Mass spectrometric measurements of stratospheric ions

Recent in situ measurements with balloon borne quadrupole mass spectrometers, between 20 and 45 km altitude, are reviewed and discussed.The major stratospheric positive ions observed are proton hydrates [H⁺(H₂O)_n] and non proton hydrates of the form H⁺X_m(H₂O)₂. The data analysis allows a derivation of the vertical mixing ratio profile of X (most probably CH₃CN), which is compared with recent model calculations. From negative ion composition data, showing the presence of NO₃^? and HSO₄^? cluster ions, the density of sulfuric acid in the stratosphere is deduced. The implications of these findings on our understanding of the sulfur chemistry is briefly treated.Finally some other aspects such as contamination, cluster break up and the use of stratospheric ion mass spectra for determination of thermochemical data and other minor constituents are discussed.     

Satellite measurements of atmospheric composition

Since 1978 a number of satellite borne sensors have been used to measure the composition of the earth's atmosphere. These include the LIMS and SAMS instruments on the Nimbus 7 satellite (launched in October 1978), the SAGE instrument on the AEM2 satellite (launched in february 1979) and various instruments on the SME spacecraft (launched October 1981). For many species, these have provided the first abundance measurements with high spatial and temporal resolution and with global coverage. In this paper the composition measurements that have become available from these programs will be reviewed. The paper will then describe some recent studies that have made use of the new data. As it is the exclusive subject of another invited paper, ozone will not be discussed in in any detail.     

A comparison of atmospheric aerosol measurements by various satellite sensors

Investigations to measure the vertical optical thickness of aerosols over ocean surfaces has been conducted using several different satellite sensors. Landsat 1 and Landsat 2 data originally confirmed that a linear relationship exists between the upwelling visible radiance and the aerosol optical thickness (about 90% of this thickness is generally in the lowest 3 km of the atmosphere). Similar relationships have also been found for sensors on GOES-1, SMS-2, NOAA-5, and NOAA-6 satellites. The linear relationship has been shown theoretically to vary with the aerosol properties, such as size distribution and refractive index, although the Landsat data obtained at San Diego showed little variability in the relationship. The differences between the results found for the various satellite sensors are discussed, and are attributed mainly to uncertainties in the calibration of the sensors. To investigate the general applicability of the technique to different locations, a global-scale ground truth experiment was conducted with the AVHRR sensor on NOAA-6 to determine the relationship at eleven ocean sites around the globe. Analysis of the data shows good agreement between the satellite and ground truth values of the aerosol optical thickness, and indicates that the technique has global application. At two of the sites, multispectral radiometric measurements of the Junge aerosol size distribution parameter were made, and showed good agreement with a value inferred from the AVHRR Channels 1 and 2 radiances.     

A new spectrometric measurement of atmospheric 63 μm emission

Absolute zenith intensities of the atomic oxygen fine structure emission at 63 μm were measured above Kiruna, Sweden, on 9 December 1981 in the altitude regime of 85 km to 237 km. The measured data are compared with theoretical predictions for this emission. Both local thermodynamic equilibrium (LTE) and non-LTE conditions were assumed for the model intensity calculations. The importance of the 63 μm emission as a cooling mechanism of the thermosphere is briefly discussed.     

On wavelet techniques in atmospheric sciences

Wavelet analysis has been formalized extensively due to the efforts of mathematicians, physicists and engineers in the last two decades. It has generated a tremendous interest in these communities both in theoretical and applied areas, in such a way that wavelet analysis is also considered now as a nucleus of shared aspirations and ideas. Initially applied to seismic signal studies in geophysics in the 1980s, wavelet techniques have been explored in the atmospheric sciences since the pioneer applications in turbulence studies. If one decides to apply the wavelet analysis to a given signal, it is worthwhile to assess the actual need of the technique itself and the best way to perform it. In atmospheric signal applications, two main directions have been followed: the singularity and the variance analysis. In this paper, the potential uses of this tool supported by some recently published works in the field of atmospheric sciences are discussed. Therefore, initially the characteristics and main properties of the wavelet analysis are presented, focusing on those that are mostly used in the analysis of atmospheric signals. Continuous and discrete wavelet transforms are also discussed, as well as the scalograms and the variance analysis. Finally, some examples of wavelet analysis applied to a wide range of atmospheric science phenomena are presented.     

