Tropical and subtropical cloud transitions in weather and climate prediction models: The GCSS/WGNE pacific cross-section intercomparison (GPCI)

International audienceA model evaluation approach is proposed in which weather and climate prediction models are analyzed along a Pacific Ocean cross section, from the stratocumulus regions off the coast of California, across the shallow convection dominated trade winds, to the deep convection regions of the ITCZ-the Global Energy and Water Cycle Experiment Cloud System Study/Working Group on Numerical Experimentation (GCSS/WGNE) Pacific Cross-Section Intercomparison (GPCI). The main goal of GPCI is to evaluate and help understand and improve the representation of tropical and subtropical cloud processes in weather and climate prediction models. In this paper, a detailed analysis of cloud regime transitions along the cross section from the subtropics to the tropics for the season June-July-August of 1998 is presented. This GPCI study confirms many of the typical weather and climate prediction model problems in the representation of clouds: underestimation of clouds in the stratocumulus regime by most models with the corresponding consequences in terms of shortwave radiation biases; overestimation of clouds by the 40-yrECMWFRe-Analysis (ERA-40) in the deep tropics (in particular) with the corresponding impact in the outgoing longwave radiation; large spread between the different models in terms of cloud cover, liquid water path and shortwave radiation; significant differences between the models in terms of vertical cross sections of cloud properties (in particular), vertical velocity, and relative humidity. An alternative analysis of cloud cover mean statistics is proposed where sharp gradients in cloud cover along the GPCI transect are taken into account. This analysis shows that the negative cloud bias of some models and ERA-40 in the stratocumulus regions [as compared to the first International Satellite Cloud Climatology Project (ISCCP)] is associated not only with lower values of cloud cover in these regimes, but also with a stratocumulus-to-cumulus transition that occurs too early along the trade wind Lagrangian trajectory. Histograms of cloud cover along the cross section differ significantly between models. Some models exhibit a quasi-bimodal structure with cloud cover being either very large (close to 100%) or very small, while other models show a more continuous transition. The ISCCP observations suggest that reality is in-between these two extreme examples. These different patterns reflect the diverse nature of the cloud, boundary layer, and convection parameterizations in the participating weather and climate prediction models. © 2011 American Meteorological Society

The global atmospheric electrical circuit and climate

Evidence is emerging for physical links among clouds, global temperatures, the global atmospheric electrical circuit and cosmic ray ionisation. The global circuit extends throughout the atmosphere from the planetary surface to the lower layers of the ionosphere. Cosmic rays are the principal source of atmospheric ions away from the continental boundary layer: the ions formed permit a vertical conduction current to flow in the fair weather part of the global circuit. Through the (inverse) solar modulation of cosmic rays, the resulting columnar ionisation changes may allow the global circuit to convey a solar influence to meteorological phenomena of the lower atmosphere. Electrical effects on non-thunderstorm clouds have been proposed to occur via the ion-assisted formation of ultra-fine aerosol, which can grow to sizes able to act as cloud condensation nuclei, or through the increased ice nucleation capability of charged aerosols. Even small atmospheric electrical modulations on the aerosol size distribution can affect cloud properties and modify the radiative balance of the atmosphere, through changes communicated globally by the atmospheric electrical circuit. Despite a long history of work in related areas of geophysics, the direct and inverse relationships between the global circuit and global climate remain largely quantitatively unexplored. From reviewing atmospheric electrical measurements made over two centuries and possible paleoclimate proxies, global atmospheric electrical circuit variability should be expected on many timescale

The Theory of Brown Dwarfs and Extrasolar Giant Planets

Straddling the traditional realms of the planets and the stars, objects below the edge of the main sequence have such unique properties, and are being discovered in such quantities, that one can rightly claim that a new field at the interface of planetary science and and astronomy is being born. In this review, we explore the essential elements of the theory of brown dwarfs and giant planets, as well as of the new spectroscopic classes L and T. To this end, we describe their evolution, spectra, atmospheric compositions, chemistry, physics, and nuclear phases and explain the basic systematics of substellar-mass objects across three orders of magnitude in both mass and age and a factor of 30 in effective temperature. Moreover, we discuss the distinctive features of those extrasolar giant planets that are irradiated by a central primary, in particular their reflection spectra, albedos, and transits. Aspects of the latest theory of Jupiter and Saturn are also presented. Throughout, we highlight the effects of condensates, clouds, molecular abundances, and molecular/atomic opacities in brown dwarf and giant planet atmospheres and summarize the resulting spectral diagnostics. Where possible, the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for publication in the Reviews of Modern Physics. 30 figures are color. Most of the figures are in GIF format to reduce the overall size. The full version with figures can also be found at: http://jupiter.as.arizona.edu/~burrows/papers/rm

