The causes of recurrent geomagnetic storms

Burlaga, L. F.; Lepping, R. P.

doi:10.1016/0032-0633(77)90090-3

Cited by 101 publications

(65 citation statements)

References 49 publications

(43 reference statements)

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“…, 1974. The C9 index, as illustrated by Burlaga and Lepping (1978), showed no discontinuities during this period, justifying the assumption made here that the coronal structures, and by inference interplanetary streams,remained largely unchanged for the whole period of observation.…”

Section: Radial Variation Of Electron Densities and Temperaturessupporting

confidence: 79%

“…These observations were made continuously during a period of 80 days, or about 2^ solar rotation periods, during which the spacecraft moved from a heliocentric distance of 0.85 to 0.45 AU. There were well-marked repetitive corotating high speed streams and rarefactions during this time, and the characte:istic density variations (Burlaga et al, 1978) were observed. The electron distribution function observed for electrons propagating toward the sun :almost always has a suprathermal (halo) population distinguishable from the thermal (core) population, as has been observed on other satellites in earth orbit for some years (Montgomery et al, 1968).…”

Section: Introductionmentioning

confidence: 78%

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The radial gradients and collisional properties of solar wind electrons

Ogilvie¹,

Scudder²

1978

J. Geophys. Res.

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The plasma instrument on Mariner 10 carried out measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. Owing to the stable coronal configuration and low solar activity during the period of observation (January 9 to March 30, 1974), the radial variations of these quantities could be obtained. The power law exponent of the core temperature was determined to be ‐0.3 ± 0.04, and the halo temperature was found to be almost independent of heliocentric distance. The exponent of the power law for the density variation was 2.5 ± 0.2, and the extrapolated value at 1 AU was consistent with measured values during the same period. Calculations of the core electron Coulomb collision time and the core‐halo equipartition time were made as a function of radial distance. These measurements indicate a macroscale picture of a Coulomb collisional core and a collisionless isothermal halo. Extrapolating back to the sun, core and halo temperatures become equal at a radial distance of ∼2–15 RS. Temperature variations were observed at the time of passage of high‐speed streams, and at the time of observation of stream interfaces, where the density falls before the temperature, Coulomb collisions in the core become much less important, and the halo density is observed to decrease by more than an order of magnitude.

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Section: Radial Variation Of Electron Densities and Temperaturessupporting

confidence: 79%

Section: Introductionmentioning

confidence: 78%

The radial gradients and collisional properties of solar wind electrons

Ogilvie¹,

Scudder²

1978

J. Geophys. Res.

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“…It is evident however, that the stream fields, though increasing, have continued to be at low levels during the rise of cycle 24, and 4 years into the cycle have barely reached the lowest levels detected since observations began. Geomagnetic activity associated with streams is typically associated with intermittent intervals of southward fields associated with large amplitude Alfvénic fluctuations (e.g., Burlaga & Lepping 1977;Tsurutani et al 2006; and references therein). The weaker fields imply that such southward fields are also likely to be reduced during the rise of cycle 24, resulting in lower levels of geomagnetic activity associated with corotating streams.…”

