Factors affecting the geoeffectiveness of shocks and sheaths at 1 AU

Lugaz, Noé; Farrugia, C. J.; Winslow, R. M.; Al-Haddad, Nada; Kilpua, Emilia; Riley, Pete

doi:10.1002/2016ja023100

Cited by 77 publications

(73 citation statements)

References 90 publications

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“…The shock/compression time usually indicates the beginning of the storm initial phase, when S Y M ‐ H goes up, whereas the IMF B z rotating southward time indicates the beginning of the storm main phase, when S Y M ‐ H starts to decrease. The amount of energy deposited in the upper atmosphere high‐latitude regions by the latter is typically larger than the amount of energy deposited by the former due to its higher geoeffectiveness (Lugaz et al, ; Shen et al, ).…”

Section: Resultsmentioning

confidence: 99%

Thermosphere Global Time Response to Geomagnetic Storms Caused by Coronal Mass Ejections

et al. 2017

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We investigate, for the first time with a spatial superposed epoch analysis study, the thermosphere global time response to 159 geomagnetic storms caused by coronal mass ejections (CMEs) observed in the solar wind at Earth's orbit during the period of September 2001 to September 2011. The thermosphere neutral mass density is obtained from the CHAMP (CHAllenge Mini‐Satellite Payload) and GRACE (Gravity Recovery Climate Experiment) spacecraft. All density measurements are intercalibrated against densities computed by the Jacchia‐Bowman 2008 empirical model under the regime of very low geomagnetic activity. We explore both the effects of the pre‐CME shock impact on the thermosphere and of the storm main phase onset by taking their times of occurrence as zero epoch times (CME impact and interplanetary magnetic field Bz southward turning) for each storm. We find that the shock impact produces quick and transient responses at the two high‐latitude regions with minimal propagation toward lower latitudes. In both cases, thermosphere is heated in very high latitude regions within several minutes. The Bz southward turning of the storm onset has a fast heating manifestation at the two high‐latitude regions, and it takes approximately 3 h for that heating to propagate down to equatorial latitudes and to globalize in the thermosphere. This heating propagation is presumably accomplished, at least in part, with traveling atmospheric disturbances and complex meridional wind structures. Current models use longer lag times in computing thermosphere density dynamics during storms. Our results suggest that the thermosphere response time scales are shorter and should be accordingly adjusted in thermospheric empirical models.

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Section: Resultsmentioning

confidence: 99%

Thermosphere Global Time Response to Geomagnetic Storms Caused by Coronal Mass Ejections

et al. 2017

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“…Further, Lugaz et al . [] found that geoeffective shock sheaths may consist of two populations: (1) those associated with shocks within transients, that is ICME‐ICME or ICME‐corotating interaction region interactions, and (2) shock sheaths associated with isolated ICMEs that we have investigated in the study. They found the former populations to be more effective storm producers.…”

Section: Discussionmentioning

confidence: 97%

Thermospheric nitric oxide response to shock‐led storms

et al. 2017

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We present a multiyear superposed epoch study of the Sounding of the Atmosphere using Broadband Emission Radiometry nitric oxide (NO) emission data. NO is a trace constituent in the thermosphere that acts as cooling agent via infrared (IR) emissions. The NO cooling competes with storm time thermospheric heating, resulting in a thermostat effect. Our study of nearly 200 events reveals that shock‐led interplanetary coronal mass ejections (ICMEs) are prone to early and excessive thermospheric NO production and IR emissions. Excess NO emissions can arrest thermospheric expansion by cooling the thermosphere during intense storms. The strongest events curtail the interval of neutral density increase and produce a phenomenon known as thermospheric “overcooling.” We use Defense Meteorological Satellite Program particle precipitation data to show that interplanetary shocks and their ICME drivers can more than double the fluxes of precipitating particles that are known to trigger the production of thermospheric NO. Coincident increases in Joule heating likely amplify the effect. In turn, NO emissions are more than double. We discuss the roles and features of shock/sheath structures that allow the thermosphere to temper the effects of extreme storm time energy input and explore the implication these structures may have on mesospheric NO. Shock‐driven thermospheric NO IR cooling likely plays an important role in satellite drag forecasting challenges during extreme events.

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“…On the other hand, preferential occurrence of interplanetary shocks was found in July and November (Echer et al, ). So we examine solar wind and geomagnetic conditions during the great‐FEE days using the following parameters: the solar wind speed V as the best predictor of substorm probability (e.g., Newell et al, ) and as a factor influencing interplanetary shock parameters (e.g., Lugaz et al, ); a parameter of interplanetary electric field fluctuations VδB calculated by an expression VδB =

V \cdot \sqrt{(δ_{italicBz}^{2} + δ_{italicBy}^{2})}

, where

((), δ_{italicBz}^{2})

and

((), δ_{italicBy}^{2})

are variances of the IMF B z and B y components; and AL index of substorm activity.…”

Section: Discussionmentioning

confidence: 99%

Flux Enhancements of > 30 keV Electrons at Low Drift Shells L < 1.2 During Last Solar Cycles

Suvorova

2017

JGR Space Physics

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We present results of statistical analysis of enhancements of >30 keV electrons observed by the NOAA/POES satellites during solar cycles 23 and 24 (1998–2016) at low drift shells L < 1.2, so‐called forbidden zone. We collected 1,750 days (~25% of the total time) when fluxes of the forbidden energetic electrons (FEE) exceeded 103 (cm2 s sr)−1. We found 530 days, when FEE fluxes reached high intensity from 104 up to 107 (cm2 s sr)−1. It was found that the FEE enhancements were observed mostly often at the declining phases and solar minimum. More than 85% of the events occurred under fast solar wind (V > 450 km/s), high substorm activity (AL >150 nT), and enhanced interplanetary electric field perturbations (VδB > 1.5 mV/m). The FEE occurrence rate peaks around the local midnight. We have also found a quite unexpected annual variation of the FEE occurrence rate with a pronounced maximum from May to September, a minor peak in December–January, and minima at the equinoxes. The May–September peak, persisting at different solar cycle phases, was assumed to originate from high conductivity in the auroral ionosphere, which is controlled by the dipole tilt angle and provides better conditions for penetration of electric field perturbations into the inner magnetosphere. This allows explanation of the shape and amplitude of annual variation in the FEE occurrence rate from the convolution of the solar wind driver with the penetration conditions.

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Factors affecting the geoeffectiveness of shocks and sheaths at 1 AU

Cited by 77 publications

References 90 publications

Thermosphere Global Time Response to Geomagnetic Storms Caused by Coronal Mass Ejections

Thermosphere Global Time Response to Geomagnetic Storms Caused by Coronal Mass Ejections

Thermospheric nitric oxide response to shock‐led storms

Flux Enhancements of > 30 keV Electrons at Low Drift Shells L < 1.2 During Last Solar Cycles

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