Solar eclipse induced variations in mesospheric ozone concentrations

A model study of the solar eclipse induced variations in mesospheric ozone concentrations was undertaken. This study includes, in addition to the Chapman reactions, the chemistry involving hydrogen species (H, OH and HO₂) which are found to be important in the destruction of odd oxygen in this altitude region. Coupled time dependent continuity equations are solved for the eclipse duration. The results from the present study are compared with earlier theoretical model and the experimental observations during the 16 February 1980 solar eclipse as well as the results obtained during earlier solar eclipses.     

Characterization of the semi-annual-oscillation in mesospheric temperatures at low-latitudes

Novel measurements of the seasonal variability in mesospheric temperature at low-latitudes have been obtained from Maui, Hawaii (20.8°N, 156.2°W) during a 25-month period from October 2001 to January 2004. Independent observations of the OH (6, 2) Meinel band (peak height ∼87 km) and the O₂ (0–1) atmospheric band emission (∼94 km) were made using the CEDAR Mesospheric Temperature Mapper. The data revealed a coherent oscillation in emission intensity and rotational temperature with a well-defined periodicity of 181 ± 7 days. The amplitude of this oscillation was determined to be ∼5–6 K in temperature and ∼8–9% in intensity for both the OH and O₂ data sets. In addition, a strong asymmetry in the shape of the oscillation was also observed with the spring maximum significantly larger than the fall peak. These data provide new evidence in support of a semi-annual-oscillation in mesospheric temperature (and airglow emission intensities) and help quantify its seasonal characteristics.     

Rocket measurements of mesospheric ionization irregularities

The Langmuir-probe technique for measurement of electron concentration in the mesosphere is capable of excellent altitude resolution, of order 1 m. Measurements from nine rocket flights frequently show small-scale ionization structures in the altitude region 60–90 km. These are believed to be identical with regions of strong coherent backscatter seem by VHF radars at Jicamarca, Peru and Urbana, Illinois. They are believed to represent intermittent turbulence attributable to nonlinear interaction of waves in the mesosphere. Parameters of the turbulent regions are estimated.     

The state experiment — mesospheric dynamics

The $\text{ST}$ructure and $\text{A}$tmospheric $\text{T}$urbulence $\text{E}$nvironment (STATE) experiment was conducted during the second week of June 1983 at Poker Flat Research Range, Alaska. The measurements focus on a study of the middle atmosphere dynamics by comparison between in-situ probe measurements and MST radar measurements. Rocket launchings were conducted at three periods which were selected by monitoring the doppler velocity spectra of the MST radar.The STATE program has included the efforts of several scientists in planning and carrying out the ground-based and rocket measurements. An overview of the program is given together with some preliminary results. The regions in intense backscatter signals detected by the MST radar are shown to correlate with large irregularities in the electron profiles measured.     

New possibilities for mesospheric electricity diagnostics

A possible cause of large variations in the electron collision frequency could be the effect of strong external electric fields of atmospheric origin. This provides a new opportunity to take measurements of electric fields in the lower ionosphere using remote sensing instruments employing radio wave techniques. It has been proposed the technique for making estimates of strong mesospheric electric field intensities on the lower edge of the ionosphere using MF radar data on the effective electron collision frequency, and the data has been presented. The technique described permits a real-time derivation from MF radar data of changes in mesospheric electric field intensities, and estimates of electric current densities. Our results give proof that the source of strong mesospheric electricity is very likely to be a current source.     

Bayesian approach to retrieval of vertical ozone profile from radiometry data

A technique for retrieving vertical distributions (profiles) of atmospheric gas constituents from data of passive remote sensing of the atmosphere is proposed. The goal of the technique based on the statistical (Bayesian) approach to solution of inverse problems is construction of probability distribution for a sought quantity throughout the interval of the studied heights. It is assumed that initial data contain measurement noise, and a priori information about properties of the profile is used. It is proposed to approximate the sought profile by a function in the form of an artificial neural network. This approximation allows optimal inclusion of a priori information into retrieval procedure, thus ensuring the most effective regularization of the problem. Efficiency of the proposed technique is demonstrated on an example of retrieval of vertical ozone profile from data of ground-based sounding of the atmosphere in the millimeter wavelength range. Results of profile retrieval from model data and from spectra of radiation temperature of the atmosphere measured in the Apatity (67° N, 33° E) in the winter of 2002–2003 are presented.     

