. The dominant driver (buoyant or magnetic) for the general circulation in Earth’s core is equally debated. In this study, these questions are explored in the light of the high-quality geomagnetic data recently acquired by satellites and at magnetic ground observatories. The analysis involves inverse geodynamo modelling, a method that uses multivariate statistics extracted from a numerical geodynamo model to infer the state of Earth’s core from a geomagnetic field model interpretation of the main field and secular variation data. To test the QG-MAC dynamic hypothesis against the data, the framework is extended in order to explicitly prescribe this force balance into the inverse problem solved at the core surface. The resulting inverse solutions achieve a quantitatively adequate fit to the data while ensuring deviations from the QG-MAC balance (which amount to an inertial driving of the flow) lower than each of the leading forces. The general circulation imaged within the core over the past two decades confirms the existence of a planetary-scale, eccentric, axially columnar gyre that comprises an intense, equatorially symmetric jet at high latitudes in the Pacific hemisphere. The dominant driver of this circulation is shown to be of buoyant nature, through a thermal wind balance with a longitudinally hemispheric buoyancy anomaly distribution. Geomagnetic forecasts initiated with the inverted core states are systematically more accurate against the true interannual geomagnetic field evolution when enforcing the QG-MAC constraint. This force balance is therefore consistent with the geomagnetic data at the large scales of Earth’s core that can be imaged by the method.

Eddy Influences on the Hadley Circulation

AbstractVariations in the width and strength of the Hadley cells are associated with many radiative, thermodynamic, and dynamical forcings. The physical mechanisms driving these responses remain unclear, in part because of the interactive nature of eddy‐mean flow adjustment. Here, a modeling framework is developed which separates the mean flow and time‐mean eddy flow in a gray radiation general circulation model with simple representations of ocean heat transport and ozone. In the absence of eddies, with moist convection and weak numerical damping, the Hadley cell is confined to the upper troposphere and has a vanishingly small poleward momentum flux. Eddies allow the cell to extend down to the surface, double its heat transport, and flux momentum poleward, the latter two being basic consequences of a deepening of the circulation. Because of convection and damping—which mimics, in part, the effect of eddy stresses—previous work may have underestimated the impact of eddies on earth's circulation. Quasigeostrophic eddy fluxes are sufficient to produce Hadley and Ferrel cells, but with a substantially greater Hadley cell strength than when all eddy impacts are considered, including eddy fluxes of moisture, mass, and momentum and eddy impacts on surface fluxes and clouds.

Диагностика насыщения внутренних атмосферных волн и определение их характеристик в стратосфере Земли с помощью радиозондовых измерений

Internal gravity waves (IGW) significantly affect the structure and circulation of Earth’s atmosphere by transporting wave energy and momentum upward from the lower atmosphere. Since IGW can propagate freely through a stably stratified atmosphere, similar effects may occur in the atmospheres of Mars and Venus. Observations of temperature and wind speed fluctuations induced by internal waves in Earth’s atmosphere have shown that wave amplitudes increase with height, but not quickly enough to correspond to the amplitude increase due to an exponential decrease in the density without energy dissipation. The linear theory of IGW explains the wave amplitude growth rate as follows: any wave amplitude exceeding the threshold value leads to instability and produces turbulence, which hinders further amplitude growth (internal wave saturation). The mechanisms that contribute most to the energy dissipation and saturation of IGW in the atmosphere are thought to be the dynamical (shear) and convective instabilities. The assumption of internal wave saturation plays a key role in radio occultation (RO) monitoring of IGW in planetary atmospheres. A radiosonde study of wave saturation processes in Earth’s atmosphere is therefore actual and important task. We report the results of determination of actual and threshold amplitudes, saturation degree, and other characteristics for the identified IGW in Earth’s atmosphere obtained from the analysis of SPARC (Stratospheric Processes And their Role in Climate) radiosonde measurements of wind speed and temperature [http://www.sparc.sunysb.edu/].

Diagnostics of internal atmospheric wave saturation and determination of their characteristics in Earth's stratosphere from radiosonde measurements

Internal gravity waves (IGW) significantly affect the structure and circulation of Earth’s atmosphere by transporting wave energy and momentum upward from the lower atmosphere. Since IGW can propagate freely through a stably stratified atmosphere, similar effects may occur in the atmospheres of Mars and Venus. Observations of temperature and wind speed fluctuations induced by internal waves in Earth’s atmosphere have shown that wave amplitudes increase with height, but not quickly enough to correspond to the amplitude increase due to an exponential decrease in the density without energy dissipation. The linear theory of IGW explains the wave amplitude growth rate as follows: any wave amplitude exceeding the threshold value leads to instability and produces turbulence, which hinders further amplitude growth (internal wave saturation). The mechanisms that contribute most to the energy dissipation and saturation of IGW in the atmosphere are thought to be the dynamical (shear) and convective instabilities. The assumption of internal wave saturation plays a key role in radio occultation monitoring of IGW in planetary atmospheres. A radiosonde study of wave saturation processes in Earth’s atmosphere is therefore actual and important task. We report the results of determination of actual and threshold amplitudes, saturation degree, and other characteristics for the identified IGW in Earth’s atmosphere obtained from the analysis of SPARC (Stratospheric Processes And their Role in Climate) radiosonde measurements of wind speed and temperature [http://www.sparc.sunysb.edu/].

Comparison of multiple linear regression and artificial neural network models for downscaling TRMM precipitation products using MODIS data

Precipitation plays a significant role to energy exchange and material circulation in Earth’s surface system. According to numerous studies, traditional point measurements based on rain gauge stations are unable to reflect the spatial variation of precipitation effectively. On the other hand, satellite remote sensing could solve this limitation by directly providing spatial distribution of rainfall over large areas. During the last years, the Tropical Rainfall Measuring Mission (TRMM) has provided researchers with a large volume of rainfall data used for the validation of atmospheric and climate models. However, due to its coarse resolution (0.25°) the improvement of its resolution appears as a fundamental task. The main aim of this study is to compare two different integrated downscaling-calibration approaches namely multiple linear regression analysis and artificial neural networks for downscaling TRMM 3B42 precipitation data. The statistical relationship among TRMM precipitation data and different environmental parameters such as vegetation, albedo, drought index and topography were tested in the island of Crete, Greece. Free distributed satellite data of coarse resolution such as those of MODIS sensor were incorporated in the overall analysis. Multiple linear regression as well as artificial neural network models was developed and applied, and extensive statistical analysis was performed by downscaling the TRMM products. The downscaled precipitation estimates as well as the TRMM products were subsequently validated for their accuracy by using an independent precipitation dataset from a ground rain gauge network. The downscaling procedure succeeded to significant improvements of monthly precipitation estimation (100 % improvement in terms of spatial resolution) in terms of spatial analysis with means of satellite remote sensing.

Titan’s liquids: Exotic behavior and its implications on global fluid circulation

Based on a validated model for cryogenic chemical systems, referred to as CRYOCHEM (“Cryogenic Chemistry Model”), surface liquids on Titan are shown to exhibit exotic behavior of density increase with temperature but decrease with pressure, unless the temperature falls below 89.8K. It is also the case for the atmospheric liquid condensates below an altitude where the liquid density is minimum. The exotic behavior is of compositional origin, which does not have an analog in the atmosphere and liquid water on Earth. As the latitudinal and seasonal variations of surface temperature are known, it is possible to map out the global liquid and vapor density variations as well as the equilibrium phase compositions, which will be useful as inputs for atmospheric general circulation models (GCMs) and investigations of Titan’s methane-equivalent of Earth’s hydrological cycle, local subsurface alkanology (equivalent to hydrology on Earth), lake convection, and clastic and chemical sedimentation in the lakes. Further, the density variations can be used to derive a general idea about global fluid circulation in the upper crust based on averaged conditions on Titan. The surface liquid should tend to flow toward the hottest spot on Titan and a return flow occurs beneath the surface, thus providing analogies with thermohaline circulation in Earth’s oceans. The vapor phase, on the other hand, has ordinary properties that make the global atmospheric circulation similar to the Hadley cell on Earth, but Titan’s cycle reaches the polar regions. The calculated compositions of surface liquids are more methane-rich than other models indicated, thus qualitatively in the right direction to satisfy polar-lake compositions deduced from loss tangents. However, quantitatively there remains a need to find yet more accurate liquid compositions and an optimum equilibrium within constraints of the atmospheric measurements.

Rheological decoupling at the Moho and implication to Venusian tectonics

Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus.

The atmospheric general circulation model with a hybrid vertical coordinate

AbstractThe paper presents a new version of the three-dimensional model of general circulation of Earth troposphere-stratosphere-mesosphere (for altitudes up to 90 km from the surface) with a hybrid vertical coordinate. A method of vertical discretization is developed according to the numerical algorithms and preserving the equivalence of algorithms used in previous models. An algorithm of semi-implicit integration in time is proposed. The new version of the model adequately represents climatic characteristics,which are confirmed by comparison of the results of numerical experiments with observation data and with the previous version of the atmospheric circulation model using sigma-coordinates.

Whole-rock geochemistry of upper Paleozoic loessite, western Pangaea: Implications for paleo-atmospheric circulation

Average bulk (major and trace-element) chemical composition of upper Paleozoic loessite (lithified loess) from several widely scattered sites in western equatorial Pangaea (western North America) approximates Upper Continental Crust (UCC), but is more similar to the bulk composition of Precambrian basement coring uplifts of the Ancestral Rocky Mountains. However, distinct compositional signatures occur among the various loessite deposits, controlled primarily by differences in Al 2O 3, MgO, Na 2O, K 2O and Rb. Furthermore, values of the Chemical Index of Alteration (CIA) of these loessites are low (55–63, skewed toward lower values), closely matching values for North American loess and Precambrian basement. Although diagenesis can account for some of the compositional differences (e.g. local SiO 2 or K 2O enrichment), it fails to explain the major differences among the sites. Rather, these differences are best explained as a result of variations in regional basement that sourced the loess, coupled with transport (wind) pathways, which varied from zonal easterlies to monsoonal westerlies in this region of tropical Pangaea from late Carboniferous to early Permian time. The low CIA values generally reflect first-cycle derivation from regional basement uplifts of the ARM and, for younger deposits, a variable contribution from the suture zone uplifts and volcanism of the Appalachian–Ouachita–Marathon collisional belt. The variations in bulk chemical composition of the loessite, coupled with previously collected detrital zircon geochronology, suggest that these low-latitude loessites are not simply the result of deflation of mid-latitude erg deposits or coastal alluvial plain sediments. These data represent a first attempt at geochemical characterization of pre-Quaternary loess, and demonstrate the utility of loess geochemistry as a proxy for paleoatmospheric circulation in Earth′s deep-time past.

Profile of Isaac M. Held

Held is best known for modeling Hadley cells, which describe the properties of atmospheric circulation in Earth’s equatorial zone. His three decades of research have garnered him numerous awards, and in 2003, Held was elected to the National Academy of Sciences. His Inaugural Article, published in a recent issue of PNAS (1), deals specifically with projected climate change in Africa’s Sahel region, the transition zone between the Sahara desert and the rainforests of Central Africa and the Guinean Coast.

大氣環流力學の數量的調査(2)

The energy of the general circulation of the atmosphere is mainly supplied by thermal energy, but in some parts of the circulation, say, in temperate latitudes, it is reasonable to consider that the energy of the circulation may be supplied by kinematical process of the earth's rotation.The kinetic energy of the earth's rotation is 242×1036 ergs and the dissipation in the earth's circulation is estimated by Brunt to be 5×107 ergs per m2 per sec.Thus the delay in the earth's rotation of 0.01_??_2 sec. per 100 years is sufficient enough to maintain the general circulation, assuming the total kinetic energy of the earth to be consumed for it.Next the thermal and dynamical energies in the equatorial circulation are compared and V. Bjerknes'model of circulation in temperate region is rejected by quantitative analysis.