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Two states of magnetotail dipolarization fronts: A statistical study.

Schmid D, Nakamura R, Plaschke F, Volwerk M, Baumjohann W - J Geophys Res Space Phys (2015)

Bottom Line: Earlier studies concluded that on average, the temperature increases while the density decreases across the DF.Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B).We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change.

View Article: PubMed Central - PubMed

Affiliation: Space Research Institute, Austrian Academy of Sciences Graz, Austria ; University of Graz, NAWI Graz Graz, Austria.

ABSTRACT

We study the ion density and temperature in the predipolarization and postdipolarization plasma sheets in the Earth's magnetotail using 9 years (2001-2009) of Cluster data. For our study we selected cases when Cluster observed dipolarization fronts (DFs) with an earthward plasma flow greater than 150km/s. We perform a statistical study of the temperature and density variations during the DF crossings. Earlier studies concluded that on average, the temperature increases while the density decreases across the DF. Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B). We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change. Both categories are associated with earthward plasma flows but with some difference: (1) category A flows are faster than category B flows, (2) the observations indicate that category B flows are directed perpendicular to the current in the near-Earth current sheet while category A flows are tilted slightly duskward from this direction, and (3) the background B z of category B is higher than that of category A. Based on these results, we hypothesize that after reconnection takes place, a bursty bulk flow emerges with category A characteristics, and as it travels earthward, it further evolves into category B characteristics, which is in a more dipolarized region with slower plasma flow (closer to the flow-braking region).

No MeSH data available.


(top) XY and (bottom) YZ position of Cluster during the observations of the 303 DF events. The colors mark the four different categories with respect to the temperature and density ratio before and after the DF crossing.
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fig02: (top) XY and (bottom) YZ position of Cluster during the observations of the 303 DF events. The colors mark the four different categories with respect to the temperature and density ratio before and after the DF crossing.

Mentions: The distribution of the 303 SSOs on the XY GSM and YZ GSM planes are shown in Figure 2.


Two states of magnetotail dipolarization fronts: A statistical study.

Schmid D, Nakamura R, Plaschke F, Volwerk M, Baumjohann W - J Geophys Res Space Phys (2015)

(top) XY and (bottom) YZ position of Cluster during the observations of the 303 DF events. The colors mark the four different categories with respect to the temperature and density ratio before and after the DF crossing.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497466&req=5

fig02: (top) XY and (bottom) YZ position of Cluster during the observations of the 303 DF events. The colors mark the four different categories with respect to the temperature and density ratio before and after the DF crossing.
Mentions: The distribution of the 303 SSOs on the XY GSM and YZ GSM planes are shown in Figure 2.

Bottom Line: Earlier studies concluded that on average, the temperature increases while the density decreases across the DF.Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B).We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change.

View Article: PubMed Central - PubMed

Affiliation: Space Research Institute, Austrian Academy of Sciences Graz, Austria ; University of Graz, NAWI Graz Graz, Austria.

ABSTRACT

We study the ion density and temperature in the predipolarization and postdipolarization plasma sheets in the Earth's magnetotail using 9 years (2001-2009) of Cluster data. For our study we selected cases when Cluster observed dipolarization fronts (DFs) with an earthward plasma flow greater than 150km/s. We perform a statistical study of the temperature and density variations during the DF crossings. Earlier studies concluded that on average, the temperature increases while the density decreases across the DF. Our statistical results show a more diverse picture: While ∼54% of the DFs follow this pattern (category A), for ∼28% the temperature decreases while the density increases across the DF (category B). We found an overall decrease in thermal pressure for category A DFs with a more pronounced decrease at the DF duskside, while DFs of category B showed no clear pattern in the pressure change. Both categories are associated with earthward plasma flows but with some difference: (1) category A flows are faster than category B flows, (2) the observations indicate that category B flows are directed perpendicular to the current in the near-Earth current sheet while category A flows are tilted slightly duskward from this direction, and (3) the background B z of category B is higher than that of category A. Based on these results, we hypothesize that after reconnection takes place, a bursty bulk flow emerges with category A characteristics, and as it travels earthward, it further evolves into category B characteristics, which is in a more dipolarized region with slower plasma flow (closer to the flow-braking region).

No MeSH data available.