J. W. MacDougall

Western University

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P. T. Jayachandran

University of New Brunswick

W. K. Hocking

Western University

A. H. Manson

University of Saskatchewan

I. S. Batista

National Institute for Space Research

C. E. Meek

University of Saskatchewan

M. A. Abdu

National Institute for Space Research

K. Igarashi

Tokyo University of Marine Science and Technology

P. Prikryl

University of New Brunswick

S. C. Mushini

University of Calgary

T. Thayaparan

Defence Research and Development Canada

Cooperative Institutions

University of Michigan–Ann Arbor

University of California, Berkeley

School of International Relations

University of Saskatchewan

National Institute for Space Research

Western University

Harvard University

Cornell University

Stanford University

Massachusetts Institute of Technology

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Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

Annales Geophysicae (1999)

P. Prikryl J. W. MacDougall I. F. Grant D. P. Steele G. J. Sofko

A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (Kp = 7- and IMF Bz < 0). The ionosondes measured electron densities of up to 9 × 1011 m-3 in the patch center, an increase above the density minimum between patches by a factor of \sim4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF By > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (flow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 field line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric field associated with the FLRs resulted in a poleward-progressing zonal flow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF By) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfvén waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfvén waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric field associated with the Alfvén waves modulated the subsolar magnetic reconnection into pulses that resulted in convection flow bursts mapping to the ionospheric footprint of the cusp.Key words. Ionosphere (polar ionosphere). Magneto- spheric physics (magnetosphere-ionosphere interactions; polar wind-magnetosphere interactions).

Field line

Backscatter (email)

Electron precipitation

10.1007/s005850050775

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Citations (1)

Equatorial electrojet and Sq current system. I.

Journal of geomagnetism and geoelectricity (1979)

J. W. MacDougall

A new method based on covariance analysis is used to map the current patterns associated with variations of the equatorial electrojet. These patterns show that the electrojet is the expected equatorial enhancement of a coherent, large scale current system. This current system is further broken down and found to be composed of a part which is identified as the standard lunar current system and a part which is probably due to localized dynamo region wind fluctuations near the equator. Neither of these parts can be identified as the Sq current system. The problem will be investigated further in the second part of this study.

Equatorial electrojet

Electrojet

10.5636/jgg.31.341

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Citations (14)

Wave structure and polarization electric field development in the bottomside F layer leading to postsunset equatorial spread F

Journal of Geophysical Research Space Physics (2015)

M. A. Abdu J. R. Souza E. A. Kherani I. S. Batista J. W. MacDougall

Abstract In this paper we present the results of a study on the characteristics of large‐scale wave structure in the equatorial ionospheric F region that serve as precursor to postsunset development of the spread F /plasma bubble irregularities. The study is based on analysis of Digisonde data from three equatorial sites in Brazil (Fortaleza, Sao Luis, and Cachimbo) for a period of about 2 months at a medium solar activity phase. Small‐amplitude oscillations in the F layer heights, extracted at a number of plasma frequencies, present characteristics as them being generated from upward propagating gravity waves. They represent wave structures in polarization electric field having zonal scale of a few hundred kilometers. Their amplitudes in the afternoon hours undergo amplification toward evening, leading to postsunset development of equatorial spread F /plasma bubble irregularities, on a statistical basis. On the days of their larger amplitudes they appear to occur in phase coherence on all days, and correspondingly, the evening prereversal vertical drift velocities are larger than on days of the smaller amplitudes of the wave structure that appear at random phase on the different days. The sustenance of these precursor wave structures is supported by the relatively large ratio (approaching unity) of the F region‐to‐total field line‐integrated Pedersen conductivities as calculated using the Sheffield University Plasmasphere‐Ionosphere Model simulation of the low‐latitude ionosphere. The significant amplification in the wave structure toward sunset and the “phase coherent” nature of their occurrences on different days are explained tentatively on the basis of the spatial resonance mechanism.

