Jean-Pierre Chaboureau

Characteristics of the TOVS Pathfinder Path-B Dataset

Abstract From 1979 to present, sensors aboard the NOAA series of polar meteorological satellites have provided continuous measurements of the earths surface and atmosphere. One of these sensors, the TIROS-N Operational Vertical Sounder (TOVS), observes earth-emitted radiation in 27 wavelength bands within the infrared and microwave portions of the spectrum, thereby creating a valuable resource for studying the climate of our planet. The NOAA–NASA Pathfinder program was conceived to make these data more readily accessible to the community in the form of processed geophysical variables. The Atmospheric Radiation Analysis group at the Laboratoire de Meteorologie Dynamique of the Centre National de la Recherche Scientifique of France was selected to process TOVS data into climate products (Path-B). The Improved Initialization Inversion (3I) retrieval algorithm is used to compute these products from the satellite-observed radiances. The processing technique ensures internal coherence and minimizes both observ...

Diurnal cycle of dust and cirrus over West Africa as seen from Meteosat Second Generation satellite and a regional forecast model.

A brightness temperature difference (BTD) technique is used to evaluate the dust and cirrus forecasts of a regional meteorological model. The technique based on a contrasted absorption property of dust and cirrus at two wavelengths within the atmospheric infrared window is applied to 3-hourly Meteosat Second Generation (MSG) observations in the 10.8- and 12-μm bands over West Africa. The satellite observation of dust coverage over the Sahara shows a well marked diurnal cycle associated with the boundary layer activity peaking at 15 UTC. A similar signature is obtained from the regional model when the dust scheme is activated. The cirrus cover over West Africa is maximum at 12 UTC as seen both from MSG and the model. The use of prognostic dust aerosol, instead of climatology, furthermore better captures the observed convective activity.

The Chuva Project: How Does Convection Vary across Brazil?

CHUVA, meaning “rain” in Portuguese, is the acronym for the Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud-Resolving Modeling and to the Global Precipitation Measurement (GPM). The CHUVA project has conducted five field campaigns; the sixth and last campaign will be held in Manaus in 2014. The primary scientific objective of CHUVA is to contribute to the understanding of cloud processes, which represent one of the least understood components of the weather and climate system. The five CHUVA campaigns were designed to investigate specific tropical weather regimes. The first two experiments, in Alcantara and Fortaleza in northeastern Brazil, focused on warm clouds. The third campaign, which was conducted in Belem, was dedicated to tropical squall lines that often form along the sea-breeze front. The fourth campaign was in the Vale do Paraiba of southeastern Brazil, which is a region with intense lightning activity. In addition to contributing to the understanding of clo...

A Simple Cloud Parameterization Derived from Cloud Resolving Model Data: Diagnostic and Prognostic Applications

A simple statistical parameterization of cloud water‐related variables that has been originally developed for nonprecipitating boundary layer clouds is extended for all cloud types including deep precipitating convection. Based on three-dimensional cloud resolving model (CRM) simulations of observed tropical maritime and continental midlatitude convective periods, expressions for the partial cloudiness and the cloud water content are derived, which are a function of the normalized saturation deficitQ1. It turns out that these relations are equivalent to boundary layer cloud relations described earlier, therefore allowing for a general description of subgrid-scale clouds. The usefulness of the cloud relations is assessed by applying them diagnostically and prognostically in a mesoscale model for a midlatitude cyclone case and a subtropical case, and comparing the simulated cloud fields to satellite observations and to reference simulations with an explicit microphysical scheme. The comparison uses a model-to-satellite approach where synthetic radiances are computed from the meteorological fields and are compared to Meteosat satellite observations both in the visible and the thermal infrared spectral channels. The impact of the statistical cloud scheme is most pronounced for shallow and deep convective cloud fields (where Q1 , 0), provided that the host models convection parameterization is able to correctly represent the ensemble average water vapor profile in the troposphere. The scheme significantly reduces the biases in the infrared and especially shortwave spectral range with respect to the explicit microphysical scheme. Furthermore, it produces more realistic (smooth) horizontal and vertical condensate distributions in both diagnostic or prognostic applications showing the potential use of this simple parameterization in larger-scale models.

Remote sensing of the vertical distribution of atmospheric water vapor from the TOVS observations: Method and validation

This paper presents a method to remotely sense the vertical distribution of atmospheric water vapor using spaceborne measurements from the TOVS instrument aboard the NOAA polar satellite series. It describes a new approach to the water vapor retrieval scheme in the improved initialization inversion (3I) method. The technique is based on a neural network scheme, which is analyzed theoretically. Cross-comparisons of its results with a wide variety of independent observations (in situ measurements or other global data sets, e.g., the special sensor microwave/imager (SSM/I) retrievals, analyses) are then carried out to fully evaluate the method. It is shown that the mean of the differences between total water vapor contents obtained from each data set represents less than 20% of the global mean value of the water vapor content. Different behaviors between TOVS and SSM/I in tropical situations are also highlighted. Concerning the vertical profile, the standard deviation between water vapor content retrieved by 3I and measured by radiosondes varies from 20% in the 1000–850 hPa layer to less than 40% in the 500–300 hPa layer. The vertical increase of the error is linked to the difficulty of measuring weak values by radiosonde instruments, radiometers, or analyses.

