Results of the new and old Umkehr algorithm compared with ozone soundings

Vertical ozone distributions from regular Umkehr observations at Arosa, Switzerland, from 1956 to 1990 retrieved with the newly developed algorithm of mateer and Deluisi (1992, J. atmos. terr. Phys. 54, 537), using Bass-Paur absorption coefficients and described in this issue, are compared with the corresponding results obtained with the old routine [Mateer and Duetsch (1964), NCAR, Boulder, Colorado, Part I, 105 pp.], officially in use at the World Ozone Data Center at Toronto. For the period 1967–1989 they are also compared with the sounding data obtained at Payerne, Switzerland with the Brewer-Mast electrochemical instrument.The annual mean values calculated from Umkehr observations increased, using the new algorithm, in layer 4 and to a lesser extent in layers 3 and 1. They decreased strongly in layer 2 and also 6 and became smaller, too, in layers 7 and 8. The new Umkehr yields annual mean values which are much closer to the sounding results than those of the old routine. The seasonal variation shows somewhat larger differences. There are big discrepancies between the trends obtained from both Umkehr algorithms and those calculated from the soundings in the region of the ozone maximum and in the troposphere. The former discrepancies may be due to the changes in the relation between total ozone and vertical distribution which occurred during the past 20 years and which are not taken into account in the definition of the a priori profiles in the new routine. It seems that useful trends can only be obtained in layer 6 and above using Umkehr observations.     

Some features of the vertical ozone distribution from millimeter wave measurements at Pushchino and Onsala observatories

A number of features of the stratospheric ozone distribution were revealed by joint millimeterwave observations of ozone emission lines at 142,175 and 110,836 GHz carried out during the winter periods of 1988–1989 and 1989–1990 at the Radioastronomical Observatory of the P.N. Lebedev Physical Institute of the Russian Academy of Sciences and at the Onsala Space Observatory of Chalmers University of Technology, Sweden. It is shown that vertical ozone variations observed at the two observatories were connected with large scale dynamical processes that occurred in the stratosphere. When the stratosphere was relatively undisturbed the ozone profiles obtained at both observatories were close to the ozone reference model given by Keating and Pitts. There were periods during a stratospheric warming when the ozone content measured at the two observatories in the 25–40 km altitude range was higher by a factor ~ 1.5 than the model values. Dynamical processes in the stratosphere also gave rise to rapid (4 h duration) and large deviations from the model ozone profile. An ozone layer depletion was observed in the 27–55 km altitude range. The observed ozone variations illustrate the sensitivity of the ozone distribution to stratospheric disturbances including stratospheric warmings.     

Comparison of stratospheric ozone profiles retrieved from microwave-radiometer and Dobson-spectrometer data

Passive Microwave Remote Sensors (MRS) can provide information on the composition of the atmosphere by measuring the thermal radiation emitted from rotational transitions of atmospheric molecules Ozone profiles simultaneously obtained from an MRS and a Dobson instrument (‘Umkehr’ method) are compared over a time period of approximately four months. The microwave measurements yield ozone concentrations which are 20–30% higher than the ‘Umkehr’ values. A critical, though not well known, parameter for the microwave inversion procedure is the foreign gas pressure broadening parameter (C) for the observed 142GHz ozone resonance. Throughout the intercomparison we used a value of 3 MHz mb⁻¹. There is recent theoretical and experimental indication that C is more likel y to be as low as 2.5 MHz mb⁻¹. If we use this new value for C all microwave retrieved profiles decrease by 20–25%, thus leading to a far better agreement with the ‘Umkehr’ results. Our measurements therefore strongly support the proposed value of 2.5 MHz mb⁻¹. A final answer on MRS ‘Umkehr’ correlation accuracy cannot be given. We feel that comparison on a day-to-day basis may be rather meaningless and monthly mean values should be used. On the other hand, there was relatively little change in these mean values during the intercomparison period The MRS showed its potential to retrieve ozone profiles also under adverse meteorological conditions, such as cloud cover or fog.     

