Formosat3 / COSMICThe Ionosphere as Signal and Noise

Christian Rocken, Bill Schreiner, Sergey Sokolovskiy, Doug Hunt, Stig Syndergard

UCAR COSMIC Project

FORMOSAT-3

Status of Constellation April 23, 2008

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Radio Occultation

Ionosphere as signal

Ionosphere is noise

Over 1 Million Profiles 4/21/06-4/15/08

Neutral Atmosphere Ionosphere

Ionospheric CalibrationWe estimate systematic ionospheric error by computing the “mean of the iono-free bending angle minus neutral bending angle (from climatology) in the 60-80 km height bin”.

We compare this quantity “smean” for daytime vs. nighttime soundings.

COSMIC Days 0-120, 2007

-20 < Lat. < 20

DAY (11<LT<15) smean= -1.19 e-7 rad

NIGHT (2<LT<6) smean=-0.37e-7 rad

We can see the day vs. night iono bias change we expect that we can monitor the change of this bias to better than 0.5e-7 rad during the 11-year solar cycle.

Relationship of F10.7 / Bending Bias/ Temperature

F10.7

BA Bias

The bending angle change of +3 e-7 rad due to change in solar activity would cause a apparent stratospheric warming of:

0.6 / 0.4 / 0.2 deg K at 30 / 25 / 20 km.

Ionosphere as “Noise” Summary In RO the ionosphere is corrected by forming the “standard” dual

frequency linear combination of L1 and L2 bending angles This correction does not completely eliminate the ionospheric

effect– Significant random noise remains which can affect profiles for weather

forecasting down to 25 km altitude – The residual ionosphere also introduces a bias, which - if left uncorrected -

could introduce a significant spurious “warming with decreasing solar activity” signal at 30 km in the stratosphere of ~ 0.6 deg K with the 11 year solar cycle.

Methods have been developed to minimize the “ionosphere as noise” so that it becomes largely insignificant below 25 km.

At altitudes 25-40 km the ionosphere remains the most significant noise source for RO

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COSMIC trans-ionospheric radio links for a 100-min period, June 29, 2007

Amount of COSMIC-observed Trans Ionospheric TEC Data

Quality of abs. TEC ~2 TECU

Current Latency of COSMIC TEC Data

Location of Low-Latency TEC Arcs

Most data are downloaded from Satellites < 100 mProcessing at CDAAC takes ~ 20 minutes

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Comparisons with ground-based data

Courtesy of Jiuhou Lei

COSMIC - Ionosonde ComparisonJan. 2008, distance < 500 km, time difference < 15 min, colors indicate ionosondes

HMF2rms=57 km

F0F2rms=0.60 MHz

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Scintillation Sensing with COSMIC

No scintillationS4=0.005

ScintillationS4=0.113

GPS/MET SNR data

Amplitude scintillations (S4 index based on 50-Hz observations)

E-Layer scintillation:

Occurs at all local times except near sun-rise (3-7 LT), strongest near sun-set (14-19 LT).

Most active between 20-60 deg north and south latitude

More pronounced in NH than SH

Stronger S4 than F-layer scintillation

F-Layer scintillation:

Occurs sunset to sunrise (19 - 5 LT).

Most active in equatorial region (+/- 30 degrees).

Weaker S4 than E-layer scintillation

Amplitude scintillations (S4 index based on 50-Hz observations)

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What comes after COSMIC? Several Options for a follow - on mission are discussed and

considered by US agencies– Participation in a Taiwan 6+ satellite follow on mission (2012)– Iridium has proposed to use (some of) its 64 future communication satellites

as a platform for RO observations (2013 ?) – CICERO plans to launch 24 satellites (starting in 2011) and to sell data

Planned improvements compared to COSMIC – Plan for lower data latency. Goal of 10-15 minutes (more ground stations,

or real-time satellite to satellite downlink) – Observations of GPS and Galileo (Glonass?, Compass?)– More TEC arcs and soundings

Community feedback on requirements and secondary space weather payloads for future mission should be provided to UCAR

Summary In the 2 years since launch COSMIC has generated and distributed

over 1.3 million ionospheric profiles and TEC arcs COSMIC is now also generating a large amount of scintillation

observations COSMIC ionospheric observations are of high quality and most

products are available within < 120 minutes of on-orbit collection, some within < 30 minutes

All data are available from www.ucar.cosmic.edu Follow on missions for COSMIC are now in planning stages and

input from the space weather community is needed

UCAR COSMIC program is presently looking for a scientist to take charge of our ionospheric processing