The UARS microwave limb sounder version 5 data set: Theory, characterization, and validation

Nitric acid (HNO3) is a major player in processes controlling the springtime depletion of polar ozone. It is the main constituent of the Polar Stratospheric Clouds (PSCs) and a primary reservoir for reactive nitrogen. Potential variations in the stratospheric circulation and temperature may alter the extent and duration of PSCs activity, influencing the future ozone levels significantly. Monitoring HNO3 and its long-term variability, especially in polar region, is then crucial for better understanding issues related to ozone decline and expected recovery. In this study we present an intercomparison between ground based HNO3 measurements, carried out by means of the Ground-Based Millimeter-wave Spectrometer (GBMS), and two satellite data sets produced by the two NASA/JPL Microwave Limb Sounder (MLS) experiments. In particular, we compare UARS MLS measurements (1991-1999) with those carried out by the GBMS at South Pole, Antarctica (90°S), Fall of 1993 and 1995. A similar intercomparison is made between Aura MLS HNO3 observations (2004 - to date) and GBMS measurements obtained during the period February 2004 - March 2007, at the mid-latitudes/high altitudes station of Testa Grigia (45.9° N, 7.7° E, elev. 3500 m), and during polar winters 2008/09 and 2009/2010 at Thule Air Base (76.5°N 68.8°W), Greenland. We assess systematic differences between GBMS and both UARS and Aura HNO3 data sets at seven potential temperature levels (θ) spanning the range 465 – 960 K. The UARS data set advected to the South Pole shows a low bias, within 20% for all θ levels but the 960 K, with respect to GBMS measurements. A very good agreement, within 5%, is obtained between Aura and GBMS observations at Testa Grigia, while larger differences, possibly due to latitude dependent effects, are observed over Thule. These differences are under further investigations but a preliminary comparison over Thule among MLS v3, GBMS, and ACE-FTS measurements suggests that GBMS measurements carried out during winter 2009 might not be reliable. These comparisons have been performed in the framework of the NASA JPL GOZCARDS project, which is aimed at developing a long-term, global data record of the relevant stratospheric constituents in the context of ozone decline. GBMS has been selected in GOZCARDS since its HNO3 dataset, although sampling different latitudes in different years, is the only one spanning a sufficiently long time interval for cross-calibrating HNO3 measurements by the UARS and Aura MLS experiments

Interstellar H2 toward HD 147888

The ultraviolet and far--ultraviolet spectra of HD 147888 allows to access the v=0 as well as higher vibrational levels of the ground H2 electronic level. We have determined column densities of the H2 molecule on vibrational levels v=0-5 and rotational levels J=0-6. The ortho to para H2 ratio for the excited vibrational states equals to 1.2. For the lowest vibrational state v=0 and rotational level J=1 the ortho to para H2 ratio is only 0.16. The temperature of ortho-para thermodynamical equilibrium is T_OP=43+-3 K. The large number of H2 absorption lines in the HST spectra allows to determine column densities even from a noisy spectra. The measurements of H2 column densities on excited vibrational levels (from the HST spectra) leads to constrains of radiation field in photon-dominated regions (PDR) models of interstellar cloud towards HD 147888

Processing EOS MLS Level-2 Data

A computer program performs level-2 processing of thermal-microwave-radiance data from observations of the limb of the Earth by the Earth Observing System (EOS) Microwave Limb Sounder (MLS). The purpose of the processing is to estimate the composition and temperature of the atmosphere versus altitude from .8 to .90 km. "Level-2" as used here is a specialists f term signifying both vertical profiles of geophysical parameters along the measurement track of the instrument and processing performed by this or other software to generate such profiles. Designed to be flexible, the program is controlled via a configuration file that defines all aspects of processing, including contents of state and measurement vectors, configurations of forward models, measurement and calibration data to be read, and the manner of inverting the models to obtain the desired estimates. The program can operate in a parallel form in which one instance of the program acts a master, coordinating the work of multiple slave instances on a cluster of computers, each slave operating on a portion of the data. Optionally, the configuration file can be made to instruct the software to produce files of simulated radiances based on state vectors formed from sets of geophysical data-product files taken as input

