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Whistler-mode chorus waves are critical for driving resonant scattering and loss of radiation belt relativistic electrons into the atmosphere. The resonant energies of electrons scattered by chorus waves increase at increasingly higher magnetic latitudes. Propagation of chorus waves to middle and high latitudes is hampered by wave divergence and Landau damping but is promoted otherwise if ducted by density irregularities. Although ducting theories have been proposed since the 1960’s, no conjugate observation of ducted chorus propagation from the equatorial magnetosphere to the ionosphere has been observed so far. Here we provide such an observation, for the first time, using conjugate spacecraft measurements. Ducted chorus waves maintain significant wave power upon reaching the ionosphere, which is confirmed by ray tracing simulations. Our results suggest that ducted chorus waves may be an important driver for relativistic electron precipitation.

On behalf of the journal, AGU, and the scientific community, the editors would like to sincerely thank those who reviewed the manuscripts for Geophysical Research Letters in 2020. The hours reading and commenting on manuscripts not only improve the manuscripts but also increase the scientific rigor of future research in the field. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. The COVID pandemic imposed additional stresses on the review process, as many reviewers had to juggle increased family commitments, hours of online meetings, remote work and instruction, lack of physical access to library resources, and other hardships to maintain the quality and timeliness of their reviews. Although we witnessed an increase in the number of submissions, the average number of days to complete a review increased by less than one day!! That says a lot about the diligence of our reviewers. We deeply appreciate their contributions in these challenging times. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. Individuals in italics provided three or more reviews for Geophysical Research Letters during the year. In total, 5,177 referees contributed to 8,786 individual reviews. Thank you again. We look forward to the coming year of exciting advances in the field and communicating those advances to our community and to the broader public.

Author(s): Rajaram, H; Diffenbaugh, N; Camargo, S; Cardenas, MB; Carey, R; Cobb, K; Cory, R; Cronin, M; Dombard, A; Donohue, K; Flesch, L; Giannini, A; Hayes, G; Hogg, A; Ilyina, T; Ivanov, V; Jacobsen, S; Korte, M; Lu, G; Morlighem, M; Magnusdottir, G; Newman, A; Opher, M; Passalacqua, P; Patricola, C; Ritsema, J; Sprintall, J; Su, H; Thornton, J; Williams, P; Yau, A | Abstract: On behalf of the journal, AGU, and the scientific community, the Editors would like to sincerely thank those who reviewed manuscripts for Geophysical Research Letters in 2018. The hours reading and commenting on manuscripts not only improves the manuscripts but also increases the scientific rigor of future research in the field. We particularly appreciate the timely reviews, in light of the demands imposed by the rapid review process at Geophysical Research Letters. With the revival of the “major revisions” decisions, we appreciate the reviewers' efforts on multiple versions of some manuscripts. Many of those listed below went beyond and reviewed three or more manuscripts for our journal, and those are indicated in italics. In total, 4,484 referees contributed to 7,557 individual reviews in journal. Thank you again. We look forward to the coming year of exciting advances in the field and communicating those advances to our community and to the broader public.

International audience; This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed.

In the first part of this paper, we present observations of thermal H+ and O+ ion outflow in the middle to high altitude polar ionosphere from the Suprathermal ion Mass Spectrometer on Akebono satellite. Variations of H+ and O+ ion flux are given as a function of the geomagnetic activity or the interplanetary magnetic field for different magnetic local time or invariant latitude regions. It is shown that the normalized H+ polar wind flux (to 2000 km altitude) varies from 107 to 108 cm−2 s−1. At both magnetically quiet and active times, the integrated H+ ion flux is largest in the noon sector (09∼15 MLT) and smallest in the midnight sector (21∼03 MLT). The O+ ion flux was found to correlate positively with the Kp index. In the second part, simultaneous observations of the polar ion outflow is presented by using two instruments for thermal ions and electrons on the Akebono satellite and Sondrestrom radar in the polar ionosphere, with focussing on the dynamics of the ion outflow and its causal relationship to the plasma pressure profile. The drift velocity in the spin plane, plasma temperatures and number density are estimated from the satellite observation at high altitudes (≥ 1500 km), while at low altitudes (≤ 900 km), these parameters are obtained from the radar observation. In the pass of 14h UT on Oct. 15, 1992 (Kp=4+), high electron temperatures and low number density obtained from the satellite observations are in good agreement with the radar observation. In this event, the high velocity (∼8 km/s at 2500 km) of the H+ outflow was significant, while lower velocity of the H+ was accompanied by low electron temperature and high density in the pass on Oct. 22, 1992 (Kp=3). Also, it should be noted that characteristic feature of the polar wind (Te, Ti < 1 eV) was successively observed as low as 70° invariant latitude.