Recent developments of the Light Climatic Observatory—ozone measuring station of the Swiss Meteorological Institute (LKO) at Arosa

Recent improvements of the instrumentation at the LKO (Light Climatic Observatory—Ozone measuring station of the Swiss Meteorological Institute), which have been carried out by the Swiss Meteorological Institute (SMI) since 1988, are described. These improvements of the station at Arosa (Switzerland) include the construction of a ‘spectrodome’ (cabin for convenient operation of two Dobson spectrophotometers), partial automation of the two Dobson spectrophotometers D15 and D101 operated side by side (automatic data transmission to a PC), the complete automation of instrument D51 to perform Umkehr measurements and the purchase of two Brewer spectrophotometers (Br40 and Br72). On the basis of digital data acquisition, all calculations to get the final results of the total amount of ozone are performed on PC. A data quality concept under current development is described. Its aim is to compare the consistency of the different quasi-simultaneous measurements and to identify possible drifts in the calibration of the instruments at an early stage.     

Tropical behavior of mesospheric ozone as observed by SMM

The seasonal behavior of low latitude mesospheric ozone, as observed by the SMM satellite solar occultation experiment, is detailed for the 1985–1989 period. Annual as well as semi-annual waves are observed in the 50–70 km altitude region. In the latitude range of ±30 the ozone phase and amplitude are functions of temperature and seasonal changes in solar flux. Temperature is the controlling factor for the equatorial region and seasonal changes in solar flux become more dominant at latitudes outside the equatorial zone (greater than ±15). There is a hemispheric asymmetry in the ozone annual wave in the 20 30 region, with northern hemispheric ozone having a larger amplitude than southern hemispheric ozone. In this region temperature is nearly in phase with ozone in both hemispheres and is reduced in amplitude in the northern hemisphere. The equatorial region is characterized by a strong semi-annual wave in addition to the annual variation, and temperature is nearly out of phase with ozone. At all latitudes there is a larger ozone concentration at sunrise than at sunset. The sunrise sunset difference increases with increasing altitude     

A new Umkehr inversion algorithm

In this paper, we describe a new Umkehr algorithm for the estimation of the vertical ozone profile from observations of the umkehr effect of Götz. The algorithm uses new ozone absorption coefficients, which result in a change in the scale of measurement, and their temperature dependence. Better a priori ozone profiles are possible because of the very large increase in the archive of ozone profile measurements. The characterization of the retrieved ozone profiles and the error analysis follow the recipe of Rodgers. The differences between the new algorithm and the old 1964 algorithm are discussed. For both algorithms, only the retrievals for layers 4–8 (1943 km) are suitable for use in ozone trend analysis. For these layers, the retrieval resolution is trivially improved over that in the 1964 algorithm. For other layers, the retrievals either respond mainly to real ozone changes in adjacent or distant layers, or are a function of low-amplitude changes over a very broad range of layers. The effect of atmospheric aerosol on the retrieved profiles has been determined, and found to be generally similar to the effect for the old algorithm, but differing in some details.     

Influence of latitudinal and longitudinal variations of ozone and water vapour on the solar semidiurnal tide

A new tidal source model, based on climatological global ozone and water vapour distributions, has been obtained for January, April, July and October. The source model is used for modelling the solar semidiurnal tide in the lower thermosphere within the framework of the classical tidal theory. The observed phase quasibimodality of the semidiurnal tide at middle latitudes is possibly formed, to a great extent, by two types of hemispheric asymmetry (changing sharply near the equinox) of the ozone distribution. Near 95 km at middle latitudes, the ozone and water vapour distribution nonzonality yields typical values ~2 m/s for maximum longitudinal variations of the zonal and meridional wind amplitudes, and the range ~0.2–0.5 h for maximum longitudinal phase variations in the Northern hemisphere, while they can reach ~10 m/s and ~1.5 h in the Southern hemisphere. The hemispheric asymmetry is mainly caused by the effect of the water vapour tidal source.     

Hough components of ozone heating

Formulae are derived for the Hough components and the mean rate of solar radiational heating by ozone absorption in the presence of a lower reflecting layer. A model of ozone densities based on observational data is presented for each of the four mid-season months January, April, July and October at heights 0(5)80 km and latitudes 0(15)90°. Diurnal and semi-diurnal components of heating are evaluated for migrating modes and discussed in relation to features of the adopted ozone model. Comparisons are made with earlier evaluations.     

Poker Flat MST radar observations of high latitude neutral winds at the mesopause during and after solar proton events

Observations with the Poker Flat, Alaska, MST radar during and after solar proton events in 1982 and 1984 suggest that winds in the altitude range of ~ 80–90 km were altered as a consequence of the influx of energetic charged particles and large electric fields at high latitudes. The atmospheric changes accompanying these events appear to result in a reduction of the semidiurnal tide and an enhancement in the diurnal tide. It is suggested that these changes could result from the alteration of the local tidal heating distribution produced by the particle precipitation, either through changes in the local ozone distribution or as a result of mesospheric Joule heating.     

