On the Importance of Radio Occultation data for Ionosphere Modeling IROWG Workshop, Estes Park, March 30, 2012
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On the Importance of Radio Occultation data for Ionosphere Modeling
IROWG Workshop, Estes Park, March 30, 2012
ABSTRACT
The availability of unprecedented amounts of Global Navigation Satellite Systems
(GNSS) ground receiver data over the last decade has been driving a new wave of
ionosphere research. Data of unprecedented time and spatial resolution have contributed
to a renaissance of ionosphere science and have open new ways of specifying and
forecasting the state of the ionosphere. Global ionosphere monitoring and forecasting
schemes are already emerging on operational stages. However, ground GNSS data
alone do not contain enough information about the vertical distribution of electron density
and must be supplemented by other measurements. Ionosonds provide vertical electron
density profiles but only below the F2 peak and at much lower spatial resolution. The best
complement to global ground GNSS measurements is provided by GNSS Radio
Occultations from a Low Earth Orbit (LEO). Ground based together with Occultation
GNSS measurements and the present ionosonde network can form a necessary and
sufficient set of observations to constrain physics based models used in data assimilation
schemes. LEO measurements of GNSS signals can also offer a way toward specification
and possibly short term prediction of ionosphere irregularities and scintillation. In this
paper measurement requirements in terms of cadence, spatial resolution, and latency for
Radio Occultation will be discussed. Possible tradeoffs between quality and quantity of
data and the background models used in data assimilation schemes and scintillation
products will be mentioned.
OUTLINE
• Motivation
• The System
• The Problem
• The Solution
• Data Needs
• Conclusions
Why the ionosphere?
IROWG Workshop, Estes Park, March 30, 2012
Would it be nice?
IROWG Workshop, Estes Park, March 30, 2012
ACTUAL SATCOM MESSAGES
SATCOM MESSAGE ERRORS
-12
-9
-7
-3
0
3
6
9
12
15
00:21:00 00:22:00 00:23:00
Universal Time (hh:mm:ss)
Rel
ati
ve
Sig
na
l S
tren
gth
(d
B)
Ascension Island
6 April 1997
Average Signal Level
Receiver Fade Margin
064. THE QUICK BROWN FOX JUMPS OVER THE LAZY DOGS BACK 01234567<9"TI
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SATCOM Message
S. Basu, private communication
http://roma2.rm.ingv.it/en/themes/11/ionospheric_scintillation
Scintillation
Fejer and Scherliess, 2001
Large Variability
Minute time scale Minute time scale
JULIA radar observations (Hysell & Burcham, 1998)
Many low and mid latitude ionospheric structures are driven from below
Need to Couple “Whole Atmosphere Model” to “Ionosphere Plasmasphere Electrodynamics”
Model
Ionosphere
Plasmasphere
Thermosphere GFS
(G
lob
al F
ore
cast
Sys
tem
s)
Wea
ther
fo
reca
st m
od
el
0 –
60
km
Wh
ole
Atm
osp
her
e M
od
el
WA
M =
Ext
end
ed
GFS
0
– 6
00
km
Ionosphere Plasmasphere Electrodynamics IPE Model
The IonoThermo Problem
• Uncertainties in energy inputs and sinks result in uncertainties in
global temperature, circulation, and neutral composition.
• Neutral changes affect production, loss and transport of ionization
and have dramatic effects on global electron density and TEC
structure.
• Variability makes it difficult to reduce the uncertainties
=> We can model generic storms but not specific ones
Several solutions
The Solution
Combine model and data: Data Assimilation
Challenges
Choose the appropriate assimilation scheme for a strongly forced
system
Find the best model representation for state evolution in time
Secure the necessary measurements
- latency
- spatial coverage
- known statistical characteristics
Ground-based GPS data provide accurate information about the horizontal
electron density distribution, but limited information about its vertical structure.
On the other hand, radio occultation data obtained from the low-Earth orbit
(LEO) satellites equipped with GPS receivers contain high-resolution
information about the vertical structure and entangled information about the
horizontal distribution of the electron density.
Combining the two data sources provides the best combination of data for
improving the ionosphere specification and opens the way for global
ionosphere forecasting, including scintillation prediction.
Spatial Coverage
Fully Coupled System (Five Years Away)
Magnetosphere Models
• Convection electric fields
• Auroral precipitation
Ionosphere
Irregularity
Models
IDEA
WAM+IPE
• Large-scale dynamics
• Wave seeding
• Plasma densities
• Electric fields
• Plasma drifts
Data Solar Wind Conditions Solar EUV Assimilated Data Ground GPS Space-based GPS Magnetometers Ionosondes Satellite Drag
• We are building a fully coupled troposphere to thermosphere system that
includes the ionosphere, electrodynamics, and data assimilation
• The new system has potential to improve specification and forecasting
even in the troposphere
• The electron density height profile cannot be accurately specified from
ground-based GPS data alone
• COSMIC GPS occultation data can provide the height distribution
information needed to specify the global 3-D Ne structure
• The correlation between Ne values measured at the same location
decreases dramatically beyond 45 minutes
• Scintillation specification requires even shorter latency for the S4 and
Sigma Phi measurements
CONCLUSIONS
Electron Density Height Profile
Electron Density Height Profile
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