COSMIC Ionospheric measurements Jiuhou Lei NCAR ASP/HAO Research review, Boulder, March 8, 2007

COSMIC launch picture provided by Orbital Sciences Corporation All six satellites stacked and launched on a Minotaur rocket Initial orbit altitude ~500 km; inclination ~72° Will be maneuvered into six different orbital planes for optimal global coverage (at ~800 km altitude) All satellites are in good health Launch on April 14, 2006 Vandenberg AFB, CA Chris Rocken Three science instruments interest us: GPS receiver, TIP and TBB

Why are the COSMIC observations important for ionospheric research and application? 1. Previous ground-based/satellite observations are still limited. 2. Data assimilation and space weather (not shown here) COSMIC radio occultation (RO) measurements can provide a global view of ionosphere (latitude, longitude, altitude information )

Ionosphere/atmosphere vertical structure Ionosphere Positive-charged ions and negative-charged electrons ( cm -3 )

First Collocated Ionospheric Profiles Schreiner et al. (GRL, 2007) In this case two almost identical profiles (red and blue) retrieved from the GPS observations from two different COSMIC satellites on April 22 (left panel). The two satellites, FM2 and FM4, were flying about four seconds after each other and were sampling almost the same region of the ionosphere. Janet Zeng The GPS receivers at the satellites almost have not instrument-bias

First Collocated Ionospheric Profiles Schreiner et al. (GRL, 2007) COSMIC ionospheric profile shows very NICE vertical structure!

Compare with ground-based observations: radar

1.The COSMIC RO electron density profiles are in good agreement with the ISR ones 2. But the agreement is better at Millstone Hill (mid-latitude) than that at Jicamarca (equator). This is probably due to the larger horizontal gradients at Jicamarca, which is ignored in the retrieval of the electron density profiles

Ionospheric characteristics F2 peak density (NmF2) F2 peak height (hmF2) Like mesopause temperature and mesopause altitude

There are 276 coincident measurements made over one month (July, 2006) for observations that had latitude/longitude differences between the COSMIC occultation and the ionosondes that were less than 2º. There is a strong correlation between the COSMIC NmF2 and those from ionosondes. The correlation coefficient was Compare with ground-based observations: ionosonde

Obsevation Empirical model Theroretical model Latitude J.Y. Liu (2006) North hemisphere summer (peak density) Two crests along the magnetic equator E X B

Obsevation Empirical model Theroretical model COSMIC data will make significant contributions to ionospheric studies, including the improvement of the global thermosphere/ionosphere models (both empirical and theoretical models) and space weather forecast. overestimate NmF2 at the peak of the equatorial anomalies, almost symmetry, and no obvious longitude variation peak density at the equatorial anomalies is smaller than that seen in COSMIC North hemisphere summer (peak density) Two crests along the magnetic equator

Obsevation Empirical model Theroretical model 1.The COSMIC peak height agrees with those from empirical and theroretical models. 2. Both observations and models show the peak height is higher in summer hemisphere than winter one North hemisphere summer (peak height)

Obsevation Empirical model Theroretical model The southern-northern asymmetry of the peak height is assocaited with the thermospheric circulation which flows from the summer to the winter hemisphere ! Summer Winter

Longitude variation Effect atmospheric tides Immel and Hagan et al. (GRL, 2006)

Electron density at 450km during daytime Longitude variation Log10(Ne, cm -3 ) 4-peak longitude variation structure during daytime prevails in all seasons

Electron density at 450km during nighttime Longitude variation Log10(Ne, cm -3 ) 4-peak longitude variation structure during nighttime is much weaker! Longitude variation during nightime is more obvious in equinox (thermospheric circulation modulates?)

Conclusion 1. The COSMIC derived ionospheric data appear to be consistent with other measurements and with model simulations. 2. The COSMIC ionospheric measurements show some interesting seasonal, longitudianl and altitudinal variations (Lei et al., JGR, 2007). 3. Next step: (i)study the ionospheric response to “space weather” event; (ii)use the NCAR-GCM models to investigate these interesting features seen in COSMIC observations. In conclusion, COSMIC RO data measured when the satellites reach their final configuration will make significant contributions to ionospheric studies, including the improvement of the global thermosphere/ionosphere models (both empirical and theoretical models) and space weather forecast.

Thanks for your attention

Retrieval for Ionosphere LEO v leo v GPS Tangent point s 1, s 2 TEC Ne Raw measurements of phase of L1 and L2 Bending angles of L1 and L2 Electron density Derivative algorithm Double freqs Inversion Janet Zeng