Substorm effects of ionosphere and HF propagation

Blagoveshchensky, D. V.; Борисова, Т. Д.

doi:10.1029/1998rs001776

Cited by 25 publications

(20 citation statements)

References 13 publications

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“…Early in the papers (Blagoveshchensky et al, 1992(Blagoveshchensky et al, , 1996Blagoveshchensky and Borisova, 2000) the effect of the maximum useable frequency (MUF) variations on the HF radio paths during substorms was revealed. Effect essence is increasing the MUF values some hours before the moment T o , decreasing those during the substorm expansive phase and increasing the MUF values again within some hours during the recovery phase.…”

Section: Introductionmentioning

confidence: 99%

Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99

2003

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Abstract. The temporal and spatial behaviour of the ionospheric parameters foF2 and h F during isolated substorms are examined using data from ionospheric stations distributed across Europe and western Asia. The main purpose is finding the forerunners of the substorm disturbances and a possible prediction of these disturbances. During the period from March 1998 to March 1999, 41 isolated substorms with intensities I = 60 − 400 nT were identified and studied. The study separated occasions when the local magnetometers were affected by the eastward electrojet (positive substorms) from those influenced by the westward electrojet (negative substorms). The deviations of the ionospheric parameters from their monthly medians ( foF2 and h F) have been used to determine the variations through the substorm. Substorm effects occurred simultaneously (< 1 h) across the entire observatory network. For negative substorms, foF2-values increase > 6 h before substorm onset, T o , reaching a maximum 2-3 h before T o . A second maximum occurs 1-2 h after the end of the substorm. The h F values 3-4 h before T o have a small minimum but then increase to a maximum at T o . There is a second maximum at the end of the expansion phase before δh F drops to a minimum 2-3 h after ending the expansion phase. For positive substorms, the timing of the first maximum of the δfoF2 and δh F values depends on the substorm length -if it is longer, the position is closer to T o . The effects on the ionosphere are significant: foF2 and h F reach 2-3 MHz (δfoF2 = 50-70% from median value) and 50-70 km (δ h F = 20-30% from median value), respectively. Regular patterns of occurrence ahead of the first substorm signature on the magnetometer offer an excellent possibility to improve short-term forecasting of radio wave propagation conditions.

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Section: Introductionmentioning

confidence: 99%

Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99

2003

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“…We will adhere to this standpoint, though it is known that a storm is not necessarily a set of substorms. Blagoveshchensky et al (1992Blagoveshchensky et al ( , 1996Blagoveshchensky et al ( , 2000 and Blagoveshchensky and Borisova (2000) have considered substorm effect on the ionosphere which is called the main effect (ME). They suggest that there are three main components that affect the variations of ionospheric parameters.…”

Section: The Main Effect On Mofmentioning

confidence: 99%

“…Thus it is very important to understand the physical mechanisms of these disturbances, so that forecasting can be more reliable and appropriate mitigation and adaption strategies adopted. Blagoveshchensky et al (1992Blagoveshchensky et al ( , 1996Blagoveshchensky et al ( , 2000Blagoveshchensky et al ( , 2006) determined the impact of moderate geomagnetic substorms (AE max =100-600 nT) on the ionosphere and HF radio propagation on mid-latitude and subpolar radio paths. This paper presents the analysis of the impact of intense geomagnetic storms (AE max =800-2000 nT) on HF radio propagation at high latitudes on several high latitude HF radio paths in north-west Russia.…”

Section: Introductionmentioning

confidence: 99%

Space weather effects on radio propagation: study of the CEDAR, GEM and ISTP storm events

2008

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Abstract. The impact of 14 geomagnetic storms from a list of CEDAR, GEM and ISTP storms, that occurred during 1997-1999, on radio propagation conditions has been investigated. The propagation conditions were estimated through variations of the MOF and LOF (the maximum and lowest operation frequencies) on three high-latitude HF radio paths in north-west Russia. Geophysical data of D st , B z , AE as well as some riometer data from Sodankyla observatory, Finland, were used for the analysis. It was shown that the storm impact on the ionosphere and radio propagation for each storm has an individual character. Nevertheless, there are common patterns in variation of the propagation parameters for all storms. Thus, the frequency range =MOF−LOF increases several hours before a storm, then it narrows sharply during the storm, and expands again several hours after the end of the storm. This regular behaviour should be useful for the HF radio propagation predictions and frequency management at high latitudes. On the trans-auroral radio path, the time interval when the signal is lost through a storm (t des ) depends on the local time. For the day-time storms an average value t des is 6 h, but for night storms t des is only 2 h. The ionization increase in the F2 layer before storm onset is 3.5 h during the day-time and 2.4 h at night. Mechanisms to explain the observed variations are discussed including some novel possibilities involving energy input through the cusp.

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“…Lateral signal reflections, backscatter, quick fading of signals at a receiving point, and unusual modes of propagation are observed. However, geomagnetic disturbances occurring in the auroral and subauroral ionosphere of the Earth, lead to even more complicated (anomalous) conditions of HF radio propagation in the subpolar regions (Blagoveshchensky and Zherebtsov, 1987;Blagoveshchensky and Borisova, 2000;Blagoveshchensky et al, 1996Blagoveshchensky et al, , 2005bMilan et al, 1998Milan et al, , 1996. This happened because there are additional small-and large-scale irregularities of the ionosphere during magnetospheric storms and substorms, (Blagoveshchensky et al, 2003a(Blagoveshchensky et al, , 2003bBuonsanto, 1999;Gonzalez et al, 1994;Lastovicka, 2002;Lyons, 1996).…”

Section: Introductionmentioning

confidence: 99%

“…To begin with there are effects of signal amplitude growth and azimuth variations during substorms on different radio paths. Relevant investigations were presented in (Blagoveshchensky and Borisova, 2000;Blagoveshchensky et al, 2005Blagoveshchensky et al, , 1996. It has been found experimentally that the effect of amplitude growth and azimuth variations take place on both short (one-hop) and long (multi-hop) highlatitude paths.…”

Section: Introductionmentioning

confidence: 99%

Irregular HF radio propagation on a subauroral path during magnetospheric substorms

2006

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Abstract. The impact of the main ionospheric trough, sporadic structures, gradients and inhomogeneities of the subpolar ionosphere during substorms on the signal amplitude, azimuthal angles of arrival, and propagation modes for the radio path Ottawa (Canada)-St. Petersburg (Russia) was considered. This subauroral path with the length of about 6600 km has approximately an east-west orientation. The main goals are to carry out numerical modeling of radio propagation for the path and to compare the model calculations with experimental results. Wave absorption and effects of focusing and divergence of rays were taken into consideration in the radio wave modeling process. The following basic results were obtained: The signal amplitude increases by 20-30 dB 1-1.5 h before the substorm expansion phase onset. At the same time the signal azimuth deviates towards north of the great circle arc for the propagation path. Compared with quiet periods there are effects due to irregularities and gradients in the area of the polar edge of the main ionospheric trough on the passing signals. Propagation mechanisms also change during substorms. The growth of signal amplitude before the substorm can be physically explained by both a decrease of the F2-layer ionization and a growth of the F2-layer height that leads to a decrease of the signal field divergence and to a drop of the collision frequency. Ionospheric gradients are also important. This increase of signal level prior to a substorm could be used for forecasting of space weather disturbed conditions.

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Substorm effects of ionosphere and HF propagation

Cited by 25 publications

References 13 publications

Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99

Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99

Space weather effects on radio propagation: study of the CEDAR, GEM and ISTP storm events

Irregular HF radio propagation on a subauroral path during magnetospheric substorms

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