Statistical representation of clouds in a regional model and the impact on the diurnal cycle of convection during Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX)

[1] A statistical cloud parameterization is presented, where in addition to earlier work the subgrid moisture/thermal variability is diagnostically determined as a sum of a turbulent and a convective contribution, the latter being a function of the convective mass flux. It is shown that the inclusion of a convective contribution allows us to reasonably reconstruct the time mean and variability of the variance of the conserved quantities total water and liquid water static energy. Application of the parameterization in a regional model during a 30-day period of the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) experiment over southern Brazil demonstrates a clear improvement in the representation of the cloud fields. The subgrid cloud parameterization significantly reduces both the biases and phase between the observed and simulated brightness temperatures in the thermal infrared band and the observed and simulated precipitation intensities, resulting in an improved representation of the diurnal cycle of convection over land. The strong impact on the diurnal cycle is mainly a consequence of reduced surface fluxes due to cloud shading and a change in tropospheric stability due to additional condensation/sublimation.

Modeling of passive microwave responses in convective situations using output from mesoscale models: Comparison with TRMM/TMI satellite observations

[1] Passive microwave observations are sensitive to the whole hydrometeor column, in contrast to infrared and visible observations, which essentially sense cloud tops. Therefore passive microwave observations are a very promising tool to study the internal structure of precipitating clouds. A microwave radiative transfer model (Atmospheric Transmission at Microwaves (ATM)) has been developed to accurately simulate brightness temperature TB fields using output from nonhydrostatic mesoscale atmospheric model, Meso-NH, simulations. The radiative transfer code takes the detailed description of the hydrometeor properties (as simulated by the Meso-NH model) into account. The sensitivity of the predicted brightness temperature TB to the hydrometeor properties is carefully analyzed. Depending on the frequency, the passive microwave simulations show different sensitivities to the hydrometeor and surface properties: The low frequencies (10–30 GHz) sense essentially the surface properties and the liquid water column, whereas the higher frequencies (30–90 GHz) are most sensitive to the large icy hydrometeors (graupel and snow). TB simulations are generated for two real convective situations studied with

Comparison between the Large-Scale Environments of Moderate and Intense Precipitating Systems in the Mediterranean Region

A characterization of the large-scale environment associated with precipitating systems in the Mediterranean region, based mainly on NOAA-16 Advanced Microwave Sounding Unit (AMSU) observations from 2001 to 2007, is presented. Channels 5, 7, and 8 of AMSU-A are used to identify upper-level features, while a simple and tractable method, based on combinations of channels 3-5 of AMSU-B and insensitive to land-sea contrast, was used to identify precipitation. Rain occurrence is widespread over the Mediterranean in wintertime while reduced or short lived in the eastern part of the basin in summer. The location of convective precipitation shifts from mostly over land from April to August, to mostly over the sea from September to December. A composite analysis depicting large-scale conditions, for cases of either rain alone or extensive areas of deep convection, is performed for selected locations where the occurrence of intense rainfall was found to be important. In both cases, an upper-level trough is seen to the west of the target area, but for extreme rainfall the trough is narrower and has larger amplitude in all seasons. In general, these troughs are also deeper for extreme rainfall. Based on the European Centre for Medium-Range Weather Forecasts operational analyses, it was found that sea surface temperature anomalies composites for extreme rainfall are often about 1 K warmer, compared to nonconvective precipitation conditions, in the vicinity of the affected area, and the wind speed at 850 hPa is also stronger and usually coming from the sea.

Radiative Transfer Simulations Using Mesoscale Cloud Model Outputs: Comparisons with Passive Microwave and Infrared Satellite Observations for Midlatitudes

Abstract Real midlatitude meteorological cases are simulated over western Europe with the cloud mesoscale model Meso-NH, and the outputs are used to calculate brightness temperatures at microwave frequencies with the Atmospheric Transmission at Microwave (ATM) radiative transfer model. Satellite-observed brightness temperatures (TBs) from the Advanced Microwave Scanning Unit B (AMSU-B) and the Special Sensor Microwave Imager (SSM/I) are compared to the simulated ones. In this paper, one specific situation is examined in detail. The infrared responses have also been calculated and compared to the Meteosat coincident observations. Overall agreement is obtained between the simulated and the observed brightness temperatures in the microwave and in the infrared. The large-scale dynamical structure of the cloud system is well captured by Meso-NH. However, in regions with large quantities of frozen hydrometeors, the comparison shows that the simulated microwave TBs are higher than the measured ones in the window...

Potential of Advanced Microwave Sounding Unit to identify precipitating systems and associated upper‐level features in the Mediterranean region: Case studies

The potential of the Advanced Microwave Sounding Unit (AMSU) observations to identify and characterize precipitating systems in the Mediterranean region is explored. Single channels or combination channels from AMSU-A are used to detect and locate upper level potential vorticity anomalies that are often associated with intensification of surface low systems and occurrence of extreme events, while AMSU-B data is used to detect precipitating areas. The motivation for the approach presented here is the direct use of satellite data as an alternative for reanalysis data sets for climatological studies of Mediterranean lows, without relying on retrieval algorithms. AMSU-A channel 8 was found to be more suitable to identify upper level southward intrusions of stratospheric air than the difference of channels 7 and 5, which detects only vertically deep intrusions. A combination of AMSU-B channels 3 and 5 is able to discriminate moderate to strongly precipitating areas with good agreement with Tropical Rainfall Measuring Mission (TRMM) derived products and independent ground-based data. A more stringent condition based on differences of channels 3 to 5 was found to be useful to detect deep convective clouds. We demonstrate the applicability of AMSU to detect upper level features and precipitating systems for selected case studies of extreme precipitation in the Mediterranean region. These tools will allow us to form a climatology of moderate to strongly precipitating systems, and to investigate their relationship with upper level features that may be precursors of extreme events, and to establish a typology of the precipitating systems in the Mediterranean region.