Rosseland and Planck mean opacities for primordial matter

We present newly calculated low-temperature opacities for gas with a primordial chemical composition. In contrast to earlier calculations which took a pure metal-free Hydrogen/Helium mixture, we take into account the small fractions of Deuterium and Lithium as resulting from Standard Big Bang Nucleosynthesis. Our opacity tables cover the density range -16 < log rho [g cm^{-3}] < -2 and temperature range of 1.8 < T [K] < 4.6, while previous tables were usually restricted to T > 10^3 K. We find that, while the presence of Deuterium does not significantly alter the opacity values, the presence of Lithium gives rise to major modifications of the opacities, at some points increasing it by approximately 2 orders of magnitude relative to pure Hydrogen/Helium opacities.Comment: 16 pages, 8 figures, submitted to MNRAS, all figures in grey-scale and at reduced resolution, for high-res colour PDF see http://www.ita.uni-heidelberg.de/~mm/publications/MayerDuschl-2.pd

Basic Methods for Computing Special Functions

This paper gives an overview of methods for the numerical evaluation of special functions, that is, the functions that arise in many problems from mathematical physics, engineering, probability theory, and other applied sciences. We consider in detail a selection of basic methods which are frequently used in the numerical evaluation of special functions: converging and asymptotic series, including Chebyshev expansions, linear recurrence relations, and numerical quadrature. Several other methods are available and some of these will be discussed in less detail. We give examples of recent software for special functions where these methods are used. We mention a list of new publications on computational aspects of special functions available on our website

Riccati equation - based generalization of Dawson’s integral function

A new generalization of Dawson’s integral function based on the link between a Riccati nonlinear differ-ential equation and a second-order ordinary differential equation is reported. The MacLaurin expansionof this generalized function is built up and to this end an explicit formula for a generic cofactor of atriangular matrix is deduce

Mesospheric temperature from UARS MLS: retrieval and validation

International audienceA research algorithm is developed to retrieve temperature at 20–90 km using 63 GHz O2 emission measurements from Microwave Limb Sounder (MLS) on Upper Atmosphere Research Satellite (UARS). The algorithm is based on a previous MLS radiative transfer model but improved to produce more accurate radiance calculations in the cases where the geomagnetic Zeeman splitting is important. A fast version of the model is developed and implemented for practical uses of the temperature retrieval, which uses a single temperature and O2 density profile as the linearization basis. The calculated radiances and linearization coefficients are fit to a set of explicit functions of the geomagnetic field and its direction at tangent heights of 0–120 km, which are pre-stored in order to speed up the computation. The new algorithm has been used to process all the data available during 1991–1997 before MLS 63 GHz radiometer was powered off. The estimated precision of MLS temperature varies from 2K at ∼20 km to 8 K at ∼80 km and increases sharply above ∼90 km. The retrieved MLS temperature are compared against CIRA’86, satellite, lidar, and rocket observations. Comparisons to CIRA’86 seasonal climatology show that the differences are latitude-and-season dependent and generally <5 K below 50 km and 10 K in the mesosphere. Comparisons with other satellite observations (ISAMS, HRDI, CRISTA1) show different patterns but a cold bias at 85–90 km seems common in all these comparisons. Comparisons to ground-based lidar measurements suggest that MLS temperatures are warmer by 2–4 K in the stratosphere and colder by 5–15 K at 85–90 km. The MLS-minus-lidar difference shows a 3–10K cold bias near 70 km for most of the sites selected. The comparisons with rocket measurements are similar to those with lidars at these altitudes, giving cold biases in the MLS temperatures at 85–90 km. Most of these biases are understandable in terms of sampling and resolution differences, and some biases can be reduced with further improvements in the MLS retrieval algorithm. Despite the existing biases, the MLS temperature have been found useful in studying large-scale mesospheric phenomena such as the temperature inversion layer