skip to main content


The NSF Public Access Repository (NSF-PAR) system and access will be unavailable from 10:00 PM ET on Friday, December 8 until 2:00 AM ET on Saturday, December 9 due to maintenance. We apologize for the inconvenience.

Title: Ion Heating in the Polar Cap Under Northwards IMF Bz

Joule heating deposits a significant amount of energy into the high‐latitude ionosphere and is an important factor in many magnetosphere‐ionosphere‐thermosphere coupling processes. We consider the relationship between localized temperature enhancements in polar cap measured with the Resolute Bay Incoherent Scatter Radar‐North (RISR‐N) and the orientation of the interplanetary magnetic field (IMF). Based on analysis of 10 years of data, RISR‐N most commonly observes ion heating in the noon sector under northwards IMF. We interpret heating events in that sector as being primarily driven by sunwards plasma convection associated with lobe reconnection. We attempt to model two of the observed temperature enhancements with a data‐driven first principles model of ionospheric plasma transport and dynamics, but fail to fully reproduce the ion temperature enhancements. However, evaluating the ion energy equation using the locally measured ion velocities reproduces the observed ion temperature enhancements. This result indicates that current techniques for estimating global plasma convection pattern are not adequately capturing mesoscale flows in the polar cap, and this can result in underestimation of the energy deposition into the ionosphere and thermosphere.

more » « less
Award ID(s):
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Space Physics
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. 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
  2. Abstract

    Based on the observations from the balloon‐borne instrument High‐altitude Interferometer WIND experiment (HIWIND) and the simulations from the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM), the Grid Agnostic MHD Environment for Research Applications (GAMERA)‐TIEGCM (GT), and the GAMERA‐TIEGCM‐RCM (GTR), we investigate the variations of summer high‐latitude thermospheric winds and their physical mechanisms from 25 to 30 June, 2018. HIWIND observations show that the meridional winds were the largest at midnight and exhibited strong day‐to‐day variations during the 6‐day period, which were generally reproduced by those three models. The day‐to‐day variations of winds were mainly associated with the interplanetary magnetic field (IMF)perturbations, while the magnetic latitude variations also contributed to the large day‐to‐day variations of the winds seen in the observations. Meanwhile, the zonal winds were mostly westward during the daytime, and the wind speed became large, especially in the afternoon, which is related to the westward ion drift velocity. The observed meridional winds tend to turn equatorward during the daytime on some days, while the simulated winds blow mostly poleward except for simulations by the GTR model on 26 June. The GTR model revealed that the equatorward meridional winds on 26 June were associated with strong and negative IMFconditions, which tilts the convection pattern to the prenoon sector. The simulations also revealed that the ring current could contribute to affecting the neutral wind variations, especially under geomagnetically active conditions.

    more » « less
  3. Abstract

    We have measured auroral zone thermospheric neutral winds in the midnight local time sector, using ground‐based optical Doppler spectroscopy of the 630.0 nm emission from atomic oxygen, originating at around 240 km altitude over Alaska. One of the most prominent features seen in winds at these latitudes is the cross‐polar jet emerging from the polar cap at local times around magnetic midnight. The standard view is that wind flows anti‐sunward in the midnight sector and spills equatorward over magnetic latitudes extending well below those of the auroral zone. The purpose of this paper is to show that this view is too simplistic. From our observatory at Poker Flat, Alaska (∼N), the anti‐sunward flow is frequently seen to stall over surprisingly short horizontal distances (100–200 km), without spilling further equatorward. This behavior is most prevalent during a low solar activity at mid‐winter when the combination of pressure gradient established by solar heating and the ion drag is not enough to allow the jet to push through the background atmosphere on the nightside. At higher latitudes, by contrast, the flow is relatively uniformly anti‐sunward around magnetic midnight even during quiet conditions. During periods of high solar and magnetic activity, the expected spilling of the midnight sector cross‐polar jet to lower latitudes often is indeed observed over Alaska. Our observation of abrupt stalling during quiet solar and geomagnetic conditions is a very significant difference from the model predictions, with potentially important ramifications‐ which is the motivation for the present study.

    more » « less
  4. 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
  5. Abstract

    In this paper, we present a case study of the radial interplanetary magnetic field (IMFBx)‐induced asymmetric solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling between the northern and southern polar caps using ground‐based and satellite‐based data. Under prolonged conditions of strong earthward IMF on 5 March 2015, we find significant discrepancies between polar cap north (PCN) and polar cap south (PCS) magnetic indices with a negative bay‐like change in the PCN and a positive bay‐like change in the PCS. The difference between these indices (PCN‐PCS) reaches a minimum of −1.63 mV/m, which is approximately three times higher in absolute value than the values for most of the time on this day (within ±0.5 mV/m). The high‐latitude plasma convection also shows an asymmetric feature such that there exists an additional convection cell near the noon sector in the northern polar cap, but not in the southern polar cap. Meanwhile, negative bays in the north‐south component of ground magnetic field perturbations (less than 50 nT) observed in the nightside auroral region of the Northern Hemisphere are accompanied with the brightening and widening of the nightside auroral oval in the Southern Hemisphere, implying a weak, but clear energy transfer to the nightside ionosphere of both hemispheres. After the hemispheric asymmetries in the polar caps disappear, a substorm onset takes place. All these observations indicate that IMFBx‐induced single lobe reconnection that occurred in the Northern Hemisphere plays an important role in hemispheric asymmetry in the energy transfer from the solar wind to the polar cap through the magnetosphere.

    more » « less