Kenneth W. Jucks

THE HITRAN MOLECULAR SPECTROSCOPIC DATABASE AND HAWKS (HITRAN ATMOSPHERIC WORKSTATION): 1996 EDITION

Since its first publication in 1973, the HITRAN molecular spectroscopic database has been recognized as the international standard for providing the necessary fundamental spectroscopic parameters for diverse atmospheric and laboratory transmission and radiance calculations. There have been periodic editions of HITRAN over the past decades as the database has been expanded and improved with respect to the molecular species and spectral range covered, the number of parameters included, and the accuracy of this information. The 1996 edition not only includes the customary line-by-line transition parameters familiar to HITRAN users, but also cross-section data, aerosol indices of refraction, software to filter and manipulate the data, and documentation. This paper describes the data and features that have been added or replaced since the previous edition of HITRAN. We also cite instances of critical data that are forthcoming.

The HITRAN molecular spectroscopic database: edition of 2000 including updates through 2001

This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments

The HITRAN molecular spectroscopic database and HAWKS (HITRAN atmospheric workstation)

Nineteen ninety-eight marks the 25th anniversary of the release of the first HITRAN database. HITRAN is recognized as the international standard of the fundamental spectroscopic parameters for diverse atmospheric and laboratory transmission and radiance calculations. There have been periodic editions of HITRAN over the past decades as the database has been expanded and improved with respect to the molecular species and spectral range covered, the number of parameters included, and the accuracy of this information. The 1996 edition not only includes the customary line-by-line transition parameters familiar to HITRAN users, but also cross-section data, aerosol indices of refraction, software to filter and manipulate the data, and documentation. This paper describes the data and features that have been added or replaced since the previous edition of HITRAN. We also cite instances of critical data that is forthcoming. A new release is planned for 1998.

Remote Sensing of Planetary Properties and Biosignatures on Extrasolar Terrestrial Planets

The major goals of NASAs Terrestrial Planet Finder (TPF) and the European Space Agencys Darwin missions are to detect terrestrial-sized extrasolar planets directly and to seek spectroscopic evidence of habitable conditions and life. Here we recommend wavelength ranges and spectral features for these missions. We assess known spectroscopic molecular band features of Earth, Venus, and Mars in the context of putative extrasolar analogs. The preferred wavelength ranges are 7-25 microns in the mid-IR and 0.5 to approximately 1.1 microns in the visible to near-IR. Detection of O2 or its photolytic product O3 merits highest priority. Liquid H2O is not a bioindicator, but it is considered essential to life. Substantial CO2 indicates an atmosphere and oxidation state typical of a terrestrial planet. Abundant CH4 might require a biological source, yet abundant CH4 also can arise from a crust and upper mantle more reduced than that of Earth. The range of characteristics of extrasolar rocky planets might far exceed that of the Solar System. Planetary size and mass are very important indicators of habitability and can be estimated in the mid-IR and potentially also in the visible to near-IR. Additional spectroscopic features merit study, for example, features created by other biosignature compounds in the atmosphere or on the surface and features due to Rayleigh scattering. In summary, we find that both the mid-IR and the visible to near-IR wavelength ranges offer valuable information regarding biosignatures and planetary properties; therefore both merit serious scientific consideration for TPF and Darwin.

Validation of the Aura Microwave Limb Sounder middle atmosphere water vapor and nitrous oxide measurements

