Assimilation of GOES-derived solar insolation into a mesoscale model for studies of cloud shading effects

Cloud cover is capable of generating mesoscale temperature gradients by shading the surface. The purposes of this paper are to utilize GOES visible imagery to assimilate cloud shading elTects into a mesoscale model and to examine the ability of a realistic treatment of moving and changing cloud fields to produce boundary layer convergence zones which may lead to preferred areas of deep convective development. A simplified version of the radiative model of Gautier et Ill. is used to convert hourly gridded GOES brightness data into surface insolation for assimilation into the mesoscale model. The conversion process is presented in detail so that readers may duplicate the assimilation scheme. A case in the Texas Panhandle on 24 and 25 April 1982 is studied. Results of the modelling study show that cloud shading produces (a) a much more complicated surface temperature field, (b) a large change in the planetary boundary layer depth, and (c) substantial boundary layer convergence zones compared to a simulation without cloud shading. These mesoscale effects, in association with synoptic-scale instability, may be important in thunderstorm and severe weather development. The techniques utilized for assimilating satellite-derived insolation may be especially important in after-the-fact mesoscale modelling of air pollution cases and in field studies.     

The impact of assimilation of satellite derived wind observations for the prediction of a monsoon depression over India using a mesoscale model

The Penn State/NCAR mesoscale model (MM5) has been used in this study to ingest and assimilate the INSAT‐CMV (Indian National Satellite System‐Cloud Motion Vector) wind observations using analysis nudging (four‐dimensional data assimilation, FDDA) to improve the prediction of a monsoon depression which occurred over the Bay of Bengal, India during 28 July 2005 to 31 July 2005. To determine the impact of assimilation of INSAT‐CMV winds on the prediction of a monsoon depression, three sets of numerical experiments (NOFDDA, FDDA and FDDA CMV) were designed. While the FDDA CMV run assimilated satellite derived winds only, the FDDA run assimilated both satellite and conventional observations. The NOFDDA run used neither satellite nor conventional observations. The results of the study indicate that the simulated sea level pressure field from the FDDA run is more consistent with the sea level pressure field from NCEP‐FNL compared to the FDDA CMV and NOFDDA runs. The highest correlation and lowest rms error of the sea level pressure field are associated with the FDDA run, and this provides a quantitative verification of the improvement due to the assimilation of satellite derived winds and the conventional upper air observations for the prediction of monsoon depression. All the three model simulated winds are in good agreement with the analysis winds at 850 hPa, 500 hPa and 200 hPa levels. The simulated structure of the spatial precipitation pattern for the assimilation experiments (FDDA and FDDA CMV) are closer to the TRMM observations with more rainfall simulated over the east coast regions in the assimilation experiments. The rms errors of the wind speed for the FDDA run show lower values at 500 hPa for all the three model runs, with a reduction in all three levels of up to 0.8–1.4 m s^?1 for the FDDA run and 0.5–1.9 m s^?1 for the FDDA CMV run with respect to the NOFDDA run. The statistical significance of the sea level pressure and the precipitation differences between the FDDA and the NOFDDA as well as the differences between the FDDA CMV and the NOFDDA have been calculated using the two‐tailed Student's t‐test and were found to be statistically significant. The influence of varying the nudging coefficients in the FDDA experiment has been studied.     

Enhanced biomass prediction by assimilating satellite data into a crop growth model

Complex crop growth models (CGM) require a large number of input parameters, which can cause large errors if they are uncertain. Furthermore, they often lack spatial information. The coupling of a CGM with a radiative transfer model offers the possibility to assimilate remote sensing data while taking into account uncertainties in input parameters. A particle filter was used to assimilate satellite data into a CGM coupled with a leaf-canopy radiative transfer model to update biomass simulations of maize. The synthetic experiment set up to test the reliability of the procedure, highlighted the importance of the acquisition time. The real case study with RapidEye observations confirmed these findings. Data assimilation increased the accuracy of biomass predictions in the majority of the six maize fields where biomass validation data was available, with improvements of up to 15%. The smallest and largest errors in biomass prediction after assimilation were 82 kg/ha and 2116 kg/ha, respectively. Furthermore, data assimilation enabled the production of biomass maps showing detailed spatial variability.     

