Jan Laštovička

Long-term trends in planetary wave activity (2-15 days) at 80-100 km inferred from radio wave absorption

Abstract The daytime radio wave absorption in the lower ionosphere measured by the A3 method (oblique incidence on the ionosphere) in central and southeastern Europe is used to study long-term trends in the planetary wave activity in the period range of 2–15 days in the upper middle atmosphere. In central Europe we have found no trends in the 1960s and 1980s, but a positive trend in the 1970s (early 1970s- early 1980s); in southeastern Europe we have not established any trend in the 1970s, but a positive one in the 1980s (beginning in late 1970s). These trends are of non-solar origin. They are possibly an indication of changes of anthropogenic origin in the Earths atmosphere.

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.

Quasi-periodic fluctuations in ionospheric absorption in relation to planetary activity in the stratosphere

Abstract Quasi-periodic fluctuations (2–15 days) in ionospheric absorption along three radio paths in Central and Southern Europe are investigated for three winter periods 1985/86, 1986/87 and 1987/88. The periods of dominant fluctuations in absorption and the time variations of their amplitudes are similar for all radio paths and every winter period. The shorter-period fluctuations are found to be associated with enhancements of planetary wave two activity in the stratosphere (30 hPa, 60°N), while longer period fluctuations appear to be associated with intensification of planetary wave one activity in the stratosphere.

Long-period fluctuations of meteorological origin observed in the lower ionosphere

Abstract Application of a correloperiodogram analysis to day and night-time radio wave absorption values for five LF radio paths (164, 155, 185, 218 and 272 kHz) in central and southern Europe during the interval 1 June 1979–30 June 1980, fluctuations with the following quasi-periods were found: 2.3–3.2, 4–6 and 10.5–12 days. They exist in all the time series investigated. Other fluctuations with periods of 7–9 days are observed mainly in central Europe. Shorter period fluctuations are most active during the solstices and especially during winter, while the longer period fluctuations (10.5–12 days) have significant amplitudes also in spring. The analysis of satellite data on the intensity of ionizing solar H Lyman-alpha and X-ray (0.1–0.8 nm) radiation, of the variations of the geomagnetic activity (aa(N)-index) and of lower thermospheric wind (

The ionosphere: morphology, development and coupling

95 km) in central Europe, shows that the fluctuations observed in absorption are caused not by fluctuations in the solar ionizing flux, but probably by fluctuations in the neutral atmosphere. This could offer a possibility of monitoring fluctuations of the planetary wave period range in the upper mesosphere and lower thermosphere by means of radio-wave absorption measurements.

DOES THE QBO AND THE MT. PINATUBO VOLCANIC ERUPTION. AFFECT THE GRAVITY WAVE ACTIVITY IN THE LOWER IONOSPHERE

Abstract The morphology of the MAP/WINE winter is examined, principally from ground-based and satellite observations. Winter anomaly is evident, occurring in bursts with a west to east shift in time. Auroral activity, particularly with reference to the times of major rocket salvoes, is generally low, with Andoya to the south of the auroral boundary in most cases. Minor stratospheric warmings, of which 4 occurred, are found to correlate with minima in radio wave absorption. Salvo R1 was launched during one of the minor warmings. Using data from a broad sector of Europe, coupling between the lower thermosphere and mesosphere is seen over large areas. Westerly winds are associated with high absorption (winter anomaly) and reversal to easterly winds with stratospheric warmings and low absorption. It is found possible to select cases, from amongst the MT series of rocket launchings, corresponding to quiet conditions, stratospheric warming, winter anomaly and particle precipitation in the general absence of other effects. Examining D- and lower E-region ionisation profiles for these caes it is found that, compared with a quiet night, the stratwarm night shows the lower E-region to have reduced ionisation. The ionisation ledge is of similar shape in all cases, but occurs over different height ranges. The observed effects all point to transport being a major factor and the need to measure vertical transport over the range of geophysical conditions examined is highlighted.

Lower ionosphere at middle latitudes: its morphology and response to meteorological and solar-terrestrial activity during the DYANA campaign 1990

All existing data (∼6 years) on gravity wave activity, inferred from the nighttime A3 (oblique incidence on the ionosphere) radio wave absorption measurements in the lower ionosphere on 270 kHz at Průhonice in Central Europe, have been exploited to get information on the effects of QBO phases and the Mt. Pinatubo volcanic eruption on the gravity wave activity in the winter half of the year. There appears to be an enhancement of gravity wave activity in the two winters just after the strong volcanic eruption of Mt. Pinatubo. This enhancement is remarkable for long-period waves (T=2–3 hours). No clear effect of the phase of QBO on the level of gravity wave activity has been found; a possible effect of QBO on the correlations between gravity wave activities in individual period bands is indicated. The results are limited by a relatively short data series; however, no more data will he available.

