Bibliography

Ionospheric Space Weather: Longitude Dependence and Lower Atmosphere Forcing

This monograph is the outcome of an American Geophysical Union Chapman Conference on longitude and hemispheric dependence of ionospheric space weather, including the

Fuller-Rowell, Timothy; Yizengaw, Endawoke; Doherty, Patricia; Basu, Sunanda;

Published by:       Published on:

YEAR: 2016     DOI:

Geomagnetic control of equatorial plasma bubble activity modeled by the TIEGCM with Kp

Describing the day-to-day variability of Equatorial Plasma Bubble (EPB) occurrence remains a significant challenge. In this study we use the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIEGCM), driven by solar (F_10.7) and geomagnetic (Kp) activity indices, to study daily variations of the linear Rayleigh-Taylor (R-T) instability growth rate in relation to the measured scintillation strength at five longitudinally distributed stations. For locations characterized by generally favorable conditions for EPB growth (i.e., within the scintillation season for that location), we find that the TIEGCM is capable of identifying days when EPB development, determined from the calculated R-T growth rate, is suppressed as a result of geomagnetic activity. Both observed and modeled upward plasma drifts indicate that the prereversal enhancement scales linearly with Kp from several hours prior, from which it is concluded that even small Kpchanges cause significant variations in daily EPB growth.

Carter, B.; Retterer, J.; Yizengaw, E.; Groves, K.; Caton, R.; McNamara, L.; Bridgwood, C.; Francis, M.; Terkildsen, M.; Norman, R.; Zhang, K.;

Published by: Geophysical Research Letters      Published on: 08/2014

YEAR: 2014     DOI: 10.1002/2014GL060953

Equatorial ionosphere; plasma bubbles; TIEGCM

An analysis of the quiet time day-to-day variability in the formation of postsunset equatorial plasma bubbles in the Southeast Asian region

Presented is an analysis of the occurrence of postsunset Equatorial Plasma Bubbles (EPBs) detected using a Global Positioning System (GPS) receiver at Vanimo. The three year data set shows that the EPB occurrence maximizes (minimizes) during the equinoxes (solstices), in good agreement with previous findings. The Vanimo ionosonde station is used with the GPS receiver in an analysis of the day-to-day EPB occurrence variability during the 2000 equinox period. A superposed epoch analysis (SEA) reveals that the altitude, and the change in altitude, of the F layer height is \~1 standard deviation (1σ) larger on the days for which EPBs were detected, compared to non-EPB days. These results are then compared to results from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), which show strong similarities with the observations. The TIEGCM is used to calculate the flux-tube integrated Rayleigh-Taylor (R-T) instability linear growth rate. A SEA reveals that the modeled R-T growth rate is 1σ higher on average for EPB days compared to non-EPB days, and that the upward plasma drift is the most dominant contributor. It is further demonstrated that the TIEGCM\textquoterights success in describing the observed daily EPB variability during the scintillation season resides in the variations caused by geomagnetic activity (as parameterized by Kp) rather than solar EUV flux (as parameterized by F_10.7). Geomagnetic activity varies the modeled high-latitude plasma convection and the associated Joule heating that affects the low-latitude F region dynamo, and consequently the equatorial upward plasma drift.

Carter, B.; Yizengaw, E.; Retterer, J.; Francis, M.; Terkildsen, M.; Marshall, R.; Norman, R.; Zhang, K.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.410.1002/2013JA019570

equatorial plasma bubbles; GPS scintillation; Ionosphere

Is Space Weather Different Over Africa, and If So, Why? An AGU Chapman Conference Report

With the increasing reliance on technology, the impact of space weather on engineered systems will certainly increase unless suitable protective measures are taken. Understanding the physics behind space weather impacts and improving the forecasting are the major objectives of the space science community. It is well recognized that many space weather impacts, especially on communications systems, arise from structures in the ionosphere. The equatorial ionosphere, in particular, is one of the most complex and is host to numerous instabilities and interactions, with many unresolved questions regarding its dynamics and variability. Radio waves, either transmitted through the ionosphere, for satellite communication and navigation, or reflected off the ionosphere for HF and radar applications, are all impacted by ionospheric variability and structure. Ionospheric irregularities or plasma \textquotedblleftbubbles\textquotedblright occurring at low latitudes are one such source of interference. These irregularities cause scintillations on satellite radio transmissions, resulting in information loss in communications, as well as degradation in positioning and navigation used in aviation and maritime industries.

