Transcript TIMED/GUVI Data for IRI IRI 2005

TIMED/GUVI Data for IRI
R. DeMajistre, L.J. Paxton, D. Bilitza and H.Kil
IRI 2005
GUVI for the ionosphere
• What is TIMED/GUVI
• Measurement methods for the nighttime
ionosphere
• Ionosonde validation
• Application – Calibration transfer
• GUVI and IRI
Motivation for future work and collaboration rather than final results
GUVI - Global UV Imager
• Scanning Spectrographic
Imager
• Covers 115-180 nm in 160
nm spectral bins
• 14 cross track spatial pixels
act as a linear array
TIMED Spacecraft
• High inclination circular
orbit, ~625 km altitude
• Covers all local times in
60 days
• Nightside passes ~25
degrees apart
Nightside measurements
4I   k[e][O  ]ds   k[e]2 ds
O+ + e
O + hn
at night
GUVI Colors
Dark at night
Dark at night
Dark at night
Dayside radiance
• GUVI ‘colors’ summed
on board – 5 bright FUV
spectral features
• Only 2 colors are
usually detected at night
• Color 3, 135.6 nm, due
almost entirely from F
region recombination
Disk Measurements
GUVI
• GUVI down-looking pixels
yield slant column
brightness through the F
Layer
• Can be converted to TEC
with some assumptions
about profile shape
• Very high spatial
resolution (~ 25x25 km)
reveals bubbles and
irregularities
Composite 135.6 nm
image for day 82, 2002
Limb Measurements
• First 32 steps of
each scan are on the
limb (100 – 520 km)
• Constrained linear
inversion yields
volume emission
rate/electron densities
Systematic monitoring of the nighttime F Region
Monitoring the Ionosphere
Coverage
• Altitude – Each scan, 150 – 500 km
• Latitude – Each orbit
• Longitude – Each day
• Local time – 60 days
• Over 3 years of data yields seasonal coverage as well
Limits
• Low signal levels away from the anomalies
• Assumption of spherical symmetry
• Recombination rate is uncertain
• Assumes one constituent ionosphere (O+)
Global Observations
• Electron densities can
be used to estimate
NMF2
• Coverage allows global
maps
• Orbit precession rate
allows inter-annual
comparisons
• Can be compared
directly with ionosonde
data or IRI
Ionosonde Comparisons
• GUVI electron density
profile fit with a Chapman
layer
• NMF2 and HMF2 taken
directly from the fit
• Same process can be
used with IRI
Ionosonde Data
Station
Juliusruh, Germany
Lat.
Long.
54.6
13.4
45
141
40.8
0.5
Kokubunji, Japan
35
139
Yamagawa, Japan
31
130
28.6
77.2
Okinawa, Japan
26
128
Waltair, India
17
83
Trivandrum, India
8.3
76.6
Sao Luis, Brazil
-2.3
315.8
Fortaleza, Brazil
-3.9
321.5
C. Paulista, Brazil
-22.7
315
B. Aires, Argentina
-34.6
301.7
Concepcion, Chile*
-36.8
287
-9.5
305.2
Wakkanai, Japan
Ebro, Spain
Delhi, India
Cachimbo, Brazil
• Ionosonde Data Supplied to from
the various stations
• Data from other stations was
supplied but had no suitable GUVI
coincident measurement
GUVI Selections
Criteria for selecting coincidences
• Within 200 km and 20 minutes
• Chapman layer fit successful
– Good fit to data
– Realistic HMF2 and NMF2
• No ‘qualifying letters’ on ionosonde data
427of 1112 observations met these criteria
• GUVI and IRI have similar
spread (~30-40%)
• GUVI compares well between
0.5 and 1.0 (106 cm-3)
• IRI bias similar in shape to
GUVI
• Both GUVI and IRI show
‘discontinuity’ at 1.0 (106 cm-3)
IRI/GUVI comparison
• Similar spread as (~30%)
• At higher NMF2, GUVI systematically low
• Slope of bias is constant (suggests
calibration of GUVI is reasonable)
Conclusion of comparisons
• At moderate NMF2, GUVI predicts
ionosonde measurements with 30% or so
• In the same range, IRI behaves the same
way with a fairly large positive bias
• At larger NMF2 both under-predict
Calibration Transfer
• The issue – Ionosonde intercalibration
– Various instrument designs
– Separate calibrations
– Independently operated
• Example solution – Ozone monitors
– ‘Standard instrument’ carried from site to site
– Makes simultaneous measurements
• Suggested approach – Orbiting UV monitoring
– Use GUVI (and/or its successors) to transfer
calibration
Regional Analysis - significant geographic differences
Inter-ionosonde Comparisons
• Significant differences between stations
• Significant regional differences
• GUVI statistics can be used to identify
areas that may need attention
– In principle, GUVI measurements should
have little geographic dependence
– Geographic differences in profile shapes and
horizontal gradients may have some influence
GUVI and IRI - Conclusions
• GUVI can provide systematic observations
– Can be used to compare with IRI
– Once differences are understood,
observations can be included in IRI
• GUVI can be used to refine ionosonde
measurements
– Provide better IRI validation
– Provide better IRI input