Altitude Coverage Research Articles

GLObal limb Radiance Imager for the Atmosphere (GLORIA): Scientific objectives

The GLObal limb Radiance Imager for the Atmosphere (GLORIA) is a joint proposal of Forschungszentrum Jülich and Forschungszentrum Karlsruhe, Germany. The instrument will provide for the first time a detailed global picture of the spatial structure of the Upper Troposphere/Lower Stratosphere region (UTLS), which plays a crucial role for the climate system. A unique combination of unprecedented spatial resolution and relatively large altitude coverage will tie processes in the UTLS region to the residual mean circulation, thereby providing detailed information on atmospheric dynamics. In particular, the instrument will demonstrate that novel information on small-scale atmospheric dynamics (e.g. gravity-wave momentum flux) can be obtained from space observations, which significantly improves the predictive capabilities of climate models and long-term weather forecasts. To achieve its objectives, GLORIA will use the first two-dimensional detector array flown in space for global limb-observations in the mid-infrared region. The detector array provides 2000 simultaneous limb-views in the altitude region from 5 to 65 km. Moderate spectral resolution is achieved by utilisation of a Michelson interferometer, which allows for measurements of atmospheric temperature fields, clouds parameters, aerosols, water vapour, ozone, and about 10 other trace species. Moreover, the first global observations of gravity-wave momentum fluxes will be obtained from GLORIA temperature observations.

A new 22-GHz radiometer for middle atmospheric water vapor profile measurements

We report on the Middle Atmospheric Water Vapor Radiometer (MIAWARA) instrument, a new ground-based 22-GHz-radiometer that provides water vapor profiles with an altitude coverage of 22-80 km. This paper focuses on the instrumentation and calibration of the new instrument. It is a noncooled instrument with a very low receiver noise temperature, even lower than receiver noise temperatures of existing cooled instruments. The calibration of MIAWARA is achieved with so-called tipping-curve and balanced calibration schemes. The combination of these two calibration techniques allows us to set up a different calibration scheme than most of the other, rarely existing, water vapor profile radiometers at 22 GHz without the commonly used liquid nitrogen calibration. With the use of tipping-curve calibrations, the instrument operates as a standalone instrument. This independence of liquid-nitrogen-cooled calibration targets and of other instruments makes MIAWARA a suitable instrument for campaign use. In addition to the instrumental and calibrational description, a validation technique for the tipping-curve calibration is presented. Finally, first results obtained by measurements carried out in the Swiss plateau are reported.

The occurrence frequency of upward ion beams in the auroral zone as a function of altitude using Polar/TIMAS and DE-1/EICS data

Abstract. We study the occurrence frequency of upward auroral ion beams as a function of altitude using three years of Polar/TIMAS ion data combined with 11 years of DE-1/ EICS ion data, in order to reach a complete altitude coverage between 5000 and 30 000 km. The most interesting result is that there is a peak in ion beam occurrence frequency and invariant energy flux and invariant particle flux at ¢ 3 RE radial distance. The peak exists at about the same altitude in both the evening and midnight MLT sectors. No solar cycle effects are found. We suggest that the peak could be due to a preferred altitude of auroral potential structures at ¢ 3 RE . To substantiate the suggestion, we also present a simple Monte Carlo simulation of ion beams. Another result is that the ion beam occurrence frequency and invariant (mapped to ionospheric altitude) energy and particle fluxes increase in the radial distance range 4–6 RE , suggesting that wave heating processes may take place in this altitude range.Key words. Magnetospheric physics (auroral phenomena; magnetosphere-ionosphere interactions) – Space plasma physics (charged particle motion and acceleration)

Total Densities Derived from Accelerometer Data

The German satellite Challenging Minisatellite Payload (CHAMP), carrying the STAR accelerometer onboard, was launched in July 2000. The CHAMP mission profile is compatible with studies of the thermosphere: it will providegood geographical and altitude coverage over a period of five years. The preprocessing of the accelerometer data consists of correcting them for maneuvers, specific events, and instrumental bias. The total density can then be reconstituted, employing a model for the aerodynamic coefficient. We have employed a theory based on diffuse reemission applied to a 15-plate macromodel. The accuracy of the observed densities depends mainly on the uncertainties of the estimated accelerometer calibration parameters and of the aerodynamic coefficient, as well as on geomagnetic activity. The six weeks of data analyzed in this preliminary study showed their high precision and model shortcomings. Assimilation of at least one year of data in a thermosphere model will significantly increase its accuracy, which, in turn, will improve satellite drag modeling.