Frequency and angular variations of land surface microwave emissivities : can we estimate SSM/T and AMSU emissivities from SSM/I emissivities

International audienc

Suivi des dynamiques d'inondation à l'échelle globale sur une décennie

Although they only cover ~6% of the Earth's ice-free land surfaces (~8.6 millions km2), natural wetlands and rice paddies play a key role in climate and hydrological processes. Firstly, they represent the world's largest methane source (CH4), the only one dominated by climate variations and account for ~40% of CH4 emitted annually to the atmosphere. In addition, wetlands play a major role for local hydrological system as they contribute in part of the fresh water input in the Oceans by river discharge that greatly influences the ocean circulation through the evolution of the Sea Surface Temperature. Approximately 60% of wetlands are only inundated at some period in the year leading to large uncertainties on their seasonal and inter-annual extents. This is particularly the case for tropical regions subject to the annual rain season as well as Boreal regions subject to the snow melt period. Despite the recognition of their role in climate and hydrological process, as well as their importance in water resources management, wetlands extent and dynamic databases still suffer of a lack of reliable information at global or regional scales over long time period. Characterizing wetlands and their dynamics over large geographical region has been investigated using different techniques with varying degrees of success. Datasets based on soil and vegetation observations represent realistic global wetland distributions, but unfortunately they suffer from a lack of information on temporal and spatial dynamics. In that context, satellite observations provide a means of monitoring wetlands and their dynamics at global and regional scales over long time periods. The objective of this study is to present a new globally applicable remote sensing technique, considering a suite of complementary satellite observations developed to quantify spatial and temporal dynamics of wetlands. The technique it self is based on the detection of inundations at the global scale using the passive microwave land-surfaces emissivities estimated from SSM/I observations, and the use of ERS scatterometer and AVHRR visible and near infrared reflectances to estimate the vegetation contribution to the passive microwave signal. Monthly wetlands extents are now estimated at the global scale over the 9-years 93-2001 period and analyzed regarding to spatial patterns and temporal evolutions. A first results evaluation is made using independent datasets such as land surfaces databases, rain fall rate from GPCP products and water level from radar altimeter measurements. The spatial and temporal wetlands estimations, comprising natural wetlands, irrigated rice culture and lake/river are relevant when compare to static wetlands observations databases. Over the globe, the results show also a high correlation with the GPCP rain data product over the 9 years of study. The correlation over specific regions will be discussed. When focusing around specific areas such as the river basins of the Ganges, the Amazon or Parana Rivers or the Congo-Niger regions, the analysis based on the comparison with water river levels derived from radar altimeter observations show a similar seasonal cycle over the 9 years. These results are encouraging and future studies could now focus on wetlands dynamics as a proxy to study for instance the impacts of ENSO or the monsoons regimes on continental processes. A promising synergy with radar altimetry that could also bring new information related to hydrological parameters, such as river discharges, is under now investigation. Finally, this study stresses the need for development of quality longer satellite estimated wetlands dynamics till upcoming days

Evaluation of "all weather" microwave-derived land surface temperatures with in situ CEOP measurements

Land surface skin temperature T s plays a key role in mete- orological and climatological processes but the availability and the accuracy of T s measurements over land are still limited, especially under cloudy con- ditions. T s estimates from infrared satellite observations can only be derived under clear sky. Passive microwave measurements are much less affected by clouds and can provide T s regardless of the cloud conditions. A neural net- work inversion including first guess information has been previously devel- oped to retrieve T s , along with atmospheric water vapor, cloud liquid wa- ter, and surface emissivities over land from Special Sensor Microwave / Im- ager measurements [ Aires et al. , 2001], with a spatial resolution of 0.25 o 0.25 o , at least twice daily. In this study, T s estimates are evaluated through care- ful comparisons with in situ measurements in different environments over a full annual cycle. Under clear sky conditions, the quality of our microwave neural network retrieval is equivalent to the infrared International Satellite Cloud Clima- tology Project products, for most in situ stations, with errors 3K as com- pared to in situ measurements. The performance of the microwave algorithm is similar under clear and cloudy conditions, confirming the potential of the microwaves under clouds. The T s accuracy does not depend upon the sur- face emissivity, as the variability of this parameter is accounted for in the processing. Our microwave T s have been calculated for more than 15 years (1993-mid2008). These "all weather" T s are a very valuable complement to the IR-derived T s , for use in atmospheric and surface models

Modeling efforts

In this section we survey the historical development of Venus models and the range of models now available, before discussing some of their remaining limitations. We also consider some approaches which have been taken to model Saturn's moon Titan, also a slowly-rotating body with an optically thick, dense atmosphere which super-rotates compared to Titan's surface