Aims. This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods. The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480−1250 GHz with SIS mixers and the 1410−1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s −1 . Results. After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations.

International audienceThe European Space Agency Rosetta Spacecraft, launched on March 2, 2004 toward Comet 67P/Churyumov-Gerasimenko, carries a relatively small and lightweight millimeter-submillimeter spectrometer instrument, the first of its kind launched into deep space. The instrument will be used to study the evolution of outgassing water and other molecules from the target comet as a function of heliocentric distance. During flybys of the asteroids (2867) Steins and (21) Lutetia in 2008 and 2010 respectively, the instrument will measure thermal emission and search for water vapor in the vicinity of these asteroids. The instrument, named MIRO (Microwave Instrument for the Rosetta Orbiter), consists of a 30-cm diameter, offset parabolic reflector telescope followed by two heterodyne receivers. Center-band operating frequencies of the receivers are near 190 GHz (1.6 mm) and 562 GHz (0.5 mm). Broadband continuum channels are implemented in both frequency bands for the measurement of near surface temperatures and temperature gradients in Comet 67P/Churyumov-Gerasimenko and the asteroids (2867) Steins and (21) Lutetia. A 4096 channel CTS (Chirp Transform Spectrometer) spectrometer having 180 MHz total bandwidth and 44 kHz resolution is, in addition to the continuum channel, connected to the submillimeter receiver. The submillimeter radiometer/spectrometer is fixed tuned to measure four volatile species – CO, CH3OH, NH3 and three, oxygen-related isotopologues of water, H2 16O, H2 17O and H2 18O. The basic quantities measured with the MIRO instrument are surface temperature, gas production rates and relative abundances, and velocity and excitation temperature of each species, along with their spatial and temporal variability. This paper provides a short discussion of the scientific objectives of the investigation, and a detailed discussion of the MIRO instrument system

The rapid changes of magnetic fields associated with large, isolated magnetic perturbations with amplitudes |ΔB| of hundreds of nanotesla and 5‐ to 10‐min periods can induce bursts of geomagnetically induced currents that can harm technological systems. This paper presents statistical summaries of the characteristics of nightside magnetic perturbation events observed in Eastern Arctic Canada from 2014 through 2017 using data from stations that are part of four magnetometer arrays: MACCS, AUTUMNX, CANMOS, and CARISMA, covering a range of magnetic latitudes from 68 to 78°. Most but not all of the magnetic perturbation events were associated with substorms: roughly two thirds occurred between 5 and 30 min after onset. The association of intense nighttime magnetic perturbation events with magnetic storms was significantly reduced at latitudes above 73°, presumably above the nominal auroral oval. A superposed epoch study of 21 strong events at Cape Dorset showed that the largest |dB/dt| values appeared within an ~275‐km radius that was associated with a region of shear between upward and downward field‐aligned currents. The statistical distributions of impulse amplitudes of both |ΔB| and |dB/dt| fit well the log‐normal distribution at all stations. The |ΔB| distributions are similar over the magnetic latitude range studied, but the kurtosis and skewness of the |dB/dt| distributions show a slight increase with latitude. Knowledge of the statistical characteristics of these events has enabled us to estimate the occurrence probability of extreme impulsive disturbances using the approximation of a log‐normal distribution.

The rapid changes of magnetic fields associated with nighttime magnetic perturbations with amplitudes |ΔB| of hundreds of nanoteslas and 5‐ to 10‐min periods can induce bursts of geomagnetically induced currents that can harm technological systems. This paper presents three cases of intervals of intense and complex nighttime magnetic perturbations in eastern Arctic Canada in 2015, augmented by observations from auroral imagers and high‐altitude spacecraft in the nightside magnetosphere. Each case occurred within 1 hr after substorm onsets. None occurred during the main phase of a geomagnetic storm, and only the first during the early recovery phase (of a moderate storm). The cases were similar in that two or three intervals occurred in this region over a span of ~1 hr; these showed a spatial progression, in that successive intervals occurred later at more western and northern stations. During several intervals, individual peak Bx impulses occurred nearly simultaneously (within 1–2 min) at several stations, while during others the impulses occurred later at more western and northern stations, and during one interval they occurred later at southern stations. During both of the cases for which auroral images were available, a westward traveling surge and a poleward auroral expansion and/or poleward boundary intensification occurred, and during two events auroral streamers coincided in time and location with magnetic perturbations. These observations appear to be consistent with several earlier studies connecting nighttime magnetic perturbation events to localized auroral structures and to dipolarizing flux bundles and bursty bulk flows in the magnetotail.

We present 2 years of observations of ≥6 nT/s magnetic perturbation events (MPEs) from 5 high latitude Arctic stations. Most MPEs occurred within 30 min of a substorm onset, but substorms were neither necessary nor sufficient to cause MPEs. Premidnight and postmidnight MPEs had different temporal relations to substorms and occurred at slightly different latitudes.