A. Zadorozhny

Nitric oxide and lower ionosphere quantities during solar particle events of October 1989 after rocket and ground-based measurements

Abstract The most dramatic demonstrations of solar activity are solar proton flares. One such very strong flare, accompanied by a solar proton event (SPE) and a large ground level enhancement of cosmic rays on Earth, was observed in October 1989. During this SPE, ion density and nitric oxide concentration profiles were measured by rockets launched from the Soviet research vessel ‘Akademik Shirshov’ in the southern part of the Indian Ocean. The rocket experiment yielded the first in-situ measurement of NO concentration increased by SPE. The NO concentrations estimated from ion-pair production rates due to measured fluxes of high energy particles agree fairly well with the observed NO concentrations in the stratopause region. The results of rocket measurements are compared with measurements of the radio wave absorption in the lower ionosphere performed at similar latitudes in central Europe. Model calculations of absorption show that while the night-time enhancement of absorption can be explained by increased electron density related to the measured increase of ion density as a consequence of enhanced penetration of high energy particles, the daytime increase of absorption needs to be explained mainly in terms of the observed increase of nitric oxide concentration.

Electric field measurements in the vicinity of noctilucent clouds and PMSE

We report mesospheric electric field structure in the vicinity of noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSEs) measured on the DECIMALS-B rocket payload launched during the international rocket-radar campaign NLC-91 from Esrange, Sweden on August 10, 1991. Unusually large vertical E- fields, Ez, about 100–300 mV/m on ascent and greater than 1 V/m on descent were detected at 82.5–84.5 km. The region of the large Ez was clearly limited by the NLC layer on the bottom and by the distinctly separated PMSE layer on the top. A narrow negative peak in the Ez height profile observed on ascent in the lower part of the NLC layer was apparently caused by the interaction of the field mill with impacting NLC particles possibly carrying negative charge. If the impact signature is due to single particles, their size is estimated to at least 0.5 µm and their concentration about 10−4 cm−3 locally. Based on the light-scattering properties of NLC such massive particles can only be a minor part of the NLC population.

Laboratory and in situ evidence for the presence of ice particles in a PMSE region

An interpretation is made of rocket data obtained from an electric field mill (EFM) sensor during the international rocket-radar campaign NLC-91. The interpretation is based on a laboratory study of the interaction of a water particle beam with the EFM recovered after the rocket flight. Both rocket and laboratory data show that the field mill is sensitive to ice microparticle impacts and that perturbations in the EFM signal observed in the vicinity of noctilucent clouds and an enhanced radar echo (PMSE) layer are caused not only by atmospheric electric fields but also by the impact of solid particles. The altitude range of the impact signatures suggests the presence of ice particles in the PMSE region above the height of the optically detected noctilucent clouds. The analysis of the rocket data on the basis of the laboratory results allows us to estimate sizes of these PMSE particles to be 13–40 nm.

Effects of charged dust on mesospheric electrical structure

Abstract Extremely low effective conductivity of the mesosphere is predicted in the region where both positive and negative charges carried by the dust exceed the charges carried by ions and electrons. This condition is similar to that leading to formation of polar mesosphere summer echoes (PMSE). The predicted effective conductivity of the dusty mesosphere is about two to three orders of magnitude less than the measured ion conductivity. The extremely low effective conductivity of the mesospheric dusty plasma can explain the existence of V/m vertical electric fields observed in the lower mesosphere and in the vicinity of noctilucent clouds and PMSE.

Recent measurements of middle atmospheric electric fields and related parameters

Abstract In 1989, two series of rocket measurements were carried out to investigate middle atmosphere electric fields. The measurements were taken both in the Northern Hemisphere on Heiss Island (80°37′N and 58°03′E) and in the Southern Hemisphere in the Indian Ocean (40–60°S and ~45°E) on board the research vessel ‘Akademik Shirshov’. Along with the vertical electric fields, aerosol content and positive ion density were also measured. Some of the rocket launches were made during the extremely strong solar proton events (SPE) of October 1989. The experiments showed the strong variability of the electric fields in the middle atmosphere at polar and high middle latitudes. In all the measurements the maximum of the vertical electric field height profile in the lower mesosphere was observed to be more than ~ 1 V/m. The electric field strength and the field direction at maximum varied considerably among the launches. A maximum value of + 12 V/m was detected at a height of about 58 km at 58°30′S on 21 October 1989 during the SPE. The simultaneous measurements of the electric field strength, positive ion density and aerosols point out both an ion -aerosol interaction and a connection between the mesospheric electric fields and aerosol content.