Section: Geoeffectiveness Of Corotating Streamsmentioning

confidence: 99%

Geomagnetic activity during the rising phase of solar cycle 24

Richardson

2013

J. Space Weather Space Clim.

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As previous studies have shown, geomagnetic activity during the solar minimum following solar cycle 23 was at low levels unprecedented during the space era, and even since the beginning of the K p index in 1932. Here, we summarize the characteristics of geomagnetic activity during the first 4 years of cycle 24 following smoothed sunspot minimum in December, 2008, and compare these with those of similar periods during earlier cycles going back to the start of K p (cycles 17-23). The most outstanding feature is the continuing low levels of geomagnetic activity that are well below those observed during the rising phases of the other cycles studied. Even 4 years into cycle 24, geomagnetic storm rates are still only comparable to or below the rates observed during activity minima in previous cycles. We note that the storm rate during the rising phases of cycles 17-23 was correlated with the peak sunspot number (SSN) in the cycle. Extrapolating these results to the low storm rates in cycle 24 suggests values of the peak SSN in cycle 24 that are consistent with the NOAA Space Weather Prediction Center prediction of 90 ± 10, indicating that cycle 24 is likely to be the weakest cycle since at least 1932. No severe (Dst < À200 nT) storms have been observed during the first 4 years of cycle 24 compared with 4 in the comparable interval of cycle 23, and only 10 intense (Dst < À100 nT) storms, compared with 21 in cycle 23. These storms were all associated with the passage of Interplanetary Coronal Mass Ejections (ICMEs) and/or their associated sheaths. The lack of strong southward magnetic fields in ICMEs and their sheaths, their lower speeds close to the average solar wind speed, a~20% reduction in the number of ICMEs passing the Earth, and weaker than normal fields in corotating highspeed streams, contribute to the low levels of geomagnetic storm activity in the rise phase of cycle 24. However, the observation of an ICME with strong southward fields at the STEREO A spacecraft on July 24, 2012, which would have been highly geoeffective had it encountered the Earth, demonstrates that strong geomagnetic storms may still occur during weak solar cycles.

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“…It is well known that they play a crucial role in disturbing the space environment as they propagate into the interplanetary medium and interact with the Earth's magnetic field producing strong geomagnetic storms (Allen 1944;Burlaga & Lepping 1977;Gosling et al 1990;Crooker & McAllister 1997;Srivastava & Venkatakrishnan 2002, 2004Srivastava et al 2009). An ability to track a CME through the heliosphere would give a far better estimate of the arrival time, the mass, and the structure of the event as the CME passes over the Earth (Harrison et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Combining STEREO SECCHI COR2 and HI1 images for automatic CME front edge tracking

Kirnosov

Chang

Pulkkinen

2016

J. Space Weather Space Clim.

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COR2 coronagraph images are the most commonly used data for coronal mass ejection (CME) analysis among the various types of data provided by the STEREO (Solar Terrestrial Relations Observatory) SECCHI (Sun-Earth Connection Coronal and Heliospheric Investigation) suite of instruments. The field of view (FOV) in COR2 images covers 2-15 solar radii (Rs) that allow for tracking the front edge of a CME in its initial stage to forecast the lead-time of a CME and its chances of reaching the Earth. However, estimating the lead-time of a CME using COR2 images gives a larger lead-time, which may be associated with greater uncertainty. To reduce this uncertainty, CME front edge tracking should be continued beyond the FOV of COR2 images. Therefore, heliospheric imager (HI1) data that covers 15-90 Rs FOV must be included. In this paper, we propose a novel automatic method that takes both COR2 and HI1 images into account and combine the results to track the front edges of a CME continuously. The method consists of two modules: pre-processing and tracking. The pre-processing module produces a set of segmented images, which contain the signature of a CME, for both COR2 and HI1 separately. In addition, the HI1 images are resized and padded, so that the center of the Sun is the central coordinate of the resized HI1 images. The resulting COR2 and HI1 image set is then fed into the tracking module to estimate the position angle (PA) and track the front edge of a CME. The detected front edge is then used to produce a height-time profile that is used to estimate the speed of a CME. The method was validated using 15 CME events observed in the period from January 1, 2008 to August 31, 2009. The results demonstrate that the proposed method is effective for CME front edge tracking in both COR2 and HI1 images. Using this method, the CME front edge can now be tracked automatically and continuously in a much larger range, i.e., from 2 to 90 Rs, for the first time. These improvements can greatly help in making the quantitative CME analysis more accurate and have the potential to assist in space weather forecasting.

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The causes of recurrent geomagnetic storms

Abstract: We studied the causes of recurrent geomagnetic activity by analyzing

Cited by 101 publications

References 49 publications

The radial gradients and collisional properties of solar wind electrons

The radial gradients and collisional properties of solar wind electrons

Geomagnetic activity during the rising phase of solar cycle 24

Combining STEREO SECCHI COR2 and HI1 images for automatic CME front edge tracking

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