IMF Draping Direction at Mars
This page contains information and files related to the determination of the
draping direction of the IMF, detected at 400 km altitudes on the Martian
dayside by MGS MAG/ER.
-
Draping direction determination
Draping direction is calculated on an orbit-by-obit basis using MGS data
from time periods when the spacecraft was above 50-60 N planetary
latitude on the Martian dayside. We use this small latitude range in an
attempt to minimize the contaminating effects of crustal magnetic fields,
which are weakest in this latitude band. Draping direction is reported
as the median azimuth angle from each orbit, with 0o pointing
locally Eastward from the spacecraft, and 90o pointing locally
Northward.
We have tried several other methods of determining draping direction -
all have strengths and weaknesses. In the future we may include the
results of some of these other methods on this page.
Some science-related discussion of the IMF draping direction can be found
in a manuscript in Icarus by Brain, Mitchell, and Halekas - accessible here.
-
Important Caveats
- IMF direction can change on any timescale, from seconds to
minutes to hours to days. Therefore, determination of the
direction of the ambient magnetic field between 50-60 N latitude
on the dayside may not provide a reliable indication of the IMF
direction over an entire MGS 2-hour orbital period. Please use
appropriate caution when using the information on this
page.
- We do not believe that IMF draping direction is accurate to more
than ~90o, due to contributions of ionospheric
current-generated magnetic fields to the ambient field measured
at 400 km altitudes by MGS. Further, anti-solar "weathervaning"
of the ambient magnetic field is observed more prominently for
one set of IMF directions (dawnward upstream IMF).
- Keep in mind that Mars "rocks" back and forth with respect to the
Sun over the course of a single year, and therefore the azimuth
angle (which is defined relative to the planetary rotation axis)
rocks back and forth by as much as 25o as
well.
- I use only publicly available MGS data, since those data have
been fully calibrated. Therefore, the timeseries will usually be
several months "behind" the current date. You can always email
me to see whether the page is as up-to-date as possible.
-
Draping Directions
Most Recent Update: 15 November 2006