The CRISTA‐2 mission

The second mission of the CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment took place in August 1997. The experiment was flown aboard the ASTROnomical Shuttle PAllet Satellite (ASTRO‐SPAS) free‐flying platform launched by the NASA space shuttle. CRISTA analyzes the infrared radiation emitted by trace gases from the Earth limb in the altitude regime from the upper troposphere to the lower thermosphere. The main aim of CRISTA is to detect small‐scale dynamically induced structures in the distribution of trace constituents in the middle atmosphere. The instrument is therefore equipped with three telescopes that simultaneously collect the infrared radiation from three different air volumes. The high spatial density of the measurement grid obtained during the first CRISTA mission in November 1994, as well as the latitudinal coverage, was considerably improved by making use of newly developed satellite pointing and maneuvering capabilities. The altitude coverage was extended to include the upper troposphere where water vapor distributions are analyzed. Dynamically induced features are observed in practically all trace gases and at various spatial scales. The smallest scales that could be analyzed on the basis of the CRISTA data set are well below 100 km. Compared to the first mission, much more emphasis was laid on measurements in the upper mesosphere and lower thermosphere—this was possible because of higher radiometric sensitivities in some channels. Atomic oxygen, carbon dioxide, and ozone densities are derived in the upper mesosphere and lower thermosphere. The mission conditions allowed the study of polar stratospheric clouds (PSC) over the Antarctic and of polar mesospheric clouds (PMC) at high northern latitudes. For the first time, summer high latitude mesopause temperatures were retrieved from CO2 15‐μm spectra using a nonlocal thermodynamic equilibrium model. The derived temperatures compare well with a temperature climatology based on rocket soundings.

Regional and local ionospheric models based on Millstone Hill incoherent scatter radar data

Local and regional statistical models to describe Millstone Hill incoherent scatter radar observations of electron density, electron temperature and ion temperature since 1976 are developed using a bin‐fit technique. The local models generate ionospheric variations with local time, day number, and altitude from 150–1000 km. The prior day's F107 and the Ap index from the previous 3 hour period are keyed inputs to specify solar and geomagnetic activity. The regional models have a latitude coverage of 32–55° geodetic and an altitude coverage of 200–600 km. These climatology models are capable of reproducing primary ionospheric variation features seen in previous studies as well as several newly revealed features, such as the semiannual variation of electron density. They are accessible through the World Wide Web at the URL http://www.openmadrigal.org.

Studies for the Odin sub-millimetre radiometer: III. Performance simulations

Odin is a small, low-cost satellite with a combined astronomical and aeronomical mission. The mission is divided on an equal basis between astronomy and aeronomy. The aeronomy objectives can be divided into four main subjects: stratospheric ozone chemistry, mesospheric ozone chemistry, the summer mesopause region, and the coupling between atmospheric regions. The primary instrument on Odin is the millimetre and sub-millimetre radiometer (SMR), which is used both for astronomy and aeronomy. It is the first satellite to use sub-millimetre frequencies for limb-sounding mode. Odin is also equipped with an optical spectrometer (OSIRIS). This paper is the third of a three-part series and describes the choices of observing modes and the expected performance of the SMR instrument for the aeronomy mission. The relevant frequencies are identified and the exact selection of lines is made. This is followed by a detailed simulation study to determine the achievable altitude coverage together with the corresponding vertical resolution for each retrievable species. An indication of the expected uncertainties is also given, showing, for example, a high-sensitivity to mesospheric water vapour and stratospheric chlorine monoxide. However, a complete analysis of observation uncertainties must await launch and the completion of the validation programme. PACS Nos.: 42.68A, 07.07D, 07.57K

Sensitivity of trace gas abundances retrievals from infrared limb emission spectra to simplifying approximations in radiative transfer modelling

The accuracy of trace gas abundances retrieved from spectrally resolved infrared limb emission measurements relies, among other things, on the appropriate modelling of radiative transfer through the actual atmosphere. We quantify the mapping of several commonly applied simplifications in radiative transfer modelling on the trace gas abundances retrieval error at the example of the Michelson interferometer for passive atmospheric sounding (MIPAS)/environmental satellite (ENVISAT) space borne Fourier transform infra-red limb emission experiment. The Karlsruhe optimized and precise radiative transfer algorithm (KOPRA) which was used as a tool for this study will be introduced. KOPRA supports accurate modelling of the particular instrument requirements of MIPAS and the observation scenarios during the ENVISAT mission, in particular with respect to its viewing direction and its altitude coverage of the atmosphere. We show that disregarding of horizontal temperature inhomogeneities and non-local thermodynamic equilibrium effects, insufficient accuracy in modelling of field-of-view and apodisation effects, and disregarding individual profiles of isotopic species play the key roles in radiative transfer modelling and lead to systematic retrieval errors which can by far exceed the expected random retrieval error caused by measurement noise.

