Defense Meteorological Satellite Program F16 Research Articles

Latitudinal Characteristics of Nighttime Electron Temperature in the Topside Ionosphere and Its Dependence on Solar and Geomagnetic Activities

This study investigates the latitudinal characteristics of the nighttime electron temperature, as observed by the Defense Meteorological Satellite Program F16 satellite, and its dependence on solar and geomagnetic activities between 2013 and 2022 in the topside ionosphere, only for the winter hemispheres. The electron temperature in both hemispheres exhibited a low-temperature zone at the equator and a double high-temperature zone at the sub-auroral and auroral latitudes along the magnetic latitude. In addition, we further studied the temperature crest/trough positions in the temperature zone at different latitudes. As the solar activity intensity decreased (increased), the temperature trough position at the equator shifted from the Southern (Northern) to the Northern (Southern) Hemisphere, and the temperature double-crest positions at the sub-auroral and auroral latitudes gradually approached (moved away from) each other. Furthermore, during the geomagnetic disturbance time, the temperature double-crest positions both moved toward lower latitudes, but the temperature trough position was not sensitive to geomagnetic activity. Our analysis demonstrates that the values and correlations of the electron temperature and density varied in different temperature characteristic zones (the temperature crest/trough positions ±2°), possibly due to the different energy control factors of the electrons at different latitudes. This may also indirectly indicate the energy coupling process between the topside ionosphere and different regions at different latitudes.

Global Distribution of Electron Temperature Enhancement at Mid‐Low Latitudes Observed by DMSP F16 Satellite

AbstractThis study investigates the global distribution of electron temperature enhancement observed by Defense Meteorological Satellite Program F16 satellite and its dependence on the season and solar activity for the solar maximum (2014) and minimum (2018) years during geomagnetic quiet times (maximum per day ap <10). Electron temperature enhancements occurred mainly over the North American‐Atlantic (260°–360°E) and Eurasia (0°–160°E) (Southern Oceania (80°–280°E)) sector in the Northern (Southern) Hemisphere and are prominent in the winter hemispheres and solar maximum year. They have obvious longitude characteristics. Interestingly, they could extend to geomagnetic equatorial regions in the North American‐Atlantic sector from high to low latitudes in the December Solstice, further crossed the magnetic equator, and merged into the Southern Hemisphere in 2014, where the maximum temperature reached ∼3500 K. Our analysis indicates that low‐energy electrons (<100 eV) associated with photoelectron from the conjugate sunlit hemisphere, can contribute to these enhancements. Furthermore, the local geomagnetic declination, magnetic equator position, and terminator position at magnetic conjugate points together can impact the global distribution of photoelectrons of different energies and therefore the electron temperature enhancement distribution. Other processes (including local electron density variation) may play certain roles as well.

The Association of Cusp‐Aligned Arcs With Plasma in the Magnetotail Implies a Closed Magnetosphere

AbstractWe investigate a 15‐day period in October 2011. Auroral observations by the Special Sensor Ultraviolet Spectrographic Imager instrument onboard the Defense Meteorological Satellite Program F16, F17, and F18 spacecraft indicate that the polar regions were covered by weak cusp‐aligned arc (CAA) emissions whenever the interplanetary magnetic field (IMF) clock angle was small, |θ| < 45°, which amounted to 30% of the time. Simultaneous observations of ions and electrons in the tail by the Cluster C4 and Geotail spacecraft showed that during these intervals dense (≈1 cm−3) plasma was observed, even as far from the equatorial plane of the tail as |ZGSE| ≈ 13 RE. The ions had a pitch angle distribution peaking parallel and antiparallel to the magnetic field and the electrons had pitch angles that peaked perpendicular to the field. We interpret the counter‐streaming ions and double loss‐cone electrons as evidence that the plasma was trapped on closed field lines, and acted as a source for the CAA emission across the polar regions. This suggests that the magnetosphere was almost entirely closed during these periods. We further argue that the closure occurred as a consequence of dual‐lobe reconnection. Our finding forces a significant re‐evaluation of the magnetic topology of the magnetosphere during periods of northwards IMF.

