The Iceland–Lofotes pressure difference: different states of the North Atlantic low-pressure zone     

By ANNIKA JAHNKE-BORNEMANN  BURGHARD BRÜMMER 《地球，A辑:动力气象学与海洋学》2009,61(4):466-475

The extended North Atlantic low-pressure zone exhibits two pressure minima in the long-term winter mean: the primary one west of Iceland and the secondary one near Norwegian Lofotes Islands. Based on the ERA-40 data set and on wintertime monthly sea level pressure (SLP) anomalies at both places, the states of co- and antivariability are investigated. The covariability represents states of a strongly or weakly developed North Atlantic low-pressure zone. The difference between these two states represents the NAO pattern. The antivariability is defined by an Iceland–Lofotes difference (ILD) index, which is positive (negative) when the anomaly in the Lofotes area is higher (lower) than that in the Iceland area. An ILD pattern is calculated as difference between SLP composites for high and low ILD indices. The ILD pattern extends horizontally beyond the two centers and affects other prominent Northern Hemisphere pressure centres: Aleutian low; Siberian high and Azores high. The pattern extends into the stratosphere and shows significant impacts on surface air temperature, Arctic sea ice concentration and sea ice motion.  相似文献   

EARLINET observations of the 14–22-May long-range dust transport event during SAMUM 2006: validation of results from dust transport modelling     

By D. MÜLLER  B. HEINOLD  M. TESCHE  I. TEGEN  D. ALTHAUSEN  L. ALADOS ARBOLEDAS  V. AMIRIDIS  A. AMODEO  A. ANSMANN  D. BALIS  A. COMERON  G. D'AMICO  E. GERASOPOULOS  J. L. GUERRERO-RASCADO  V. FREUDENTHALER  E. GIANNAKAKI  B. HEESE  M. IARLORI  P. KNIPPERTZ  R. E. MAMOURI  L. MONA  A. PAPAYANNIS  G. PAPPALARDO  R.-M. PERRONE  G. PISANI  V. RIZI  M. SICARD  N. SPINELLI  A. TAFURO  M. WIEGNER 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):325-339

We observed a long-range transport event of mineral dust from North Africa to South Europe during the Saharan Mineral Dust Experiment (SAMUM) 2006. Geometrical and optical properties of that dust plume were determined with Sun photometer of the Aerosol Robotic Network (AERONET) and Raman lidar near the North African source region, and with Sun photometers of AERONET and lidars of the European Aerosol Research Lidar Network (EARLINET) in the far field in Europe. Extinction-to-backscatter ratios of the dust plume over Morocco and Southern Europe do not differ. Ångström exponents increase with distance from Morocco. We simulated the transport, and geometrical and optical properties of the dust plume with a dust transport model. The model results and the experimental data show similar times regarding the appearance of the dust plume over each EARLINET site. Dust optical depth from the model agrees in most cases to particle optical depth measured with the Sun photometers. The vertical distribution of the mineral dust could be satisfactorily reproduced, if we use as benchmark the extinction profiles measured with lidar. In some cases we find differences. We assume that insufficient vertical resolution of the dust plume in the model calculations is one reason for these deviations.  相似文献   

Dust mobilization and transport in the northern Sahara during SAMUM 2006 – a meteorological overview     

By PETER KNIPPERTZ  ALBERT ANSMANN  DIETRICH ALTHAUSEN  DETLEF MÜLLER  MATTHIAS TESCHE  EIKE BIERWIRTH  TILMAN DINTER  THOMAS MÜLLER  WOLFGANG VON HOYNINGEN-HUENE  KERSTIN SCHEPANSKI  MANFRED WENDISCH  BERND HEINOLD  KONRAD KANDLER  REAS PETZOLD  LOTHAR SCHÜTZ  INA TEGEN 《Tellus. Series B, Chemical and physical meteorology》2009,61(1):12-31

