Validation of the operational IASI level 2 processor using AIRS and ECMWF data

The algorithms being implemented in EUMETSAT’s IASI Level 2 Product Processing Facility are validated with real case situations using AIRS data and comparing the retrieved atmospheric states with ECMWF analyses. The tests have been performed for clear-sky ocean scenes during daytime.

The Empirical Orthogonal Function (EOF) retrievals show very good performance, with retrieved atmospheric states standard deviations between 1 and 2 K in temperature and 10% and 20% in relative humidity when compared with ECMWF analysis in the troposphere. The EOF retrievals show relatively smooth profiles.

Results from an iterative retrieval show a standard deviation between 2 and 3 K in temperature and 10% and 30% in relative humidity when compared with ECMWF analyses in the troposphere. They tend to show meteorologically reasonable discontinuities in both temperature and relative humidity. This seems to be the reason why they do not compare as well with ECMWF analyses as the EOF retrievals do. Whether they are closer to reality or not will have to be tested with co-located radiosondes or similar more accurate data, which generally do not exhibit such smooth vertical profiles as ECMWF analyses do.     

Molecular analysis of the graviperception signal transduction in the flagellate Euglena gracilis: Involvement of a transient receptor potential-like channel and a calmodulin

Euglena gracilis, a unicellular, photosynthetic flagellate is a model system for environmentally controlled behavior responses. The organism shows pronounced negative gravitaxis. This movement is based on physiological mechanisms, which in the past had been only indirectly assessed. It was shown that mechano-sensitive calcium channels are involved in the gravitaxis response. Recent studies have demonstrated that members of the transient receptor potential (TRP) family function as mechano-sensitive channels in several different cell types. We have sequenced part of a TRP gene in Euglena and applied RNA interference (RNAi) to confirm that these channels are involved in graviperception. It was found that RNAi against the putative TRP channel abolished gravitaxis. The genes of three calmodulins were sequences in Euglena, one of which was previously known in its protein structure (cal 1). The other two were unknown (cal 2 and cal 3). Cal 2 has been analyzed in detail. The biosynthesis of the corresponding proteins of cal 1 and cal 2 was inhibited by means of RNA interference to see whether this blockage impairs gravitaxis. RNAi of cal 1 leads to a long-term loss of free swimming in the cells (while euglenoid movement persists). It induced pronounced cell form aberrations and the division of cells was hampered. After recovery from RNAi the cell showed precise negative gravitaxis again. Thus cal 1 does not seem to be involved in gravitaxis. In contrast, the blockage of cal 2 has no pronounced influence on motility and cell form but leads to a complete loss of gravitactic orientation for more than 30 days showing that this calmodulin is an element in the signal transduction chain. The data are discussed in the context of the current model of the gravitaxis signal transduction chain in Euglena gracilis.     

Flux-Transport Solar Dynamos

Large-scale solar dynamo models were first built by Parker (1955). Over the past half a century these models have evolved significantly. We discuss here the development of a class of large-scale dynamo models which include, along with the α-effect and Ω-effect, an important third process, flux transport by meridional circulation. We present the properties of this ‘flux-transport’ dynamo, including the crucial role meridional circulation plays in giving this dynamo predictive power.     

The Structure of the Chromosphere Properties Pertaining to Element Fractionation

We review the structure and dynamics of the solar chromosphere with emphasis on the quiet Sun and properties that are relevant to element fractionation mechanisms. Attention is given to the chromospheric magnetic field, its connections to the photosphere, and to the dynamical evolution of the chromosphere. While some profound advances have been made in the “unmagnetized” chromosphere, our knowledge of the magnetically controlled chromosphere, more relevant for the discussion of element fractionation, is limited. Given the dynamic nature of the chromosphere and the poorly understood magnetic linkage to the corona, it is unlikely that we will soon know the detailed processes leading to FIP fractionation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Reservoir for Comet Material: Circumstellar Grains

Primitive meteorites and interplanetary dust particles contain small quantities of dust grains with highly anomalous isotopic compositions. These grains formed in the winds of evolved stars and in the ejecta of stellar explosions, i.e., they represent a sample of circumstellar grains that can be analyzed with high precision in the laboratory. Such studies have provided a wealth of information on stellar evolution and nucleosynthesis, Galactic chemical evolution, grain growth in stellar environments, interstellar chemistry, and the inventory of stars that contributed dust to the Solar System. Among the identified circumstellar grains in primitive solar system matter are diamond, graphite, silicon carbide, silicon nitride, oxides, and silicates. Circumstellar grains have also been found in cometary matter. To date the available information on circumstellar grains in comets is limited, but extended studies of matter returned by the Stardust mission may help to overcome the existing gaps.     

Comparison of remote sensing experiments from airborne and space platforms

Recent technological advances in the development of instruments and platforms like aircraft, balloons, satellites, the space station and, very recently, Zeppelin dirigibles, have opened up many new applications for remote sensing. This paper is an attempt to summarise and compare advantages and disadvantages as well as limitations, restrictions and perspectives of passive remote sensing instruments used on the different platforms and it should help to select the best platform for a special application for Earth observation.     

Most suitable conditions for aerosol monitoring from space

Numerical modelling is used to search for the most suitable conditions, with the object of determining the atmospheric turbidity (aerosol optical depth) from upward emerging spectral radiances in cloudfree pixels over water surfaces. The most suitable conditions are those where the influence of the turbidity on the radiance most strongly outweighs that of the other optically acting constituents. Since the actual values of these constituents of atmosphere and surface are usually known only within certain limits, using the most suitable conditions minimizes the uncertainty in the turbidity to be derived from satellite measurements. As a result, favorable zenith angles of the satellite and favorable wavelengths are presented for an atmosphere with maritime aerosols with and without Saharan dust. The results represent an advance on a paper published by the authors in 1981 [1].     

Expectations for Crater Size and Photometric Evolution from the Deep Impact Collision

The NASA Discovery Deep Impact mission involves a unique experiment designed to excavate pristine materials from below the surface of comet. In July 2005, the Deep Impact (DI) spacecraft, will release a 360 kg probe that will collide with comet 9P/Tempel 1. This collision will excavate pristine materials from depth and produce a crater whose size and appearance will provide fundamental insights into the nature and physical properties of the upper 20 to 40 m. Laboratory impact experiments performed at the NASA Ames Vertical Gun Range at NASA Ames Research Center were designed to assess the range of possible outcomes for a wide range of target types and impact angles. Although all experiments were performed under terrestrial gravity, key scaling relations and processes allow first-order extrapolations to Tempel 1. If gravity-scaling relations apply (weakly bonded particulate near-surface), the DI impact could create a crater 70 m to 140 m in diameter, depending on the scaling relation applied. Smaller than expected craters can be attributed either to the effect of strength limiting crater growth or to collapse of an unstable (deep) transient crater as a result of very high porosity and compressibility. Larger then expected craters could indicate unusually low density (< 0.3 g cm⁻³) or backpressures from expanding vapor. Consequently, final crater size or depth may not uniquely establish the physical nature of the upper 20 m of the comet. But the observed ejecta curtain angles and crater morphology will help resolve this ambiguity. Moreover, the intensity and decay of the impact “flash” as observed from Earth, space probes, or the accompanying DI flyby instruments should provide critical data that will further resolve ambiguities.