scholarly journals Travelling Ionospheric Disturbances in the F Region

1958 ◽  
Vol 11 (1) ◽  
pp. 91 ◽  
Author(s):  
GH Munro
Keyword(s):  
Seasonal Variation ◽  
Radio Frequency ◽  
Diurnal Variation ◽  
Diurnal Variations ◽  
Ionospheric Disturbances ◽  
Frequency Of Occurrence ◽  
Travelling Ionospheric Disturbances ◽  
F Region ◽  
Seasonal And Diurnal Variations ◽  
Single Radio

Observations of the horizontal movements of travelling ionospheric disturbances recorded on a single radio frequency from April 1948 to March 1957 are analysed for seasonal and diurnal variations of occurrence and of direction and speed of travel. Recording was mainly in daylight hours but some limited night results are included. The average number of disturbances recorded was six per day over the period. Observing accuracy and significance of the deduced data are discussed. The frequency of occurrence has a diurnal variation with a marked midday maximum and a seasonal variation with minima at the equinoxes.

scholarly journals A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

1997 ◽  
Vol 15 (8) ◽  
pp. 1048-1056 ◽  
Author(s):  
R. L. Balthazor ◽  
R. J. Moffett
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Ionospheric Disturbance ◽  
Magnetic Equator ◽  
Ionospheric Disturbances ◽  
Atmospheric Gravity Waves ◽  
Opposite Hemisphere ◽  
Travelling Ionospheric Disturbances ◽  
F Region ◽  
Atmospheric Gravity

Abstract. A global coupled thermosphere-ionosphere-plasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A 'fast' dominant mode and two slower modes are identified. We find that, at the magnetic equator, all the clearly identified modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the 'fast' AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGWs first interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex effects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic field lines by the neutral air pressure wave.

Seasonal and diurnal variations of geomagnetic activity and their role in Space Weather forecast

2001 ◽  
Vol 79 (6) ◽  
pp. 907-920 ◽  
Author(s):  
W Lyatsky ◽  
A M Hamza
Keyword(s):  
Solar Wind ◽  
Seasonal Variation ◽  
Diurnal Variation ◽  
Geomagnetic Activity ◽  
Space Weather ◽  
Weather Forecast ◽  
Diurnal Variations ◽  
Ionospheric Conductivity ◽  
Solar Wind Parameters ◽  
Possible Cause

A possible test for different models explaining the seasonal variation in geomagnetic activity is the diurnal variation. We computed diurnal variations both in the occurrence of large AE (auroral electrojet) indices and in the AO index. (AO is the auroral electrojet index that provides a measure of the equivalent zonal current.) Both methods show a similar diurnal variation in geomagnetic activity with a deep minimum around (3–7) UT (universal time) in winter and a shallower minimum near 5–9 UT in equinoctial months. The observed UT variation is consistent with the results of other scientists, but it is different from that expected from the Russell–McPherron mechanism proposed to explain the seasonal variation. It is suggested that the possible cause for the diurnal and seasonal variations may be variations in nightside ionospheric conductivity. Recent experimental results show an important role for ionospheric conductivity in particle acceleration and geomagnetic disturbance generation. They also show that low ionospheric conductivity is favorable to the generation of auroral and geomagnetic activity. The conductivity in conjugate nightside auroral zones (where substorm generation takes place) is minimum at equinoxes, when both auroral zones are in darkness. The low ionospheric conductivity at equinoxes may be a possible cause for the seasonal variation in the geomagnetic activity with maxima in equinoctial months. The diurnal variation in geomagnetic activity can be produced by the UT variation in the nightside ionospheric conductivity, which in winter and at equinoxes has a maximum around 4–5 UT that may lead to a minimum in geomagnetic activity at this time. We calculated the correlation patterns for the AE index versus solar-wind parameters inside and outside the (2–7) UT sector related to the minimum in geomagnetic activity. The correlation patterns appear different in these two sectors indeed, which is well consistent with the UT variation in geomagnetic activity. It also shows that it is possible to improve significantly the reliability of the Space Weather forecast by taking into account the dependence of geomagnetic activity not only on solar-wind parameters but also on UT and season. Our test shows that a simple account for the dependence of geomagnetic activity on UT can improve the reliability of the Space Weather forecast by at least 50% in the 2–7 UT sector in winter and equinoctial months. PACS No.: 91.25Le

scholarly journals Investigation of the Diurnal Variation of Marine Boundary Layer Cloud Microphysical Properties at the Azores