The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.  相似文献   

Impact of swell on simulations using a regional atmospheric climate model     

By BJÖRN CARLSSON  ANNA RUTGERSSON  ANN-SOFI SMEDMAN 《地球，A辑:动力气象学与海洋学》2009,61(4):527-538

When long, fast swell waves travel in approximately the same direction as the wind, the surface stress is reduced compared with under wind-sea conditions. Using measurements from the Östergarnsholm site in the Baltic Sea, new expressions of the roughness length were developed for wind sea and swell. These new expressions were implemented in the RCA3 regional climate model covering Europe. A 3-year simulation and two case studies using the wavefield from the ECMWF reanalysis (ERA-40) were analysed using the improved formulations. Wind-following swell led to a significant reduction of mean wind stress and heat fluxes. The mean surface layer wind speed was redistributed horizontally and the marine boundary layer cooled and dried slightly. This cooling was most pronounced over North Sea and the Norwegian Sea (almost 0.2 °C annually on average) whereas the drying was most pronounced over the Mediterranean Sea (almost 0.4 g kg⁻¹). Somewhat less convective precipitation and low-level cloudiness over the sea areas were also indicated, in particular over the Mediterranean Sea. The impact on the atmosphere, however, is significantly locally greater in time and space.  相似文献   

Are response function representations of the global carbon cycle ever interpretable?     

By SILE LI  REW J. JARVIS  DAVID T. LEEDAL 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):361-371

Response function models are often used to represent the behaviour of complex, high order global carbon cycle (GCC) and climate models in applications which require short model run times. Although apparently black-box, these response function models need not necessarily be entirely opaque, but instead may also convey useful insights into the properties of the parent model or process. By exploiting a transfer function (TF) framework to analyse the Lenton GCC model, this paper attempts to demonstrate that response function representations of GCC models can sometimes also provide structural information on the parent model from which they are identified and calibrated. We take a fifth-order TF identified from the impulse response of the Lenton model atmospheric burden, and decompose this to show how it can be re-expresses in a generic five-box form in sympathy with the structure of the parent model.  相似文献   

Wind sensitivity of the inter-ocean heat exchange     

By HANNA CORELL  JOHAN NILSSON  KRISTOFER DÖÖS  GÖRAN BROSTRÖM 《地球，A辑:动力气象学与海洋学》2009,61(5):635-653

An idealised two-basin model is used to investigate the impact of the wind field on the heat exchange between the ocean basins. The scalar potential of the divergent component of the horizontal heat flux is computed, which gives a 'coarse-grained' image of the surface heat flux that captures the large-scale structure of the horizontal heat transport. Further the non-divergent component is examined, as well as the meridional heat transport and the temperature–latitude overturning stream function. A sensitivity analysis examines the heat transport response to changes in wind stress at different latitudes. The results are compared with results from an eddy-permitting global circulation model. The westerly wind stress over the Southern Ocean has two effects: a local reduction of the surface heat loss in response to the equatorward surface Ekman drift, and a global re-routing of the heat export from the Indo-Pacific. Without wind forcing, the Indo-Pacific heat export is released to the atmosphere in the Southern Ocean, and the net heat transport in the southern Atlantic is southward. With wind forcing, the Indo-Pacific export enters the Atlantic through the Aghulas and is released in the Northern Hemisphere. The easterlies enhance the poleward heat transport in both basins.  相似文献   

The tropospheric cycle of H₂: a critical review     

By D. H. EHHALT  F. ROHRER 《Tellus. Series B, Chemical and physical meteorology》2009,61(3):500-535

  相似文献   

Leakage and spillover effects of forest management on carbon storage: theoretical insights from a simple model     

By FEDERICO MAGNANI  RODERICK C. DEWAR †  MARCO BORGHETTI 《Tellus. Series B, Chemical and physical meteorology》2009,61(2):385-393