Trace constituents measurements deduced from spectrometric observations on-board spacelab

The observation of infrared absorption lines by means of a grille spectrometer on board Spacelab 1 allows the determination of Co₂ and CO in the low thermosphere and in the middle atmosphere. Equal abundances of CO and CO₂ are found at 115 ± 5 km altitude. CO₂ is observed to depart from its homospheric volume mixing ratio near 100 km, dropping by a factor of 10,15 km higher. The CO largest number density is observed near 70 km altitude, close to the H Lyman alpha photoproduction peak.The analysis of one run dedicated to the observation of water vapor shows a middle atmospheric mixing ratio of this species within the limits : 3 to 8 ppmv up to 70 km altitude, with the indication of an increase from 30 to 50 km altitude. The H₂O mixing ratio drops very rapidly above 70 km.The comparison of the results from strong and weak H₂O and CO₂ lines shows the need to refine the line profile model.     

A balloon-borne sun-tracking multichannel photometer for atmospheric aerosol measurements

A balloon borne multichannel photometer for measurement of atmospheric scattering in the near ultraviolet and the visible wavelength regions has been developed at the Physical Research Laboratory, Ahmedabad for study of the size distribution and number density of aerosols at tropospheric and lower stratospheric altitudes. The instrumentation involves tracking the sun in elevation and scanning in azimuth. The payload was recently flown on a 100 kg. balloon from the Hyderabad Balloon Facility on 18 April 1984. The balloon reached a float altitude of 35 km and good quality data has been obtained from an altitude of 6 km upto float altitude. Data analysis is still in progress. The present paper details the instrument design and presents a few illustrations of the instrument performance from this flight.     

Advanced techniques for plasma composition and dynamics measurements

Magnetic and RF mass spectrometers have been used routinely in ionospheric research, while traditional ionospheric, magnetospheric, and interplanetary plasma measurements have been made with several types of electrostatic analyzers. Proper interpretation of these data is possible if the spectral peaks are well defined, although ambiguities between fast, light ions and slow, heavy ions cannot always be satisfactorily resolved. Recent and planned experiments involve the study of plasmas which are sufficiently energetic that the spectral peaks overlap. Furthermore, these studies of ionosphere/magnetosphere coupling and of the interaction of the solar wind with the atmospheres of Venus and comets require unambiguous identification of the ion masses with simultaneous mapping of the three-dimensional velocity distribution function of each ion species. This challenge has been partially met by several new types of instruments; the two most common types involve either (1) sequential electrostatic and magnetic analyses or (2) sequential electrostatic and time-of-flight analyses. Some new instruments have also incorporated measurements of total kinetic energy, electric charge, or secondary emission coefficients as diagnostic tools. This paper reviews these recent advances and points out areas where further development is expected and needed.     

Generalised variational assimilation of cloud-affected brightness temperature using simulated hyper-spectral atmospheric infrared sounder data

Assimilated channel brightness temperature data from infrared sounders accounting for cloud effects have a positive effect on weather forecasting, especially in weather-sensitive areas. When cloud effects are included, the channel brightness temperature deviations follow a non-Gaussian distribution. However, classical variational data assimilation follows a Gaussian distribution. When processing the cloud-affected brightness temperature, useful data are lost through the cloud detection process, thus assimilating some channel brightness temperatures with weight function peaks above the cloud top. Furthermore, strict quality control of brightness temperature removes outliers. By adopting the generalised variational assimilation method, which assumes that errors follow a non-Gaussian distribution, this paper assimilates the cloud-affected brightness temperature using simulated data for the hyper-spectral atmospheric infrared sounder (AIRS). A channel set is formed by dynamically selecting AIRS channels. The experiments for retrieving temperature and humidity data demonstrate that the generalised variational assimilated cloud-affected brightness temperature method performs better than the classical method.     

Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques

Recent advances in satellite techniques hold great potential for mapping global gravity wave (GW) processes at various altitudes. Poor understanding of small-scale GWs has been a major limitation to numerical climate and weather models for making reliable forecasts. Observations of short-scale features have important implication for validating and improving future high-resolution numerical models. This paper summarizes recent GW observations and sensitivities from several satellite instruments, including MLS, AMSU-A, AIRS, GPS, and CLAES. It is shown in an example that mountain waves with horizontal wavelengths as short as 30 km now can be observed by AIRS, reflecting the superior horizontal resolution in these modern satellite instruments. Our studies show that MLS, AMSU-A and AIRS observations reveal similar GW characteristics, with the observed variances correlated well with background winds. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS can detect GWs with better vertical but poorer horizontal resolutions. To resolve different parts of the broad GW spectrum, both satellite limb and nadir observing techniques are needed, and a better understanding of GW complexities requires joint analyses of these data and dedicated high-resolution model simulations.     

Validation of satellite-derived atmospheric temperature and water vapor concentration using radiosonde and rocketsonde measurements

Measurements of the spectral radiance of the earth's atmosphere from satellites can be related to the vertical structures of temperature and humidity. Derived profiles of these quantities are compared with radiosonde and rocketsonde observations, as well as with horizontal and vertical cross-sections of the atmosphere. In some regions of the atmosphere, particularly where large gradients are found, significant differences occur. A method for overcoming these by use of Typical Shape Functions is discussed. Transmittances computed from theory require modifications which are not well defined, and radiances measured from some satellite instruments disagree with computed values in ways which suggest calibration or instrument problems.     

Application of HF Doppler measurements for the investigation of internal atmospheric waves in the ionosphere

We present results of the spectral analysis of data series of Doppler frequency shifted signals reflected from the ionosphere, using experimental data received at Kazan University, Russia. Spectra of variations with periods from 1 min to 60 days have been calculated and analyzed for different scales of periods. The power spectral density for spring and winter differs by a factor of 3–4. Local maxima of variation amplitude are detected, which are statistically significant. The periods of these amplitude increases range from 6 to 12 min for winter, and from 24 to 48 min for autumn. Properties of spectra for variations with the periods of 1–72 h have been analyzed. The maximum of variation intensity for all seasons and frequencies corresponds to the period of 24 h. Spectra of variations with periods from 3 to 60 days have been calculated. The maxima periods of power spectral density have been detected by the MUSIC method for the high spectral resolution. The detected periods correspond to planetary wave periods. Analysis of spectra for days with different level of geomagnetic activity shows that the intensity of variations for days with a high level of geomagnetic activity is higher.     

Global N2O cycles — Terrestrial emissions, atmospheric accumulation and biospheric effects

Tropospheric nitrous oxide concentration has increased by 0.2 – 0.4% per year over the period 1975 to 1982, amounting to net addition to the atmosphere of 2.8 – 5.6 Tg N₂O-N per year. This perturbation, if continued into the future, will affect stratospheric chemical cycles, and the thermal balance of the Earth. In turn it will have direct and indirect global effects on the biosphere. Though the budget and cycles of N₂O on Earth are not yet fully resolved, accumulating information and recent modelling efforts enable a more complete evaluation and better definition of gaps in our knowledge.     