[1] The quality of the version 2.2 (v2.2) middle atmosphere water vapor and nitrous oxide measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System (EOS) Aura satellite is assessed. The impacts of the various sources of systematic error are estimated by a comprehensive set of retrieval simulations. Comparisons with correlative data sets from ground-based, balloon and satellite platforms operating in the UV/visible, infrared and microwave regions of the spectrum are performed. Precision estimates are also validated, and recommendations are given on the data usage. The v2.2 H2O data have been improved over v1.5 by providing higher vertical resolution in the lower stratosphere and better precision above the stratopause. The single-profile precision is � 0.2–0.3 ppmv (4–9%), and the vertical resolution is � 3–4 km in the stratosphere. The precision and vertical resolution become worse with increasing height above the stratopause. Over the pressure range 0.1–0.01 hPa the precision degrades from 0.4 to 1.1 ppmv (6–34%), and the vertical resolution degrades to � 12–16 km. The accuracy is estimated to be 0.2–0.5 ppmv (4–11%) for the pressure range 68–0.01 hPa. The scientifically useful range of the H2O data is from 316 to 0.002 hPa, although only the 82–0.002 hPa pressure range is validated here. Substantial improvement has been achieved in the v2.2 N2O data over v1.5 by reducing a significant low bias in the stratosphere and eliminating unrealistically high biased mixing ratios in the polar regions. The single-profile precision is � 13–25 ppbv (7–38%), the vertical resolution is � 4–6 km and the accuracy is estimated to be 3–70 ppbv (9–25%) for the pressure range 100–4.6 hPa. The scientifically useful range of the N2O data is from 100 to 1 hPa.

SPECTRAL EVOLUTION OF AN EARTH-LIKE PLANET

We have developed a characterization of the geological evolution of the Earths atmosphere and surface in order to model the observable spectra of an Earth-like planet through its geological history. These calculations are designed to guide the interpretation of an observed spectrum of such a planet by future instruments that will characterize exoplanets. Our models focus on planetary environmental characteristics whose resultant spectral features can be used to imply habitability or the presence of life. These features are generated by H2O, CO2, CH4, O2, O3, N2O, and vegetation-like surface albedos. We chose six geological epochs to characterize. These epochs exhibit a wide range in abundance for these molecules, ranging from a CO2-rich early atmosphere, to a CO2/CH4-rich atmosphere around 2 billion years ago, to a present-day atmosphere. We analyzed the spectra to quantify the strength of each important spectral feature in both the visible and thermal infrared spectral regions, and the resolutions required to optimally detect the features for each epoch. We find a wide range of spectral resolutions required for observing the different features. For example, H2O and O3 can be observed with relatively low resolution, while O2 and N2O require higher resolution. We also find that the inclusion of clouds in our models significantly affects both the strengths of all spectral features and the resolutions required to observe all these.

The spectrum of earthshine: a pale blue dot observed from the ground

We report the visible reflection spectrum of the integrated Earth, illuminated as it would be seen as a spatially unresolved extrasolar planet. The spectrum was derived from observation of lunar earthshine in the range 4800-9200 A at a spectral resolution of about 600. We observe absorption features of ozone, molecular oxygen, and water. We see enhanced reflectivity at short wavelengths from Rayleigh scattering and apparently negligible contributions from aerosol and ocean water scattering. We also see enhanced reflectivity at long wavelengths starting at about 7300 A, corresponding to the well-known red reflectivity edge of vegetation because of its chlorophyll content; however, this signal is not conclusive because of the breakdown of our simple model at wavelengths beyond 7900 A.

Smithsonian stratospheric far‐infrared spectrometer and data reduction system

The Smithsonian far-infrared spectrometer is a remote sensing Fourier transform spectrometer that measures the mid- and far-infrared thermal emission spectrum of the stratosphere from balloon and aircraft platforms. The spectrometer has had nine successful balloon flights from 1987 to 1994, flying at float altitudes of 36–39 km and collecting 131 hours of midlatitude stratospheric limb spectra. The spectrometer also flew on a NASA DC-8 aircraft, as part of the second Airborne Arctic Stratospheric Expedition (AASE-II), collecting 140 hours of overhead spectra at latitudes ranging from the equator to the north pole. We present here a brief description of the instrument, a discussion of data reduction procedures, an estimation of both random and systematic errors, an outline of the procedure for retrieving mixing ratio profiles, and an explanation of the method of deriving temperature and pressure from the far- and mid-infrared spectra.

