Evaluation of cloud thermodynamic phase parametrizations in the LMDZ GCM by using POLDER satellite data: Evaluation of cloud thermodynamic phase parametrizations in theLMDZ GCM by using POLDER satellite data

Realistic simulations of clouds are of uppermost importance for climate modelling using general circulation models. Satellite data are well suited to evaluate model parametrizations. In this study we use the Laboratoire de Me´te´orologie Dynamique general circulation model (LMDZ). We evaluate the current LMDZ cloud phase parametrization, in which the repartition of condensed cloud water between liquid and ice is a function of the local temperature. Three parameters are used to derive a relation between liquid cloud water content and temperature, two of which are not physically based. We use the POLDER-1 satellite data to infer more realistic parameters by establishing statistical relationships between cloud top thermodynamical phase and cloud top temperature, consistently in both satellite data and model results. We then perform a multitude of short model integrations and derive a best estimate for the lowest local temperature where liquid water can exist in a cloud (Tice = -32°C in our parametrization). The other parameter which describes the shape of the transition between ice and liquid water is also estimated. A longer simulation has then been performed with the new parameters, resulting in an improvement in the representation of the shortwave cloud radiative forcing

Polarized light scattering by inhomogeneous hexagonal monocrystals. Validation with ADEOS-POLDER measurements

Various in situ measurements of the light-scattering diagram in ice clouds were performed with a new nephelometer during several airborne campaigns. These measurements were favorably compared with a theoretical scattering model called Inhomogeneous Hexagonal Monocrystal (IHM) model. This model consists in computing the scattering of light by an ensemble of randomly oriented hexagonal ice crystals containing spherical impurities of soot and air bubbles. It is achieved by using a combination of ray tracing, Mie theory, and Monte Carlo techniques and enables to retrieve the six independent elements of the scattering matrix. This good agreement between nephelometer measurements and IHM model provides an opportunity to use this model in order to analyze ADEOS-POLDER total and polarized reflectance measurements over ice clouds. POLDER uses an original concept to observe ice cloud properties, enabling to measure reflectances and polarized reflectances, for a given scene, under several (up to 14) viewing directions. A first analysis of ice cloud spherical albedoes over the terrestrial globe for November 10, 1996, and April 23, 1997, shows a rather good agreement between measurements and modeling. Moreover, polarized reflectances are also calculated and show a satisfactory agreement with measurements

Advancing global & regional reanalyses

This report outlines the structure of and summarizes the recommendations made at the 5th International Conference on Reanalysis (ICR5), attended by 259 participants from 37 countries, in Rome (Italy), on 13-17 November 2017. It first summarizes the conference structure. Then, the key recommendations of ICR5 are given for the five main conference topics: production; observations (data rescue and preparation); data assimilation methods; quality assurance of reanalysis; and applications in science, services, and policymaking. Lastly, five high-level recommendations are proposed to managing agencies on how best to advance the field of reanalyses, which serves tens of thousands of users, via enhanced research, development, and operations

Evaluation of cloud thermodynamic phase parametrizations in the LMDZ GCM by using POLDER satellite data: Evaluation of cloud thermodynamic phase parametrizations in theLMDZ GCM by using POLDER satellite data

Realistic simulations of clouds are of uppermost importance for climate modelling using general circulation models. Satellite data are well suited to evaluate model parametrizations. In this study we use the Laboratoire de Me´te´orologie Dynamique general circulation model (LMDZ). We evaluate the current LMDZ cloud phase parametrization, in which the repartition of condensed cloud water between liquid and ice is a function of the local temperature. Three parameters are used to derive a relation between liquid cloud water content and temperature, two of which are not physically based. We use the POLDER-1 satellite data to infer more realistic parameters by establishing statistical relationships between cloud top thermodynamical phase and cloud top temperature, consistently in both satellite data and model results. We then perform a multitude of short model integrations and derive a best estimate for the lowest local temperature where liquid water can exist in a cloud (Tice = -32°C in our parametrization). The other parameter which describes the shape of the transition between ice and liquid water is also estimated. A longer simulation has then been performed with the new parameters, resulting in an improvement in the representation of the shortwave cloud radiative forcing