Observations of QP radar echo structure consistent with neutral wind shear control of the initiation mechanism

The semidiumal variations in quasi‐periodic echo structure parameters associated with midlatitude sporadic E layers observed with the Chung‐Li VHF radar located in Taiwan (24.9 N, 121.2 E; 52 MHz) are presented. The results show that the periodicity decreases with increasing range rate and that the spread of Doppler velocities increases as the altitude coverage of the echoes increases. These characteristics are shown to be consistent with the variations to be expected if the shears in the neutral wind and the variations in the background mean flow are the dominant mechanisms controlling the initiation of the echo structures.

High‐resolution studies of atmosphere‐ionosphere coupling at Arecibo Observatory, Puerto Rico

Very accurate measurements of electron density can be made at Arecibo Observatory, Puerto Rico, by applying the coded long‐pulse (CLP) radar technique [Sulzer, 1986a] to plasma line echoes from daytime photoelectrons [Djuth et al., 1994]. In the lower thermosphere above Arecibo, background neutral waves couple to the ionospheric plasma, typically yielding ∼1–3% electron density “imprints” of the waves. These imprints are present in all observations made to date; they are decisively detected at 30–60 standard deviations above the “noise level” imposed by the measurement technique. Complementary analysis and modeling efforts provide strong evidence that these fluctuations are caused by internal gravity waves. Properties of the neutral waves such as their period and vertical wavelength are closely mirrored by the electron density fluctuations. Frequency spectra of the fluctuations exhibit a high‐frequency cutoff consistent with calculated values of the Brunt‐Väisälä frequency. Vertical half wavelengths are typically in the range 2–25 km between 115‐ and 160‐km altitude, and the corresponding phase velocities are always directed downward. Some waves have vertical wavelengths short enough to be quenched by kinematic viscosity. In general, the observed electron density imprints are relatively “clean” in that their vertical wavelength spectrum is characteristically narrow‐banded. It is estimated that perturbations in the horizontal wind field as small as 2–4 m/s can give rise to the observed electron density fluctuations. However, the required wind speed can be significantly greater depending on the orientation of the neutral wave's horizontal wave vector relative to the geomagnetic field. Limited observations with extended altitude coverage indicate that wave imprints can be detected at thermospheric heights as high as 500 km.

Long-lasting fog episode monitored by radioacoustic systems

A long-lasting and deep-fog episode, occurred in the western region of the Po Valley (Italy) during February 1992, has been studied by means of remote-sensing systems, coupled to more conventional meteorological instruments operating at ground level. The temperature profiles were monitored by a metric RASS and the three components of the wind profiles were measured by a Doppler Sodar. The typical altitude coverage of the metric RASS is 80–1000 m; therefore, it is suitable to measure fog-capping thermal inversions and temperature profiles above the fog layer, so that it makes it possible to follow with continuity the growth, the evolution and the end of the fog episode accompanied by subsidence conditions.

Selection of sounding channels for the High Resolution Dynamics Limb Sounder

We describe the scientific design work behind the selection of the IR spectral passbands for the 21 sounding channels of the High Resolution Dynamics Limb Sounder (HIRDLS), which is scheduled to fly aboard the Earth Observing System chemistry platform at the beginning of the next century. At least one radiometer channel must be used for each gas that is being measured. Preferably the interfering contributions to the radiance by other gases in a channel should be small, but the principal requirements are that the desired emission be measured with high signal-to-noise ratio and that there be separate channels for the measurement of interfering species. However, more than one channel is required for providing full altitude coverage of those target gases such as CO(2), H(2)O, and O(3), which have emission bands whose centers become optically thick in the middle atmosphere. Further channels, in which gaseous absorption is low, are required for the characterization of aerosol effects. We describe the HIRDLS channels selected for each gas, with emphasis on signal-to-noise considerations and altitude coverage, the elimination of contaminating signal between channels, and nonlocal thermodynamic equilibrium processes for high-altitude sounding and space view definition.

