JOP167 Evolution and dynamics of the ionosphere

AUTHORS:
J. Lilensten, M. Kretzschmar (Grenoble Observatory, France), J. Aboudarham
(Meudon Observatory, France)

PARTICIPATING INSTRUMENTS:
SOHO instruments: EIT, SUMER, CDS
Other instruments: EISCAT, SuperDARN

SCIENTIFIC OBJECTIVE AND JUSTIFICATION:
The Earth ionosphere originates in two solar sources:
1) the EUV - XUV flux is energetic enough to ionize the thermospheric gaz
above about 80 km
2) the solar wind accelerated in the magnetosphere precipitates in the
auroral oval and gives birth to the high latitude ionosphere
 
At ground, the high latitude ionosphere is observed by two different
techniques
1) the coherent radars (i.e. SuperDARN in this proposal) give access to the
large scale dynamics
2) the incoherent radars (i.e. EISCAT in this proposal) give access to the
local densities, temperatures and velocities
 
A large effort of modeling has been performed in the last years in our teams
in different directions
1) The solar EUV - XUV spectrum has been modeled using two different
techniques involving SUMER and / or EIT observations (Kretzschmar et al.,
2001, Kretzschmar, 2002)
2) The Earth ionosphere modeling has been compared to the ground based
observations (Diloy et al., 1996, Blelly et al., 1996, Witasse et al., 1999,
Lilensten and Blelly, 2002, Lilensten and Cander, 2003). In any ionospheric
model, the unknowns are the solar inputs and the atmospheric composition and
temperature.

The present JOP proposal aims at building a coordinated campaign experiment
between SOHO, SuperDARN and EISCAT.
- We need EIT standard full Sun images. The choice of the wavelength is made
to deduce the differents parts of the sun covered by "quiet areas", coronal
holes, and active areas. From the reference spectra that we have built for
each zone, we will deduce a full sun EUV - XUV flux.
- As it is not possible to observe anymore the solar disc, it would be very
valuable if SUMER could observe the solar limb over a quiet sun area. We
therefore need to avoid the presence of prominences. Then, we could
calibrate our reference spectrum and reach a much better precision.
- Observations with CDS would be also very useful in order to extend our
reference spectra to higher temperatures. The target will be a quiet Sun
area.
- This flux will be used in the ionospheric model to compute the electron
and ion densities, temperatures and velocities.
- A ground based campaign will be running both EISCAT and SuperDARN. Their
observations will be compared to the model. >From the descrepancies, we will
deduce a correction to the thermospheric models.

This will be of particular interrest in case if a major eruption of CME,
giving birth to a magnetic storm in the Earth's atmosphere. Then, we would
"see" the modification of the ionosphere and the thermosphere due to the
enhancement of the EUV spectrum and some hours later, the modifications in
the composition and dynamics due to the particles.

References:
* Diloy P.Y., A. Robineau, J. Lilensten, P.L. Blelly and J. Fontanari, A
numerical model of the ionosphere including the E-region above EISCAT, Ann.
geophysicæ, 14, 191-200,1996.
* Blelly, P-L, J. Lilensten, A. Robineau, J. Fontanari, and D. Alcaydé,
Calibration of a numerical ionospheric model using EISCAT data : effect of
the neutral atmosphere and the suprathermal electrons on the ionospheric
plasma structure, Ann. geophysicæ, 14, 1375-1390,1996
* O. Witasse, J. Lilensten, C. Lathuillere and P.L. Blelly , Modeling the OI
630.0 and 557.7 nm thermospheric dayglow during EISCAT-WINDII coordinated
measurements, J. Geophys. Res., 104, 24639-24655, 1999.
* M. Kretzschmar, J. Lilenten and J. Aboudarham, Modeling the solar EUV flux
: on the variability of the EUV emission as measured by SUMER,
SOLSPA-Euroconference : solar cyle and space weather, ESA SP Series (SP
477), p 237-240, Naples, September 2001
* M. Kretzschmar, PhD Thesis, Universite Joseph Fourier, Grenoble, December
2002
* J. Lilensten and P.L. Blelly, The TEC and F2 parameters as tracers of the
ionosphere and thermosphere, JASTP, 64, 775-793, 2002
* J Lilensten, Lj R Cander , Calibration of the TEC derived from GPS
measurements and from ionospheric models using the EISCAT radar, accepted in
JASTP, 2003

OPERATIONAL CONSIDERATIONS:
Due to the available observing time with EISCAT and SuperDARN, we need SOHO
observations between the 20th of may to the 23d of may, as continuous as
possible.
The target for SUMER is any region above a quiet Sun area (avoiding
prominences) and above a coronal hole.
The target for CDS is to get spectra of 3 different solar zones: quiet Sun,
coronal hole and active region.

DETAILED OBSERVING SEQUENCES PER INSTRUMENT
EIT: Best wavelengths would be 171 and/or 284 A, at least every two hours;
if possible, both wavelengths.
SUMER: First order with detector B, image format: 1024x120, in the range
742-784 A, in order to cover a temperature range between 10^4 and 10^6 K
(lines: N I, N II, N III, S IV, N IV, O V, Ne VIII, Mg VIII, Mg IX).
Exposure time is not critical.
CDS: GIS mode, in the range 170-221 A, including Fe IX to Fe XVI lines,
covering temperatures from 10^6 to 10^6.5 K. Exposure time is not critical.
If there is enough time available, it would be interesting to have an
undersampled image of the solar disk.

PROPOSED OBSERVATION DATES AND TARGET:
From the 20th of may to the 23d of may, as continuously as possible.