Effect of sudden impulses on currents in the auroral ionosphere under northward interplanetary magnetic field conditions: A case study

Abstract

We examine the response of auroral magnetic records to the passage of an interplanetary shock at a time when the interplanetary magnetic field was northward. We restrict our attention solely to the sector within 3 hours of local magnetic midnight for a single case selected when a bursty bulk flow event was recorded in the near tail by ISEE 2. Over most of the nightside at high latitudes only a weak disturbance if any is seen. At lower latitudes a plateau is seen in the H component, coincident with the bursty bulk flow event. At 65° latitude from about midnight to 3:00 LT a weak pair of negative bays is observed, also coincident with the bursty bulk flow event. We conclude that the tail and the auroral ionosphere were closely coupled during this sudden impulse, but the auroral zone disturbance appears to be mainly the brief activation of a section of the auroral electrojet rather than a classic substorm. No expansion or motion of the electrojet was observed, and the activation was no longer than that of the bursty bulk flow in the tail.

Storm Sudden Commencements Without Interplanetary Shocks

“…They also investigated effects of speed and direction of IP shocks on SSC rise times and found that the faster IP shocks, the shorter the rising time of the SSC, and that significantly slanted IP shocks may lead to a delay in the rise of the SSC. Russell et al (1992Russell et al ( , 1994 have found that the square root of the dynamic pressure (P dyn ) of IP shocks has a high correlation with SSCs. They also found that the response differs according to the local time and the direction of the IMF.…”

Driven reconnection and bursty bulk flows

“…Present analysis indicates that the driven reconnection is a possible candidate for triggering the BBFs. The driving force can be either pressure pulses (Russel et al, 1994) or quasi-steady fluctuations in the solar wind. However, observational constraints on the driving force and subsequently on the fluctuation amplitude as well as features like the local organisation of BBF events should be incorporated in a self-consistent model and the present model does not include these features.…”

“…There have been various models proposed so far for the bursty bulk flows. Russel et al (1994) suggested that BBFs can be triggered by the sudden changes in solar wind dynamic pressure. Lakhina (1992Lakhina ( , 1996 proposed a mechanism for BBFs based on the bursty driven reconnection in the magnetotail.…”

Observations of solar wind directly driven auroral electrojets and gravity waves

“…The auroral electrojet has been observed for many years [Kisabeth and Rostoker, 1971;Akasofu, 1977]. It has been found that the auroral electrojet occurs in response to variations of solar wind pressure [Russell et al, 1994] and in association with magnetospheric particle precipitation [Sandholt et al, 1994].…”