Validation of CH4 and N2O measurements by the cryogenic limb array etalon spectrometer instrument on the Upper Atmosphere Research Satellite

CH 4 and N 2 O are useful as dynamical tracers of stratospheric air transport because of their long photochemical lifetimes over a wide range of altitudes. The cryogenic limb array etalon spectrometer (CLAES) instrument on the NASA UARS provided simultaneous global measurements of the altitude profiles of CH 4 and N 2 O mixing ratios in the stratosphere between October 1, 1991, and May 5, 1993. Data between January 9, 1992, and May 5, 1993 (388 days), have been processed using version 7 data processing software, and this paper is concerned with the assessment of the quality of this data set. CLAES is a limb-viewing emission instrument, and approximately 1200 profiles were obtained each 24-hour period for each constituent over a nominal altitude range of 100 to 0.1 mbar (16 to 64 km). Each latitude was sampled 30 times per day between latitudes 34°S and 80°N, or 34°N and 80°S depending on the yaw direction of the UARS, and nearly all local times were sampled in about 36 days. This data set extends the altitude, latitude, and seasonal coverage of previous experiments, particularly in relation to measurements at high winter latitudes. To arrive at estimates of experiment error, we compared CLAES profiles for both gases with a wide variety of correlative data from ground-based, rocket, aircraft, balloon, and space-borne sensors, looked at the repeatability of multiple profiles in the same location, and carried out empirical estimates of experiment error based on knowledge of instrument characteristics. These analyses indicate an average single-profile CH 4 systematic error of about 15% between 46 and 0.46 mbar, with CLAES biased high. The CH 4 random error over this range is 0.08 to 0.05 parts per million, which translates to about 7% in the midstratosphere. For N 2 O the indicated systematic error is less than 15% at all altitudes between 68 and 2 mbar, with CLAES tending to be high below 6.8 mbar and low above. The N 2 O random error is 20 to 5 ppb between 46 and 2 mbar, which also translates to 7% in the low to midstratosphere. Both tracers have useful profile information to as low as 68 mbar, excluding the tropics, and as high as 0.2 mbar (CH 4 ) and 1 mbar (N 2 O). The global fields show generally good spatial correlation and exhibit the major morphological and seasonal features seen in previous global field data. Several morphological features are pointed out for regions and conditions for which there have been essentially no previous data. These include the differential behavior of the tracer isopleths near and inside the Antarctic winter vortex, and local maxima in the tropics in 1992, probably associated with the Mount Pinatubo sulfate aerosol layer. Overall, the results of this validation exercise indicate that the version 7 CH 4 and N 2 O data sets can be used with good confidence for quantitative and qualitative studies of stratospheric and lower-mesospheric atmospheric structure and dynamics.

Validation of hydrogen fluoride measurements made by the Halogen Occultation Experiment from the UARS platform

The Halogen Occultation Experiment (HALOE) on UARS uses the method of solar occultation limb sounding to measure the composition and structure of the stratosphere and mesosphere. One of the HALOE channels is spectrally centered at 3.4 μm to measure the vertical profile and global distribution of hydrogen chloride. The mean difference between HALOE and 14 balloon correlative underflight measurements ranges from 8% to 19% throughout most of the stratosphere. This difference is within the limits of error bar overlap for the two data sets. The mean differences between HALOE and HCl data from ATMOS flights on the space shuttle is of the order of 15 to 20% for the 1992 flight and 10% for the 1993 flight. Generally, HALOE results tend to be low in these comparisons. Also, comparisons with two-dimensional model calculations and HALOE data are in good qualitative agreement regarding vertical profile shapes and features in a pressure versus latitude cross section. HCl values increase from ∼0.3 parts per billion by volume (ppbv) to 1 ppbv in the lower stratosphere to 2.6 ppbv to 3.3 ppbv just above the stratopause which is the upper limit of HALOE single-profile measurements. There is a dependence of HCl results on the angle between the orbit plane and the Earth-Sun vector with HCl varying by ±9% in the upper stratosphere. This variation appears to be altitude dependent and it is not discernible in the data below about 10 mbar.