Ozone variability related to several SEP events occurring during solar cycle no. 23

Data from geostationary operational environmental satellite (GOES) series were used to identify intense solar energetic particle (SEP) events occurred during the solar activity cycle no. 23. We retrieved O₃, NO, NO₂, HNO₃, OH, HCl and OHCl profiles coming from different satellite sensors (solar occultation and limb emission) and we looked for the mesospheric/stratospheric response to SEPs at high terrestrial latitudes. The chemistry of the minor atmospheric components is analysed to evaluate the associated odd nitrogen (NO_x) and odd hydrogen (HO_x) production, able to cause short (h) and medium (days) term ozone variations. We investigated the effects of SEPs on the polar atmosphere in three different seasons, i.e., January 2005, April 2002 and July 2000. The inter-hemispheric variability of the ozone, induced by the SEP series of January 2005, has been compared with the effects connected both to larger and quite similar events. We found that during SEP events: (i) solar illumination is the key factor driving SEP-induced effects on the chemistry of the polar atmosphere; (ii) even events with limited particle flux in the range 15–40 MeV are able to change the abundance of the minor constituents in the mesosphere and upper stratosphere.     

Ozone variations observed during the International Ozone Rocket Sonde Intercomparison

The International Ozone Rocket Sonde Intercomparison (IORI) conducted at Wallops Island during October 1979 provided a unique opportunity to observe ozone variations in great detail from several observing systems. The measurement period lasted 15 days during which time ozone observations were taken by ground-based, balloon, rocket, and satellite instruments. These data provided a unique opportunity for diagnosing regional stratospheric variability over a 2 week period. Examination of NMC analyses indicated that during this period the stratospheric polar vortex moved southeastward bringing air from high latitudes to Wallops Island above 10 mb. A concurrent change was observed in the upper stratosphere ozone fields observed by Nimbus-7 SBUV and in the ozone vertical distribution measured by the rocket soundings. In this study the satellite and rocket measurements are compared. The agreement is good, certainly within the errors of the measurements.     

The influence of the several very large solar proton events in years 2000–2003 on the neutral middle atmosphere

Solar proton events (SPEs) are known to have caused changes in constituents in the Earth’s polar neutral middle atmosphere. The past four years, 2000–2003, have been replete with SPEs. Huge fluxes of high energy protons entered the Earth’s atmosphere in periods lasting 2–3 days in July and November 2000, September and November 2001 and October 2003. The highly energetic protons produce ionizations, excitations, dissociations and dissociative ionizations of the background constituents, which lead to the production of HO_x (H, OH, HO₂) and NO_y (N, NO, NO₂, NO₃, N₂O₅, HNO₃, HO₂NO₂, ClONO₂, BrONO₂). The HO_x increases lead to short-lived ozone decreases in the polar mesosphere and upper stratosphere due to the short lifetimes of the HO_x constituents. Large mesospheric ozone depletions (>70%) due to the HO_x enhancements were observed and modeled as a result of the very large July 2000 SPE. The NO_y increases lead to long-lived stratospheric ozone changes because of the long lifetime of the NO_y family in this region. Polar total ozone depletions >1% were simulated in both hemispheres for extended periods of time (several months) as a result of the NO_y enhancements due to the very large SPEs.     

Signatures of the Sudden Stratospheric Warming events of January–February 2008 in Seoul,S. Korea

The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H₂O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H₂O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H₂O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles.     

Air depression over south pole during Antarctic spring and its possible influence on ozone content in this region

Air depression during Antarctic spring, its long-term behaviour and connection with ozone content has been investigated on base of rocket data for polar regions and total ozone data sets for South pole (TOMS data) for 1979–1990. It was shown, that air pressure depression near South polar region in September in the lower stratosphere has a visible (about 5% per decade) negative trend similar to the tendency which total ozone records reveal. Rather high correlation (+0.82) between air pressure in the stratosphere and total ozone content for spring in Antarctica was found.     

Change in the rigidity dependence of the galactic cosmic ray modulation in 2008–2009

Observations of charged particle fluxes in the stratosphere of the polar regions represent the cosmic rays variations with energy above 100 MeV. At the end of 2009 these fluxes reached the highest level for the time of observations from mid 1957 and were by 17% higher than the previous extremum value of May 1965. In the mean time the ground-based neutron monitors showed the remarkably less count rate enhancement. These results argue for the significant change in the energy spectrum of incoming particles in 2008–2009 in the energy range of ∼100–1500 MeV/n.     

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.     