Vectorizing a mesoscale meteorological model on the cyber 205

A mesoscale meteorological numerical model is chosen for performing the CYBER 205 vectorization technique. Three computational modules of the model (vertical diffusion, horizontal advection, and a computation including surface contrasts) are selected as working examples. A vectorization technique, denoted as “orthogonal vectorization,” is developed which is based on the model's computational structure and the CYBER 205's computer-parallelism and vector processing. Experimental results showed that for the selected examples, a speed-up by a factor of ten of the model execution on the CYBER 205 has been achieved. Provided further experiments and developments are performed, such an increase in executional speed is expected to produce profound impacts on mesoscale modeling in particular, and on atmospheric modeling in general.     

Parallelization of the GESIMA mesoscale atmospheric model

The implementation of the GESIMA mesoscale atmospheric model on message passing, distributed memory parallel computers is presented. Particular emphasis is given to the parallelization of the conjugate gradient solver using pre-conditioning by an incomplete LU factorization. Performance results are presented for the Cray T3D and Cray T3E systems, which show good scalability over a range of problem sizes and numbers of processors.     

On the interpretation and classification of mesoscale cyclones from satellite infrared imagery

Subjective interpretation of cloud imagery is commonly used to identify mesoscale cyclones in cold air streams (mesocyclones) over the southern oceans. To determine mesocyclone attributes, and evaluate the classification of their cloud vortex signatures, Defense Meteorological Satellite Program ( DMSP) Infrared (IR) imagery is analysed for selected transition and winter season months of 1988 and 1989. Mesocyclones occupy a statistically smaller size range compared with synoptic scale ( frontal) vortices, and have maximum frequencies of occurrence in transition season months. The mesocyclone classification scheme separates the different signature types most reliably in winter, which is also the season when they are most frequently represented on hemispheric-scale synoptic chart analyses. Characteristic patterns of cloud form and level associated with vortex types, provide insights into mesocyclone dynamics that are now being evaluated using microwave techniques.     

Desert dust aerosols observed in a tropical humid city: a case study over Hong Kong

Observations from the AErosol RObotic NETwork (AERONET) sunphotometers, MODerate resolution Imaging Spectroradiometer (MODIS) satellite images, back-trajectory modelling and ‘in-situ’ PM10 measurements in Hong Kong confirmed that two dust storms on 16–17 April 2006 and 27–30 April 2009, with source areas in northwest China, affected the city. The impacts of the dust on the air quality of Hong Kong were quantified using aerosol optical properties from AERONET data and local PM10 (particle size less than 10 μm) concentrations. Combined analysis of back trajectories and the microphysical properties of the dust aerosols from AERONET inversion data suggest that the dust particulates are sometimes associated with industrial chemicals on arrival in Hong Kong. This is the first remote-sensing study to observe the presence and characteristics of Asian dust carried into the humid tropical region of south China.     

The methods for inferring surface fluxes from satellite data,and their use for atmosphere model validation

This paper reviews the methods developed to infer surface fluxes from satellite data, with or without the aid of other meteorological information. These methods are based on physical modelling or on statistical relations between satellite measurements and surface parameters. However,their accuracy and their possible applications differ from each other. In particular, the surface radiation budget can be obtained over sea and over particular land areas with rather good accuracy. Some of these methods could constitute the basis for future use in atmosphere models (for climate modelling or meteorological forecasting), but the quality of most of them has still to be assessed. They are therefore rarely directly used to test atmospheric models (weather prediction or climate global circulation models). A preferred approach consists of comparisons between satellite data (either direct measurements or well-established retrieved parameters) and the same parameters derived from models.     

