Formosat 3 COSMIC The Ionosphere as Signal and

Formosat 3 / COSMIC The 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

Radio Occultation Ionosphere as signal Ionosphere is noise

Over 1 Million Profiles 4/21/06 -4/15/08 Neutral Atmosphere Ionosphere

We 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”. Ionospheric Calibration 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. 37 e-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. 5 e-7 rad during the 11 year solar cycle.

Relationship of F 10. 7 / Bending Bias/ Temperature F 10. 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 L 1 and L 2 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

Amount of COSMIC-observed Trans Ionospheric TEC Data Quality of abs. TEC ~2 TECU COSMIC transionospheric radio links for a 100 -min period, June 29, 2007

Current Latency of COSMIC TEC Data Location of Low-Latency TEC Arcs Most data are downloaded from Satellites < 100 m Processing at CDAAC takes ~ 20 minutes

Comparisons with ground-based data Courtesy of Jiuhou Lei

COSMIC - Ionosonde Comparison Jan. 2008, distance < 500 km, time difference < 15 min, colors indicate ionosondes F 0 F 2 rms=0. 60 MHz HMF 2 rms=57 km

Scintillation Sensing with COSMIC No scintillation S 4=0. 005 Scintillation S 4=0. 113 GPS/MET SNR data

Amplitude scintillations (S 4 index based on 50 -Hz observations) E-Layer scintillation: Occurs at all local times except near sun-rise (3 -7 LT), strongest near sunset (14 -19 LT). Most active between 20 -60 deg north and south latitude More pronounced in NH than SH Stronger S 4 than F-layer scintillation

Amplitude scintillations (S 4 index based on 50 -Hz observations) F-Layer scintillation: Occurs sunset to sunrise (19 - 5 LT). Most active in equatorial region (+/- 30 degrees). Weaker S 4 than E-layer scintillation

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