Long-period fluctuations observed in the ionospheric absorption variations

Abstract A large number of radio wave absorption, ƒ min , and IPHA data measured in Europe and East Asia are investigated over the DYANA campaign period (1 January–31 March 1990) from the point of view of their response to meteorological and solar/geomagnetic forcing, of winter anomaly, and of a brief description of the state of the lower ionosphere on rocket salvo days. European mid-latitudinal measurements of electron density are briefly mentioned. The meteorological/solar control of the mid-latitudinal lower ionosphere during DYANA is considerably weaker than during MAP/WINE (winter 1983/84), but is evidently stronger than during MAP/SINE (summer 1987). The most distinct feature of the DYANA winter is a quite different response of the mid-latitudinal lower ionosphere to meteorological variability (namely to the 10 hPa North Pole temperature— indirect characteristics of a global state of the polar vortex) in the first and second halves of the DYANA period. The winter anomaly displays an expected magnitude and pattern during the DYANA winter. There is an expected weaker response of the lower ionosphere to the strong minor stratospheric warming of the first half of February. All three rocket salvos at Biscarosse (CEL) were carried out when the state of the lower ionosphere was within the range of normal (non-extremal) conditions. Various rocket salvos at Andoya took place on days of considerably different conditions in the lower ionosphere at higher mid-latitudes. Partial reflection measurements at Nizhny Novgorod show a clear tendency to a decrease of the electron density gradient between 70 and 80 km during March 1990.

On some sources of uncertainty in the Lyman-α ionization-rate calculation

РезюмеС nомощыо nосле¶rt;овamельноо nрuмененuя aнaлuзa сnекmрa мощносmu, aвmокорреляцuонноо aнaлuзa u бысmроŭ Фурье mрaнсформaцuu (БФТ) к ¶rt;невным u ночным ¶rt;aнным nо nолощенuю uз nяmu НЧ рa¶rt;uо mрaсс (164 кГц, 155 кГц, 185 кГц, 218 кГц u 272 кГц) нa¶rt; Евроnоŭ в nерuо¶rt; 1 uюня 1979–30 uюня 1980. былu нaŭ¶rt;ены сле¶rt;ующuе основные (фун¶rt;aменmaльные) nовmоряющuеся nерuо¶rt;ы: 3.5–5 ¶rt;неŭ u 10.5–12 ¶rtнеŭ. Онu nрuсрmсmвуюm во всех uссле¶rt;овaнных временных ря¶rt;aх. 6- u 9-суmочные колебaнuя нaблю¶rt;aюmся mолько в более северных рa¶rt;uоmрaссaх (185 кГц u 272 кГц). Плaнеmaрные колебaнuя сaмые aкmuвные осенью u осенью u особенно зuмоŭ. Более ¶rt;олоnерuо¶rt;ные волны (10.5–12 ¶rt;неŭ) uмеюm знaчumельную aмnлumу¶rt;у u леmом.SummaryBy subsequent application of power spectrum analysis, autocorrelation analysis and fast Fourier transform (FFT) of the day- and night-time absorption values of five LF radio-paths (164 kHz, 155 kHz, 185 kHz, 218 kHz and 272 kHz) in Europe during the interval 1 June 1979–30 June 1980, fluctuations with the following basic (fundamental), commonly recurrent periods were found: 3.5–5 days and 10.5–12 days. They exist in all investigated time series, while 6- and 9-day fluctuations are observed on the northern radio-paths (185 kHz and 272 kHz). Shorterperiod oscillations are most active during autumn and especially during winter, while the longerperiod oscillation (10.5–12-day) has significant amplitudes also in summer.

Influence of the IMF sector boundaries on cosmic rays and tropospheric vorticity

SummaryThe effect of the uncertainty and variability in the absorption cross-section, ionization cross-section and the Lyman-α line shape on the Lyman-α ionization-rate calculation is studied. The effect of the variability of the Lyman-α line shape seems to be negligible. The effect of the ionization cross-section is rather small. The greatest and very significant effect, particularly at lower altitudes, is due to the discrepancy in the absorption cross-section data. Some ionospheric and atmospheric consequences are briefly discussed.