MODULE 1: CONUS VERSUS GLOBAL IONOSPHERE Part A: Midlatitudes

1. Satellite Based Augmentation SystemsBrazilian Ionosphere GroupTraining at Stanford UniversityOctober 27-30, 2003

2. MODULE 1: CONUS VERSUS GLOBAL IONOSPHERE Part A: Midlatitudes

3. This module covers: Why? Topics CONUS VERSUS GLOBAL IONOSPHERE Part A An introduction to the ionosphere Understanding ionospheric basics so that the concerned ionospheric phenomena can be understood Creation of the ionosphere, and the effects of solar zenith angle and ionospheric dynamics

4. Introduction to the Ionosphere • Introduction to the ionosphere • Upper atmosphere • Ion and electron production due to photoionization and particle precipitation • Chemical loss • Ionospheric dynamics under the control of the intrinsic geomagnetic field • References • Introduction to Ionospheric Physics [Rishbeth and Garriott, 1969] • Geophysical Handbook [Air Force Research Laboratory, …] • The Earth’s Ionosphere [Kelley, 1989] • Ionospheres [Schunk 2000]

5. Earth’s Upper Atmosphere

6. Photoionization Examples of Photoionozation Photon from the Sun h Examples of Dissociative Ionozation atomic (or molecular) gas O oxygen Ionization Threshold Energies e- O+ electron ion

7. Production Optical Depth Chapman Production Function Normalized Chapman production function versus reduced height z, parametric in solar zenith angle . [Rishbeth and Garriot, 1969] h0: reference height

8. Layers of Ionization • Electron production profiles by solar irradiances at the EUV band • Radiation at different wavelengths contributes to the creation of E- and F-layers • For SSN = 60 • X(E), 8 – 140 Å • UV(E), 796 – 1027 Å • E = UV(E) + X(E) • F, 140 – 796 Å • E+F, 8 – 1027 Å

9. Ionization due to Aurora Precipitation Computed ionization rates for O+, O2+, and N2+, respectively, due to precipitating charged particles at various energy levels

10. Loss of Ions and Electrons Charge Exchange Radiative Recombination (slow) k ~ 10-12 (250/Te)0.7 Airglow Emission (red line) (k ~ 10-10) kf /kr 1.13 Dissociative Recombination K ~ 10-7(300/Te)0.5

11. Ionospheric Dynamics - C • Ionospheric plasma motions under the control of the geomagnetic field • ExB drift • Neutral wind drag • Diffusion • Collision vs. gyro-rotation • Collision frequency • Gyro-frequency • F-region and E-region

12. Ionospheric DynamicsDynamo Electric Fields Vertical Drift Zonal Drift

13. High Latitude Plasma Convection Electric Potential

14. Plasma EB Drift At 180 km: i (O+) ~ 220 Hz, in ~ 10 Hz • Motions of electron and ion under an external electric field (E) • In the same or opposite direction of E • Gyro-rotation • The direction of motion of a charged particle is under control of magnetic field (B) so that the particle gyro-rotates around the B field • Motions under both E and B fields • Both electrons and ions move in the E  B direction • In the ionosphere, ion-neutral (mostly) and electron-neutral collisions also affect motions of charged particles • The effects due to the collisions compete with gyro-rotations, and the superior determines the motion directions Gyro-frequencies:

15. Ionospheric Dynamics - B • Thermospheric wind • Tidal forces: solar heating • HWM model • Um and Uz in 2-D • Um and Uz in 1-D

16. Plasma Motions Controlled by B-Field • In regions where  >> in (F region), plasma move in directions either perpendicular to magnetic field B (in the EB direction) driven by electric field E, or parallel to B driven by horizontal wind vn(gradient of pressure pi is not included) vi,up vi,∥ I vn B

17. Dynamical Effects • Plasma move into different regions where the lifetime of the plasma changes due to the altitude-dependent chemical loss processes • As the plasma move into a different region, dominant effects change • Example: F-layer rises, plasma on the bottom side leave from a chemical-dominant region and enter a region where diffusion dominates

18. Fluid Dynamic Equations for the Ionosphere Mass and Momentum Conservation

19. Ionization, chemical loss, and dynamics

20. Neutral, Ion, and Electron Densities Middle Latitudes

21. Seasonal Variations at Mid-Latitudes

22. Seasonal Variations at Low-Latitudes

23. 11 Year Solar Cycle • Solar activity caries from minimum to maximum with a 11-year cycle • During years of high sun-spot number years, solar radiation enhances at most of its spectrum, including solar flares and coronal mass ejections • Increased solar activities directly affect ionospheric densities through photoionization and coupling of magnetosphere, ionosphere, and thermosphere, which gives rise to ionospheric disturbances