Mean winds in the winter middle atmosphere above northern Scandinavia

Wind measurements which were carried out during the MAP/WINE Campaign in northern Scandinavia between 2 December 1983 and 24 February 1984 are used to derive background winds and monthly as well as winter mean values from the ground up to 90 km altitude. These mean winds compare favourably to the wind field proposed for the revised CIRA 86, which is deduced from satellite measurements. The vertical structure of the zonal monthly means is similar in both data sets during January and February. The winter mean zonal winds are observed to be slightly stronger in the stratosphere and lower mesosphere during the MAP/WINE winter than the satellite winds proposed for CIRA 86. The long term mean meridional winds are in good agreement up to 60 km. They indicate a dominant influence of quasistationary planetary waves up to 90 km and an ageostrophic poleward flow between 60 km and 85 km over northern Scandinavia, which maximizes at 76 km at about 8 m s⁻¹. The observed short term variability of the wind is discussed with respect to a possible impact of saturating gravity waves on the momentum budget of the middle atmosphere.     

Dynamics of the Antarctic and Arctic mesosphere and lower thermosphere regions—I. The prevailing wind

The dynamics of the Antarctic and Arctic mesopause regions (ca. 95 ±15 km) are investigated through comparative analyses of winds measured by radars at the Scott Base (78°S), Molodezhnaya (68°S), and Mawson (67°S) stations in the Antarctic, and the near-conjugate stations of Heiss I. (81°N) and Poker Flat (65°N) in the Arctic region. The data were analyzed specifically to delineate hemispheric differences in mean monthly prevailing wind climatologies, and show the circulation systems in the Arctic and Antarctic mesosphere and lower thermospheres to exhibit significant asymmetries. These asymmetries may be attributable to hemispheric differences in dynamical forcing due to one or more of the following: insolation absorption by ozone, other mesospheric heat sources such as exothermic chemical reactions, tropospheric forcing of vertically or obliquely propagating gravity waves which engage in mesospheric mean-flow interactions, and dissipation of planetary waves which find ducting channels through the middle atmosphere.Interannual variability is also examined in the Molodezhnaya and Heiss I. data, which cover the periods 1967–1986 and 1968–1985, respectively. Accompanying significant year-to-year variability, eastward winds at 95 km over the Antarctic (Molodezhnaya station) exhibit a trend of decreasing amplitude from 1968 to 1977 that is not reflected in the Arctic data (Heiss I.); for instance, the annual mean wind decreases in a monotonie sense from 20–25 to 5 m s⁻¹ during this period. It cannot be unambiguously established whether this trend represents a decrease in intensity accompanying secular changes in thermal forcing, or a latitudinal contraction or shifting of the mesospheric jet system. The annual mean winds at Molodezhnaya remain at the 4–8 m s⁻¹ level from 1977 to 1986.In addition, existing empirical models are evaluated against the data, and are shown to be deficient in reproducing some salient characteristics of the high-latitude circulation systems. This latter result especially questions the common practice of deriving winds based on the geostrophic approximation in this altitude/latitude regime.     

Climatology of gravity waves in the middle atmosphere

An attempt is made at the statistical analysis of small-scale disturbances in the stratosphere and mesosphere with the aid of meteorological rocket observations at many stations from 77°N to 8°S for several years.By applying a high-pass filter to daily rocket data in the height range 20–65 km, wind and temperature fluctuations with characteristic vertical scales close to or less than 10 km are obtained, which are considered to be due to internal gravity waves. Results are expressed in terms of parameters which tend to emphasize smallscale vertical fluctuations and which should provide qualitative measures of gravity wave activity.It is found that the gravity wave activity shows a notable annual cycle in higher latitudes with the maximum in wintertime, while it shows a semiannual cycle in lower latitudes with the maxima around equinoxes. It is also found from the standard deviation around the monthly mean that the temporal variability of gravity waves is very large.     