Greenhouse gases and future long-term changes in the stratospheric temperature and the ozone layer

A numerical two‐dimensional (2D) interactive dynamical–radiative–photochemical model including aerosol physics is used to examine the expected long‐term changes in stratospheric temperature and the Earths ozone layer due to anthropogenic pollution of the atmosphere by the greenhouse gases CO2, CH4 and N2O. The model time‐dependent runs were made for the period from 1975 to 2050. The results of the calculations show that the basic mechanism by which greenhouse gases influence the ozone layer is stratospheric cooling accompanied by a weakness in the efficiency of the catalytic cycles of ozone destruction due to temperature dependencies of the photochemical gas‐phase reactions. Modification of polar stratospheric clouds (PSCs) caused by anthropogenic growth of the greenhouse gases is important only for the polar ozone. An essential influence of the greenhouse gases on the ozone by a modification of the stratospheric sulphate aerosol is revealed. The aerosol changes caused by the greenhouse gases modify the distribution of the ozone‐active gaseous chlorine, bromine and nitrogen components by means of heterogeneous reactions on the aerosol surface, resulting in a significant decrease in springtime polar ozone depletion of the Antarctic ozone hole.

On the role of charged dust in mesospheric electric fields

A strong interaction of charged dust with electrons and ions similar to that leading to formation of polar mesosphere summer echoes (PMSE) assumes to take also place in the lower mesosphere. This assumption predicts extremely low effective conductivity of the region where both positive and negative charges carried by the dust exceed the charges carried by ions and electrons. The low effective conductivity of the mesospheric dusty plasma can explain the existence of V/m vertical electric fields observed in the lower mesosphere and in the vicinity of noctilucent clouds and PMSE. Gravitational sedimentation of charged dust as well as currents of the global atmospheric electric circuit and precipitating high-energy electrons and protons can produce the V/m fields under these conditions. The proposed theory allows understanding the observed behavior of the mesospheric vertical electric fields: their large variability, universal diurnal variation, increasing during solar proton events and geomagnetic disturbances.

Universal diurnal variation of mesospheric electric fields

Abstract Rocket measurement data of the vertical electric fields in the mesosphere are analysed. Available data indicate that there exists a diurnal variation of the mesospheric electric fields with universal time. This variation is more pronounced at middle latitudes. The large vertical electric fields with strength exceeding ∼1 V/m are present in the lower mesosphere only about between 12:00 UT and 01:00 UT, coinciding the maximum of universal diurnal variation of a fair-weather electric field on the earths surface (the Carnegie curve). This suggests that thunderstorm activity affects the electric field structure in the mesosphere.

Contribution of solar UV radiation to the observed ozone variations during the 21st and 22nd solar cycles

A two-dimensional dynamical radiative-photochemical model of the ozonosphere including aerosol physics is used to examine the changes of the Earths ozone layer occurred during the 21st and 22nd solar cycles. The calculated global total ozone changes in the latitude range 60°S—60°N caused by 11-year variation of solar UV radiation, volcanic eruptions, and anthropogenic atmospheric pollution containing CO2, CH4, N2O and chlorine and bromine species are in a rather good agreement with the observed global ozone trend. The calculations show that the anthropogenic pollution of the atmosphere is a main reason of the ozone depletion observed during the last two solar cycles. However, the 11-year solar UV variation as well as volcanic eruptions of El Chichon and Mt. Pinatubo also gave a significant contribution to the observed global ozone changes.

Nitric oxide density measurements at middle latitudes

SummaryThe measurements of nitric oxide density were made by the photoionization method at 30–90km in several rocket flights near Volgograd. TheseNO densities are well within the range of other measurements below 60km, but become rather high above 70km. The upper mesosphericNO densities estimated by two different methods from ionospheric data in Central Europe (50 °N) are rather high, as well. The appropriateNO densities in the upper mesosphere still seem to be an open question.