24. Global Ionosphere

25. This module covers: Why? Topics CONUS VERSUS GLOBAL IONOSPHERE Part B The mid-latitude ionosphere and storms Context for understanding ionospheric algorithms applied to WAAS Understand why low-latitude algorithms will differ from WAAS algorithms Ionospheric structure and behavior over US Quiet versus storm-time behavior at mid-latitudes

26. Electron Density Profiles at Mid-Latitudes • Altitude profiles ofthe ion composition and ne measured using incoherent scatter radar at Arecibo • Daytime: top panel • Nighttime: bottom panel • Peak at ~300 km

27. ne Diurnal and Latitudinal Variations • ne profiles versus UT measured using incoherent scatter radar at Arecibo (Puteor Rico, LT = UT – 4 hrs) and Millstone Hill (Massachusetts: LT = UT – 4.7 hrs) • Diurnal variations • Peak at ~300 km • Maximum in the afternoon at ~ 2 LT • Minimum at dawn at ~5 LT • Latitudinal variations

28. TEC in CONUS: Nominal Conditions • A snapshot of TEC derived from GPS dual-frequency observations using a ground-based GPS receiver network under nominal ionospheric conditions • Small TEC spatial gradient allows a planar fit to represent its nominal behavior

29. TEC in CONUS: Storm Conditions • Under storm conditions, large gradient in ionospheric density and TEC can occur in the CONUS region • Storm-time ionosphere may not be well represented by a planar fit • A threat model must developed to provide warning and realistic error bound must be provided to WAAS to protect the system from the increased errors

30. Corona Mass Ejection Above: Helical structure in a CME observed with LASCO on June 2, 1998. Right: The August 11, 1999, eclipse.

31. Sun-Earth Connection and Living With a Star • Varying • Radiation, Energetic particles • Solar wind • Interacting • Magnetic fields, plasma, energetic particles • Ionosphere and Atmosphere

33. Magnetosphere-Ionosphere Coupling

34. Geomagnetic Storms During April 2002

35. Storm Effects • Charged particle precipitation in the auroral zone • Significant enhanced plasma convection at high latitudes • Penetration of electric fields into middle and low latitudes • Steepened mid-latitude ionospheric trough • Storm-time Enhanced Density (SED) • Ionospheric Undulation and irregularities at subauroral latitudes • Enhanced equatorial anomaly • Triggering of equatorial “bubbles” or irregularities and causing scintillation • Auroral electron jet • Joule heating and friction heating • Heating in the high-latitude thermosphere • Traveling ionospheric disturbances (TID): positive storm effects • Enhanced equatorward wind • Positive storm effects • Possibly suppressing equatorial irregularities • Global thermospheric circulation change • Thermospheric composition change: negative storm effects • Erosion of the plasmasphere

36. SED

37. Storm Effects

38. Negative Storm Effects

39. Positive and Negative Storm Effects • Storm-time positive and negative TEC changes as well as large TEC gradient at mid-latitudes present a great challenge to WAAS

40. Mid-Latitude Irregularities during a Storm

41. MODULE 1: CONUS VERSUS GLOBAL IONOSPHERE Part B: Low Latitudes

42. This module covers: Why? Topics CONUS VERSUS GLOBAL IONOSPHERE, Part B The low latitude ionosphere Understand why low-latitude SBAS is challenging The Equatorial Ionization Anomaly (EIA) Local time behavior of the EIA Plasma depletions (bubbles) Scintillation Storm versus quiet time behavior

43. [Placeholders] • Global TEC map pointing out equatorial feature • Overlay geomag equator if possible • Classic picture of EIA formation with arrows • TOPEX plot showing anomaly • Statistics relative to planar fit • Picture of E with pre-reversal enhancement • Post-sunset plasma instability • Picture of depletion size/scale • TEC plots of depletions –– Dehel • Depletions and scintillation • Plot of amplitude scintillation • Some statistics of scintillation • Attila storm versus quiet statistics • Summary

44. Equatorial Ionization Anomaly (EIA)

45. TOPEX Altimeter • TOPEX/Poseidon satellite carries a dual-frequency radar measuring the height of sea level • Ionospheric vertical TEC is derived from the differential delay of the signals • Vertical TEC is measured above oceans at mid- and low-latitudes for many years

46. Equatorial Anomaly Shown in TEC • Low latitude ionospheric structures under nominal conditions • Large gradient and curvature: Equatorial anomaly

47. Dynamical Effects at Low-Latitudes

48. Dynamical Processes in the Equatorial Ionosphere

49. Ionospheric Plasma Vertical DriftIn the Equatorial Region • Averaged patterns of vertical plasma drift in the equatorial region • Plasma move upward during daytime and downward at nighttime • A pre-reversal enhancement occurs around dusk

50. Equatorial Anomaly Shown in ne Calculated electron contours (log10ne) as a function of altitude and latitude at 2015 LT for equinox conditions