Leakage (spillover) refers to the unintended negative (positive) consequences of forest carbon (C) management in one area on C storage elsewhere. For example, the local C storage benefit of less intensive harvesting in one area may be offset, partly or completely, by intensified harvesting elsewhere in order to meet global timber demand. We present the results of a theoretical study aimed at identifying the key factors determining leakage and spillover, as a prerequisite for more realistic numerical studies. We use a simple model of C storage in managed forest ecosystems and their wood products to derive approximate analytical expressions for the leakage induced by decreasing the harvesting frequency of existing forest, and the spillover induced by establishing new plantations, assuming a fixed total wood production from local and remote (non-local) forests combined. We find that leakage and spillover depend crucially on the growth rates, wood product lifetimes and woody litter decomposition rates of local and remote forests. In particular, our results reveal critical thresholds for leakage and spillover, beyond which effects of forest management on remote C storage exceed local effects. Order of magnitude estimates of leakage indicate its potential importance at global scales.  相似文献   

Modelling the formation of residual dune ridges behind barchan dunes in North-east Brazil     

NOAM LEVIN  HAIM TSOAR†  HANS JÜRGEN HERRMANN‡  §  LUIS P. MAIA¶  VANDA CLAUDINO-SALES 《Sedimentology》2009,56(6):1623-1641

Residual dune ridges are often formed by vegetation growing along a line some distance upwind of the lower stoss slope of migrating dunes. This process is common in areas where vegetation germinates along the edge of the water during the rainy period when the water level is higher and interdune areas are flooded. The phenomenon occurs on a large scale in North‐east Brazil, because of the rise and fall in groundwater level at the end of the rainy season. Each residual dune ridge corresponds to the position of the dune during the wet period in each year. Therefore, variations in the distance between these residual dune ridges could be used potentially to monitor climatic fluctuations in rainfall and wind. To examine the potential use of these residual dune ridges for the reconstruction of past climatic fluctuations, a model that simulates them under varying conditions of wind, rainfall and evaporation rates was formulated. The model was tested for sensitivity to climatic variability in North‐east Brazil and validated against residual dune ridge displacements as measured in the field and from high spatial resolution satellite images. Based on the results, it is concluded that residual dune ridges may not form in North‐east Brazil in years which are exceptionally dry, as may happen during El‐Niño events. When this type of event happens, the distance between adjacent residual dune ridges corresponds to more than one year and, therefore, the correlation between dune displacements and wind power becomes weak or even disappears. Additionally, because of biotic, aeolian and hydrological processes, these arcuate residual dune ridges may not preserve their initial shape for long periods. The presence of residual dune ridges testifies to the temporary flooding which may or may not be seasonal. However, the potential for using residual dune ridges to reconstruct the palaeo‐climate of wind regime on a yearly basis or to identify past El‐Niño events seems to be limited.  相似文献   

The effects of black carbon and sulphate aerosols in China regions on East Asia monsoons   总被引：7，自引：0，他引：7  

By YU LIU  JIAREN SUN  BAI YANG 《Tellus. Series B, Chemical and physical meteorology》2009,61(4):642-656

In this paper, we examine the direct effects of sulphate and black carbon (BC) aerosols in China on East Asia monsoons and its precipitation processes by using the Community Atmosphere Model (CAM) 3.0 model. It is demonstrated that sulphate and BC aerosols in China both have the effects to weaken East Asia monsoons in both summer and winter seasons. However, they certainly differ from each other in affecting vertical structures of temperature and atmospheric circulations. Their differences are expected because of their distinct optical properties, that is, scattering versus absorbing. Even for a single type of aerosol, its effects on temperature structures and atmospheric circulations are largely season-dependent. Applications of T -test on our results indicate that forcing from BC aerosols over China is relatively weak and limited. It is also evident from our results that the effects of synthetic aerosols (sulphate and BC together) on monsoons are not simply a linear summation between these two types of aerosols. Instead, they are determined by their integrated optical properties. Synthetic aerosols to a large degree resemble effects of sulphate aerosols. This implies a likely scattering property for the integration of BC and sulphate aerosols in China.  相似文献