Massively parallel implementation of the mesoscale compressible community model

Computational fluid dynamics and meteorology in particular are among the major consumers of high performance computer technology. The next generation of atmospheric models will be capable of representing fluid flow phenomena at very small scales in the atmosphere. The mesoscale compressible community (MC2) model represents one of the first successful applications of a semi-implicit, semi-Lagrangian scheme to integrate the compressible governing equations for atmospheric flow in a limited area domain. A distributed-memory SPMD implementation of the MC2 model is described and the convergence rates of various parallel preconditioners for a Krylov type GMRES elliptic solver are reported. Parallel performance of the model on the Cray T3E MPP and NEC SX-4/32 SMP is also presented.     

Revisiting satellite radiative flux computations at the top of the atmosphere

Most satellite observations of radiative fluxes at the top of the atmosphere (TOA) are at narrow spectral intervals and at particular viewing angles. Critical elements in the formulation of TOA shortwave (SW) radiative fluxes are (1) the transformation from narrowband to broadband values (n/b) and (2) the application of angular distribution models (ADMs) to correct for anisotropy. In this article, the n/b transformations are based on theoretical simulations with a radiative transfer model Moderate Resolution Atmospheric Transmission (MODTRAN) 3.7 using land classification types based on the International Geosphere-Biosphere Programme (IGBP) scheme and a range of realistic atmospheric conditions. The newly developed ADMs are a combination of MODTRAN-3.7 simulations and the Clouds and the Earth's Radiant Energy System (CERES)-observed ADMs. To evaluate the impact of the proposed corrections, they are implemented with observations from the Spinning Enhanced Visible Infrared Imager (SEVIRI) on the Meteorological Satellite (METEOSAT) 8 to derive TOA fluxes and compared to similar quantities from CERES. It is shown that the estimated TOA radiative fluxes have –3% bias and 7% root mean square error (RMSE) when compared with CERES observations at a monthly timescale.     

Provincial nature of chlorophyll and sea surface temperature observed by satellite

Monthly composite SeaWiFS derived chlorophyll, National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) derived sea surface temperature (SST) and QuikScat derived wind data of 2003–2005 (January–December) were analysed to study the provincial nature of chlorophyll‐a (chl‐a), SST and wind speed in the Arabian sea and Bay of Bengal. The study was confined to five provinces, three in the Arabian Sea and two in the Bay of Bengal. Results indicate provincial variability in the SST‐chl‐a relation. It suggests that the correlation between chlorophyll and SST is not always negative. A negative correlation was observed in provinces 1, 2 and 3 for all the seasons, whereas, except for the month of January–February, it was positively correlated for province 4. Analysis shows the provincial specific nature of chlorophyll variability to physical forcing and suggests that treatment of such a problem should not be undertaken on the basin scale.     

False topographic perception phenomena observed with the satellite images of Moon's surface

False Topographic Perception Phenomena (FTPP) are commonly observed in images of rugged terrain on the surface of the Earth acquired by polar-orbiting satellites. It is interesting to note that due to the absence of atmosphere, vegetation and presence of numerous craters on its surface, the Moon illustrates very vividly and uniquely FTPP, which is less obvious with images of the Earth. In this article images of the Moon taken during the six missions of the NASA Apollo programme and from the Chandrayan-1 Indian satellite are used to demonstrate FTPP on the surface of the Moon. Numerous craters present on the surface of the Moon are perceived as hillock/plateau and vice versa. Combinations of various interrelated factors, for example topographic relief, observer position, Sun azimuth and elevation angles, are responsible for FTPP. Craters in the northern hemisphere of the Moon exhibit FTPP as the Moon's surface was imaged from southern side under equatorial illumination.     

Shape and radiative properties of convective systems observed from infrared satellite images

The main purpose of this study is to identify a series of parameters to characterize the shape and internal structure of a convective system (CS). One year of brightness temperatures derived from Meteosat 3 (July 1992-June 1993) (ISCCP-B3 data) was used to develop this work. The identification of convective systems was performed by pixels whose brightness infrared temperature values (T _ir) were below 245 K. The main results obtained are: (a) the shape of a given system which can be categorized in three classes: (i) linear systems, (ii) circular and elliptical systems and (iii) fragmented systems; (b) the restitution of a given CS using only statistical information; (c) the identification of the distribution of the number of coldest tops inside a given system; and (d) the evaluation of the stage of the life cycle through a statistical study of internal structure and radiative parameters.     

