03/26/2025
By Lynne Schaufenbil

Please join the Lowell Center for Space Science and Technology for a seminar by Dr.Cesar E. Valladares, Institute for Scientific Research, Boston College, on Thursday, April 17 at 11 a.m.

Title: "On the Future of the LISN Network and Its Use to Understand N1K Irregularities"

Abstract:

This presentation will show recent advances obtained with the Low-latitude Ionospheric Sensor Network (LISN) associated with the formation of low-latitude plasma depletions and its effects on Space Weather. It will also present new plans to use LISN to forecast the state of the ionosphere and the onset of plasma bubbles. Recently, it has been demonstrated that during the SSW event of February 2016, a highly asymmetric anomaly was observed that varied as a function of longitude, reversing the asymmetry similarly to the SSW event of February 2016. Increased scintillations were measured as the TEC depletions moved eastward. It is suggested that the variability of the anomaly’s asymmetry is associated with a zonal gradient of the meridional neutral wind that can enhance L-band scintillations through the wind gradient instability when ΔU·ΔN < 0.

The LISN network and the Jicamarca digisonde have also been used to diagnose near-one-kilometer (N1K) irregularities. These structures are characterized by a prominent 1 km scale size detected with satellites. N1K irregularities generate moderate to high levels of scintillations and are associated with a frequency-type spread in ionograms. Satellite in-situ observations reveal that N1K irregularities occur within an extended (>1000 km) and continuous longitudinal sector, where plasma densities are lower than adjacent sectors outside the N1K region. Digisonde measurements indicate that the F layer within the N1K region rises, producing the apparent satellite density decrease. TEC latitudinal profiles during N1K irregularities exhibit a highly asymmetric equatorial ionization anomaly (EIA) in which the southern crest is absent. These observations point to the involvement of a plasma instability distinct from Rayleigh-Taylor in initiating N1K irregularities. The final point of this presentation will deal with a theoretical model that can create N1K irregularities and increase the S4 index.

Please contact Lynne Schaufenbil if you wish to attend either in-person or via Zoom.