July 27, 2015 to August 21, 2015
Nordita, Stockholm
Europe/Stockholm timezone

Statistics and accuracy of magnetic null identification

Aug 10, 2015, 4:10 PM
25m
FD5 (FD5)

FD5

FD5

Oral Workshop, August 10-14 Afternoon I

Speaker

Elin Eriksson (Swedish Institute of Space Physics, Uppsala, Sweden and Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden)

Description

Regions with vanishing magnetic field, also referred to as magnetic nulls, are of high interest in plasma physics. Near magnetic nulls particles become unmagnetized and can by interacting with electric fields be accelerated up to high energies. Magnetic nulls have been observed and studied before using in-situ observations for selected events. Here we present the first statistical study of magnetic nulls in the Earth's nightside magnetosphere. In addition we study how local disturbances in the magnetic field can affect the null type identification and we present a method to estimate the reliability of the null type identification. We study the magnetic nulls using full resolution data from the Cluster spacecraft when their maximum separation are less than one ion inertial length. This is fulfilled in 2003 when the spacecraft separation was approximately 200 km. The magnetic nulls are found using two methods: Poincaré index and Taylor Expansion. The use of Taylor Expansion allows us to find nulls outside the spacecraft tetrahedron volume. All together 25 time intervals containing magnetic nulls are found. We find most of the nulls in the magnetopause current sheet, but a few of them are found in the tail current sheet. We find the currents associated with each null and classify the types of the nulls. We present a detailed analysis of two typical examples of the observed nulls. The first one is from August 6, 2003 00:45:40.02 - 00:45:41.02 UT and the second is from October 28, 2003 04:16:01.0 - 04:16:02.0 UT. In both examples the spacecraft are in the magnetotail and observe magnetic nulls crossing the volume surrounding the spacecraft. In one of the events the type of the magnetic null is changed for a short moment during the crossing. We interpret this jump as being due to local disturbances in the magnetic field. We present a general method of how to estimate the effect local disturbances have on the null type identification. The obtained results are highly relevant for MMS studies of reconnection diffusion regions.

Primary author

Elin Eriksson (Swedish Institute of Space Physics, Uppsala, Sweden and Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden)

Co-authors

Andris Vaivads (Swedish Institute of Space Physics, Uppsala, Sweden) Mats André (Swedish Institute of Space Physics, Uppsala, Sweden) Volodymyr Khotyayintsev (Department of Theoretical Physics, Taras Shevchenko National University of Kyiv, Ukraine) Yuri Khotyaintsev (Swedish Institute of Space Physics, Uppsala, Sweden)

Presentation materials