CRISTA-NF measurements of water vapor during the SCOUT-O3 Tropical Aircraft Campaign

The new remote sensing experiment CRISTA-NF (Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere – New Frontiers) successfully participated in the SCOUT-O3 Tropical Aircraft Campaign in November and December 2005. CRISTA-NF operated aboard the high-altitude research aircraft M-55 Geophysica. Mid-infrared spectra (4–15 μm) were measured in the limb sounding geometry with high spatial resolution (250 m vertical sampling, 5–15 km along track sampling). Measurements were carried out during transfer flights between Oberpfaffenhofen, Germany, and Darwin, Australia, as well as during several local flights near Darwin. Water vapor volume mixing ratios in the upper troposphere and lower stratosphere were derived from the CRISTA-NF radiance measurements by utilizing a rapid radiative transfer forward model and the optimal estimation retrieval approach. CRISTA-NF water vapor measurements below the hygropause have a total retrieval error of 15–40% (i.e. root mean square of accuracy and precision). The systematic terms are dominating in the retrieval error budget. The contributions of a priori information to the retrieval results are less than 5–10%. The vertical resolution of the observations is about 250–500 m when permitted by instrument sampling. In this paper we present first results for three transfer flights of the campaign. Being generally in good agreement with corresponding ECMWF operational analyzes, the CRISTA-NF measurements show significantly higher variability and local structures in the upper tropospheric water vapor distributions.     

Periodic and aperiodic ozone variations in the middle and upper stratosphere

Umkehr, ozonesonde and satellite observations were used to determine the height/latitude distribution of the amplitude and phase of the periodic components of the variation of the ozone mixing ratio in the middle and upper stratosphere. The amplitude of the first (annual) harmonic is small in the subtropics and increases to a maximum at polar latitudes. It also increases with height in the mid and upper stratosphere to an apparent maximum just below the stratopause. The second (semi-annual) harmonic has an amplitude that is largest in tropical regions and in subpolar regions at a level of about 40 km. There seems to be very little ozone variation above 30 km with dominant periods close to the quasi-biennial period of total ozone observed in the tropics. The percent of the total variance of the ozone mixing ratio accounted for by the first harmonic is larger than 60 percent at all heights from 20° – 60° latitude in both hemispheres (except near 40 km in the Northern Hemisphere). The percent of the total variance accounted for by the second harmonic is maximum at a height of about 40 km in the tropics and at subpolar latitudes where, as mentioned, its amplitude is also largest.The phase of the first harmonic shows a marked transition from a winter/spring maximum below 30 km to a summer maximum at 30 km, changing rapidly to a maximum in winter in both hemispheres. The regions of minimum amplitude of the annual variation and the marked phase shifts with height both indicate the separation by levels of the dominant physical control mechanisms on the periodic changes of the ozone mixing ratio in the middle and upper stratosphere. Changes below 30 km respond primarily to dynamic influences in the lower stratosphere while above 30 km the periodic variations result mainly from photochemical processes. Above 40 km these variations are strongly temperature dependent.     

Kinetic temperature and carbon dioxide from broadband infrared limb emission measurements taken from the TIMED/SABER instrument

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment is one of four instruments on NASA’s Thermosphere–Ionosphere–Energetics and Dynamics (TIMED) satellite. SABER measures broadband infrared limb emission and derives vertical profiles of kinetic temperature (Tk) from the lower stratosphere to approximately 120 km, and vertical profiles of carbon dioxide (CO₂) volume mixing ratio (vmr) from approximately 70 km to 120 km. In this paper we report on SABER Tk/CO₂ data in the mesosphere and lower thermosphere (MLT) region from the version 1.06 dataset. The continuous SABER measurements provide an excellent dataset to understand the evolution and mechanisms responsible for the global two-level structure of the mesopause altitude. SABER MLT Tk comparisons with ground-based sodium lidar and rocket falling sphere Tk measurements are generally in good agreement. However, SABER CO₂ data differs significantly from TIME-GCM model simulations. Indirect CO₂ validation through SABER-lidar MLT Tk comparisons and SABER-radiation transfer comparisons of nighttime 4.3 μm limb emission suggest the SABER-derived CO₂ data is a better representation of the true atmospheric MLT CO₂ abundance compared to model simulations of CO₂ vmr.     

高层大气臭氧对于太阳紫外辐射27天波动的响应

本文利用Ｓｏｌａｒ Ｍｅｓｏｓｐｈｅｒｅ Ｅｘｐｌｏｒｅｒ（ＳＭＥ）卫星１９８２年和１９８３年太阳紫外辐射和赤道地区５０－９０ｋｍ臭氧分布的红外观测资料，对臭氧地太阳紫外辐射２７天振荡的响应进行了研究，并且利用大气光化波动模式对其进行了理论计算，计算结果与实测结果基本一致。     

Winds and waves in the middle atmosphere as observed by ground-based radars

Ground-based radars have proved to be powerful instruments for studying dynamical processes in the middle atmosphere. They have been used successfully in the last few years during Pre-MAP and MAP projects. This paper briefly reviews the following ground-based radar methods: the new MST radar technique for remote sensing of the mesosphere, stratosphere and troposphere, and the well known techniques for mesospheric measurements such as the ionospheric drift experiment, the meteor radar and the MF radar experiments. A survey of observational results obtained with the various techniques is presented. Particular emphasis is directed to winds and waves as well as their interaction, all of which play an important role in the structure and dynamics of the middle atmosphere.     

Response of the extratropical middle atmosphere to the September 2002 major stratospheric sudden warming

The effects of a major stratospheric sudden warming (SSW) at extratropical latitudes have been investigated with wind and temperature observations over a Brazilian station, Cachoeira Paulista (22.7°S, 45°W) during September–October 2002. In response to the warming at polar latitudes a corresponding cooling at tropical and extratropical latitudes is prominent in the stratosphere. A conspicuous signature of latitudinal propagation of a planetary wave of zonal wavenumbers 1 and 2 from polar to low latitude has been observed during the warming period. The polar vortex which split into two parts of different size is found to travel considerably low latitude. Significant air mass mixing between low and high latitudes is caused by planetary wave breaking. The meridional wind exhibits oscillations of period 2–4 days during the warming period in the stratosphere. No wave feature is evident in the mesosphere during the warming period, although a 12–14 day periodicity is observed after 2 weeks of the warming event, indicating close resemblance to the results of other simultaneous investigations carried out from high latitude Antarctic stations. Convective activity over the present extratropical station diminishes remarkably during the warming period. This behavior is possibly due to destabilization and shift of equatorial convective active regions towards the opposite hemisphere in response to changes in the mean meridional circulation in concert with the SSW.     

Measurements of H I and O VI velocity distributions in the extended solar corona with UVCS/SOHO and UVCS/Spartan 201

The Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory, UVCS/SOHO, and the Ultraviolet Coronal Spectrometer on the Spartan 201 satellite, UVCS/Spartan, have been used to measure H I 1215.67 Å line profiles in polar coronal holes of the Sun at projected heliocentric heights between 1.5 and 3.0 R_⊙. UVCS/SOHO also measured line profiles for H I 1025.72 Å, O VI 1032/1037 Å, and Mg X 625 Å. The reported UVCS/SOHO observations were made between 5 April and 21 June 1996 and the UVCS/Spartan observations were made between 11 and 12 April 1993. Both sets of measurements indicate that a significant fraction of the protons along the line of sight in coronal holes have velocities larger than those for a Maxwellian velocity distribution at the expected electron temperature. Most probable speeds for O⁵⁺ velocity distributions along the lines of sight are smaller than those of H⁰ at 1.5 R_⊙, are comparable at about 1.7 R_⊙ and become significantly larger than the H⁰ velocities above 2 R_⊙. There is a tendency for the O⁵⁺ line of sight velocity distribution in concentrations of polar plumes to be more narrow than those in regions away from such concentrations. UVCS/SOHO has identified 31 spectral lines in the extended solar corona.     

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.     

Gravity wave propagation studies using the Indian MST radar observations

The Indian MST radar facility at Gadanki (13.5°N, 79.2°E) has been utilised to study the propagation of gravity waves from the troposphere/lower stratosphere to the mesosphere and their interaction with the radar backscattered signal variations. The main objective is to correlate vertically propagating gravity waves derived from the tropospheric velocity fields with the dynamics of mesospheric scattering centres. The tropospheric wind velocities and signal strengths over the entire height range have been subjected to power spectral and wavelet analysis to determine the predominant wave periods/amplitudes and the coupling between the lower atmosphere and mesosphere. Results show that (a) the gravity waves are clearly detectable near tropopause heights, (b) while relatively higher period gravity waves (20–50 min) interact with mesospheric scattering centres, the lower period waves (<20 min) are absorbed in the troposphere itself, (c) the mesospheric scattering layers are affected by gravity waves of complementary periods.     

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.     

Gravity waves from sodium-dayglow observations

The sampling interval of sodium dayglow observations was progressively reduced from one hour to two minutes for investigation of mesospheric dynamics, especially for daytime detection of the periods of gravity waves in the mesosphere and the lower thermosphere. The observations were analysed by usual power spectrum technique. The prominent periods, observed for the present, vary between 5 to 27 minutes in general agreement with results obtained by other techniques.     

A simple model for the interhemispheric coupling of the middle atmosphere circulation

The interhemispheric coupling of the middle atmosphere general circulation is characterized by a global anomaly pattern of the zonal-mean temperature. This pattern reflects an anomalous stratospheric and mesospheric residual circulation, in which a weaker (stronger) stratospheric winter circulation is linked to an upward (downward) shift of its upper mesospheric branch reaching from the summer to the winter pole. This phenomenon is robust in observational data and several middle atmosphere general circulation models. In the present study, the recently proposed mechanism of the interhemispheric coupling is unequivocally proven within the framework of a zonally symmetric model that excludes any additional effects due to resolved waves and non-zonally propagating gravity waves. Two simulations are conducted that differ in the strength of the polar vortex. A weaker polar vortex results in a downward shift of the winter mesospheric gravity wave drag. This leads to changes also in the summer upper mesosphere via a feedback solely between gravity wave breaking and the zonal-mean state. The accompanying temperature anomaly reproduces the pattern of the interhemispheric coupling.