A multi-sensor approach for assessing the impacts of ultraviolet-absorbing aerosols on top of atmosphere radiative fluxes

One year (June 2006–May 2007) of the Clouds and the Earth's Radiant Energy System (CERES) top of atmosphere (TOA) shortwave (SW) and longwave (LW) fluxes are used with Ozone Monitoring Instrument-Aerosol Index (OMI-AI) data to assess the direct radiative effects of ultraviolet (UV)-absorbing aerosols. We show that TOA SW aerosol radiative effects from UV-absorbing aerosols alone are almost double that compared to when considering all aerosols. These aerosols account for nearly all of the seasonal variation in direct SW radiative effect (SWRE) over the oceans and a significant portion of that over land.

Overall, TOA clear-sky SWREs over ocean and land surfaces were estimated to be –4.3 and –4.9 W m^–2, respectively, with both values being in line with previous estimates. When only regions where UV-absorbing aerosols are considered, the SWRE over the ocean becomes more negative between March and August, when the concentration of dust aerosols in the North Atlantic is greatest. Larger concentrations of UV-absorbing aerosols generally exist over land surfaces, increasing the OMI-AI to 0.54 compared to 0.20 over ocean, increasing SW cooling estimates over land. The SWRE also varies as a function of land-surface type and surface albedo. The lowest concentration of absorbing aerosols and therefore the least SW cooling occurs over forests, with the OMI-AI?=?0.36 and the non-bias-adjusted SWRE?=?–1.45 W m^–2. Over other surfaces, the concentrations of absorbing aerosols are greater (AI > 0.5), thereby increasing the SWRE to between –2 and –3 W m^–2. However, as surface brightness increases, the correlation between the AI and the SWRE decreases, and it becomes more difficult to attribute the SWRE estimates to absorbing aerosol concentrations. In particular, the SWRE estimates over bare-soil regions were found to be negative, but completely uncorrelated with the OMI-AI. We concluded that the uncertainty of the SWRE estimates increases as a function of increasing albedo.

The TOA radiative effects of absorbing aerosols to longwave radiation (LWREs) are also examined over North Africa and the North Atlantic, where substantial concentrations of elevated dust aerosols exist. LW warming was found to offset SW cooling over the ocean 20–30% during the spring and summer months. Even greater LW warming was found over land in North Africa and South Asia, with a mean value of +3.8 W m^–2 between March and August, representing an increase of over 100% compared to the other seasons. Our analysis indicates that the OMI provides complementary information to the Moderate Resolution Imaging Spectroradiometer (MODIS) for studying aerosol radiative effects.     

Joint analysis of temperature and ocean colour satellite images for mesoscale activities in the Gulf of Biscay

In the framework of the Ocean Colour European Archive Network (OCEAN) programme of the European Commission and the European Space Agency, a joint team composed of ACRI, GM-Images and Ecole des Mines de Paris proposed to analyse jointly Coastal Zone Color Scanner (CZCS) (chlorophyll) and Advanced Very High Resolution Radiometer (AVHRR) (temperature) data in order to study mesoscale dynamics features in the Gulf of Biscay. A large archive of AVHRR data, between 1978-1990, was analysed with the support of EPSHOM (Etablissement Principal du Service Hydrographique et Oceanographique de la Marine), together with about one hundred pairs of AVHRR and CZCS images. The method used to process AVHRR and CZCS data is presented in this paper. Interesting oceanographic results have been obtained. Mesoscale features such as eddies and plumes have been observed and detailed. Thestructures have been identified and classified according to an accurate typology. The appearance and evolution of mushroom-like structures have been noted, which may promote a high efficiency in the mixing of water masses. The benefit of the fusion of images is discussed. Although the locations of structures observed in both image types differ perceptibly, the increased number of observations leads to better mapping and monitoring of the features, both in space and time.     

