skip to main content


Title: Source Region and Propagation of Dayside Large‐Scale Traveling Ionospheric Disturbances
Abstract

We examined the source region of dayside large‐scale traveling ionospheric disturbances (LSTIDs) and their relation to cusp energy input. Aurora and total electron content (TEC) observations show that LSTIDs propagate equatorward away from the cusp and demonstrate the cusp region as the source region. Enhanced energy input to the cusp initiated by interplanetary magnetic field (IMF) southward turning triggers the LSTIDs, and each LSTID oscillation is correlated with a TEC enhancement in the dayside oval with tens of minutes periodicity. Equatorward‐propagating LSTIDs are likely gravity waves caused by repetitive heating in the cusp. The cusp source can explain the high LSTID occurrence on the dayside during geomagnetically active times. Poleward‐propagating ΔTEC patterns in the polar cap propagate nearly at the convection speed. While they have similar ΔTEC signatures to gravity wave‐driven LSTIDs, they are suggested to be weak polar cap patches quasiperiodically drifting from the cusp into the polar cap via dayside reconnection.

 
more » « less
Award ID(s):
1907698 1907483
NSF-PAR ID:
10374865
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Geophysical Research Letters
Volume:
47
Issue:
19
ISSN:
0094-8276
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Dayside solar‐produced concentratedFregion plasma can be transported from the midlatitude region into the polar cap during geomagnetically disturbed period, creating plasma density irregularities like polar cap patches, which can cause scintillation and degrade performance of satellite communication and navigation at polar latitudes. In this paper, we observed and investigated a dynamic formation process of a polar cap patch during the 13 October 2016 intense geomagnetic storm. During the storm main phase, storm‐enhanced density (SED) was formed within an extended period of strong southward interplanetary magnetic field (IMF) Bzcondition. Total electron content (TEC) map shows that a polar cap patch was segmented from the SED plume. The Sondrestrom Incoherent Scatter Radar (ISR) was right underneath the segmentation region and captured the dynamic process. It shows that the patch segmentation was related with a sudden northeastward flow enhancement reaching ~2 km/s near the dayside cusp inflow region. The flow surge was observed along with abruptEregion electron temperature increase,Fregion ion temperature increase, and density decrease. The upstream solar wind and IMF observations suggest that the flow enhancement was associated with dayside magnetic reconnection triggered by a sudden and short period of IMF Bynegative excursion. Quantitative estimation suggests that plasma density loss due to enhanced frictional heating was insufficient for the patch segmentation because the elevatedFregion density peaking at ~500 km made dissociative recombination inefficient. Instead, the patch was segmented from the SED by low‐density plasma transported by the fast flow channel from earlier local time.

     
    more » « less
  2. Abstract. During minor to moderate geomagnetic storms, caused by corotatinginteraction regions (CIRs) at the leading edge of high-speed streams (HSSs), solar windAlfvén waves modulated the magnetic reconnection at the daysidemagnetopause. The Resolute Bay Incoherent Scatter Radars (RISR-C andRISR-N), measuring plasma parameters in the cusp and polar cap, observedionospheric signatures of flux transfer events (FTEs) that resulted in theformation of polar cap patches. The patches were observed as they moved over the RISR, and the Canadian High-Arctic Ionospheric Network (CHAIN)ionosondes and GPS receivers. The coupling process modulated the ionospheric convection and the intensity of ionospheric currents, including the auroral electrojets. The horizontal equivalent ionospheric currents (EICs) are estimated from ground-based magnetometer data using an inversion technique. Pulses of ionospheric currents that are a source of Joule heating in the lower thermosphere launched atmospheric gravity waves, causing travelingionospheric disturbances (TIDs) that propagated equatorward. The TIDs wereobserved in the SuperDual Auroral Radar Network (SuperDARN) high-frequency (HF) radar groundscatter and the detrended total electron content (TEC) measured by globallydistributed Global Navigation Satellite System (GNSS) receivers. 
    more » « less
  3. Abstract

    We present high‐resolution Resolute Bay Incoherent Scatter Radar (RISR) measurements in the cusp region during an IMF southward turning. The simultaneous RISR‐N and RISR‐C operation provided 3‐D observations of the dayside polar region, and offered an opportunity to identify the cusp dynamics and polar cap patch formation. Associated with the IMF southward turning, the F‐region density and temperature increased in the cusp, and the increase was particularly evident in the topside ionosphere. The high‐density plasma drifted into the polar cap by an enhanced poleward convection, and became a polar cap patch. The patch plasma was initially dominated by density originating in the cusp, and then later the subauroral ionospheric plasma also contributed to the density enhancement. Weak upflows were present but their contribution within the RISR altitude range was minor. We suggest that the patch source region switches due to dynamic variations of the cusp precipitation and convection from lower latitudes. RISR also detected a flow vortex embedded in the large‐scale convection, which is likely a poleward moving auroral form (PMAF) signature. Joule heating peaked in the cusp E and lower F‐regions. The F‐region Pedersen conductivity increased more than the Hall conductivity, and the high conductivity region extended poleward associated with the patch density enhancement. A 1‐D cusp simulation reproduced the density and temperature enhancements by soft electron precipitation, indicating the importance of soft electron precipitation for the cusp dynamics and the initial part of the patch formation.

     
    more » « less
  4. Abstract

    Much theoretical and observational work has been devoted to studying the occurrence ofFregion polar cap patches in the Northern Hemisphere; considerably less work has been applied to the Southern Hemisphere. In recent years, the Madrigal database of mappings of total electron content (TEC) has improved in Southern Hemisphere coverage, to the point that we can now carry out a study of patch frequency and occurrence. We find that Southern Hemisphere patch occurrence is very similar to that of the Northern Hemisphere with a half‐year offset, plus an offset in universal time of approximately 12 hr. This is further supported by running an ionospheric model for both hemispheres and applying the same patch‐to‐background technique. Further, we present a simple physical mechanism involving a sunlit dayside plasma source concurrent with a dark polar cap, which yields a patch‐to‐background pattern very much like that seen in the TEC mappings for both hemispheres.

     
    more » « less
  5. We use simultaneous auroral imaging, radar flows, and total electron content (TEC) measurements over Alaska to examine whether there is a direct connection of large-scale traveling ionospheric disturbances (LSTIDs) to auroral streamers and associated flow channels having significant ground magnetic decreases. Observations from seven nights with clearly observable flow channels and/or auroral streamers were selected for analysis. Auroral observations allow identification of streamers, and TEC observations detect ionization enhancements associated with streamer electron precipitation. Radar observations allow direct detection of flow channels. The TEC observations show direct connection of streamers to TIDs propagating equatorward from the equatorward boundary of the auroral oval. The TIDs are also distinguished from the streamers to which they connect by their wave-like TEC fluctuations moving more slowly equatorward than the TEC enhancements from streamer electron precipitation. TIDs previously observed propagating equatorward from the auroral oval have been identified as LSTIDs. Thus, the TIDs here are likely LSTIDs, but we lack sufficient TEC coverage necessary to demonstrate that they are indeed large scale. Furthermore, each of our events shows TID’s connection to groups of a few streamers and flow channels over a period in the order of 15 min and a longitude range of ∼15–20°, and not to single streamers. (Groups of streamers are common during substorms. However, it is not currently known if streamers and associated flow channels typically occur in such groups.) We also find evidence that a flow channel must lead to a sufficiently large ionospheric current for it to lead to a detectable LSTID, with a few tens of nT ground magnetic field decreases not being sufficient. 
    more » « less