A comparison of cloud droplet radii measured from space

International audienceCloud droplet effective radius (CDR) can be estimated from the spectral signature of cloud reflectance. The technique has been applied to measurements of the Advanced Very High Resolution Radiometer instrument and more recently to the Moderate Resolution Imaging Spectroradiometer (MODIS). Another technique relies on the directional signature of the polarized reflectance and has been applied to observations from Polarization and Directionality of the Earth's Reflectances (POLDER) onboard Advanced Earth Observation Satellite (ADEOS). Although the latter technique requires very specific conditions, we argue that, when applicable, it is very accurate. A large fraction of successful POLDER estimates are derived from measurements over stratocumulus cloud fields. During portions of 2003, POLDER and MODIS acquired near coincident observations. The data can then be used for an evaluation of the two CDR products. The two datasets are highly correlated over the oceans albeit with a MODIS high bias of about 2 μm. The correlation breaks down when POLDER retrieves small droplets (less than 7 μm), which occurs over most land surfaces as well as polluted oceanic areas. We discuss the possible causes for biases and errors. Although differences in the two CDR estimates are expected because of the differences in the spatial scale and vertical weighting function, we did not find a fully satisfactory explanation for the bias and lack of correlation over land surfaces. It seems, however, that the spatial variability as seen by MODIS is larger than that deduced from POLDER measurements, in particular over land surfaces

Significant changes between the ISCCP C and D cloud climatologies

International audienceWe analyse one year of cloud data from the ISCCP C and D datasets. The two datasets differ by their retrieval algorithms and their definitions of the cloud types defined from the cloud top pressure and cloud optical depth. The differences between the two datasets are first described in terms of the total cloud cover, as well as its repartition in low, middle, and high level cloudiness. We also project the ISCCP C cloud classes into the ISCCP D cloud types to circumvent the problem of different cloud type definitions in the two datasets. The differences between the two datasets are then also investigated in terms of the most frequent cloud type

Evaluation of cloud thermodynamic phase parametrizations in the LMDZ GCM by using POLDER satellite data

International audienceRealistic simulations of clouds are of uppermost importance for climate modelling using general circulation models. Satellite data are well suited to evaluate model parametrizations. In this study we use the Laboratoire de Météorologie Dynamique general circulation model (LMDZ). We evaluate the current LMDZ cloud phase parametrization, in which the repartition of condensed cloud water between liquid and ice is a function of the local temperature. Three parameters are used to derive a relation between liquid cloud water content and temperature, two of which are not physically based. We use the POLDER-1 satellite data to infer more realistic parameters by establishing statistical relationships between cloud top thermodynamical phase and cloud top temperature, consistently in both satellite data and model results. We then perform a multitude of short model integrations and derive a best estimate for the lowest local temperature where liquid water can exist in a cloud (Tice = −32°C in our parametrization). The other parameter which describes the shape of the transition between ice and liquid water is also estimated. A longer simulation has then been performed with the new parameters, resulting in an improvement in the representation of the shortwave cloud radiative forcing

Evaluation of cloud thermodynamic phase parametrizations in the LMDZ GCM by using POLDER satellite data: Evaluation of cloud thermodynamic phase parametrizations in theLMDZ GCM by using POLDER satellite data

Realistic simulations of clouds are of uppermost importance for climate modelling using general circulation models. Satellite data are well suited to evaluate model parametrizations. In this study we use the Laboratoire de Me´te´orologie Dynamique general circulation model (LMDZ). We evaluate the current LMDZ cloud phase parametrization, in which the repartition of condensed cloud water between liquid and ice is a function of the local temperature. Three parameters are used to derive a relation between liquid cloud water content and temperature, two of which are not physically based. We use the POLDER-1 satellite data to infer more realistic parameters by establishing statistical relationships between cloud top thermodynamical phase and cloud top temperature, consistently in both satellite data and model results. We then perform a multitude of short model integrations and derive a best estimate for the lowest local temperature where liquid water can exist in a cloud (Tice = -32°C in our parametrization). The other parameter which describes the shape of the transition between ice and liquid water is also estimated. A longer simulation has then been performed with the new parameters, resulting in an improvement in the representation of the shortwave cloud radiative forcing

Réflexions sur la température moyenne de la planète

International audienc

A database of global reference sites to support validation of satellite surface albedo datasets (SAVS 1.0)

Validating the accuracy and long-term stability of terrestrial satellite data products necessitates a network of reference sites. This paper documents a global database of more than 2000 sites globally which have been characterized in terms of their spatial heterogeneity. The work was motivated by the need for potential validation sites for geostationary surface albedo data products, but the resulting database is useful also for other applications. The database (SAVS 1.0) is publicly available through the EUMETSAT website (http://savs.eumetsat.int/, doi:10.15770/EUM_SEC_CLM_1001). Sites can be filtered according to different criteria, providing a flexible way to identify potential validation sites for further studies and a traceable approach to characterize the heterogeneity of these reference sites. The present paper describes the detailed information on the generation of the SAVS 1.0 database and its characteristics