Reactive-diffusion waves in the mesospheric photochemical system

The influence of horizontal eddy diffusion on photochemical oscillations of minor gas constituents in the mesopause region of the Earth’s atmosphere is investigated. It is shown that, when the spectrum of oscillations contains a pronounced second subharmonic (nonlinear response of the photochemical system to diurnal variations of solar radiation), reaction-diffusion waves in the form of travelling fronts and pulses of the phase of two-day oscillations may be excited in this region of the atmosphere.     

3D Imaging of the OH mesospheric emissive layer

A new and original stereo imaging method is introduced to measure the altitude of the OH nightglow layer and provide a 3D perspective map of the altitude of the layer centroid. Near-IR photographs of the OH layer are taken at two sites separated by a 645 km distance. Each photograph is processed in order to provide a satellite view of the layer. When superposed, the two views present a common diamond-shaped area. Pairs of matched points that correspond to a physical emissive point in the common area are identified in calculating a normalized cross-correlation coefficient (NCC). This method is suitable for obtaining 3D representations in the case of low-contrast objects. An observational campaign was conducted in July 2006 in Peru. The images were taken simultaneously at Cerro Cosmos (12°09′08.2″ S, 75°33′49.3″ W, altitude 4630 m) close to Huancayo and Cerro Verde Tellolo (16°33′17.6″ S, 71°39′59.4″ W, altitude 2272 m) close to Arequipa. 3D maps of the layer surface were retrieved and compared with pseudo-relief intensity maps of the same region. The mean altitude of the emission barycenter is located at 86.3 km on July 26. Comparable relief wavy features appear in the 3D and intensity maps. It is shown that the vertical amplitude of the wave system varies as exp (Δz/2H) within the altitude range Δz = 83.5–88.0 km, H being the scale height. The oscillatory kinetic energy at the altitude of the OH layer is comprised between 3 × 10⁻⁴ and 5.4 × 10⁻⁴ J/m³, which is 2–3 times smaller than the values derived from partial radio wave at 52°N latitude.     

Application of heterogeneous mesospheric ion-chemistry model to MST radar echoes over low latitude

MST radar studies at low latitude stations have documented regions in the mesosphere from where enhanced echoes (Low Latitude Mesospheric Echoes (LMEs)) are observed. Such echoes cannot, in general, be explained by considering the dynamical aspects (such as turbulence, winds, waves, etc.) of the region alone. Mesospheric dust/aerosols can enhance the radar echoes considerably and dust is known to exist at all heights and latitudes of the mesosphere. This study investigates the presence of dusty plasma in the mesosphere through the heterogeneous ion-chemistry of the region.Dust of meteoric origin is incorporated in the conventional ion chemistry scheme and the equilibrium height profiles of charged and neutral dust densities corresponding to effective dust sizes (radii) of 1, 10 and 30 nm are computed for the equatorial quiet daytime conditions.The model derived dust density profiles show structures with respect to dust size, height and season that are indicative of the possible role of mesospheric dust in the production/enhancement mechanisms of the LMEs observed over the equatorial station at Gadanki (13.5°N, 79.2°E), India.     

Multi-year high latitude mesospheric neutral wind observations using a Fabry–Perot interferometer

From 1995 to 1999, a Fabry–Perot Interferometer was stationed at Resolute Bay, Canada (75°N, 95°W) to measure the mesospheric neutral winds in the polar cap from the OH nightglow emission during winter seasons. A 12-h wave is the most prominent feature in the neutral winds. The wave amplitude has large day-to-day variations and inter-annual variability, whereas the phase of the wave appears to be largely consistent for year to year. Small phase shift from early winter to later winter was noticed during most of the seasons when early winter data were available. The 12-h wave showed stronger variability during the 1995/1996 winter season, which may be related to nonlinear interactions with planetary waves. Large negative zonal winds were observed during stratospheric sudden warming events.     