Sub‐Auroral Ion Drifts (SAID) Developed Over the Northern Winter Hemisphere at Dawn During 2016–2017

AbstractWe investigated the rare events of sunward (westward) sub‐auroral ion drifts (SAID) development in the dawn magnetic local time (MLT) sector by utilizing horizontal ion velocity measurements collected by the Defense Meteorological Satellite Program F16 spacecraft. We surveyed the 2‐year time period of 2016–2017 and found only 15 SAID detections made in the 3–6 MLT sector over the northern winter hemisphere: seven in 2016 and eight in 2017. Results show that the dawnside SAID developed poleward of the ring‐current‐related plasma density trough, called ring ionospheric trough (RIT). With a few inner‐magnetosphere observations, we demonstrated that the favorable conditions were created by (a) the proton/ring current injections occurring across the newly‐formed dawnside plasmapause where (b) the ring current ions became unstable. As a result of (a), the outward SAID electric (E) field developed via short‐circuiting, mapped down to the ionosphere as a poleward E field and drove the sunward (westward) SAID flow in the dawn MLT sector. As a result of (b), a localized heat source developed near the newly‐formed dawnside plasmapause in the hot zone and the resultant downward heat flux led to stable auroral red (SAR) arc development when the electron temperature was sufficiently high. Then, the dawnside SAID flow developed parallel with the RIT and SAR arc.

The Dependence of Cold and Hot Patches on Local Plasma Transport and Particle Precipitation in Northern Hemisphere Winter

AbstractBy using a database of 4,634 cold patches (high density and low electron temperature) and 4,700 hot patches (high density and high electron temperature) from Defense Meteorological Satellite Program F16 in 2005–2018 winter months (October–March), we present a statistical survey of the distributions of polar cap patches for different interplanetary magnetic field (IMF) orientations and ionospheric convection geometries. We investigate the dependence of cold and hot patches on local plasma transport and soft‐electron precipitation. Our results indicate that: in winter, (a) more cold and hot patches occur in the stronger anti‐sunward flow organized by different IMF orientations. (b) cold patches are frequent near the central polar cap, while hot patches are closer to the auroral oval. (c) enhanced anti‐sunward flow (E × B drift) mainly contributes to cold patch occurrence under Bz < 0, and soft‐electron precipitation contributes to hot patch occurrence both under southward and northward IMF.

Special Sensor Microwave Imager/Sounder Updates for the Global Precipitation Measurement V07 Data Suite

Observations from the Special Sensor Microwave Imager/Sounder (SSMIS) onboard the Defense Meteorological Satellite Program F16, F17, F18, and F19 spacecrafts provide a significant portion of the microwave radiometer data within the Global Precipitation Measurement (GPM) mission constellation. In preparation for the GPM Version 7 (V07) data release, SSMIS corrections developed over a decade ago and incorporated in GPM Version 5 (V05) are reexamined and updated. The calibration updates presented here include pointing parameters affecting geolocation and viewing geometry, along-scan bias adjustments to account for scan edge falloffs and sun angle corrections to account for heating anomalies including an emissive reflector. To address errors in the V05 geolocation, the sensor roll, pitch, yaw, half cone angle, and timing offsets are reanalyzed and updated. The along-scan bias adjustment is updated in a manner consistent with recent Special Sensor Microwave Imager updates to account for variations in scene temperature. Finally, significant improvements to the SSMIS sun angle correction are made by using data from the entire mission, extending the corrections to include the higher frequency channels, and deriving a more consistent channel-to-channel correction. From V05 to V07, the geolocation adjustment is approximately 5–10 km, the earth incidence angle difference is 0–0.4°, and the average brightness temperature change is 0–2 K, but individual pixels may be up to several kelvin difference depending on sensor and channel. The result of these updates is a significant improvement in the quality and long-term consistency of the SSMIS data that are included in the GPM V07 dataset.

