an assessment of the nrlmsise-00 density thermosphere description in presence of space weather...
TRANSCRIPT
An assessment of the NRLMSISE-00 density thermosphere description in presence of
space weather events
C. Lathuillère and M. Menvielle
• The data and the method• Statistical analysis for year 2004• 8 larger events of 2004• Conclusion
STAR/CHAMP densities – May 3rd, 2003
Den
sitie
s (1
0-15
g.cm
-3)
The datato thesun
daytime and night time orbit sections are considered
separately
… between -50° and 50° in latitude, with a 1° sampling
rate with respect to the latitude
STAR/CHAMP densities – May 3rd, 2003
STAR atmosphere density along CHAMP trajectory at about 400 km altitude
Den
sitie
s (1
0-15
g.cm
-3) ~5:30 pm LT at equator
~5:30 am LT at equator
Inclination:87°
TOTAL MASS DENSITY at the satellite altitude (10-15 g/cm3) 10 LT 22 LT
The method: Running SVD analysis over 15 consecutive orbits (about 1 day)
The projection on the first component accounts for large scale variations: spatial variations are captured by the first principal component, and time variations are captured by the associated projection coefficient: C1.
Residuals account for smaller scales, as tides and gravity waves
Comparison with NRLMSISE-00 model
NRLMSIS:with MgII proxy and ap
CHAMP data
Normalized coefficient:
C1 CHAMP / C1 NRLMSIS_quietC1 NRLMSIS/ C1 NRLMSIS_quiet
NRLMSIS_quiet:with MgII proxy and Ap=4
MgII proxy: The composite MgII index (Viereck et al, 2004) is used as a proxy for solar EUV instead of F10.7
NRLMSIS_quiet is used as a reference, that accounts for LT, seasonal variations, solar activity…
- Statistical analysis: binning of normalized C1 coefficients as a function of ap
- Analysis of the height larger events
Day time Night time
x : CHAMP data
x : NRLMSIS model
correlation coefficient between CHAMP data and ap
ap index ap index
Den
sity
per
turb
atio
n
Binning is done using the value of ap from the previous 3 hour interval
x Day time
+ Night time
Linear fit
y =1.9 x – 0.9
x Day time
+ Night time
x Day time
+ Night time
Day and Night time with ap <100
x Day time
+ Night time
Day and Night with ap <100
Quadratic fit
y =1.92 x2 – 3 x + 2.14
Density perturbation: CHAMP data and NRLMSIS model
Day of 2004
ap magnetic index
Day time Night time
- the relative density increase is greatly underestimated by the model
- the model seems to correctly represent the shape of the perturbation
3 days
The perturbations appear later in the data than in the model and this timing discrepancy is slightly larger during night ( 3-4.5 hours) than during day time.
Density perturbation: CHAMP data and NRLMSIS model normalized to the amplitude of the data perturbation
Normalization factor mean value = 2.3
3 days
Conclusion
• NRLMSISE-00 correctly estimates the main features of the thermosphere density response to geomagnetic activity:
- the morphology of UT variations - the larger relative increase during night than during day time But it underestimates :
• the amplitude of the density response (by about a factor 2)• and its phase lag (up to 4.5 hours)
Altitudes about 400km. Latitudes between 50S and 50N