<i>The Solar–Terrestrial Environment</i>

Hargreaves, J. K.; Siscoe, G. L.

doi:10.1063/1.2807625

Cited by 123 publications

(140 citation statements)

References 0 publications

Supporting

Mentioning

136

Contrasting

Unclassified

Order By: Relevance

“…and thus during daylight hours the electron density at the Eregion peak depends roughly on T −0.25 (Brekke, 1997;Hargreaves, 1992). From Eqs.…”

Section: Discussionmentioning

confidence: 90%

Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)

Hall¹,

Brekke²,

Cannon³

2007

Ann. Geophys.

View full text Add to dashboard Cite

Abstract.We have examined the long time series of observations of E-region virtual height and critical frequency hitherto made by the Tromsø ionosonde at 70 • N, 19 • E. Combining a simplistic trend analysis with a rigorous treatment of errors we identify a negative trend in critical frequency. While a similar analysis of the virtual height h E also suggests a negative trend, a closer examination reveals a possible weak positive trend prior to ∼1975 and a strong negative trend from ∼1975 to present. These two metrics of essentially the same feature of the ionosphere do not exhibit the same signature since critical frequency is controlled by photochemistry within the E-layer while height is controlled by pressure level. We further find that the trend in critical frequency is a daylight/summer phenomenon, no significant trend being evident in the winter subset of the data. On the other hand, the trends in virtual height are independent of season/daylight.

show abstract

“…and thus during daylight hours the electron density at the Eregion peak depends roughly on T −0.25 (Brekke, 1997;Hargreaves, 1992). From Eqs.…”

Section: Discussionmentioning

confidence: 90%

Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)

Hall¹,

Brekke²,

Cannon³

2007

Ann. Geophys.

View full text Add to dashboard Cite

show abstract

“…The angular distribution of the protons is assumed to be isotropic over the upper atmosphere, which is valid close to the Earth [Hargreaves, 1992]. An SIC modeling run has also been undertaken without any proton forcing (i.e., zero proton fluxes), reasonable at Halley for low K p conditions.…”

Section: Nighttime Riometer Absorption Using the Sodankylä Ion And Nementioning

confidence: 99%

Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy

et al. 2007

View full text Add to dashboard Cite

[1] In the polar atmosphere, significant chemical and ionization changes occur during solar proton events (SPEs). The access of solar protons to this region is limited by the dynamically changing geomagnetic field. In this study, we have used riometer absorption observations to investigate the accuracy of a model to predict K p -dependent geomagnetic rigidity cutoffs, and hence the changing proton fluxes. The imaging riometer at Halley, Antarctica is ideally situated for such a study, as the rigidity cutoff sweeps back and forth across the instrument's field of view, providing a severe test of the rigidity cutoff model. Using observations from this riometer during five solar proton events, we have confirmed the basic accuracy of this rigidity model. However, we find that the model can be improved by setting a lower K p limit (i.e., K p = 5 instead of 6) at which the rigidity modeling saturates. We also find that, for L > 4.5, the apparent L-shell of the beam moves equatorward. In addition, the Sodankylä Ion and Neutral Chemistry (SIC) model is used to determine an empirical relationship between integral proton precipitation fluxes and nighttime ionosphere riometer absorption, in order to allow consideration of wintertime SPEs. We find that during the nighttime, the proton flux energy threshold is lowered to include protons with energies of >5 MeV in comparison with >10 MeV for the daytime empirical relationships. In addition, we provide an indication of the southern and northern geographic regions inside which SPEs play a role in modifying the neutral chemistry of the stratosphere and mesosphere.Citation: Clilverd, M. A., C. J. Rodger, T. Moffat-Griffin, and P. T. Verronen (2007), Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy,

show abstract

“…The dispersed signature results from electrons with different energies orbiting at different velocities away from the injection region; the drift velocity of a particle is directly proportional to its energy (e.g. Hargreaves, 1992). Both satellites show evidence of a second enhancement in electron flux at ∼14:53 UT.…”

Section: Observations Of the Sscmentioning

confidence: 99%

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

et al. 2007

View full text Add to dashboard Cite

Abstract. The arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ∼09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLO-RIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (P dyn ) were identified. A number of increases in P dyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs.

show abstract

The Solar–Terrestrial Environment

Cited by 123 publications

References 0 publications

Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)

Climatic trends in E-region critical frequency and virtual height above Tromsø (70° N, 10° E)

Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy

The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005

Contact Info

Product

Resources

About