Solar and Geomagnetic Activity Impact on Occurrence and Spatial Size of Cold and Hot Polar Cap Patches

AbstractThis paper is a statistical survey of polar cap patches in relation to solar and geomagnetic activity. Ten thousand six hundred eighty‐eight patches have been identified from in situ plasma observations of the Defense Meteorological Satellite Program F16 satellite for 14 years (2005–2018). These patches are divided into two groups: (a) cold patches, which consist of dense but cold plasma; and (b) hot patches, which consist of dense but hot plasma. The statistical results indicate that (a) the occurrence of cold patches is clearly dependent on solar and geomagnetic activity, but hot patches don not show such dependence; (b) both cold and hot patches preferably appear in the winter season; (c) the spatial size of both cold and hot patches decreases (increases) with solar (geomagnetic) activity; (d) the spatial size of cold patches appears larger than that of hot patches under similar solar and geomagnetic activity.

Auroral Energy Flux Distribution Over the Nightside Auroral Oval Observed by the DMSP F16/SSUSI: Seasonal, Geomagnetic, and Solar Activity Dependences

AbstractThe present work investigates variations in the relative strengths of average premidnight and postmidnight aurorae. The average auroral energy flux data for the southern hemisphere in 2004–2015 are taken from the Special Sensor Ultraviolet Spectrographic Imager onboard the Defense Meteorological Satellite Program F16 satellite. The main findings are as follows: (1) In local winter, the maximum auroral energy flux over the oval is located in the premidnight sector (18:00–00:00 magnetic local time) under geomagnetically quiet condition (Kp = 1) and moves toward the postmidnight sector (00:00–06:00 magnetic local time) as the Kp index increases. (2) In local summer, the maximum energy flux occurs in the postmidnight for higher solar activities (F10.7 > 100 sfu). (3) The premidnight bulge of the auroral energy flux is most prominent under winter, solar minimum and geomagnetically quiet (Kp = 1) conditions. (4) Relatively more auroral energy tends to be deposited in the postmidnight sector than in the premidnight sector as Kp increases. These results show that the auroral energy over the nightside oval is redistributed on average as the season, solar flux, and geomagnetic activity change. This would substantially affect the thermosphere and ionosphere at high latitudes.

Mapping the South Atlantic Anomaly continuously over 27 years

The South Atlantic Anomaly (SAA) is a region of reduced magnetic intensity where the inner radiation belt makes its closest approach to the Earth's surface. Satellites in low-Earth orbit pass though the SAA periodically, exposing them to several minutes of strong radiation each time, creating problems for scientific instruments, human safety, and single event upsets (SEU). For the first time, we are able track the SAA movement continuously over 27 years, using overlapping satellites in similar orbits with similar instruments. The Defense Meteorological Satellite Program (DMSP) spacecraft have been carrying the Special Sensor J (SSJ) precipitating energetic particle spectrometers since 1982. The instruments are susceptible to MeV electrons and protons that pass through the spacecraft skin and instrument case and get counted. This “backgroundˮ is easily identified and we use it to map the movement of the SAA. Comparison with energetic particle data from the Energetic Particle Telescope (EPT) instrument on the Proba-V spacecraft indicates that the best match with the SSJ data occurs in the energy range above about 2.6 MeV for electrons and above about 29 MeV for protons. The peak flux and extent of the SAA from both the SSJ and EPT instruments are nearly identical in longitude while in latitude, the peak EPT flux is 5° south of the peak SSJ flux. However, the shapes of the SAA in latitude and the locations of the outer radiation belts are nearly identical. We find that the SAA moves 0.06° N/yr and 0.28° W/yr. We also find a difference with the movement and location of the SAA from the contamination by high energy particles on the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on DMSP F16 (Shaefer et al., 2016). However, the SSUSI instrument is located on the opposite side/bottom of the spacecraft and Shaefer et al. (2016) estimated that most of the particle noise pulses in the SSUSI instrument are produced by protons greater than about 45 MeV. Thus the contamination in the SSUSI instrument is produced by a different population of particles that the contamination in the SSJ/5 instrument which would lead to differences in movement and location of the SAA. While this study focuses on the SAA movement on a yearly basis, further analysis will allow us to investigate the movement on shorter time scales, the variation of the flux intensity, the spatial extent of the SAA, and the dynamics of the outer radiation belt.