Dynamic regime of the mesopause—lower thermosphere at mid-latitudes of the northern hemisphere by radio meteor observations

The coherent pulse Meteor Automatic Radar System (MARS) based at Kharkov (49°30′N, 36°51′E) was used to measure zonal winds in the altitude range 80–105 km in the period from November 1986 to December 1990. It was found that, for the greater part of the year, the zonal prevailing wind component was in the eastward direction. The change from eastward to westward direction begins in the lower thermosphere in February–March, propagating downwards to the mesosphere, and it remains there until June–July. The structure of semidiurnal tides has general regularities at different sites. Annual variations in the monthly mean values of semidiurnal vertical wavelengths are practically the same, both in the northern and southern hemispheres. Wavelengths are more than 100 km in summer months, whereas they are less than 60 km in winter months.Studies of internal gravity wave (IGW) parameters in the height range of 80–105 km have shown that the internal gravity wave amplitude does not exceed 30 m/s, the vertical wavelength is in the range of 10–30 km, the horizontal wavelengths are 100–800 km and the horizontal phase velocities are in the range 20–160 m/s. The propagation and breaking of upward and downward IGW at heights of 80–100 km have been recorded.     

Multiple molecular scattering and albedo action on the solar spectral irradiance in the region of the UVB ( ⩽ 320 nm) : a preliminary inventory

Solar UVB, a fundamental element in our environment, was measured with cadmium cells by Paul Götz in Arosa more than sixty years ago and described in his book entitled : Das Strahlungsklima von Arosa [Götz (1926). Springer, Berlin]. Afterwards, in order to ensure uniformity in field experiments, he introduced in his atmospheric measurements a chemical sensor, the Bioclimatic Ultraviolet Dosimeter. This dosimeter, by its cylindrical form, was adapted to an instantaneous measurement of the global UVB radiation at different sites. The global radiation embraces the whole of the group of direct solar irradiances with molecular scattering (sky radiation) and ground reflection (albedo) together with its scattered spectral component.Numerical results from detailed theoretical calculations aimed at evaluating the various absolute effects associated with height, solar zenith angle and surface albedo have been obtained for the standard atmosphere. The variations with solar zenith angles from 0 to 90 and albedos between 0 and 1 are presented for a spherical terrestrial atmosphere at selected wavelengths between 301 and 325 nm in the UVB region     

Vertical structure of AGW associated ionospheric fluctuations in the E- and lower F-region observed with EISCAT—a case study

The vertical structure of AGW (atmospheric gravity wave) associated fluctuations of ionospheric plasma parameters for the 100–240 km altitude range in the daytime of 7 September 1988 has been investigated by making use of the data provided by the Tromsø measurements in the EISCAT CP1 observation mode.The wave power profile vs height has been studied by integrating the power spectral density in each altitude. The essential feature of the power variation can be explained in terms of the energy conservation of AGWs propagating in a dissipative thermosphere. Intrinsic propagation parameters of the dominant AGW have been successfully estimated with a method based on the retrieval of the Doppler effect due to the horizontal prevailing wind. From the fluctuation structure analysis in a time-altitude frame, a downcoming AGW has been clearly identified. This downcoming wave might have been reflected from a wind shear at the altitude around 200 km, which is inferred from the meridional prevailing wind profile.     

Dynamics of the Antarctic and Arctic mesosphere and lower thermosphere regions—II. The semidiurnal tide

The semidiurnal tidal dynamics of the Antarctic and Arctic mesopause regions (95 ± 15 km) are investigated through comparative analyses of monthly mean tidal wind fields determined from radar measurements at the Scott Base (78°S), Molodezhnaya (68°S), and Mawson (67°S) stations in the Antarctic, and the near-conjugate stations of Heiss I. (81°N) and Poker Flat (65°) in the Arctic region. The main feature common to all stations is the fall equinoctial maximum in amplitude (10–20 m s⁻¹), which is also reproduced by the most recent numerical tidal model. However, the wintertime amplitude growth with height and the shorter vertical wavelengths characterizing the model are features not reflected in the data. There is also a spring equinoctial maximum in the Antarctic data which the model does not reproduce.Examination of interannual variability reveals characteristics similar to those noted in Part I for the mean zonal wind; namely, some degree of year-to-year variability superimposed on apparent long-term decreases of order 0.3–0.5 m s⁻¹ yr⁻¹ (depending on month) in the Southern Hemisphere semidiurnal tidal amplitudes. Numerical simulations presented herein indicate that changes of this magnitude cannot even be induced (via mode coupling) by a change in the mean zonal wind field of order 30%, and are more plausibly explained by a secular change in the tidal forcing by ozone insolation absorption. However, contrary to Part I, the annual mean tidal amplitude is not characterized by any significant secular trend, remaining within the 10.0 ± 2.5 m s⁻¹ range throughout the 1970–1986 period. Analyses of other data sets are required to ascertain confidence in the apparent trend reported here.     