Estimates of mesospheric gravity wave activity over convection from a global model

A new convective gravity wave source spectrum parameterization has been implemented in the Whole Atmosphere Community Climate Model version 2 (WACCM2). This parameterization specifies the momentum flux phase speed spectrum of gravity waves in the Tropics based on the properties of underlying convection; Hence, this parameterization provides realistic global estimates of gravity wave activity. In this paper, we show the estimated gravity wave phase speed spectra in the Tropics from a WACCM2 simulation, at the source level and at 85 km. Spatial distribution of gravity wave activity at 85 km is also presented. Subsequently, we discuss the factors that are primarily responsible for the estimated differences in gravity wave distribution across phase speeds with latitude and asymmetries in direction of gravity wave propagation in the mesosphere. We also examine which of the model assumptions can lead to uncertainties in our estimates of mesospheric gravity wave activity and we discuss how these assumptions provide challenges for comparison with observations of gravity waves in the mesosphere.     

A mathematical description of the annual variation of the temperature-height profile of the stratosphere at Berlin

Since 1958, daily temperature-height profiles have been measured up to 35–40 km at Berlin by means of radiosondes. An attempt is made here to describe these profiles as a function of the noon solar zenith angle, χ. It is shown that the basic annual variation of the measured profiles, T(h), can be presented as T(h) = T_o(h) cos^n(h)_χ. The subsolar temperature, T_o(h), and exponent, n(h), have been determined empirically from the summer and autumn data when the radiative balance is obviously dominant. Neither term depends on the solar cycle. Warmings in winter and coolings in spring are treated as disturbances in the annual variation, due to dynamics, and are described separately as ± ΔT(h).     

On the initial perturbation of mesospheric dust associated irregularities by high powered radio waves

Important observational manifestations of subvisible mesospheric dust are Polar Mesospheric Summer Echoes (PMSEs) which are produced by scattering from electron irregularities produced by dust charging. It has been observed that the PMSE strength can be artificially modified by using a ground-based ionospheric heating facility to perturb the electron irregularity source region that is believed to produce PMSE. Recently it has become evident that significant diagnostic information may be available about the dust layer from the temporal behavior of the electron irregularities during the heating process which modifies the background electron temperature. Particularly interesting and important periods of the temporal behavior are during the turn-on and turn-off of the radio wave heating. Most past theoretical models and experimental investigations have concentrated primarily on the later period. The objective here is to consider the temporal behavior and possibilities for diagnostic information available during the turn-on period of the radio wave. First, approximate analytical models are developed and compared to a more accurate full computational model as a reference. Then from the temporal behavior of the electron irregularities during the turn-on of the radio wave, the analytical models are used to obtain possible diagnostic information for various charged dust and background plasma quantities.     

A superposed epoch study of the effects of solar wind stream interface events on the upper mesospheric and lower thermospheric temperature

The response of mesosphere and lower thermosphere (MLT) temperature to energetic particle precipitation over the Earth’s polar regions is not uniform due to complex phenomena within the MLT environment. Nevertheless, the modification of MLT temperatures may require an event-based study to be better observed. This work examines the influence of precipitation, triggered by solar wind stream interfaces (SI) event from 2002 to 2007, on polar MLT temperature. We first test the relationship between the ionospheric absorption measured by the SANAE IV (South African National Antarctic Expedition IV) riometer and the layer of energetic particle precipitation from POES (Polar Orbiting Environmental Satellites). The combined particle measurements from POES 15, 16, 17 and 18 were obtained close in time to the pass of the SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) temperature retrieval. Here, a superposed epoch technique is described and implemented to obtain average temperature profiles during SI-triggered particle precipitation. The superposed epoch average shows no significant temperature decrease below 100 km prior to the onset of SI-triggered precipitation, whereas a clear superposed average temperature decrease is observed at 95 km after the SI impact. A case study of SI event also yields similar observations. Results indicate that cooling effects due to the production of mesospheric odd hydrogen might be major contributors to temperature decrease under compressed solar wind stream.     