Ground-based sensing of water vapor in the stratosphere and mesosphere

We report on new developments of the WVMS instrument that provide extended altitude coverage (25-75 km) and precision that have not been achieved before with ground based microwave remote sensing of water vapor. This paper emphasizes the technical details of the instrument, experimental techniques, and especially accuracy and calibration issues.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

EISCAT data base for ionospheric modelling: F-region and topside ionosphere

The EISCAT incoherent scatter radar system has now been providing long-term observations of the highlatitude ionosphere for more than a decade. Regular observations of F-region electron density, electron temperature, ion temperature and ion drift with the UHF radar began in 1981. The commission of the VHF radar in 1987 allowed the altitude coverage of such measurements to be extended well into the topside ionosphere. We present an overview of this data base in the context of the International Reference Ionosphere (IRI), including a description of the various experiment modes. Most of these observations have been obtained from the ionosphere approximately overhead of the transmitter at a geomagnetic latitude of ∼66° N; the remainder cover latitudes from about 5° south to 10° north of the radar location. Emphasis is given to regular observations of the standard ionospheric parameters provided by EISCAT's common programme operations, including an overview of results from positive ion composition analysis. Future prospects related to developments of the radar system are also outlined.

Temperature minima in the average thermal structure of the middle mesosphere (70–80 km) from analysis of 40‐ to 92‐km SME global temperature profiles

Global temperatures have been derived for the upper stratosphere and mesosphere from analysis of Solar Mesosphere Explorer (SME) limb radiance profiles. The analysis of additional SME wavelength radiances at 304, 313, and 442 nm provides for extension of the original SME 60‐ to 90‐km temperature climatology (Clancy and Rusch, 1989a) to a much expanded altitude coverage of 40–92 km. The SME temperatures represent fixed local time observations at 1400–1500 LT, with partial zonal coverage of 3–5 longitudes per day over the 1982–1986 period. These new SME temperatures are compared to the CIRA 86 climatology (Fleming et al., 1990) as well as stratospheric and mesospheric sounder (SAMS); (Barnett and Corney, 1984), National Meteorological Center (NMC); (Gelman et al., 1986), and individual lidar and rocket observations. Significant areas of disagreement between the SME and CIRA 86 mesospheric temperatures are 10 K warmer SME temperatures in the 55‐ to 65‐km altitude region and 10–20 K warmer SME temperatures at altitudes above 80 km. The 1981–1982 SAMS temperatures are in much closer agreement with the SME temperatures between 40 and 75 km. Although much of the SME‐CIRA 86 disagreement probably stems from the poor vertical resolution of the observations comprising the CIRA 86 model, some portion of the differences may reflect 5‐ to 10‐year temporal variations in mesospheric temperatures. The CIRA 86 climatology is based on 1973–1978 measurements. Relatively large (1 K/yr) 5‐ to 10‐year trends in temperatures as functions of longitude, latitude, and altitude have been observed for both the upper stratosphere (Clancy and Rusch, 1989a) and mesosphere (Clancy and Rusch, 1989b; Hauchecorne et al. 1991). The SME temperatures also exhibit enhanced amplitudes for the semiannual oscillation (SAO) of upper mesospheric temperatures at low latitudes, which are not evident in the CIRA 86 climatology. The so‐called mesospheric “temperature inversions” at wintertime midlatitudes, which have been observed by ground‐based lidar (Hauchecorne et al., 1987) and rocket in situ measurements (Schmidlin, 1976), are shown to be a climatological aspect of the mesosphere, based on the SME observations. The winter midlatitude “temperature inversion” is evident in both winter hemispheres and appears more distinctly as a low‐altitude (75 km) temperature minimum at southern midlatitudes. Furthermore, the SME temperatures indicate the related presence of low‐latitude temperature minima at 80‐km altitude during the equinoxes. Both the low‐latitude semiannual minima and the midlatitude annual minima in middle mesospheric temperatures appear to result from the strong SAO in mesospheric temperatures.