Sunset

Plasmasphere

Field line

Middle latitudes

10.1002/2015ja021235

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Citations (47)

Traveling ionospheric disturbances near London, Canada

Journal of Atmospheric and Solar-Terrestrial Physics (2009)

J. W. MacDougall G. Li P. T. Jayachandran

Sunrise

Sunset

10.1016/j.jastp.2009.09.016

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Citations (19)

Solar flux effects on the equatorial evening vertical drift and meridional winds over Brazil: A comparison between observational data and the IRI model and the HWM representations

Advances in Space Research (2010)

M. A. Abdu I. S. Batista C. G. M. Brum J. W. MacDougall A. M. Santos

Meridional flow

10.1016/j.asr.2010.06.009

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Citations (28)

Mesosphere/lower thermosphere prevailing wind model

cosp (2002)

Yu. I. Portnyagin T.V. Solovjova E. G. Merzlyakov J. Forbes S. E. Palo

Source

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Citations (0)

Polar cap voltage saturation

Journal of Geophysical Research Atmospheres (2006)

J. W. MacDougall P. T. Jayachandran

Cross polar cap voltage saturation has been observed by various measurement techniques. An example of the saturation is shown in this paper and an explanation is proposed in terms of magnetospheric current behavior. The cross cap voltage saturation might be associated with either a voltage source or a current source effect since the cross cap potential and cross cap current are related by Ohm's law. The cross cap current is the difference between the Region 1 current influx to the polar cap boundary and the Region 2 current. Because, during high interplanetary magnetic field (IMF) −Bz conditions, the Region 2 current is significantly enhanced, the cross cap current, and hence cross cap voltage, is not anomalously higher than usual. Our measurements show agreement with Region 2 (partial ring current) enhancement during high IMF −Bz conditions.

Polar cap

Saturation (graph theory)

Saturation current

10.1029/2006ja011741

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Citations (17)

Use of varying shell heights derived from ionosonde in calculating Total Electron Content (TEC) using GPS, a new method.

37th COSPAR Scientific Assembly (2008)

S. C. Mushini Thayyil Jayachandran Richard B. Langley J. W. MacDougall

Ionosonde

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30 Gbit/s PAM4 transmission using an 8-GHz directly modulated multi-section laser

Optics Express (2022)

Marcos Troncoso Costas Ahmed Galib Reza Hima Putta Ankit Sharma Gaurav Jain

This paper describes the characterization of a novel directly modulated multi-section laser with a master-slave configuration. Amplitude and phase noise measurements show relative intensity noise values of around -150 dB/Hz and a 3-dB linewidth of around 3 MHz. The laser's suitability for optical access networks, enabled by the chirp reduction from the external injection locking, is shown by demonstrating unamplified 30 Gbit/s C-band transmission over 25 km and 50 km of single mode fiber using PAM4, as well as 30 Gbit/s PAM4 and PAM8 amplified transmission over 75 km.

Relative intensity noise

Laser linewidth

Chirp

Gigabit

10.1364/oe.457603

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Citations (2)

Oscillations of the equatorward boundary of the ion auroral oval – radar observations

Journal of Geophysical Research Atmospheres (2008)

P. T. Jayachandran Natsuo Sato Yusuke Ebihara A. S. Yukimatu Akira Kadokura

Three SuperDARN radars in the afternoon‐midnight sector of the auroral oval detected a boundary oscillation, originating near ∼1800 MLT sector. Analysis of the phase of the oscillations measured in three meridians indicates that the disturbance has a longitudinally (azimuthally) isolated source and away from which it propagates. The eastward and westward phase speeds are 2.6 and 3.6 km/s respectively and the period is roughly 28 minutes. An examination of the geo‐synchronous magnetic field inclination also revealed oscillations similar to the oscillations of the boundary. Solar wind and IMF conditions were steady during the period except for variations of the IMF By component. The IMF By component showed variations similar to the oscillations in the boundary and the geo‐synchronous magnetic field inclination. During reduced and negative IMF By, the boundary was moving equatorward, while during increased or positive IMF By it was moving poleward. The variations in the magnetic field inclination measured at geosynchronous orbit by the GOES satellites were consistent with these boundary motions: decreases (more stretched) and increases (more dipolar) in the inclination corresponded to equatorward and poleward moving boundaries, respectively. Polar cap convection also showed changes in the direction of the convection in response to the change in the IMF B y component. Observed oscillation of the boundary can be explained by stretching of the tail field lines due to asymmetric merging associated with changes in the By component of the interplanetary magnetic field.

Substorm

Oscillation (cell signaling)

Field line

10.1029/2007ja012870

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Citations (1)