2014 ◽  
Vol 27 (23) ◽  
pp. 8827-8835 ◽  
Author(s):  
Xiquan Dong ◽  
Baike Xi ◽  
Peng Wu
Keyword(s):  
Boundary Layer ◽  
Diurnal Variation ◽  
Marine Boundary Layer ◽  
Surface Wind ◽  
Number Concentration ◽  
Diurnal Variations ◽  
Cloud Layer ◽  
Entire Study ◽  
Microphysical Properties ◽  
Seasonal And Diurnal Variations

Abstract A new method has been developed to retrieve the nighttime marine boundary layer (MBL) cloud microphysical properties, which provides a complete 19-month dataset to investigate the diurnal variation of MBL cloud microphysical properties at the Azores. Compared to the corresponding daytime results presented in the authors' previous study over the Azores region, all nighttime monthly means of cloud liquid water path (LWP) exceed their daytime counterparts with an annual-mean LWP of 140 g m−2, which is ~30.9 g m−2 larger than daytime. Because the MBL clouds are primarily driven by convective instabilities caused by cloud-top longwave (LW) radiative cooling, more MBL clouds are well mixed and coupled with the surface during the night; thus, its cloud layer is deeper and its LWP is higher. During the day, the cloud layer is warmed by the absorption of solar radiation and partially offsets the cloud-top LW cooling, which makes the cloud layer thinner with less LWP. The seasonal and diurnal variations of cloud LWC and optical depth basically follow the variation of LWP. There are, however, no significant day–night differences and diurnal variations in cloud-droplet effective radius (re), number concentration (Nd), and corresponding surface measured cloud condensation nuclei (CCN) number concentration (NCCN) (at supersaturation S = 0.2%). Surface NCCN increases from around sunrise (0300–0600 LT) to late afternoon, which strongly correlates with surface wind speed (r = 0.76) from 0300 to 1900 LT. The trend in hourly-mean Nd is consistent with NCCN variation from 0000 to 0900 LT but not for afternoon and evening with an averaged ratio (Nd/NCCN) of 0.35 during the entire study period.

scholarly journals Anomalies in Ionosonde Records Due to Travelling Ionospheric Disturbances

1958 ◽  
Vol 11 (1) ◽  
pp. 79 ◽  
Author(s):  
LH Heisler
Keyword(s):  
Seasonal Distribution ◽  
Ionospheric Disturbances ◽  
Travelling Ionospheric Disturbances ◽  
F Region

Anomalies which frequently appear on ionosonde records of the F region during the passage of travelling disturbances are classified into four main types; and the diurnal and seasonal distribution of their occurrence is discussed.

scholarly journals Seasonal and Diurnal Variations of Ozone near the Mesopause from Observations of the 11.072-GHz Line

2009 ◽  
Vol 26 (10) ◽  
pp. 2192-2199 ◽  
Author(s):  
A. E. E. Rogers ◽  
M. Lekberg ◽  
P. Pratap
Keyword(s):  
Seasonal Variation ◽  
Seasonal Variations ◽  
Atomic Hydrogen ◽  
Diurnal Variations ◽  
Mixing Ratio ◽  
Mesopause Region ◽  
Mixing Ratios ◽  
Rates Of Change ◽  
Broadband Emission ◽  
Seasonal And Diurnal Variations

Abstract Ground-based observations of the 11.072-GHz line of ozone were made from January 2008 through January 2009. These observations provide an estimate of the diurnal and seasonal variations of ozone in the mesopause region. The 11-GHz line is more sensitive to the ozone at higher altitudes than ground observations of the 142-GHz line, because of the reduced Doppler line width. The observations show an increase in the volume mixing ratio of ozone above 80 km at night by more than a factor of 10 and a seasonal variation of about a factor of 2, which is consistent with the semiannual variations of atomic hydrogen in the mesopause region. The diurnal amplitude and rates of change of the mixing ratios at sunrise and sunset are compared with ground-based observations of the 142-GHz line and the observations of the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite, as well as with a simplified chemical model of the creation and destruction of ozone in the mesopause region.