Far-ultraviolet imaging spectrograph and scanning grating spectrometers for the Remote Atmospheric and Ionospheric Detection System

The Remote Atmospheric and Ionospheric Detection System (RAIDS) experiment is an optical remote sensing platform consisting of eight sensors, (spectrographs, spectrometers, and photometers) covering the wavelength range 550 to 8744 Å. RAIDS employs a mechanical scan platform to view the Earth's limb and measure line-of-sight column emission from tangent altitudes from 50 to 750 km. These measurements provide vertical profiles of atmospheric dayglow and nightglow from the mesosphere to the upper regions of the F-region ionosphere. RAIDS will be flown on the National Oceanographic and Atmospheric Administration (NOAA) J weather satellite through the auspices of the U.S. Air Force Space Test Program. The RAIDS wavelength and altitude coverage allows remote sensing of the major and many minor constituents in the thermosphere and ionosphere. These measurements will be used as part of a proof of concept for remote sensing of ionospheric and neutral density profiles. The RAIDS database will be used to study composition, thermal structure, and couplings between the mesosphere, thermosphere, and ionosphere. RAIDS is a joint venture of the Naval Research Laboratory (NRL) and The Aerospace Corporation. We describe the subset of RAIDS instruments developed at NRL covering the far to near UV regions (1300 to 4000 Å).

Prospects for Temperature Sounding with Satellite and Ground-based RASS Measurements

Temperature profiles from the TIROS-N Operational Vertical Sounder (TOVS) were combined with low-altitude virtual temperature profiles measured by a ground-based 915-MHz/2-kHz radio acoustic sounding system (RASS) at Denver, Colorado. Low-level temperature inversions of more than 20°C in 100 m, as measured by radiosonde, were successfully resolved by RASS, providing critical information that TOVS alone could not. Conversely, TOVS augmented the RASS altitude coverage, which was typically limited to the first 1–2 km above ground, due to strong acoustic attenuation at 2 kHz. (A 405-MHz/0.9-kHz RASS measures to significantly higher altitudes.) The complementary nature of TOVS and RASS is demonstrated with examples chosen from extreme cases that illustrate the capabilities and limitations of the separate and combined systems.

A Comparison of Temperature Soundings Obtained from Simultaneous Radiometric, Radio-Acoustic, and Rawinsonde Measurements

Atmospheric temperature soundings retrieved from a radio-acoustic sounding system (RASS), a six-channel microwave radiometer system, and a combined RASS/radiometer system during two seasons at Denver, Colorado, are compared. The retrieval technique employed, which operationally produces temperature soundings from the radiometer measurements, extends the RASS altitude coverage and provides a simple way to combine RASS and radiometer measurements. Accuracy is evaluated by comparing the retrieved soundings with colocated rawinsonde soundings. Little difference in accuracy among systems is observed during summer, but the winter dataset, characterized by strong low-level temperature inversions, demonstrates the superior vertical resolution of RASS within its measurement altitude range. At higher altitudes, the quality of temperature soundings retrieved from RASS alone are comparable to those of the radiometer alone. Some improvement in accuracy results from combining RASS and radiometer information.

Observational results using the microwave temperature profiler during the Airborne Antarctic Ozone Experiment

The Microwave Temperature Profiler (MTP) measures profiles of air temperature versus altitude. The altitude coverage is about 5 km at a flight altitude of 20 km (66,000 feet), and the profiles are obtained every 14 s. The MTP instrument is installed on NASA's ER‐2 aircraft, which flew 13 missions over Antarctica during the Airborne Antarctic Ozone Experiment. Altitude temperature profiles were used to derive potential temperature cross sections. These cross sections have been useful in detecting atmospheric waves. Many wave encounters have been identified as “mountain waves.” The mountain waves are found to extend from the lowest altitudes measured to the highest (about 24 km). The southern part of the Palmer Peninsula was found to be associated with mountain waves more than half the time. Altitude temperature profiles were also used to measure the lapse rate along the flight track. Lapse rate versus latitude plots do not show significant changes at the ozone hole boundary.

The altitude coverage of temperature measurements using RASS with wind profiler radars

The Radio Acoustic Sounding System (RASS) technique for measuring temperature profiles with good time and height resolution has been applied using wind profiling radars operating at three frequencies (49.8, 404.37 and 915MHz). The performance of the three systems is discussed in terms of the altitude coverage of the temperature measurements and physical processes limiting the coverage. The lower frequencies can probe greater altitudes, but the 49.8MHz wind profilers have a minimum range of about 2.1 km limiting their usefulness for some studies. These preliminary results indicate that the use of RASS in concert with wind profilers has promise for operational meteorology.