On the measurements of the moon’s infrared temperature and its relation to the phase angle

Radiometric measurements of the thermal radiation originating from the moon’s surface were obtained using an infrared detector operating at wavelengths between 8 and 14 μm. The measurements cover a full moon cycle. The variation of the moon’s temperature with the lunar phase angle was established. The lunar temperatures were 391 ± 2.0 K for the full moon, 240 ± 3.5 K for the first quarter, and 236 ± 3 K for the last quarter. For the rest of the phase angles, the lunar temperature varied between 170 and 380 K. Our results are comparable with those obtained previously at these phase angles. For the new moon phase, the obtained temperature was between 120 and 133 K. With the exception of the new moon phase, our measurements at all the phase angles were consistent with those obtained using Earth-based data and those obtained by the Diviner experiment and the Clementine spacecraft. At the new phase, our measurements were comparable with those obtained from the ground but were significantly higher than those obtained by the Diviner and Clementine data. We attribute this inconsistency to either the calibration curve of our detector, which does not perform well at very low temperatures, or to infrared emission from the atmosphere. A simple linear model to predict the lunar temperature as a function of the phase angle was proposed. The experimental errors that affect the measured temperatures are discussed.     

Time-series analysis of GPS measurements for long-span bridge movements using wavelet and model prediction techniques

This study aims at assessing the safety behavior of the Incheon long-span bridge using high rate (10?Hz) geodetic monitoring global positioning system (GPS). The time series of wavelet spectrum analysis is utilized to assess the dynamic behavior of the bridge. The coefficients and model errors of the time series autoregressive-moving average (ARMA) model are used to evaluate the movement performances of the bridge. The results show that: (i) the accuracy of GPS measurements to extract the dynamic behavior of the bridge is 97.27% when compared with the design results. (ii) the behavior of the bridge is within the safety limits of the bridge design with minimum observed changes for the historical GPS measurements in time and frequency domains, the mean deflection of bridge deck is 8.26?mm and frequency changes of bridge is 0.004?Hz compared with the design results. (iii) the time series analysis of the wavelet spectrum and ARMA model coefficients can be used to detect the significant frequency changes and study the rigidity of the bridge performance, respectively; and the both methods are found to be suitable techniques to estimate the performance changes of the GPS measurements in the time and frequency domains during the monitoring time period.     

MLR events and associated triggered emissions observed by DEMETER

This paper gives an overview of different sets of new Magnetospheric Line Radiation (MLR) observed by the satellite DEMETER. Different types of emissions have been observed: emissions called Power Line Harmonic Radiation (PLHR) with frequency lines exactly separated by 50/100 or 60/120 Hz, emissions with frequency lines not exactly separated by 50/100 or 60/120 Hz and drifting in frequency (MLR). By comparison with past observations one can say that some MLR events are due to man-made PLHR which may suffer a non-linear gyro-resonant interaction at the magnetic equator. It is also shown that periodic emissions are very often associated with the MLR. In this case the origin of these waves is natural. The lines are produced by the periodicity and the frequency band limits of the individual elements which causes the appearance of lines on the spectrograms. Finally the paper shows that MLR can trigger emissions.     

Intercomparisons of temperature,density and wind measurements from in situ and satellite techniques

Intercomparisons between satellite retrieved temperatures (TIROS N series) and those derived from radiosonde and rocketsonde profiles have been made covering the years 1980–1984. Differences in the measurement parameters between 100 and 0.4 mbar (～16–55 km) are described; generally radiosonde/satellite differences are less than 1°K, while rocketsonde/satellite differences reach 7–8°K in the upper stratosphere. Comparisons between the various $\text{in situ}$ devices indicate that radiosonde/rocketsonde differrences are less than 1°K while precision studies of the rocketsonde instrument find that the rocketsonde measurements are internally consistent to less than 1°K up to 50 km and to less than 3°K to 60 km. Density data obtained with the small rocketsondes ($\text{in situ}$ thermistors and inflatable spheres) and with the large sounding rocket systems show that density measurements usually agree to within 15 percent up to 85 km. Comparisons of the various atmospheric parameters obtained from different instruments are important, however the usefulness of intermixing the measurements is obvious and increased emphasis should be placed on procedures for intermingling such data. Suggestions are made on how this might be accomplished.