Simultaneous optical observations of long-period gravity waves during AIDA '89

Ground-based optical instrumentation supported the AIDA '89 wind measurement comparisons by describing the gravity waves affecting the 80–100 km altitude region during clear dark hours over Puerto Rico. This study tabulates the characteristics of gravity waves with fractional column emission rate amplitudes up to 30% and with periods greater than 45 min as seen in the O₂ airglow layer by MORTI, a sensor of O₂ rotational temperature and column emission rate in twelve look directions. Data from seven other sensors operating at Guanica and the Arecibo Observatory are then compared with the MORTI data to check the consistency of the entire data set with the wave parameters, primarily velocities, deduced from MORTI. Nine nights of visually distinct crests and troughs were found, one of which was dominated by an evanescent wave and the rest by internal waves. The nights of 5/6 April and 4/5 May 1989 were selected for multi-sensor comparisons. The comparisons showed substantial agreement between the MORTI characterizations and the observations by others, and most differences were attributed to complexities introduced by higher frequency components with shorter coherence distances. Nightly summaries of the O₂ rotational temperature and column emission rate are also given.     

The mean zonal circulation in the meteor zone above Garchy (France) and Kiruna (Sweden)

The large set of data obtained from 6 years of observations by the Garchy meteor radar yields a picture of the mean zonal circulation in the 75–105 km range at 47°N. The annual wind pattern shows that the lower meteor heights (80–90 km) are characterized by strong vertical and seasonal changes and mark a region of transition between the mesospheric monsoonal circulation observed up to around 85 km and another type of circulation above 90 km characterized by a strong steady eastward circulation in the summer and a weak circulation during the rest of the year. These features were also observed over Kiruna (68°N) by another CNET meteor radar situated at this place for 1 yr. The annual wind component prevails in the meteor range and is nearly out of phase below and above the 85–90 km level. Comparisons made with the results from other stations show that these characteristics are probably planetary in character.     

Balloon measurements of stratospheric ion conductivities over the tropics

Conductivity measurements of negative and positive ions were made from about 20 to 35 km by two identical balloon-borne spherical probes at Hyderabad (17.5°N, 78.6°E), India on 22 April 1989 and 22 December 1990. One balloon was launched at 0158 h IST (Indian Standard Time) which reached its ceiling around 0330 h IST. After that time, it floated for about 3 h, 1.5 h before sunrise and 1.5 h after sunrise. Thus it gave data for both day- and night-time conditions at float altitude. The other balloon was launched at 0535 h IST. It gave data for daytime only. Several interesting results have been obtained at the float altitudes. During the night, in the flight of 22 April 1989 the conductivity values of positive ions were found to be about 1.5 times those of negative ions at the float altitude. During the day, in the flight of 22 April 1989, the positive ion conductivity values were found to increase with the increase of solar elevation angle at around 37.5 km altitude. The negative ion conductivity values, however, did not show any day-night variation. In the flight of 22 December 1990, these features were not seen. Instead, a pocket was found where conductivity values were very high (of the order of 10⁻¹¹ mho m⁻¹) at an altitude of about 32.5 km. Also in this flight, the positive ion conductivity was always found to be approximately equal to that of the negative ion conductivity.     

A quasi-simple ablation model for large meteorite entry: theory vs observations

An approximate, analytic, single-body, one-dimensional ablation model has been developed to predict the entry behavior of large meteorites during their hypersonic drag interaction with the Earth's atmosphere. The entry predictions are compared against multistation photographic data from Pribram, Lost City and the recent Innisfree Meteorite. Typical results indicate that the ablation parameter, σ, is ~0.02 to 0.03 s²/km², in the vicinity of the peak ablation altitude, in good agreement with the intersection method of McIntosh which has also been applied separately to each fragment of Innisfree. The altitude associated with the peak ablation in these cases, ranges from ~25 to 40 km. Initial preatmospheric masses are also estimated, ~20 kg for Innisfree, ~60 kg for Lost City and ~250–3200kg for Pribram. Gas cap radiation is found to play a dominant role in the heat transfer predictions for such objects. This is especially so in the more general case, for velocities ≳ 16 km/s. In addition, it was determined that for bronzite type chondrites, preferential survival occurred for initial radii ~2–8 cm, where a relative minimum in the percent mass loss is predicted. This minimum occurs precisely in the region where turbulent convective heat transfer and gas cap radiation are of comparable importance. Finally, for velocities >30 km/s, percent mass loss is predicted to be near 100% for initial radii between 1 cm and 10 m for bronzite type meteorites.