Characteristics and source of the electron density irregularities in the Earth’s ionosphere Hyosub Kil Johns Hopkins University / Applied Physics Laboratory Speaker : Tae-yong Yang Advisor : Jaeheung Park 3rd UST JC

Contents Introduction Predicted ionospheric morphology on the basis of production Actual ionosphere and generation mechanism of the irregularities in different latitudes Low latitudes High latitudes Middle latitudes Future work

Ionosphere Shortwave solar electromagnetic radiation heats and excites atoms and molecules in Earth’s atmosphere. It rips molecules apart and tears electrons. The free electrons and positive ions then form several weakly ionized layers of plasma. F region: O + by extreme UV (10 – 100 nm) E region: O 2 + and NO + by soft X-ray (1-10 nm) and far ultraviolet ( nm) D region: O 2 + and N 2 + by hard x-ray (<1 nm)

n e (cm -3 ) = 1.24 x10 4 f 2 f : plasma frequency (MHz) scintillation electron density irregularities Communication error

Ionospheric source and sink Sun – Production of ionosphere (Solar radiation) Solar activity – rotation(27days), solar cycle(11 years), flare, CME, etc. Solar zenith angle – Daily, Seasonal variation Sun and Earth distance – Aphelion, Perihelion Neutral atmosphere – Annihilation of ionosphere Chemical composition Interaction – Electric field, Drag

Predicted Electron density by solar radiation Year (solar cycle) Sunspot # Electron density Local time (h) Electron density

Sun March June December September Electron density Sun Latitude (deg) Month Northern Hemisphere Summer

photoionization radiative recombination dissociative recombination Production Loss dissociative recombination

Low latitude Equatorial Ionization Anomaly (EIA) Plasma bubble

Equatorial ionization anomaly (Appleton anomaly) Plasma density peaks form around ±10~15° magnetic latitudes Electron density Sun Total Electron Content (TEC): vertical plasma column density TECU = m -2

E B Magnetic equator E x B NorthSouth Δ-Δ- p Δ-Δ- p Formation of Equatorial Ionization Anomaly (EIA) 11 Uplift of the ionosphere by the eastward electric field causes an increase of plasma density in the equatorial region. Then the equatorial plasma diffuses downward along the magnetic field lines by the pressure gradient and gravity.

ROCSAT-1 satellite 600 km [ Shiokawa et al., Ann Geo., 2000 ] All-sky image Radar map at Jicamarca in Peru

Nighttime O I nm radiance map produced by using the TIMED/GUVI data. The two distinguishing phenomena in the low-latitude F region are the equatorial ionization anomaly (EIA) and equatorial plasma bubbles (EPB). O + + e O* O nm emission EIA bubble

Rayleigh-Taylor Instability g n1n2n1n2 J1J1 J2J2 + - B Growth rate: Log (electron density) (cm -3 ) Altitude (km)

3-D bubble morphology: shell structure

Kil et al. [JGR, 2009] ROCSAT-1 satellite Year: 1999 – 2002 Altitude: 600 km The bubble distributions obtained from ROCSAT-1 during solar maximum period ( ). Bubble occurrence rate

High latitude Stormtime disturbance

Stormtime disturbance – electric field effect B-field _ E V E B-field aurora Downward view from the north _ _ _ _ _ solar wind particles dawn dusk Electric fields originated from the solar wind and magnetosphere affect the plasma motion in high latitudes.

sunlit darkness

Stormtime disturbance – wind effect sun N S heating wind B Uplift the ionosphere Auroral heating Neutral winds modify the F-region height by transporting plasmas along the magnetic field lines.

Middle latitude Traveling ionospheric disturbances (TID) Statistical occurrence of field-aligned irregularities

[Saito et al., GRL, 2000] middle-latitude phenomena – traveling ionospheric disturbance (TID) polar region heating propagation of atmospheric disturbance Creates TID by electric field by neutral drag B

23 VHF coherent scatter radar At Daejeon (36.18°N, °E; dip lat. 26.7°) The location of Daejeon in South Korea, where the VHF radar is operated. The radar beam is perpendicular to the geomagnetic field line at F-region altitudes. MU radar

Yang et al. [GRL, preparation] Yang et al. [JGR, 2015]

- The occurrence rate of the post-sunrise FAIs is largest in equinoxes, but the occurrence rate of the nighttime FAIs is largest in summer. The occurrence rates of the post-sunset and nighttime FAIs are greater than those of the pre-sunrise and post-sunrise FAIs. - The FAI occurrence rate shows an increasing tendency with an increase of the solar flux.

Future work Q1. What are the representative characteristics of the E and F region FAIs and how do the characteristics vary with local time, season, and solar cycle? Q2. What is the role of sporadic E and medium-traveling ionospheric disturbances in the creation of the FAIs Q3. What is the spatial extent of the FAIs?

Thank you for your attention.

Equatorial ionization anomaly Sub-storm Dissociative recombination Anomaly / Irregularities / Disturbances Polar cap Dst(disturbance storm time) :8 개 중저위도에 위치한 관측소에서 측정한 지자기 변화의 H 성분의 순간 평균값으로 정의 Geomagnetic storm : initial/main/recovery phase

ionosphere Electron density Local Time (h) Altitude Electron density

Stormtime disturbance – electric field effect Before a storm During a storm (undershielding) Solar wind electric field dawn dusk Penetration electric field

ROCSAT observation at the altitude of 600 km Formation of the density enhanced layer off equatorial region during daytime can be explained by the diurnal variation of vertical plasma drift. 31