scholarly journals The ionosphere and radio interferometry

1997 ◽  
Vol 40 (4) ◽  
Author(s):  
T. A. Th. Spoelstra
Keyword(s):  
Gravity Waves ◽  
Daily Variation ◽  
Lower Thermosphere ◽  
Time Of Day ◽  
Ionospheric Disturbances ◽  
Frequency Of Occurrence ◽  
Radio Interferometry ◽  
Travelling Ionospheric Disturbances ◽  
Propagation Parameters ◽  
Definition Of

This paper reviews the effects of the ionosphere on radio astronomjcal observations, what we can learn about the ionosphere from radio interferometry, and a procedure to correct for these effects. This study analyzes the results obtained from observations of celestial point soUl.ces with the Westerbork Synthesis Radio Telescope, WSRT, in the Netherlands from the period 1970-1991. The main conc1usions are: 1) A1though seasona1 effects are c1ear, the occurrence and "strength" of ionospheric irregu1arities show no dependence on solar activity. 2) Assuming that the frequency of occurrence of ionospheric disturbances in Spring and Autumn are similar, Ihe "ionospheric" Winter starts on day 348 ± 3 and ali seasons last for three months. 3) Travelling ionospheric disturbances, TIDs, occur most frequently during daytime in Winter periods. 4) The propagation parameters of these travelling ionospheric irregularities and their periods indicate that these belong main1y to the c1ass of medium sca]e TIDs. 5) Radio interferometry is a powerful tool to locate irregularities causing scintillation and to determine their dimensions. 6) The occurrence of non-periodic irregu1arities is, however, not a function of time of day. 7) The daily variation in the amplitude and frequency of occurrence of the TIDs suggest that the generation of gravity waves may be caused by winds and tides in the lower thermosphere/mesosphere. On the basis of the availab1e data, a definition of a "disturbance measure" indicating to what extent the ionosphere is "quiet" is proposed. Procedures to correct for ionospheric effects and an eva1uation of the different methods to obtain information on the ionospheric e1ectron content are reviewed in sections 8 and 9, respectively.

A Discussion on the early days of ionospheric research and the theory of electric and magnetic waves in the ionosphere and magnetosphere - Early work in Australia, New Zealand and at the Halley Stewart Laboratory, London

1975 ◽  
Vol 280 (1293) ◽  
pp. 35-46
Keyword(s):  
Magnetic Field ◽  
New Zealand ◽  
University Research ◽  
Ionospheric Disturbances ◽  
Pulse Technique ◽  
Postgraduate Students ◽  
Travelling Ionospheric Disturbances ◽  
F Region ◽  
King's College ◽  
Profound Influence

Ionospheric research began in Australia in 1927 after the formation of the Radio Research Board. A. L. Green, by measuring polarization of downcoming waves travelling in the opposite direction to the Earth’s magnetic field confirmed that electrons were the effective particles. Builder, Pulley and Wood designed equipment for the automatic recording of critical frequencies. Martyn & Pulley found evidence for high temperatures at F region levels. Munro discovered travelling ionospheric disturbances. In New Zealand the earliest measurements were made by Munro in 1927—8. The New Zealand Radio Research Board later supported the measurement of critical frequencies, absorption and collisional frequency of Peddie, White, Banwell and Straker. Australian and New Zealand postgraduate students contributed to Appleton’s group at King’s College and at the Halley Stewart Laboratory, London. Builder introduced the pulse technique and took part in the Polar Year (1932-3) expedition to Tromso. Pulley designed the first manual ionogram equipment. Both returned to work in Sydney. White measured reflexion coefficients and collisional frequencies of electrons and later returned to Canterbury University, New Zealand. The early ionospheric researches sponsored by the Australian and New Zealand Research Boards had a profound influence by expanding university research and the training of many postgraduate students.

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