Space weather phenomena in the ionosphere and their effect on GNSS IPXX　ICAO ISTF/4 New Delhi, India, 5th to 7th February 2014 Space weather phenomena in the ionosphere and their effect on GNSS (Presented by Japan) SUMMARY This paper presents a short review of major space weather phenomena observed in mid- and low-latitude ionosphere. Their effect on GNSS also mentioned.

Sudden Ionospheric Disturbance (SID) SOHO/SEM [count/s] EUV X-ray flux GOES [W/m2] 35 [TECU] GPS TEC TIMED/GUVI O, N2 [R] 10 15 UT [hour] [Tsurutani et al., 2005] [Tsugawa et al., 2007]

Sudden Ionospheric Disturbance (SID) Amplitude +Several 10 TECU Depending on flare class Time scale Increase in several minutes Enhancement lasts for several hours Spatial structure Global scale in the sunlit hemisphere Depending on solar zenith angle Other characteristics HF radio absorption (Dellinger phenomena) Possibility of loss-of-lock on GNSS signals due to solar radio burst Effect on GNSS Augmented GPS (due to TEC model correction error) Loss-of-lock on GPS signals

Ionospheric Storm One-month Average Negative Storm Positive Storm JST Wakkanai Okinawa foF2 [MHz] JST (UT+9h) One-month Average Negative Storm Positive Storm Kp

Ionospehric Storm Amplitude ±Several 10 TECU compared to quiet conditions Time scale Several hours to several days Spatial structure Small spatial TEC gradient Other characteristics Basically occurring during and/or after magnetic storms Effect on GNSS Augmented GPS (due to TEC model correction error)

Equatorial Ionization Anomaly 20:40 JST, 23 Jan 2002 20:40 JST, 24 Jan 2002

Equatorial Ionization Anomaly Amplitude ±Several 10 TECU Time scale Spatial structure Large latitudinal TEC gradient Other characteristics Day-to-day variation is not negligible (increase, disappearance, hemispheric asymmetry, etc) Affected by magnetic storms Effect on GNSS Augmented GPS (due to TEC model correction error)

Storm enhanced density (SED) [Foster et al., JGR, 2005]

Short summary of SED Amplitude +Several 10 to 100TECU Time scale Several hours (?) Spatial structure Steep horizontal TEC gradient Narrow in zonal direction Extending in NW-SE direction Other characteristics Often observed from noon to sunset during the large geomagnetic storm Sometimes accompanied with ionospheric irregularity Effect on GNSS Differential GPS Augmented GPS (due to TEC model correction error) Loss-of-lock on GPS signals

GPS-TEC Observations for Space Weather Absolute TEC ROTI (~10km scale irregularity) Loss-of-Lock (~100m scale irregularity) (21:20 JST) 12:20 UT (21:40 JST) 12:40 UT (22:00 JST) 13:00 UT 3D simulation of plasma bubble [Courtesy of Dr. T. Yokoyama (NICT) ]

Short summary of EPB Amplitude -Several 10 to -100TECU Time scale Several 10 minutes to several hours Spatial structure Steep horizontal TEC gradient Narrow in zonal direction Extending along the magnetic field line Other characteristics Often observed mid- to low latitudes after the sunset. Almost always accompanied with ionospheric irregularity Effect on GNSS Differential GPS Augmented GPS (due to TEC model correction error) Loss-of-lock on GPS signals

Traveling Ionospheric Disturbances (TID) Large -scale TID (LSTID) [Tsugawa et al., JGR., 2003] Medium -scale TID (MSTID) [Tsugawa et al., GPS solut., 2007]

Traveling Ionospheric Disturbances (TID) Amplitude A few TECU Time scale MS: Several 10 minutes LS: Several hours Spatial structure MS: Wavelengths of several 100 km LS: Wavelengths of 1,000 – 3,000 km, Zonally extended wavefront Other characteristics MS: Southwestward and Southeastward propagations in nighttime and daytime, respectively. LS: Related with magnetic storm Effect on GNSS Differential GPS Augmented GPS (due to TEC model correction error)

Summary of Ionospheric Space Weather Phenomena Solar Act./ Mag. Storm dependence SED Amplitude Large SID LSTID Med. Ion. Strom Eq. Ion. Anomaly Small Plasma Bubble Lower Atm. dependence MSTID Sporadic E 10km 100km 1000km Global Spatial Scale