About the relationship between auroral electrojets and ring currents

International audienceThe relationship between the storm-time ring current and the auroral electrojets is investigated using IMAGE magnetometer data, DSt and H-SYM, and solar wind data. Statistical results as well as the investigation of single events show that the auroral electrojets occur also during nonstorm conditions without storm-time ring current development and even during the storm recovery phase of increasing DSt. A close correlation between electrojet intensity and ring current intensity was not found. Though the eastward electrojet moves equatorward during the storm main phase there is no unequivocal relationship between the movement of the westward electrojet and the ring current development. All these results suggest that the auroral electrojets and the ring current develop more or less independently of each other

Magnetospheric convection from Cluster EDI measurements compared with the ground-based ionospheric convection model IZMEM

Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for more than seven and a half years (2001–2008) have been used to derive a statistical model of the high-latitude electric potential distribution for summer conditions. Based on potential pattern for different orientations of the interplanetary magnetic field (IMF) in the GSM y-z-plane, basic convection pattern (BCP) were derived, that represent the main characteristics of the electric potential distribution in dependence on the IMF. The BCPs comprise the IMF-independent potential distribution as well as patterns, which describe the dependence on positive and negative IMF<I>B<sub>z</sub></I> and IMF<I>B<sub>y</sub></I> variations. The full set of BCPs allows to describe the spatial and temporal variation of the high-latitude electric potential (ionospheric convection) for any solar wind IMF condition near the Earth's magnetopause within reasonable ranges. The comparison of the Cluster/EDI model with the IZMEM ionospheric convection model, which was derived from ground-based magnetometer observations, shows a good agreement of the basic patterns and its variation with the IMF. According to the statistical models, there is a two-cell antisunward convection within the polar cap for northward IMF<I>B<sub>z</sub></I>+≤2 nT, while for increasing northward IMF<I>B<sub>z</sub></I>+ there appears a region of sunward convection within the high-latitude daytime sector, which assumes the form of two additional cells with sunward convection between them for IMF<I>B<sub>z</sub></I>+≈4–5 nT. This results in a four-cell convection pattern of the high-latitude convection. In dependence of the ±IMF<I>B<sub>y</sub></I> contribution during sufficiently strong northward IMF<I>B<sub>z</sub></I> conditions, a transformation to three-cell convection patterns takes place

Characteristics of the electrojet during intense magnetic disturbances

Hall current variations in different time sectors during six magnetic storms from the summer seasons in 2003 and 2005 (Ritter, 2018) are examined, namely three storms in the day–night meridional sector and three storms in the dawn–dusk sector. The sequence of the phenomena, their structure and positions, and the strength of the polar (PE) and the auroral (AE) Hall electrojets were investigated using scalar magnetic field measurements obtained from the CHAllenging Minisatellite Payload (CHAMP) satellite in accordance with the study of Ritter et al. (2004a). We analyzed the correlations of the PE and AE as well as the obtained regression relations of the magnetic latitude MLat and the electrojet current intensity I with auroral and ring current activity, the interplanetary magnetic field, and the Newell et al. (2007) coupling function for the state of the solar wind. The following typical characteristics of the electrojets were revealed:The PE appears in the daytime sector at MLat&thinsp; ∼ 80°–73°, with a westward or an eastward direction depending on the interplanetary magnetic field (IMF) By component (By&thinsp; &lt; &thinsp;0&thinsp;nT or By&thinsp; &gt; &thinsp;0&thinsp;nT). Changes in the current flow direction in the PE can occur repeatedly during the storm, but only due to changes in the IMF By orientation. The PE increases with the intensity of the IMF By component from I ∼ 0.4&thinsp;A&thinsp;m−1 for By ∼ 0&thinsp;nT up to I ∼ 1.0&thinsp;A&thinsp;m−1 for By ∼ 23&thinsp;nT. The MLat position of the PE does not depend on the direction and intensity of the By component.There is no connection between MLat and I in the PE and the symmetric part of the magnetospheric ring current (index SymH). There is a correlation between I in the PE and the AsyH index, but only a very weak interconnection of this index with the MLat of the PE.Substorms occurring before the storm's main phase are accompanied by the appearance of an eastward electrojet (EE) at MLat&thinsp; ∼ 64° as well as that of a westward electrojet (WE). In the nighttime sector, a WE appears at MLat&thinsp; ∼ 64°. During the main phase both electrojets persist. The daytime EE and the nighttime WE shift toward sub-auroral latitudes of MLat&thinsp; ∼ 56° and grow in intensity up to I ∼ 1.5&thinsp;A&thinsp;m−1. The WE is then located about 6° closer to the pole than the EE during evening hours and about 2°–3° closer during daytime hours.</p

Recovery phase of magnetic storms induced by different interplanetary drivers

Statistical analysis of Dst behaviour during recovery phase of magnetic storms induced by different types of interplanetary drivers is made on the basis of OMNI data in period 1976-2000. We study storms induced by ICMEs (including magnetic clouds (MC) and Ejecta) and both types of compressed regions: corotating interaction regions (CIR) and Sheaths. The shortest, moderate and longest durations of recovery phase are observed in ICME-, CIR-, and Sheath-induced storms, respectively. Recovery phases of strong ($Dst_{min} < -100$ nT) magnetic storms are well approximated by hyperbolic functions $Dst(t)= a/(1+t/\tau_h)$ with constant $\tau_h$ times for all types of drivers while for moderate ($-100 < Dst_{min} < -50$ nT) storms $Dst$ profile can not be approximated by hyperbolic function with constant $\tau_h$ because hyperbolic time $\tau_h$ increases with increasing time of recovery phase. Relation between duration and value $Dst_{min}$ for storms induced by ICME and Sheath has 2 parts: $Dst_{min}$ and duration correlate at small durations while they anticorrelate at large durations.Comment: 18 pages, 4 figures, 2 tables, submitted to JGR special issue "Response of Geospace to High-Speed Streams

Self‐consistent modeling of the large‐scale distortions in the geomagnetic field during the 24–27 September 1998 major magnetic storm

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94715/1/jgra17531.pd

Quantifying the improvement of surrogate indices of hepatic insulin resistance using complex measurement techniques

We evaluated the ability of simple and complex surrogate-indices to identify individuals from an overweight/obese cohort with hepatic insulin-resistance (HEP-IR). Five indices, one previously defined and four newly generated through step-wise linear regression, were created against a single-cohort sample of 77 extensively characterised participants with the metabolic syndrome (age 55.6±1.0 years, BMI 31.5±0.4 kg/m2; 30 males). HEP-IR was defined by measuring endogenous-glucose-production (EGP) with [6–62H2] glucose during fasting and euglycemic-hyperinsulinemic clamps and expressed as EGP*fasting plasma insulin. Complex measures were incorporated into the model, including various non-standard biomarkers and the measurement of body-fat distribution and liver-fat, to further improve the predictive capability of the index. Validation was performed against a data set of the same subjects after an isoenergetic dietary intervention (4 arms, diets varying in protein and fiber content versus control). All five indices produced comparable prediction of HEP-IR, explaining 39–56% of the variance, depending on regression variable combination. The validation of the regression equations showed little variation between the different proposed indices (r2 = 27–32%) on a matched dataset. New complex indices encompassing advanced measurement techniques offered an improved correlation (r = 0.75, P<0.001). However, when validated against the alternative dataset all indices performed comparably with the standard homeostasis model assessment for insulin resistance (HOMA-IR) (r = 0.54, P<0.001). Thus, simple estimates of HEP-IR performed comparable to more complex indices and could be an efficient and cost effective approach in large epidemiological investigations