Variability of the Columbia River plume observed in visible and infrared satellite imagery

Abstract

Variability of the Columbia River plume in coastal waters off the northwestern United States, 1979-1985, was observed in sea surface temperature and phytopiankton pigment images derived from Advanced Very High Resolution Radiometer and Coastal Zone Colour Scanner data. The orientation, shape, intensity and relative temperature of the plume vary in response to coastal winds and wind-driven surface currents. From October to April, plume water is oriented northward along the coast. Following the spring transition in April or May, the plume is oriented southward, either adjacent to the coast or offshore. Transition between the winter and summer forms can be observed in the satellite imagery. Brief reversals of the prevailing seasonal winds cause rapid changes in the orientation and shape of the plume. Remote sensing of the Columbia River plume offers valuable information for oceanographic studies and fisheries management in the region. Derivation of an appropriate visible-infrared signature for plume waters and tracking of tidal pulses in the plume is suggested as a promising direction for future research.     

Study of aerosols and molecular extinction effects in ultraviolet DIAL remote sensing in the lower atmosphere

Light passing through the atmosphere is scattered and absorbed by the molecules and particles in the atmosphere. This can adversely restrict and limit not only the signal-to-noise ratio (SNR) but also the accuracy and sensitivity of measurements, especially in long-path remote sensing. Usually, in differential absorption lidar (DIAL) techniques, errors are increased mainly because of the different extinction and backscattering properties of the atmosphere at the DIAL probe wavelengths. In this work we have investigated the effects of background aerosol and molecular extinction in DIAL remote sensing in the lower atmosphere for several visibilities at ultraviolet (UV) wavelengths by taking into account the dependence of refraction on the air temperature and pressure. For simplicity, we neglected the spatial inhomogeneity of aerosols in the lower atmosphere. Because of the weak attenuation produced by oxygen and other gaseous atmospheric constituents in this region compared with that from ozone, only ozone is considered as significant among the expected errors. Values for the total attenuation (km^?1) at wavelengths 200–400 nm are tabulated for several values of visibility. The acquired results show that the absorption and scattering by the molecules and aerosols vary with wavelength and visibility. The aerosol attenuation in the UV region varies smoothly and thereby errors caused by aerosol scattering can be neglected in remote sensing by UV-DIAL. In addition, aerosols play a very important role in lidar remote sensing in the lower atmosphere by scattering and absorption of radiation, which is considered as a significant factor. At high altitudes, the aerosol concentration is lower than at the ground; the molecular scattering is important, especially for wavelengths greater than 310 nm, where ozone attenuation is not important. The obtained results are important for accurate UV-DIAL measurements of concentration as well as when real-world signals are not available, for example when designing lidar and simulating or when access to real-world signals is not possible.     

Validation of satellite observed thermal emission with in-situ measurements over an urban surface

The Basel Urban Boundary Layer Experiment (BUBBLE) is a joint European research project under the umbrella of COST (Coopération Européenne dans la domaine de la recherche Scientifique et Technique, COST 715: Meteorology applied to urban pollution problems). Besides very detailed field measurements of the structure and dynamics of the urban boundary layer, a series of satellite data has been analyzed and validated. Satellite data from MODIS, NOAA-AVHRR (14, 15, and 16) and Landsat-ETM were used and recorded during June and July 2002 in parallel to the BUBBLE field campaign. MODIS and NOAA-AVHRR data represent day and nighttime surface radiation temperatures in 930 m and 1100 m grid size. Landsat-ETM offers a unique resolution on 60 m, but with only daytime imagery at about the same time of MODIS overpass is available. This enables the validation of satellite measurements from different sensors with ground measurements at locations with various degrees of spatial homogeneity/heterogeneity (urban/rural land use). Several different algorithms for NOAA-AVHRR data were compared with in-situ measurements. The results show a very high correlation of the long wave emissions measured by the satellite with the in-situ measurements showing an accuracy of ± 3% to 5% on average, even in urban environments.