Storm time coupling between the magnetosheath and the polar ionosphere

AbstractThe present study demonstrates the feasibility of using plasma and magnetic field data from Defense Meteorological Satellite Program (DMSP) satellites to estimate the Alfvénic reflectances (α) in the polar cap ionosphere during periods of geomagnetic disturbance. Quantitative values of α are then used to support calculations of field‐aligned Poynting flux (S||i) transmitted along open field lines from magnetosheath generators to the conjugate polar ionospheres. Analyzed data were acquired during high‐latitude passes of DMSP F16 during the 17 March 2013 magnetic storm. Between the main phase onset and the day's end, plasma velocity and magnetic field perturbations manifest the phase relations predicted by Alfvén and Fälthammar (1963) for electromagnetic coupling. The most reliable (sunward‐antisunward) components of measured plasma velocities and magnetic perturbations are consistent with that α ranging between 0.65 and 0.97, with a mean of ~0.8. Subsequent calculations indicate that incident S||i varied between 0.2 and 0.02 W/m2 with a mean of 0.085. We suggest that these reported ranges of α and S||i reflect both large variations in IMF BZ and the growth of antisunward neutral winds in the polar caps during the storm's main phase.

Equatorward propagating auroral arcs driven by ULF wave activity: Multipoint ground‐ and space‐based observations in the dusk sector auroral oval

AbstractObservations of multiple equatorward propagating arcs driven by a resonant Alfvén wave on closed field lines are presented. Data sets from the European Incoherent Scatter Svalbard Radar (ESR) and Meridian Scanning Photometer in Longyearbyen, All‐Sky Camera in Ny Ålesund, ground magnetometer data in Svalbard, and Defense Meteorological Satellite Program (DMSP) F16 satellite were utilized to study the arc structures. The arcs had an equatorward phase propagation of ~0.46 km s−1 and were observed in the dusk ionosphere from 1800 to 2030 magnetic local time. Analysis of the optical data indicates that the Alfvén wave had a frequency of 1.63 mHz and an azimuthal wave number, m ~ −20 (the negative sign indicating a westward propagation). Inverted‐V electron populations associated with field‐aligned currents of between 0.5 and 0.8 μA m−2 are observed by DMSP F16 inside the arc structures. In addition to electron density enhancements associated with the arcs, the ESR data show elevated ion temperatures in between the arcs consistent with electric field enhancements and ionospheric heating effects. The combination of ESR and DMSP F16 data indicates that the wave energy was dissipated through ionospheric Joule and/or ion frictional heating and acceleration of particles into the ionosphere, generating the auroral displays. The fine‐scale structuring, in addition to the propagation direction and scale size, would suggest that the auroral features are the signatures of a field line resonance driven by an interaction with a compressional fast mode wave propagating earthward from the magnetotail.

Dynamic properties of throat aurora revealed by simultaneous ground and satellite observations

AbstractThroat aurora is defined as south‐north aligned auroral arcs equatorward of the dayside cusp aurora and was suggested to be the results of cold magnetospheric plasma interaction with magnetopause reconnection, but its observational properties have not yet been well established. In this paper we carefully examine a sequence of throat auroras observed over Svalbard on 27 December 2003. Observations from 630.0 nm [OI] show that poleward moving throat auroras frequently show brightening followed by dimming in auroral intensity, and sometimes, the brightening throat aurora is a precursor of poleward moving auroral forms. Simultaneous all‐sky images and HF radar backscatter observations along geomagnetic meridian show that the throat aurora brightening is drifting with ionospheric E × B convection and is colocated with enhanced spectral width poleward of the convection reversal boundary (CRB), while its dimming tends to be in the vicinity of the CRB. This leads us to propose that the throat aurora brightening and dimming may be on the open and closed field lines, respectively. Particle data from NOAA 16 confirm that the dimming throat aurora is associated with precipitation of magnetosheath‐like particles mixed with magnetospheric ions (>30 keV), which is characteristic of the low‐latitude boundary layer. For particle data from Defense Meteorological Satellite Program F16, we notice that the dimming throat aurora is associated with lower fluxes of magnetosheath‐like electrons accompanied with magnetospheric electrons, which is most likely on closed field lines. The dynamic properties of throat aurora presented in this paper are thus important to understand its generation mechanisms.