Mesospheric nitric oxide and ozone measurements in polar winter at 69°N

Two rocket experiments were carried out just before and after the polar night at Andoya (69°N), Norway to investigate transport of nitric oxide produced by auroral processes into the middle atmosphere and its influence on the ozone chemistry. Nitric oxide densities of (2–5) × 10⁸cm⁻³ found in the 70–90 km region are one to two orders of magnitude larger than those at middle latitudes. The influence on ozone densities in the 70–90 km region due to such enhanced nitric oxide abundance is found to be insignificant as compared to that due to transport in the middle of February. The larger ozone densities found in February (in spite of longer sunlit duration) than in November in the 40–60 km region again support predominance of transport over photochemical loss.     

Performance and early results from the stratospheric and mesospheric sounder (SAMS) on Nimbus 7

The design and performance of SAMS, an infrared limb-scanning instrument for sounding the temperature and composition of the atmosphere from 15 to 150 km altitude, are reviewed. Some examples of preliminary results on temperature and water vapour and nitrous oxide abundance versus latitude and height are presented.     

Ground-based measurement of strato–mesospheric CO by a FTIR spectrometer over Poker Flat,Alaska

Upper atmospheric CO above 24 km has been observed over Poker Flat (147°W, 65°N, altitude 0.61 km), Alaska using ground-based solar absorption infrared spectroscopy. This is the first reported detection of stratospheric–mesospheric CO using this method from the ground. The results clearly indicate that there is a seasonal variation of the CO profile with enhanced abundances in spring while remaining low from May onwards.The Poker Flat Research Range is one of the many measurement sites that constitute the Network for the Detection of Stratospheric Change (NDSC). The method used in this work, estimating the CO partial column abundances above the middle stratosphere, can be applied to spectra observed using FTIR spectrometry at many other NDSC sites. This suggests the availability of this established technique as a new method for CO measurements in the upper atmosphere.     

First observation of upper mesospheric semi annual oscillations using ground based airglow measurements from Indian low latitudes

We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O₂ emission monitoring. The deduced mesospheric OH and O₂ temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5  months periodicity) oscillation in both OH and O₂ data.     

Investigation of vertical profile of rain microstructure at Ahmedabad in Indian tropical region

The microstructure of rain has been studied with observations using a vertical looking Micro Rain Radar (MRR) at Ahmedabad (23.06°N, 72.62°E), a tropical location in the Indian region. The rain height, derived from the bright band signature of melting layer of radar reflectivity profile, is found to be variable between the heights 4600 m and 5200 m. The change in the nature of rain, classified on the basis of radar reflectivity, is also observed through the MRR. It has been found that there are three types of rain, namely, convective, mixed and stratiform rain, prevailing with different vertical rain microstructures, such as, Drop Size Distribution (DSD), mean drop size, rain rate, liquid water content and average fall speed of the drops at different heights. It is observed that the vertical DSD profile is more inhomogeneous for mixed and stratiform type rain than for convective type rain. It is also found that the large number of drops of size <0.5 mm is present in convective rain whereas in stratiform rain, drops concentration is appreciable up to 1 mm. A comparison of measurements taken by ground based Disdrometer and that from the 200 m level obtained from MRR shows good agreement for rain rate and DSD at smaller rain rate values. The results may be useful for understanding rain structures over this region.     

评定线轮廓度误差的通用数学模型

建立了用最小二乘法评定平面曲线轮廓度的通用数学模型。运用该模型可对任意平面曲线的轮廓度进行评定，从而将直线度、圆度、椭圆度以及任何线轮廓度的评定归结在统一的模式中。由于所建立的模型直观、明了，很容易在计算机上实现，因而可在生产实际中普遍推广应用。举例说明了线轮廓度误差可分离成形状误差、参数误差和位姿误差，给出了分离公式和误差补偿原则。