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Proposal ID Ruedi_119

Date of Proposal
97/07/16

firstname
Isabelle

lastname
Ruedi

institute
Institute for Astronomy

address
ETH-Zentrum
8092 Zurich
SWITZERLAND

email
ruedi@astro.phys.ethz.ch

phone
+41 - 1 - 632 3805

fax
+ 41 - 1 -632 1205

proposal
Sunspots are the seats of considerable dynamics. The most obvious
are the Evershed and inverse Evershed effects.

The Evershed effect is characterised by line shifts in the
penumbra and superpenumbra corresponding to a material outflow.
These velocities can reach values of 6 km/s and are almost
horizontal, following the magnetic field lines. Therefore they
can only be observed at a certain distance from disc centre where
the velocity vector has a significant component along the line of
sight. The magnitude of the observed velocities depends on the
spectral lines under consideration and is largest for the
spectral lines originating most deeply in the atmosphere.

In the chromosphere and lower transition region, the velocities
are directed outwards, this phenomenon is referred to as the
inverse Evershed effect. The flow is also almost horizontal above
the superpenumbra and becomes increasingly vertical towards the
umbra. Both subsonic and supersonic velocities are observed. The
subsonic velocities tend to increase with temperature, from less
than 5 km/s observed in O I to 40 km/s in O V. The supersonic
component is seen only in the transition region and is
approximately 100 km/s, independently of the temperature at which
it is observed. From the absence of supersonic flows at
chromospheric temperatures, it is expected that the flow shocks
at greater heights.

We propose to use SUMER and CDS to probe the Inverse Evershed
effect and dynamic phenomena associated with brightenings in the
sunspot or its superpenumbra, while MDI would in parallel provide
information on the normal Evershed effect and the general magnetic
structure of the sunspot and its surroundings. The different
observed lines should give us considerable information to
investigate the vertical and horizontal structure of these flows
and possibly allow the detection of shocks.

The EIT images will help to clarify the general structure of the
active region observed.

inside_collab
Joe Gurman

consortium
no

topic
Sunspots

topic
sunspots

title
Inverse Evershed Effect


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