Context. Total and spectral solar irradiance are key parameters in the assessment of solar influence on changes in the Earth's climate. Aims. We present a reconstruction of daily solar irradiance obtained using the SATIRE-S model spanning 1974 to 2013 based on full-disc observations from the KPVT, SoHO/MDI, and SDO/HMI. Methods. SATIRE-S ascribes variation in solar irradiance on timescales greater than a day to photospheric magnetism. The solar spectrum is reconstructed from the apparent surface coverage of bright magnetic features and sunspots in the daily data using the modelled intensity spectra of these magnetic structures. We cross-calibrated the various data sets, harmonizing the model input so as to yield a single consistent time series as the output. Results. The model replicates 92% (R 2 = 0.916) of the variability in the PMOD TSI composite including the secular decline between the 1996 and 2008 solar cycle minima. The model also reproduces most of the variability in observed Lyman-α irradiance and the Mg II index. The ultraviolet solar irradiance measurements from the UARS and SORCE missions are mutually consistent up to about 180 nm before they start to exhibit discrepant rotational and cyclical variability, indicative of unresolved instrumental effects. As a result, the agreement between model and measurement, while relatively good below 180 nm, starts to deteriorate above this wavelength. As with earlier similar investigations, the reconstruction cannot reproduce the overall trends in SORCE/SIM SSI. We argue, from the lack of clear solar cycle modulation in the SIM record and the inconsistency between the total flux recorded by the instrument and TSI, that unaccounted instrumental trends are present. Conclusions. The daily solar irradiance time series is consistent with observations from multiple sources, demonstrating its validity and utility for climate models. It also provides further evidence that photospheric magnetism is the prime driver of variation in solar irradiance on timescales greater than a day.
Abstract. THEMIS was launched onDuring the coast phase the probes were put into a string-of-pearls configuration at 100s of km to 2R E along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007.THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents.These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.2
[1] A series of seven hot flow anomaly (HFA) events has been observed by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) C spacecraft just upstream from the subsolar bow shock from 0100 to 1300 UT on 19 August 2008. Both young (no shocks at edges, two distinct ion populations) and mature (strong shocks at edges, a single hot ion population) HFAs have been observed. Further upstream, THEMIS B observed four proto-HFAs (density and magnetic field strength depletions, plasma heating but no flow deflections) which later developed into HFAs observed by THEMIS C. We present evidence indicating that electromagnetic right-hand resonant ion beam instabilities heat ions inside HFAs. Observations of small-amplitude perturbations (DB/B < 50%) consistent with the resonant ion beam instability in a proto-HFA, 30 s electromagnetic waves (DB/B ∼ 1) in a young HFA, and magnetic pulsations in a mature HFA (DB/B ∼ 4) indicate that they are at early, middle, and late (nonlinear) stages of the electromagnetic right-hand resonant ion beam instabilities. Both young and mature HFAs are associated with strong electromagnetic waves near the lower hybrid frequency (0.1-1 Hz). The lower hybrid waves are the likely source of the electron heating inside HFAs. THEMIS B observations of four proto-HFAs which later developed into HFAs observed by THEMIS C indicate that these four HFAs might extend beyond 14 R E upstream from the bow shock, while the other three HFAs may extend between 5 and 14 R E upstream from the bow shock. We present an example of an HFA that lies displaced toward the side of the tangential discontinuity with a quasi-parallel bow shock configuration rather than lying centered on the driving interplanetary magnetic field discontinuity.
[1] The intensification of the nightside whistler-mode chorus emissions is observed in the low-density region outside the plasmapause during the injection of anisotropic plasma sheet electrons into the inner magnetosphere. Time History of Events and Macroscale Interactions During Substorms data of the electron phase space density over the energy range between 0.1 keV and 30 keV are used to develop an analytical model for the distribution of injected suprathermal electrons. The path-integrated gain of chorus waves is then evaluated with the HOTRAY code by tracing whistler-mode chorus waves in a hot magnetized plasma. The simulated wave gain is compared to the observed wave electric field and magnetic field, respectively. The results indicate that lower-energy (<1 keV) plasma sheet electrons can penetrate deeper toward the Earth but cause little chorus intensification, while higher-energy (1 keV to tens of kiloelectron volts) electrons can be injected at relatively higher L-shells and are responsible for the intensification of lower-band and upper-band whistler-mode chorus. Compared to the lower-band chorus, a relatively higher electron anisotropy is required to generate upper-band chorus. In addition, higher plasma density results in stronger wave intensity and a broader frequency band of chorus waves.
to 1441 UT, when the five THEMIS probes (THA, THB, THC, THD, and THE) were located near the subsolar magnetopause, a sunward flow was observed in the magnetosheath. A fast antisunward flow (À280 km/s) was observed in the magnetosheath before the sunward flow. Although THA observed this fast anti-sunward flow, THC and THD, which were also in the magnetosheath, instead observed a slow flow, indicating that the fast flow was small in scale. With the observed flow vectors and the magnetopause normal directions estimated from tangential discontinuity analysis, we conclude that this fast flow creates an indentation on the magnetopause, 1 R E deep and 2 R E wide. The magnetopause subsequently rebounds, rotating the flow direction sunward along the surface of the magnetopause. The fast flow is likely related to the radial interplanetary magnetic field.
Early observations by the THEMIS ESA plasma instrument have revealed new details of the dayside magnetosphere. As an introduction to THEMIS plasma data, this paper presents observations of plasmaspheric plumes, ionospheric ion outflows, field line resonances, structure at the low latitude boundary layer, flux transfer events at the magnetopause, and wave and particle interactions at the bow shock. These observations demonstrate the capabilities of the plasma sensors and the synergy of its measurements with the other THEMIS experiments. In addition, the paper includes discussions of various performance issues with the ESA instrument such as sources of sensor background, measurement limitations, and data formatting problems. These initial results demonstrate successful achievement of all measurement objectives for the plasma instrument.
[1] We present ground-based and in situ observations from March 13, 2007. The THEMIS satellites were in the evening sector conjugate to THEMIS ground-based imagers. At $0507 UT there was an optical onset on inner CPS field lines. This involved near-simultaneous brightening of 1 MLT hour longitudinal segment of the onset arc. The part of the arc that brightened was that closest to the equatorward boundary of the diffuse (proton) aurora. Within one minute, a dipolarization front moved across four THEMIS satellites. Based on their locations, the order in which they detected the dipolarization front, and the auroral evolution, we assert that the expansion phase began earthward of the four satellites and evolved radially outwards. We conclude that this onset occurred in an azimuthally localized region of highly stretched field lines.
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