Publications

Journal article

Goetz C, Koenders C, Richter I, Altwegg K, Burch J, Carr C, Cupido E, Eriksson A, Güttler C, Henri P, Mokashi P, Nemeth Z, Nilsson H, Rubin M, Sierks H, Tsurutani B, Vallat C, Volwerk M, Glassmeier KHet al., 2016,

First detection of a diamagnetic cavity at comet 67P/Churyumov-Gerasimenko

, Astronomy & Astrophysics, Vol: 588, ISSN: 1432-0746

Context. The Rosetta magnetometer RPC-MAG has been exploring the plasma environment of comet 67P/Churyumov-Gerasimenko since August 2014. The first months were dominated by low-frequency waves which evolved into more complex features. However, at the end of July 2015, close to perihelion, the magnetometer detected a region that did not contain any magnetic field at all. Aims. These signatures match the appearance of a diamagnetic cavity as was observed at comet 1P/Halley in 1986. The cavity here is more extended than previously predicted by models and features unusual magnetic field configurations, which need to be explained. Methods. The onboard magnetometer data were analyzed in detail and used to estimate the outgassing rate. A minimum variance analysis was used to determine boundary normals. Results. Our analysis of the data acquired by the Rosetta Plasma Consortium instrumentation confirms the existence of a diamagnetic cavity. The size is larger than predicted by simulations, however. One possible explanation are instabilities that are propagating along the cavity boundary and possibly a low magnetic pressure in the solar wind. This conclusion is supported by a change in sign of the Sun-pointing component of the magnetic field. Evidence also indicates that the cavity boundary is moving with variable velocities ranging from 230-500 m/s.

Journal article

Phan TD, Shay MA, Eastwood JP, Angelopoulos V, Oieroset M, Oka M, Fujimoto Met al., 2016,

Establishing the Context for Reconnection Diffusion Region Encounters and Strategies for the Capture and Transmission of Diffusion Region Burst Data by MMS

, Space Science Reviews, Vol: 199, Pages: 631-650, ISSN: 0038-6308

© 2015, The Author(s). This paper describes the efforts of our Inter-Disciplinary Scientist (IDS) team to (a) establish the large-scale context for reconnection diffusion region encounters by MMS at the magnetopause and in the magnetotail, including the distinction between X-line and O-line encounters, that would help the identification of diffusion regions in spacecraft data, and (b) devise possible strategies that can be used by MMS to capture and transmit burst data associated with diffusion region candidates. At the magnetopause we suggest the strategy of transmitting burst data from all magnetopause crossings so that no magnetopause reconnection diffusion regions encountered by the spacecraft will be missed. The strategy is made possible by the MMS mass memory and downlink budget. In the magnetotail, it is estimated that MMS will be able to transmit burst data for all diffusion regions, all reconnection jet fronts (a.k.a. dipolarization fronts) and separatrix encounters, but less than 50 % of reconnection exhausts encountered by the spacecraft. We also discuss automated burst trigger schemes that could capture various reconnection-related phenomena. The identification of candidate diffusion region encounters by the burst trigger schemes will be verified and improved by a Scientist-In-The-Loop (SITL). With the knowledge of the properties of the region surrounding the diffusion region and the combination of automated burst triggers and further optimization by the SITL, MMS should be able to capture most diffusion regions it encounters.

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Journal article

Ball WT, Haigh JD, Rozanov EV, Kuchar A, Sukhodolov T, Tummon F, Shapiro AV, Schmutz Wet al., 2016,

High solar cycle spectral variations inconsistent with stratospheric ozone observations

, Nature Geoscience, Vol: 9, Pages: 206-209, ISSN: 1752-0894

Journal article

Chadney JM, Galand M, Koskinen TT, Miller S, Sanz-Forcada J, Unruh YC, Yelle RVet al., 2016,

EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars

, Astronomy & Astrophysics, Vol: 587, ISSN: 1432-0746

The composition and structure of the upper atmospheres of Extrasolar GiantPlanets (EGPs) are affected by the high-energy spectrum of their host starsfrom soft X-rays to EUV. This emission depends on the activity level of thestar, which is primarily determined by its age. We focus upon EGPs orbiting K-and M-dwarf stars of different ages. XUV spectra for these stars areconstructed using a coronal model. These spectra are used to drive both athermospheric model and an ionospheric model, providing densities of neutraland ion species. Ionisation is included through photo-ionisation andelectron-impact processes. We find that EGP ionospheres at all orbitaldistances considered and around all stars selected are dominated by thelong-lived H$^+$ ion. In addition, planets with upper atmospheres where H$_2$is not substantially dissociated have a layer in which H$_3^+$ is the major ionat the base of the ionosphere. For fast-rotating planets, densities ofshort-lived H$_3^+$ undergo significant diurnal variations, with the maximumvalue being driven by the stellar X-ray flux. In contrast, densities oflonger-lived H$^+$ show very little day/night variability and the magnitude isdriven by the level of stellar EUV flux. The H$_3^+$ peak in EGPs with upperatmospheres where H$_2$ is dissociated under strong stellar illumination ispushed to altitudes below the homopause, where this ion is likely to bedestroyed through reactions with heavy species. The inclusion of secondaryionisation processes produces significantly enhanced ion and electron densitiesat altitudes below the main EUV ionisation peak, as compared to models that donot include electron-impact ionisation. We estimate infrared emissions fromH$_3^+$, and while, in an H/H$_2$/He atmosphere, these are larger from planetsorbiting close to more active stars, they still appear too low to be detectedwith current observatories.

Journal article

Weiss Z, Steers EBM, Mushtaq S, Hoffmann V, Pickering JCet al., 2016,

The use of radiative transition rates to study the changes in the excitation of Cu ions in a Ne glow discharge caused by small additions of H-2, O-2 and N-2

, Spectrochimica Acta Part B: Atomic Spectroscopy, Vol: 118, Pages: 81-89, ISSN: 1873-3565

The excitation of Cu+ ions in a Ne glow discharge with small additions of H2, O2 and N2 was studied. Ratios of radiative transition rates between different Cu II levels in a discharge in neon, with and without the molecular gas added, were calculated, and the formalism of transition rate ratio (TRR) diagrams was developed and used to study the changing excitation conditions. Virtually no changes in the excitation of Cu+ ions occur in a neon discharge if nitrogen is added. Additions of hydrogen and oxygen to neon as the discharge gas affect excitation of the 4d, 5s and some other Cu II levels in the vicinity of the ionization energy of neon (21.56 eV). Also some lower Cu II levels, excited by radiative decay of those higher energy levels, are affected. The 4p 3P2 level at 15.96 eV is enhanced by additions of hydrogen. It was suggested that this enhancement is caused by the asymmetric charge transfer reaction between neutral copper atoms and the H2+ molecular ions.

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Journal article

Russell CT, Wei HY, Cowee MM, Neubauer FM, Dougherty MKet al., 2016,

Ion cyclotron waves at Titan

, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 2095-2103, ISSN: 2169-9402

During the interaction of Titan's thick atmosphere with the ambient plasma, it was expected that ion cyclotron waves would be generated by the free energy of the highly anisotropic velocity distribution of the freshly ionized atmospheric particles created in the interaction. However, ion cyclotron waves are rarely observed near Titan, due to the long growth times of waves associated with the major ion species from Titan's ionosphere, such as CH4+ and N2+. In the over 100 Titan flybys obtained by Cassini to date, there are only two wave events, for just a few minutes during T63 flyby and for tens of minutes during T98 flyby. These waves occur near the gyrofrequencies of proton and singly ionized molecular hydrogen. They are left-handed, elliptically polarized, and propagate nearly parallel to the field lines. Hybrid simulations are performed to understand the wave growth under various conditions in the Titan environment. The simulations using the plasma and field conditions during T63 show that pickup protons with densities ranging from 0.01 cm−3 to 0.02 cm−3 and singly ionized molecular hydrogens with densities ranging from 0.015 cm−3 to 0.25 cm−3 can drive ion cyclotron waves with amplitudes of ~0.02 nT and of ~0.04 nT within appropriate growth times at Titan, respectively. Since the T98 waves were seen farther upstream than the T63 waves, it is possible that the instability was stronger and grew faster on T98 than T63.

Journal article

Ceppi P, McCoy DT, Hartmann DL, 2016,

Observational evidence for a negative shortwave cloud feedback in middle to high latitudes

, GEOPHYSICAL RESEARCH LETTERS, Vol: 43, Pages: 1331-1339, ISSN: 0094-8276

Journal article

Raghuram S, Bhardwaj A, Galand M, 2016,

Prediction of forbidden ultraviolet and visible emissions in comet 67P/Churyumov-Gerasimenko

, Astrophysical Journal, Vol: 818, ISSN: 1538-4357

Remote observation of spectroscopic emissions is a potential tool for theidentification and quantification of various species in comets. CO Cameron band(to trace \cod) and atomic oxygen emissions (to trace H$_2$O and/or CO$_2$, CO)have been used to probe neutral composition in the cometary coma. Using acoupled-chemistry emission model, various excitation processes controlling COCameron band and different atomic oxygen and atomic carbon have been modelledin comet 67P-Churyumov-Gerasimenko at 1.29~AU (perihelion) and at 3~AUheliocentric distances, which is being explored by ESA's Rosetta mission. Theintensities of CO Cameron band, atomic oxygen and atomic carbon emission linesas a function of projected distance are calculated for different CO and CO$_2$volume mixing ratios relative to water. Contributions of different excitationprocesses controlling these emissions are quantified. We assess how CO$_2$and/or CO volume mixing ratios with respect to H$_2$O can be derived based onthe observed intensities of CO Cameron band, atomic oxygen, and atomic carbonemission lines.The results presented in this work serve as base linecalculations to understand the behaviour of low out-gassing cometary coma andcompare them with the higher gas production rate cases (e.g. comet Halley).Quantitative analysis of different excitation processes governing thespectroscopic emissions is essential to study the chemistry of inner coma andto derive neutral gas composition.

Journal article

Mushtaq S, Steers EBM, Churchill G, Barnhart D, Hoffmann V, Pickering JC, Putyera Ket al., 2016,

Does asymmetric charge transfer play an important role as an ionization mode in low power-low pressure glow discharge mass spectrometry?

, Spectrochimica Acta Part B-Atomic Spectroscopy, Vol: 118, Pages: 56-61, ISSN: 0584-8547

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Journal article

Volwerk M, Richter I, Tsurutani B, Gotz C, Altwegg K, Broiles T, Burch J, Carr CM, Cupido E, Delva M, Dosa M, Edberg NJT, Eriksson A, Henri P, Koenders C, Lebreton JP, Mandt KE, Nilsson H, Opitz A, Rubin M, Schwingenschuh K, Stenberg Wieser G, Szego K, Vallat C, Vallieres X, Glassmeier KHet al., 2016,

Mass-loading, pile-up, and mirror-mode waves at comet 67P/Churyumov-Gerasimenko

, Annales Geophysicae, Vol: 34, Pages: 1-15, ISSN: 1432-0576

. The data from all Rosetta Plasma Consortium instruments and from the ROSINA COPSinstrument are used to study the interaction of the solar wind with the outgassing cometary nucleusof 67P/Churyumov-Gerasimenko. During 6 and 7 June 2015, the interaction was first dominatedby an increase in the solar wind dynamic pressure, caused by a higher solar wind ion density. Thispressure compressed the draped magnetic field around the comet, and the increase in solar windelectrons enhanced the ionization of the outflow gas through collisional ionization. The new ionsare picked up by the solar wind magnetic field, and create a ring/ring-beam distribution, which, in ahigh-β plasma, is unstable for mirror mode wave generation. Two different kinds of mirror modesare observed: one of small size generated by locally ionized water and one of large size generatedby ionization and pick-up farther away from the comet.

Journal article

Edberg NJT, Eriksson AI, Odelstad E, Vigren E, Andrews DJ, Johansson F, Burch JL, Carr CM, Cupido E, Glassmeier KH, Goldstein R, Halekas JS, Henri P, Koenders C, Mandt K, Mokashi P, Nemeth Z, Nilsson H, Ramstad R, Richter I, Stenberg Wieser Get al., 2016,

Solar wind interaction with comet 67P: impacts of corotating interaction regions

, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 949-965, ISSN: 2169-9402

We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a CME, are traced from Earth via Mars (using Mars Express and MAVEN) and to comet 67P from October to December 2014. When the comet is 3.1-2.7 AU from the Sun and the neutral outgassing rate ∼1025−1026 s−1 the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30 km. The ionospheric low-energy (∼5 eV) plasma density increases significantly in all events, by a factor >2 in events 1-2 but less in events 3-4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionisation, and possibly charge exchange processes and acceleration of mass loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (∼10-100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around of the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.

Journal article

Sigsbee K, Kletzing CA, Smith CW, MacDowall R, Spence H, Reeves G, Blake JB, Baker DN, Green JC, Singer HJ, Carr CM, Santolik Oet al., 2016,

Van Allen Probes, THEMIS, GOES, and Cluster Observations of EMIC waves, ULF pulsations, and an electron flux dropout

, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 1990-2008, ISSN: 2169-9402

We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, THEMIS-A (P5), Cluster 2, and Geostationary Operational Environmental Satellite (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 hours from 12–14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervals of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He+ EMIC waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst < −100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near pre-storm values, possibly in response to strong ultra-low frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.

Journal article

Felici M, Arridge CS, Coates AJ, Badman SV, Dougherty MK, Jackman CM, Kurth WS, Melin H, Mitchell DG, Reisenfeld DB, Sergis Net al., 2016,

Cassini observations of ionospheric plasma in Saturn's magnetotail lobes

, Journal of Geophysical Research: Space Physics, Vol: 121, Pages: 338-357, ISSN: 2169-9402

Studies of Saturn's magnetosphere with the Cassini mission have established the importance of Enceladus as the dominant mass source for Saturn's magnetosphere. It is well known that the ionosphere is an important mass source at Earth during periods of intense geomagnetic activity, but lesser attention has been dedicated to study the ionospheric mass source at Saturn. In this paper we describe a case study of data from Saturn's magnetotail, when Cassini was located at ≃ 2200 h Saturn local time at 36 RS from Saturn. During several entries into the magnetotail lobe, tailward flowing cold electrons and a cold ion beam were observed directly adjacent to the plasma sheet and extending deeper into the lobe. The electrons and ions appear to be dispersed, dropping to lower energies with time. The composition of both the plasma sheet and lobe ions show very low fluxes (sometimes zero within measurement error) of water group ions. The magnetic field has a swept-forward configuration which is atypical for this region, and the total magnetic field strength is larger than expected at this distance from the planet. Ultraviolet auroral observations show a dawn brightening, and upstream heliospheric models suggest that the magnetosphere is being compressed by a region of high solar wind ram pressure. We interpret this event as the observation of ionospheric outflow in Saturn's magnetotail. We estimate a number flux between (2.95 ± 0.43) × 109 and (1.43 ± 0.21) × 1010 cm−2 s−1, 1 or about 2 orders of magnitude larger than suggested by steady state MHD models, with a mass source between 1.4 ×102 and 1.1 ×103 kg/s. After considering several configurations for the active atmospheric regions, we consider as most probable the main auroral oval, with associated mass source between 49.7 ±13.4 and 239.8 ±64.8 kg/s for an average auroral oval, and 10 ±4 and 49 ±23 kg/s for the specific auroral oval morphology found

Journal article

Hood AW, Cargill PJ, Browning PK, Tam KVet al., 2016,

An MHD avalanche in a multi-threaded coronal loop

, Astrophysical Journal, Vol: 817, ISSN: 1538-4357

Journal article

Kasoar M, Voulgarakis A, Lamarque JF, Shindell DT, Bellouin N, Collins WJ, Faluvegi G, Tsigaridis Ket al., 2016,

Regional and global climate response to anthropogenic SO<inf>2</inf> emissions from China in three climate models

, Atmospheric Chemistry and Physics Discussions, Vol: 2016, ISSN: 1680-7367

We use the HadGEM3-GA4, CESM1, and GISS ModelE2 climate models to investigate the global and regional aerosol burden, radiative flux, and surface temperature responses to removing anthropogenic sulfur dioxide (SO2) emissions from China. We find that the models differ by up to a factor of six in the simulated change in aerosol optical depth (AOD) and shortwave radiative flux over China that results from reduced sulfate aerosol, leading to a large range of magnitudes in the regional and global temperature responses. Two of the three models simulate a near-ubiquitous hemispheric warming due to the regional SO2 removal, with similarities in the local and remote pattern of response, but overall with a substantially different magnitude. The third model simulates almost no significant temperature response. We attribute the discrepancies in the response to a combination of substantial differences in the chemical conversion of SO2 to sulfate, translation of sulfate mass into AOD, and differences in the radiative forcing efficiency of sulfate aerosol in the models. The model with the strongest response (HadGEM3-GA4) compares best with observations of AOD regionally, however the other two models compare similarly (albeit poorly) and still disagree substantially in their simulated climate response, indicating that total AOD observations are far from sufficient to determine which model response is more plausible. Our results highlight that there remains a large uncertainty in the representation of both aerosol chemistry as well as direct and indirect aerosol radiative effects in current climate models, and reinforces that caution must be applied when interpreting the results of single-model studies of aerosol influences on climate. Model studies that implicate aerosols in climate responses should ideally explore a range of radiative forcing strengths representative of this uncertainty, in addition to thoroughly evaluating the models used against observations.

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Journal article

Kasoar M, Voulgarakis A, Lamarque J-F, Shindell DT, Bellouin N, Collins WJ, Faluvegi G, Tsigaridis Ket al., 2016,

Supplementary material to &quot;Regional and global climate response to anthropogenic SO&lt;sub&gt;2&lt;/sub&gt; emissions from China in three climate models&quot;

Book chapter

Haigh JD, 2016,

Blue Sky; Mirages, haloes and sundogs; Rainbows; Space Weather; Sunshine; Sunspots and Climate

, 30-Second Meteorology: The 50 Most Significant Events and Phenomena, Each Explained in Half a Minute, Editors: Scaife, ISBN: 978-1-7824-0310-4

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Journal article

Good SW, Forsyth RJ, 2016,

Interplanetary coronal mass ejections observed by MESSENGER and Venus Express

, Solar Physics, Vol: 291, Pages: 239-263, ISSN: 1573-093X

Interplanetary coronal mass ejections (ICMEs) observed by the MESSENGER and Venus Express spacecraft have been catalogued and analysed. The ICMEs were identified by a relatively smooth rotation of the magnetic field direction consistent with a flux rope structure, coinciding with a relatively enhanced magnetic field strength. A total of 35 ICMEs were found in the surveyed MESSENGER data (primarily from March 2007 to April 2012), and 84 ICMEs in the surveyed Venus Express data (from May 2006 to December 2013). The ICME flux rope configurations have been determined. Ropes with northward leading edges were about four times more common than ropes with southward leading edges, in agreement with a previously established solar cycle dependence. Ropes with low inclinations to the solar equatorial plane were about four times more common than ropes with high inclinations, possibly an observational effect. Left- and right-handed ropes were observed in almost equal numbers. In addition, data from MESSENGER, Venus Express, STEREO-A, STEREO-B and ACE were examined for multipoint signatures of the catalogued ICMEs. For spacecraft separations below 15° in heliocentric longitude, the second spacecraft observed the ICME flux rope in 82 % of cases; this percentage dropped to 49 % for separations between 15 and 30°, to 18 % for separations between 30 and 45°, and to 12 % for separations between 45 and 60°. As the spacecraft separation increased, it became increasingly likely that only the sheath and not the flux rope of the ICME was observed, in agreement with the notion that ICME flux ropes are smaller in longitudinal extent than the shocks or discontinuities that they often drive. Furthermore, this study has identified 23 ICMEs observed by pairs of spacecraft close to radial alignment. A detailed analysis of these events could lead to a better understanding of how ICMEs evolve during propagation.

Journal article

Kurth WS, Hospodarsky GB, Gurnett DA, Lamy L, Dougherty MK, Nichols J, Bunce EJ, Pryor W, Baines K, Stallard T, Melin H, Crary FJet al., 2016,

Saturn kilometric radiation intensities during the Saturn auroral campaign of 2013

, Icarus, Vol: 263, Pages: 2-9, ISSN: 1090-2643

The Saturn auroral campaign carried out in the spring of 2013 used multiple Earth-based observations, remote-sensing observations from Cassini, and in situ-observations from Cassini to further our understanding of auroras at Saturn. Most of the remote sensing and Earth-based measurements are, by nature, not continuous. And, even the in situ measurements, while continuously obtained, are not always obtained in regions relevant to the study of the aurora. Saturn kilometric radiation, however, is remotely monitored nearly continuously by the Radio and Plasma Wave Science instrument on Cassini. This radio emission, produced by the cyclotron maser instability, is tightly tied to auroral processes at Saturn as are auroral radio emissions at other planets, most notably Jupiter and Earth. This paper provides the time history of the intensity of the radio emissions through the auroral campaign as a means of understanding the temporal relationships between the sometimes widely spaced observations of the auroral activity. While beaming characteristics of the radio emissions are known to prevent single spacecraft observations of this emission from being a perfect auroral activity indicator, we demonstrate a good correlation between the radio emission intensity and the level of UV auroral activity, when both measurements are available.

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Journal article

Badman SV, Provan G, Bunce EJ, Mitchell DG, Melin H, Cowley SWH, Radioti A, Kurth WS, Pryor WR, Nichols JD, Jinks SL, Stallard TS, Brown RH, Baines KH, Dougherty MKet al., 2016,

Saturn's auroral morphology and field-aligned currents during a solar wind compression

, Icarus, Vol: 263, Pages: 83-93, ISSN: 1090-2643

On 21–22 April 2013, during a coordinated auroral observing campaign, instruments onboard Cassini and the Hubble Space Telescope observed Saturn’s aurora while Cassini traversed Saturn’s high latitude auroral field lines. Signatures of upward and downward field-aligned currents were detected in the nightside magnetosphere in the magnetic field and plasma measurements. The location of the upward current corresponded to the bright ultraviolet auroral arc seen in the auroral images, and the downward current region was located poleward of the upward current in an aurorally dark region. Within the polar cap magnetic field and plasma fluctuations were identified with periods of ∼20 and ∼60 min. The northern and southern auroral ovals were observed to rock in latitude in phase with the respective northern and southern planetary period oscillations. A solar wind compression impacted Saturn’s magnetosphere at the start of 22 April 2013, identified by an intensification and extension to lower frequencies of the Saturn kilometric radiation, with the following sequence of effects: (1) intensification of the auroral field-aligned currents; (2) appearance of a localised, intense bulge in the dawnside (04–06 LT) aurora while the midnight sector aurora remained fainter and narrow; and (3) latitudinal broadening and poleward contraction of the nightside aurora, where the poleward motion in this sector is opposite to that expected from a model of the auroral oval’s usual oscillation. These observations are interpreted as the response to tail reconnection events, initially involving Vasyliunas-type reconnection of closed mass-loaded magnetotail field lines, and then proceeding onto open lobe field lines, causing the contraction of the polar cap region on the night side.

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Journal article

Roussos E, Krupp N, Mitchell DG, Paranicas C, Krimigis SM, Andriopoulou M, Palmaerts B, Kurth WS, Badman SV, Masters A, Dougherty MKet al., 2016,

Quasi-periodic injections of relativistic electrons in Saturn’s outer magnetosphere

, Icarus, Vol: 263, Pages: 101-116, ISSN: 1090-2643

Quasi-periodic, short-period injections of relativistic electrons have been observed in both Jupiter’s and Saturn’s magnetospheres, but understanding their origin or significance has been challenging, primarily due to the limited number of in-situ observations of such events by past flyby missions. Here we present the first survey of such injections in an outer planetary magnetosphere using almost nine years of energetic charged particle and magnetic field measurements at Saturn. We focus on events with a characteristic period of about 60–70 min (QP60, where QP stands for quasi-periodic). We find that the majority of QP60, which are very common in the outer magnetosphere, map outside Titan’s orbit. QP60 are also observed over a very wide range of local times and latitudes. A local time asymmetry in their distribution is the most striking feature, with QP60 at dusk being between 5 and 25 times more frequent than at dawn. Field-line tracing and pitch angle distributions suggest that most events at dusk reside on closed field lines. They are distributed either near the magnetopause, or, in the case of the post-dusk (or pre-midnight) sector, up to about 30 RS inside it, along an area extending parallel to the dawn–dusk direction. QP60 at dawn map either on open field lines and/or near the magnetopause. Both the asymmetries and varying mapping characteristics as a function of local time indicate that generation of QP60 cannot be assigned to a single process. The locations of QP60 seem to trace sites that reconnection is expected to take place. In that respect, the subset of events observed post-dusk and deep inside the magnetopause may be directly or indirectly linked to the Vasyliunas reconnection cycle, while magnetopause reconnection/Kelvin–Helmholtz (KH) instability could be invoked to explain all other events at the duskside. Using similar arguments, injections at the dawnside magnetosphere may result from solar-wind induced storm

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Journal article

Ceppi P, Hartmann DL, Webb MJ, 2016,

Mechanisms of the negative shortwave cloud feedback in middle to high latitudes

, Journal of Climate, Vol: 29, Pages: 139-157, ISSN: 0894-8755

Increases in cloud optical depth and liquid water path (LWP) are robust features of global warming model simulations in high latitudes, yielding a negative shortwave cloud feedback, but the mechanisms are still uncertain. Here the importance of microphysical processes for the negative optical depth feedback is assessed by perturbing temperature in the microphysics schemes of two aquaplanet models, both of which have separate prognostic equations for liquid water and ice. It is found that most of the LWP increase with warming is caused by a suppression of ice microphysical processes in mixed-phase clouds, resulting in reduced conversion efficiencies of liquid water to ice and precipitation. Perturbing the temperature-dependent phase partitioning of convective condensate also yields a small LWP increase. Together, the perturbations in large-scale microphysics and convective condensate partitioning explain more than two-thirds of the LWP response relative to a reference case with increased SSTs, and capture all of the vertical structure of the liquid water response. In support of these findings, a very robust positive relationship between monthly mean LWP and temperature in CMIP5 models and observations is shown to exist in mixed-phase cloud regions only. In models, the historical LWP sensitivity to temperature is a good predictor of the forced global warming response poleward of about 45°, although models appear to overestimate the LWP response to warming compared to observations. The results indicate that in climate models, the suppression of ice-phase microphysical processes that deplete cloud liquid water is a key driver of the LWP increase with warming and of the associated negative shortwave cloud feedback.

Journal article

Rabin SS, Melton JR, Lasslop G, Bachelet D, Forrest M, Hantson S, Li F, Mangeon S, Yue C, Arora VK, Hickler T, Kloster S, Knorr W, Nieradzik L, Spessa A, Folberth GA, Sheehan T, Voulgarakis A, Prentice IC, Sitch S, Kaplan JO, Harrison S, Arneth Aet al., 2016,

The Fire Modeling Intercomparison Project (FireMIP), phase 1: Experimental and analytical protocols

, Geoscientific Model Development, Vol: 9, ISSN: 1991-959X

The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over two decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. Here we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. The works published in this journal are distributed under the Creative Commons Attribution 3.0 License. This license does not affect the Crown copyright work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 3.0 License and the OGL are interoperable and do not conflict with, reduce, or limit each other.

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Conference paper

Murray J, Fox S, O'Shea S, Thornton J, Trembath J, Fugal J, Pickering J, Fox C, Brooke J, Harlow C, Bower K, Ulanowski J, Baran A, Brindley H, Ritter G, Last Aet al., 2016,

The cirrus coupled cloud-radiation experiment-II

A cirrus study has been undertaken during the second Cirrus Cloud-Radiation Experiment field campaign based in Prestwick, Scotland. We report on a case study describing the radiation and microphysics measurements and cloud modelling work.

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Conference paper

Palchetti L, Olivieri M, Pompei C, Labate D, Brindley H, Natale GD, Bianchini Get al., 2016,

The Far Infrared FTS for the FORUM Mission

A wide-band FTS has been designed to perform the spectral observation of the entire infrared Earth's outgoing emission, including the far infrared portion, for the FORUM space mission.

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Citations: 4

Conference paper

Pickering JC, Clear C, Liggins F, Belmonte MT, Thorne APet al., 2016,

High resolution fourier transform spectrometry of astrophysically important elements from IR to VUV

Modern astronomical spectrographs continue to require accurate high resolution atomic data for interpretation of many astrophysical spectra. The Imperial College London laboratory astrophysics program using high resolution Fourier Transform spectrometry is described.

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Conference paper

Brindley H, Murray J, Bellisario C, Harlow C, Woolley A, Fox S, Last A, Pickering Jet al., 2016,

Estimating far infrared surface emissivity over greenland from the tropospheric airborne fourier transform spectrometer (TAFTS)

We report on efforts to obtain observationally based estimates of far-infrared surface emissivity over snow and ice. We highlight one flight from the CIRCCREX-COSMICS airborne campaign over Greenland during March 2015.

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Journal article

Vanniere B, Czaja A, Dacre H, Woollings T, Parfitt Ret al., 2016,

A Potential Vorticity Signature for the Cold Sector of Winter Extratropical Cyclones

, Quarterly Journal of the Royal Meteorological Society, Vol: 142, Pages: 432-442, ISSN: 1477-870X

The cold sector of mid-latitude storms is characterised by distinctive features such as strong surface heat fluxes, shallow convection, convective precipitation and synoptic subsidence. In order to evaluate the contribution of processes occurring in the cold sector to the mean climate, an appropriate indicator is needed. This study describes the systematic presence of negative PV behind the cold front of extratropical storms in winter. The origin of this negative PV is analysed using ERA-Interim data, potential vorticity tendencies averaged over the depth of the boundary layer are evaluated. It is found that negative PV is generated by diabatic processes in the cold sector and by Ekman pumping at the low centre, whereas positive PV is generated by Ekman advection of potential temperature in the warm sector. We suggest here that the negative PV at low-levels can be used to identify the cold sector. A PV-based indicator is applied to estimate the respective contributions of the cold sector and the remainder of the storm to upward motion, and large scale and convective precipitation. We compare the PV-based indicator with other distinctive features that could be used as markers of the cold sector, and find that potential vorticity is the best criterion when taken alone, and the best when combined with any other.

Journal article

Martinovic MM, Zaslavsky A, Maksimovic M, Meyer-Vernet N, Segan S, Zouganelis I, Salem C, Pulupa M, Bale SDet al., 2016,

Quasi-thermal noise measurements on STEREO: Kinetic temperature deduction using electron shot noise model

, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 121, Pages: 129-139, ISSN: 2169-9380

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Citations: 9

Journal article

Ceppi P, Hartmann DL, 2016,

Clouds and the Atmospheric Circulation Response to Warming

, JOURNAL OF CLIMATE, Vol: 29, Pages: 783-799, ISSN: 0894-8755

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