著者人数：11名, Accepted: 1995-12-13, 資料番号: SA1001669000

著者人数：13名, Accepted: 1994-06-27, 資料番号: SA1001259000

Accepted: 1992-08-24, 資料番号: SA1001658000

Accepted: 1993-09-29, 資料番号: SA1001676000

The imaging and rapid-scanning ion mass spectrometer (IRM) is part of the Enhanced Polar Outflow Probe (e-POP) instrument suite on the Canadian CASSIOPE small satellite. Designed to measure the composition and detailed velocity distributions of ions in the ∼1–100 eV/q range on a non-spinning spacecraft, the IRM sensor consists of a planar entrance aperture, a pair of electrostatic deflectors, a time-of-flight (TOF) gate, a hemispherical electrostatic analyzer, and a micro-channel plate (MCP) detector. The TOF gate measures the transit time of each detected ion inside the sensor. The hemispherical analyzer disperses incident ions by their energy-per-charge and azimuth in the aperture plane onto the detector. The two electrostatic deflectors may be optionally programmed to step through a sequence of deflector voltages, to deflect ions of different incident elevation out of the aperture plane and energy-per-charge into the sensor aperture for sampling. The position and time of arrival of each detected ion at the detector are measured, to produce an image of 2-dimensional (2D), mass-resolved ion velocity distribution up to 100 times per second, or to construct a composite 3D velocity distribution by combining successive images in a deflector voltage sequence. The measured distributions are then used to investigate ion composition, density, drift velocity and temperature in polar ion outflows and related acceleration and transport processes in the topside ionosphere.

The Enhanced Polar Outflow Probe (e-POP) on the polar-orbiting CASSIOPE small satellite (325×1500 km, 80° inclination) is a suite of 8 plasma instruments, including imaging plasma and neutral particle sensors, magnetometers, dual-frequency Global Positioning System (GPS) receivers, charge coupled-device (CCD) cameras, a radio wave receiver and a beacon transmitter. The scientific objective of e-POP is to make observations of mesoscale and microscale plasma processes in the topside high-latitude ionosphere at the highest-possible resolution, specifically to study the microscale characteristics of plasma outflow and related acceleration processes, the occurrence morphology of neutral escape, and the effects of auroral currents on plasma outflow and those of plasma microstructures on radio propagation: the strategy is to use the large data storage and high-speed telemetry downlink capacity of a companion, experimental communications payload on board CASSIOPE to support the high-resolution observations of particle distributions, waves and magnetic fields to 10-ms time scale (∼100 m spatial scale) and the imaging of the aurora on 100-ms time scale, as well as imaging studies of the ionosphere in conjunction with ground-based transmitters and ground receiving stations on comparable (10–100 ms) time scales.

The Suprathermal Electron Imager (SEI) on the Enhanced Polar Outflow Probe (e-POP) experiment uses a microchannel-plate-intensified charge-coupled device (CCD) detector to record two-dimensional, energy-angle images of electron distributions for energies up to 350 eV. Alternatively, the SEI can be biased to measure positive ions at energies that include the ambient ionospheric population (

Field-aligned currents couple energy between the Earth's magnetosphere and ionosphere and are responsible for driving both micro and macro motions of plasma and neu- tral atoms in both regimes. These currents are believed to be a contributing energy source for ion acceleration in the polar ionosphere and may be detected via measurements of magnetic gradients along the track of a polar orbiting spacecraft, usually the north-south gradients of the east-west field component. The detection of such gradients does not require observatory class measurements of the geomagnetic field. The Magnetic Field instrument (MGF) mea- sures the local magnetic field onboard the Enhanced Polar Outflow Probe (e-POP) satellite by using two ring-core fluxgate sensors to characterize and remove the stray spacecraft field. The fluxgate sensors have their heritage in the MAGSAT design, are double wound for re- duced mass and cross-field dependence, and are mounted on a modest 0.9 m carbon-fiber boom. The MGF samples the magnetic field 160 times per sec (∼ 50 meters) to a resolution

The Fast Auroral Imager (FAI) consists of two charge-coupled device (CCD) cameras: one to measure the 630 nm emission of atomic oxygen in aurora and enhanced night airglow; and the other to observe the prompt auroral emissions in the 650 to 1100 nm range. High sensitivity is realized through the combination of fast lens systems (f/0.8) and CCDs of high quantum efficiency (>90 % max). The cameras have a common 26 degree field-of-view to provide nighttime images of about 650 km diameter from apogee at 1500 km. The near infrared camera provides up to two images of 0.1 s exposure per second with a spatial resolution of a few km when the camera is pointing in the nadir direction, making it suitable for studies of dynamic auroral phenomena. The 630-nm camera has been designed to provide one image of 0.5 s exposure every 30 seconds. Launch of the satellite occurred on September 29, 2013. Following a description of the instrument, sample auroral images are presented.