Yizengaw, Endawoke; Doherty, Patricia; Fuller-Rowell, Tim;

Published by: Space Weather      Published on: 07/2013

YEAR: 2013     DOI: 10.1002/swe.20063

atmosphere ionosphere interactions; ionospheric irregularities; space weather

The day-to-day longitudinal variability of the global ionospheric density distribution at low latitudes during low solar activity

One important characteristic of longitudinal variability of the ionosphere is the global wavenumber-4 signature. Recent investigations have focused mainly on the climatological pattern during daytime and evening sectors. We investigate the day-to-day variability of the wavenumber-4 structure of the longitudinal ionospheric density distribution using the global total electron content (TEC) measurements from Global Positioning Systems receivers on the ground. The quiet time (Kp <= 3) day-to-day occurrence of the wavenumber-4 is obtained during periods of low solar flux conditions for the years 2008 and 2009. We find that the wavenumber-4 structure occurs at all local time sectors; however, the daytime TEC wavenumber-4 structures are clearer and can persist until the midnight hours. The most significant occurrence is observed during the 1000\textendash2400 LT sector while the minimum number of wavenumber-4 structure is observed between the 0400 and 0600 LT sector. Around the nighttime sector, more wavenumber-4 occurrence is observed during the premidnight sector than the postmidnight hours. The seasonal occurrence probability of the wavenumber-4 pattern is at a maximum during the March\textendashApril equinox and June\textendashJuly solstice. December\textendashJanuary is the period when the wavenumber-4 occurrence is less dominant than the rest of the year.

Pacheco, E.; Yizengaw, E.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2013

YEAR: 2013     DOI: 10.1002/jgra.50241

day-to-day; Ionosphere; longitudinal variability; TEC; wavenumber-4

Global Longitudinal Dependence Observation of the Neutral Wind and Ionospheric Density Distribution

Yizengaw, Endawoke;

Published by: International Journal of Geophysics      Published on: Jan-01-2012

YEAR: 2012     DOI: 10.1155/2012/342581

Longitudinal differences of ionospheric vertical density distribution and equatorial electrodynamics

Accurate estimation of global vertical distribution of ionospheric and plasmaspheric density as a function of local time, season, and magnetic activity is required to improve the operation of space-based navigation and communication systems. The vertical density distribution, especially at low and equatorial latitudes, is governed by the equatorial electrodynamics that produces a vertical driving force. The vertical structure of the equatorial density distribution can be observed by using tomographic reconstruction techniques on ground-based global positioning system (GPS) total electron content (TEC). Similarly, the vertical drift, which is one of the driving mechanisms that govern equatorial electrodynamics and strongly affect the structure and dynamics of the ionosphere in the low/midlatitude region, can be estimated using ground magnetometer observations. We present tomographically reconstructed density distribution and the corresponding vertical drifts at two different longitudes: the East African and west South American sectors. Chains of GPS stations in the east African and west South American longitudinal sectors, covering the equatorial anomaly region of meridian \~37\textdegreeE and 290\textdegreeE, respectively, are used to reconstruct the vertical density distribution. Similarly, magnetometer sites of African Meridian B-field Education and Research (AMBER) and INTERMAGNET for the east African sector and South American Meridional B-field Array (SAMBA) and Low Latitude Ionospheric Sensor Network (LISN) are used to estimate the vertical drift velocity at two distinct longitudes. The comparison between the reconstructed and Jicamarca Incoherent Scatter Radar (ISR) measured density profiles shows excellent agreement, demonstrating the usefulness of tomographic reconstruction technique in providing the vertical density distribution at different longitudes. Similarly, the comparison between magnetometer estimated vertical drift and other independent drift observation, such as from VEFI onboard Communication/Navigation Outage Forecasting System (C/NOFS) satellite and JULIA radar, is equally promising. The observations at different longitudes suggest that the vertical drift velocities and the vertical density distribution have significant longitudinal differences; especially the equatorial anomaly peaks expand to higher latitudes more in American sector than the African sector, indicating that the vertical drift in the American sector is stronger than the African sector.

Yizengaw, E.; Zesta, E.; Moldwin, M.; Damtie, B.; Mebrahtu, A.; Valladares, C.; Pfaff, R.;

Published by: Journal of Geophysical Research      Published on: 07/2012

YEAR: 2012     DOI: 10.1029/2011JA017454

Tomography; vertical drift

Multi-instrument observations of the ionospheric and plasmaspheric density structure

Yizengaw, E; Moldwin, MB;

Published by:       Published on:

YEAR: 2008     DOI: