Publications

Journal article

Franci L, Papini E, Micera A, Matteini L, Stawarz J, Lapenta G, Burgess D, Hellinger P, Landi S, Verdini A, Montagud-Camps Vet al., 2022,

Fully kinetic simulations of the near-Sun solar wind plasma: turbulence, reconnection, and particle heating

<jats:p>&lt;p&gt;We model the development of plasma turbulence in the near-Sun solar wind with high-resolution fully-kinetic particle-in-cell (PIC) simulations, initialised with plasma conditions measured by Parker Solar Probe during its first solar encounter (ion and electron plasma beta &amp;#8804; 1 and a large amplitude of the turbulent fluctuations). The power spectra of the plasma and electromagnetic fluctuations are characterized by multiple power-law intervals, with a transition and a considerable steepening in correspondence of the electron scales. In the same range of scales, the kurtosis of the magnetic fluctuations is observed to further increase, hinting at a higher level of intermittency. We observe a number of electron-only reconnection events, which are responsible for an increase of the electron temperature in the direction parallel to the ambient field. The total electron temperature, however, exhibits only a small increase due to the cooling of electrons in the perpendicular direction, leading to a strong temperature anisotropy. We also analyse the power spectra of the different terms of the electric field in the generalised Ohm&amp;#8217;s law, their linear and nonlinear components, and their alignment, to get a deeper insight on the nature of the turbulent cascade. Finally, we compare our results with those from hybrid simulations with the same parameters, as well as with spacecraft observations.&lt;/p&gt;</jats:p>

Journal article

Pyakurel P, Phan T, Shay M, Stawarz J, Øieroset M, Cassak P, Haggerty C, Drake J, Li TC, Burch J, Ergun R, Gershman D, Giles B, Torbert R, Strangeway R, Russell Cet al., 2022,

On the short-scale spatial variability of electron inflows in electron-only magnetic reconnection in the turbulent magnetosheath observed by MMS

<jats:p>&lt;p&gt;In the Earth&amp;#8217;s turbulent magnetosheath downstream of the quasiparallel bow shock region, magnetic reconnection without ion coupling was observed with bi-directional super-Alfv&amp;#233;nic electron jets. The lack of ion coupling was attributed to the small-scale sizes of the current sheets. In an electron-only reconnection event that occurred on 26 December 2016, we examine the detailed properties of electron inflows observed by all 4 MMS spacecraft. Even though the farthest MMS probe in the outflow direction from the X-line was no more than 8 electron skin depth, the electron inflows have significant asymmetry and highly variable amplitudes. We compare MMS observations with 2D-kinetic PIC simulation and find that the asymmetry in the inflow stems directly from the tilt of the out-of-plane (guide) magnetic field structure in the reconnection plane, with inflow asymmetry enhanced in the downstream region.&lt;/p&gt;</jats:p>

Journal article

Adhikari S, Shay MA, Parashar TN, Matthaeus WH, Sharma Pyakurel P, Stawarz JE, Eastwood JPet al., 2022,

Reconnection and Turbulence: A Qualitative Approach to their Relationship

<jats:p>&lt;p&gt;Over the past few decades, the relationship between turbulence and reconnection has emerged as a subject of interest. For example, various properties of reconnection have been studied in different turbulent environments using plasma simulations. In other approaches, reconnection is studied as a subsidiary process occurring in turbulence. Turbulent features are also studied as consequences of instabilities associated with large scale reconnection. Only recently, we have attempted to answer some of the fundamental questions such as: &amp;#8220;What are the turbulent-like features of laminar magnetic reconnection?&amp;#8221;, &quot;Is magnetic reconnection fundamentally an energy cascade?&quot; both related to the interplay between reconnection and turbulence. Using 2.5D particle in cell simulations, we have found that laminar magnetic reconnection in a quasi-steady phase exhibits a Kolmogorov-like power spectrum. Most notably, the energy transfer process in magnetic reconnection is also found to be similar to that of a turbulent system suggesting that reconnection involves an energy cascade. The reconnection rate is correlated to both the magnetic energy spectrum in the ion-scales and the cascade of energy. Further, similarities between reconnection and turbulence in terms of the electric field spectrum, their components, and pressure-strain interaction will be highlighted.&lt;/p&gt;</jats:p>

Journal article

Robertson S, Eastwood J, Stawarz J, Russell C, Giles B, Burch Jet al., 2022,

Survey of EDR-associated Magnetopause Flux Ropes with MMS

<jats:p>&lt;p&gt;Flux ropes are twisted magnetic field structures produced during magnetic reconnection. They are thought to be important for energy transport and particle acceleration and are commonly observed throughout space plasma environments, including at the Earth&amp;#8217;s magnetopause. Flux Transfer Events (FTEs), which typically contain flux ropes, have been observed to grow in size and flux content as they are convected over the magnetopause and into the magnetotail, contributing to flux transport in the Dungey cycle. More recently, small-scale flux ropes have been observed inside the Electron Diffusion Region (EDR) during magnetopause reconnection.&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;br&gt;In this study, we investigate the link between the EDR and flux ropes, presenting a survey of 245 flux ropes observed by the Magnetospheric Multiscale (MMS) mission on days during which the spacecraft also encountered the EDR. MMS measures the thermal electron and ion 3D distributions at 30 msec and 150 msec time resolution, respectively, and at spacecraft separations down to a few kilometres allowing the study of such electron-scale phenomena. We find that flux ropes are more likely to be observed closer to the EDR, and that flux ropes observed closer to the EDR tend to have greater axial magnetic field strength and therefore greater flux content. We suggest that we could be sampling a subset of flux ropes that are recently formed by the EDR and discuss how this impacts current theories for flux rope evolution on the magnetopause.&lt;/p&gt;</jats:p>

Journal article

Stawarz JE, Eastwood JP, Phan T, Gingell IL, Pyakurel PS, Shay MA, Robertson SL, Russell CT, Le Contel Oet al., 2022,

Turbulence-driven magnetic reconnection and the magnetic correlation length in collisionless plasma turbulence

<jats:p>&lt;p&gt;&lt;span&gt;Observations of Earth&amp;#8217;s magnetosheath from the Magnetospheric Multiscale (MMS) mission have provided an unprecedented opportunity to examine the detailed structure of the multitude of thin current sheets that are generated by plasma turbulence, revealing that a novel form of magnetic reconnection, which has come to be known as electron-only reconnection, can occur within magnetosheath turbulence. These electron-only reconnection events occur at thin electron-scale current sheets and have super-Alfv&amp;#233;nic electron jets that can approach the electron Alfv&amp;#233;n speed; however, they do not appear to have signatures of ion jets. It is thought that electron-only reconnection can occur when the length of the reconnecting current sheets along the outflow direction is short enough that the ions cannot fully couple to the newly reconnected magnetic field lines before they fully relax. In this work, we examine how the correlation length of the magnetic fluctuations in a turbulent plasma, which constrains the length of the current sheets that can be formed by the turbulence, impacts the nature of turbulence-driven magnetic reconnection. Using observations from MMS, we systematically examine 60 intervals of magnetosheath turbulence &amp;#8211; identifying 256 small-scale reconnection events, both with and without ion jets. We demonstrate that the properties of the reconnection events transition to become more consistent with electron-only reconnection when the magnetic correlation length of the turbulence is below ~20 ion inertial lengths. We further discuss the implications of the results in the context of other turbulent plasmas by considering observations of turbulent fluctuations in the solar wind. &lt;br&gt;&lt;/span&gt;&lt;/p&gt;</jats:p>

Journal article

Misal H, Kountouris I, Voulgarakis A, Rovithakis Aet al., 2022,

Eliciting public preferences for wildfire management policies in Crete, Greece

<jats:p>&lt;p&gt;Fire regimes form an integral part of terrestrial biomes in the Mediterranean region as they provide essential disturbances which change&amp;#160;the&amp;#160;structure and function of plants that favour Mediterranean type climates. Fire is inextricably linked to such ecosystems and cannot be excluded from them. However, the intensification of human activities in Greece, coupled with increasingly unpredictable wildfires has created huge imbalances and jeopardised the ecological integrity of ecosystems. Expansions into the wildland urban interface, rural abandonment, and the focus on fire suppression are increasing the vulnerability and flammability of the Greek environment. The duality of fire is delicate, both at local and national level, catastrophic wildfires singe deeply on landscapes and economies, social burns can take just as long to heal. In Greece, this is further exacerbated by the burgeoning socio-economic and political complexities that have catalysed the current ineffective and unsustainable fire management strategies. Damages from wildfires affect ecosystem services which can lead to a reduction in human wellbeing. Understanding the interactions between ecosystems and humans through environmental valuation is key to implementing effective policy. This study uses economic valuation methods in the form of a choice experiment to elicit public preference for a wildfire management policy in Crete. A survey was deployed around the island, with respondents asked about their preferences between different management strategies. The policies outlined in the survey are made up of the following attributes: risk of fire, agricultural production, landscape quality and post-wildfire damage mitigation. Results from this study indicate a positive preference by the public for a new proposed policy. The findings from this study can be used for decision making in Crete and other similar southern European environments

Journal article

Kasoar M, Corsaro C, Voulgarakis A, 2022,

Metrics for Regional Climate Responses to Regional Pollutant Emissions

<jats:p>&lt;p&gt;The Absolute Global Temperature change Potential (AGTP) and Absolute Global Precipitation change Potential (AGPP) are widely used climate change indices.&amp;#160; They can be applied quickly and easily to estimate the global mean temperature and precipitation responses to a pulse emission of a long-lived climate pollutant at a given time horizon, making them invaluable policy-relevant metrics.&amp;#160; They can also be extended to short-lived climate pollutants - where a sustained emission is more useful to consider than a pulse emission - by using their time-integrated forms (iAGTP and iAGPP).&lt;/p&gt;&lt;p&gt;However, these metrics are only useful when taking a global-average perspective, and do not allow us to account for the regional nature of either emissions or their climate response.&amp;#160; Although long-lived greenhouse gases induce a relatively homogeneous radiative forcing (RF) which is not sensitive to emission location, nonetheless due to transport of heat there is not a one-to-one correspondence between the RF in a region and the local temperature response.&amp;#160; Moreover when considering short-lived pollutants such as aerosols, the region of emission is potentially critical because the short lifetime of such pollutants results in an inhomogeneous distribution of RF.&amp;#160; Therefore, for both long-lived and short-lived pollutants the AGTP/AGPP (or iAGTP/iAGPP) are not adequate when looking at climate responses on a regional scale, even though this would be the most relevant when evaluating different policy scenarios or climate change impacts.&lt;/p&gt;&lt;p&gt;Here, we combine the results of simulations from the Precipitation Driver Response Model Intercomparison Project (PDRMIP) where emissions (or concentrations) of multiple long- and short-lived climate pollutants were perturbed globally in nine

Conference paper

LaMoury A, Hietala H, Eastwood J, Vuorinen L, Plaschke Fet al., 2022,

Magnetosheath jets at the magnetopause: reconnection onset conditions

<jats:p>&lt;p&gt;Magnetosheath jets are localised pulses of high dynamic pressure plasma observed in Earth&amp;#8217;s magnetosheath. They are believed to form from the interaction between the solar wind and ripples in Earth&amp;#8217;s collisionless bow shock, before propagating into the turbulent magnetosheath. Upon impacting the magnetopause, jets can influence magnetospheric dynamics. In particular, previous studies have suggested that, by virtue of their internal magnetic field orientations, jet impacts may be able to trigger local magnetic reconnection at the magnetopause. This is most notable during traditionally unfavourable solar wind conditions, such as intervals of northward interplanetary magnetic field. This idea has been supported by a small number of case studies and simulations. We present a large statistical study into the properties of jets near the magnetopause. We examine the components of the magnetic reconnection onset condition &amp;#8211; the competing effects of magnetic shear angle and plasma beta &amp;#8211; to determine how jets may affect magnetopause reconnection in a statistical sense. We find that, due to their increased beta, jet plasma is typically not favourable to reconnection, often more so than the non-jet magnetosheath. Most jets do contain some reconnection-favourable plasma, however, suggesting that jets may be able to both trigger and suppress magnetopause reconnection. We complement this with new case studies of jets interacting with the magnetopause.&lt;/p&gt;</jats:p>

Conference paper

Plaschke F, Koller F, Preisser Renteria LF, LaMoury AT, Hietala H, Temmer M, Roberts OWet al., 2022,

Magnetosheath jet occurrence in solar wind parameter space

<jats:p>&lt;p&gt;Plasma jets in the magnetosheath are identified as strong local enhancements in dynamic pressure. Being created at the bow shock, they are able to traverse the entire magnetosheath and impact the magnetopause. There, they can severely indent the boundary, set up waves on it, and trigger magnetic reconnection. They are a key yet heavily underexplored element in the solar wind &amp;#8211; magnetosphere coupling. Jets are mostly (but not exclusively) observed downstream of the quasi-parallel shock. Consequently, they have been observed significantly more often under low interplanetary magnetic field cone angle conditions.&lt;/p&gt;&lt;p&gt;In this study, we revisit the occurrence of jets, this time taking into account the whole space of parameters of solar wind input conditions. We answer the question where in this space jet occurrences cluster and how the emerging patterns change when the solar wind input becomes significantly different in nature, e.g., under the influence of coronal mass ejections or stream interaction regions.&lt;/p&gt;</jats:p>

Journal article

Hellinger P, Montagud-Camps V, Franci L, Matteini L, Papini E, Verdini A, Landi Set al., 2022,

Ion-scale transition of plasma turbulence: Pressure-strain effect

<jats:p>&lt;p&gt;We investigate properties of solar-wind like plasma turbulence using direct numerical simulations. We analyze the transition from large (magnetohydrodynamic) scales to ion ones using two-dimensional hybrid (fluid electrons, kinetic ions) simulations of decaying turbulence. To quantify turbulence properties we apply spectral transfer and Karman-Howarth-Monin equations for extended compressible Hall MHD to the simulated results. The simulation results indicate that the transition from MHD to ion scales (the so called ion break) results from a combination of an onset of Hall physics and of an effective dissipation owing to the pressure-strain energy-exchange channel and resistivity. We discuss the simulation results in the context of the solar wind.&lt;/p&gt;</jats:p>

Journal article

Matteini L, Hellinger P, Landi S, Franci L, Tenerani A, Velli Met al., 2022,

Kinetic Instabilities from Ion Beams and Differential Streaming in the Close-Sun Solar Wind: Hybrid Expanding Simulations

<jats:p>&lt;p&gt;Parker Solar Probe observations in the inner heliosphere have demonstrated that non-thermal features in solar wind ion distributions are particularly enhanced and dominant in the close-Sun environment. Proton beams and large differential flows of alpha particles are ubiquitously observed, also in slow, though Alfv&amp;#233;nic, streams, qualitatively at odds with typical observations at 1AU, where non-Maxwellian features are usually less apparent in the slow solar wind. All this reinforces the idea, also supported by past Helios and Ulysses explorations, that preferential ion heating and acceleration take place already in the Corona and signatures of the kinetic processes involved are gradually washed out during expansion. To explore further properties of ion differential streaming during expansion, as well as associated kinetic instabilities and their possible role in plasma heating, we perform expanding box hybrid simulations of a multi-species solar wind composed by proton core, beam and alpha particles, focussing on the role of wave-particle interactions in shaping distribution functions and controlling relative drifts. Radial trends and typical distributions found in simulations are then compared with PSP and Solar Orbiter observations in the inner Heliosphere.&lt;/p&gt;</jats:p>

Conference paper

Horner G, Gryspeerdt E, 2022,

Investigating the evolution of tropical cirrus clouds from deep convection

<jats:p>&lt;p&gt;Tropical convective clouds, particularly their large cirrus outflows, play an important role in modulating the energy balance of the Earth&amp;#8217;s atmosphere. Understanding the evolution of these clouds, and how they change in response to anthropogenic emissions is therefore important to understand past and future climate change. Previous work has focused on tracking individual convective cores and their evolution into anvil cirrus and subsequent thin cirrus clouds in satellite data.&lt;/p&gt;&lt;p&gt;In this work we have introduced a novel approach to investigating the evolution of tropical convective clouds by creating a &amp;#8216;Time Since Convection&amp;#8217; (TSC) dataset. Using reanalysis windspeeds, the time since the air at each location last experienced a convective event (as defined by the presence of a deep convective core) is calculated. Used in conjunction with data from the DARDAR and CERES products, we can build a composite picture of the radiative and microphysical properties of the clouds as a function of their time since convection.&lt;/p&gt;&lt;p&gt;As with previous studies, we find that cloud properties are a strong function of time since convection, with decreases in the optical thickness, cloud top height, and cloud fraction over time. These changes in in cloud properties also have a significant radiative impacts, with the longwave and shortwave component of the cloud radiative effect also being a strong function of time since convection. In addition, using the DARDAR product, a combination of CloudSat radar and the CALIPSO lidar measurements, we build composite cross sections of convective clouds, characterising their vertical evolution and how it is influenced by external meteorological and initial conditions flagged in the TSC dataset.&lt;/p&gt;</jats:p>

Journal article

Kilpua E, Good S, Ala-Lahti M, Osmane A, Fontaine D, Pal S, Räsänen J, Bale S, Zhao L, Hadid L, Janvier M, Yordanova Eet al., 2022,

Magnetic field fluctuations in CME-driven sheath regions

<jats:p>&lt;p&gt;The sheath regions driven by coronal mass ejections (CMEs) are large-scale heliospheric structures where magnetic field fluctuations are observed over various temporal scales. Their internal structure and nature of embedded&amp;#160; fluctuations are currently poorly understood. We report here the key characteristics of&amp;#160; magnetic field fluctuations in CME-driven sheaths, including their spectral index, intermittency, amplitude and compressibility. The results highlight the gradual formation of sheaths over several days as they propagate through interplanetary and the presence of intermittent coherent structures such as strong current sheets. The Jensen-Shannon permutation entropy and complexity analysis suggest that sheath fluctuations are stochastic, but have lower entropy and higher complexity than the preceding wind.&amp;#160; We also show the analysis results during the slow sheath at ~0.5 AU detected by Parker Solar Probe, highlighting that slow CMEs can have prominent sheaths with distinct fluctuation properties.&amp;#160;&lt;/p&gt;</jats:p>

Journal article

Blasl KA, Nakamura T, Plaschke F, Nakamura R, Hasegawa H, Stawarz JE, Liu Y-H, Peery SA, Holmes JC, Hosner M, Schmid D, Roberts OW, Volwerk Met al., 2022,

Multi-scale observations and evolution of the magnetopause Kelvin-Helmholtz waves during southward IMF

<jats:p>&lt;p&gt;The mass and energy transfer across Earth&amp;#8217;s magnetopause is caused by a variety of different plasma processes. One of these processes is the Kelvin-Helmholtz instability (KHI), excited by the velocity shear between the fast-flowing magnetosheath plasma and the relatively stagnant magnetosphere. It has been frequently observed during periods of northward interplanetary magnetic field (IMF), however much less is known about its behaviour during southward IMF conditions.&lt;/p&gt;&lt;p&gt;We present the first Magnetospheric Multiscale (MMS) observations of KH waves and vortices at the dusk-flank magnetopause during southward IMF conditions on September 23, 2017. The instability criterion for the KHI was fulfilled during this event. The boundary normal vectors, obtained by using multi-point methods, are consistent with the predicted structures of the KH waves. We further performed a series of realistic 2D and 3D fully kinetic PIC simulations based on the plasma parameters observed during this MMS event. A comparison to results from these simulations demonstrated quantitative consistencies with the MMS data in many aspects such as the flow and total pressure variations in the KH waves, and the signatures of the non-linearly rolled up KH vortices including the Low Density Faster Than Sheath (LDFTS) plasma.&lt;/p&gt;&lt;p&gt;The simulations further showed that secondary instabilities are excited at the edges of the primary KHI. The Rayleigh-Taylor instability (RTI) can lead to the penetration of high-density arms into the magnetospheric side and disturb the structures of the vortex layer, leading to irregular variations of the surface waves. This can be an important factor in explaining the lower observational probability of KH waves during southward IMF than northward IMF. In the non-linear growth stage of the primary KHI, the lower-hybrid drift instabi

Journal article

Teixeira J, Burton C, Kelley DI, Folberth G, O'Connor FM, Betts R, Voulgarakis Aet al., 2022,

Representing socio-economic factors in INFERNO using the Human Development Index

<jats:p>&lt;p&gt;INFERNO human fire ignitions and fire suppression functions excluded the representation of socio-economic factors (aside population density) that can affect anthropogenic behaviour regarding fire ignitions. To address this, we implement a socio-economic factor in the fire ignition and suppression parametrisation in INFERNO based on an Human Development Index (HDI) term. The HDI is calculated based on three indicators designed to capture the income, health, and education dimensions of human development. Therefore, we assume this leads to a representation where if there is more effort in improving human development, there is also investment on higher fire suppression by the population. Including this representation of socio-economic factors in INFERNO we were able to reduce large positive biases that were found for the regions of Temperate North America, Central America, Europe and Southern Hemisphere South America without significant impact to other regions, improving the model performance at a regional level and better representing processes that drive fire behaviour in the Earth System.&lt;/p&gt;</jats:p>

Journal article

Pisa D, Soucek J, Santolik O, Hanzelka M, Maksimovic M, Vecchio A, Khotyaintsev Y, Chust T, Kretzschmar M, Matteini L, Horbury Tet al., 2022,

Observations of the Time Domain Sampler receiver from the Radio and Plasma Wave instrument during the Solar Orbiter Earth flyby&#160;

<jats:p>&lt;p&gt;On November 27, 2021, Solar Orbiter completed its only flyby of Earth on its way to the following Sun&amp;#8217;s encounter in March 2022. Although this fast flyby was performed primarily to decrease the spacecraft&amp;#8217;s velocity and change orbit to get closer to the Sun, the Radio and Plasma Wave (RPW) instrument had the opportunity to perform high cadence measurements in the Earth&amp;#8217;s magnetosphere. We review the main observation of the Time Domain Sampler (TDS) receiver, a part of the RPW instrument, made during this flyby at frequencies below 200 kHz. The TDS receiver operated in a high cadence mode providing us with the regular waveform snapshot with 62 ms length every ten seconds for two electric components. Besides the regular captures, we have got more than five hundred onboard classified snapshots and the statistical products with a sixteen-second cadence. Before entering the terrestrial magnetosphere around 02:30UT, the spacecraft wandered through the foreshock region, registering intense bursts of Langmuir waves. After the bowshock crossing, Solar Orbiter was for more than two hours in the morning sector of the magnetosphere, recording various plasma wave modes. The closest approach was reached at 04:30UT above North Africa at an altitude of 460 km. Then the spacecraft continued into the Earth&amp;#8217;s tail and entered the magnetosheath around 13:00UT. After 15:00UT, the Solar Orbiter crossed the bowshock, and bursts of Langmuir waves were detected again pointing out to the deep downstream foreshock region. Further from the Earth, intense Auroral Kilometric Radiation (AKR) at frequencies above 100 kHz was also detected.&lt;/p&gt;</jats:p>

Journal article

Pal S, Kilpua E, Good S, Lynch B, Palmerio E, Asvestari E, Pomoell J, Stevens Met al., 2022,

Eruption and Interplanetary Evolution of a Stealth Streamer-blowout CME Observed at ~0.5 AU&#160;

<jats:p>&lt;p&gt;The orbit of the Parker Solar Probe (PSP) during the 5th encounter with the Sun presented an opportunity for a multi-observation analysis including the observations of Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) coronagraphs and Large Angle and Spectrometric Coronagraph (LASCO) coronagraphs. Streamer-blowout coronal mass ejections (SBO-CMEs) are the dominant CME population during solar minimum. With the aid of extrapolated coronal fields and remote observations of the off-limb low corona, we study the initiation of an SBO-CME preceded by consecutive CME eruptions following a multi-stage sympathetic breakout scenario. The suprathermal electron pitch-angle distributions (PADs) and magnetic field observations by PSP suggest that draping of interplanetary magnetic field lines about the CME caused a curvature in the adjacent heliospheric current sheet, initiated magnetic reconnection with the CME flux rope about ~45 hours before it encountered PSP, and eroded ~38% of its initial poloidal magnetic flux at ~0.5 AU. This study covering inner heliospheric observation and analysis of SBO-CME magnetic content provides important implications for the origin of twisted magnetic field lines in SBO-CME flux ropes as the flux rope is not perturbed much by the interplanetary propagation. Also, the multi-spacecraft observations allowed us to estimate the distances where reconnection between the flux rope and its surroundings may be initiated.&amp;#160;&lt;/p&gt;</jats:p>

Journal article

Laker R, Horbury T, Matteini L, Woolley T, Stawarz J, Bale Set al., 2022,

On the Deflections of Switchbacks

<jats:p>&lt;p&gt;Following their presence during Parker Solar Probe&amp;#8217;s (PSP) first encounter, switchbacks have become an active area of research with several proposed mechanisms for their formation. Many of these theories have testable predictions, although it is not trivial to compare simulation results with in-situ data from PSP. For example, there is some debate regarding the deflection direction of switchbacks, with some theories predicting a consistent magnetic deflection in the +T direction in the RTN coordinate system. Such arguments are largely focussed on the first two PSP encounters, as these are the most studied encounters in the literature. We examine the deflection direction of switchbacks for the first eight PSP encounters, with the aim to clear up any ambiguity regarding this property of switchbacks. Much like the earlier results of Horbury et al. 2020 (during the first encounter) we find that switchbacks tend to deflect in the same direction for hours at a time. Although there is some consistency in deflection direction within an individual encounter, crucially we find that there is no preferred deflection direction across all the encounters. We speculate about the cause of these results and what implications they may have for switchback formation theories.&lt;/p&gt;</jats:p>

Journal article

Desai R, Eastwood J, Eggington J, Chittenden J, Horne Ret al., 2022,

Magnetospheric compressions, magnetopause shadowing and the last-closed-drift-shell

<jats:p>&lt;p&gt;Fluxes in the outer radiation belt can vary by orders of magnitude in response to solar wind driving conditions. Magnetopause shadowing, where electron and proton drift paths intersect the magnetopause boundary, is a fundamental loss process which operates on sub-day timescales and can result in rapid loss across the outer radiation belt. Accurate characterisation of this is therefore required to fully account for outer radiation belt dynamics and to avoid unrealistic fluxes impacting long-term forecasts. In this paper we utilise particle simulations of the radiation belts integrated within evolving global MHD simulations, to provide high-resolution high-fidelity simulations of the phenomenon of magnetopause shadowing. We model a variety of magnetopause compression scenarios corresponding to extreme cases of interplanetary shock impacts, and gradual increases in solar wind dynamic pressure. We thus constrain how time-dependent topological variation of the magnetospheric fields results in a complex interplay of open and closed particle drift paths, and examine the role of the electric field in modulating escaping particles trajectories as well as corresponding prompt injections into the inner magnetosphere.&lt;/p&gt;</jats:p>

Journal article

Myhre G, Stjern C, Samset B, Forster P, Quaas J, Takemura T, Voulgarakis A, Jia H, Jouan C, Sand M, Olivie Det al., 2022,

The timescales of climate responses to carbon dioxide and aerosols

<jats:p>&lt;p&gt;Enhanced emissions of both greenhouse gases and aerosols generate climate responses on a wide range of time scales. An initial radiative response triggers a set of rapid adjustments, which are eventually followed by surface-temperature-driven feedbacks. While a lot happens during the first days and months after a perturbation, the monthly mean data typically used in climate studies are too coarse to show the temporal evolution of responses. In these analyses, we take a closer look at how the climate system responds during the very first hours and days after a sudden increase in carbon dioxide (CO2), in black carbon (BC) or in sulfate (SO4). Five models have performed PDRMIP simulations with hourly output, and we also compare results to monthly PDRMIP and CMIP6 results. We find that the effect of increasing ocean temperatures kicks in after a couple of months. Rapid precipitation reductions are for all three climate perturbations established after just a couple of days, and does for BC not differ much from the full-time response. &amp;#160;For CO2 and SO4, the magnitude of the precipitation response gradually increases with surface warming, and for CO2 the sign of the response changes for negative to positive after two years. Rapid cloud adjustments are typically established within the first 24 hours and while the magnitude of cloud feedbacks for CO2 and SO4 increases over time, the latitude-height pattern of the total cloud changes is clearly present after one year. While previously known that climate responses to BC are dominated by rapid adjustments, this work underlines the swiftness of the processes involved.&lt;/p&gt;</jats:p>

Conference paper

Jia H, Quaas J, Gryspeerdt E, Böhm C, Sourdeval Oet al., 2022,

Addressing the difficulties in quantifying the Twomey effect for marine warm clouds from multi-sensor satellite observations and reanalysis

<jats:p>&lt;p&gt;Aerosol&amp;#8211;cloud interaction is the most uncertain component of the overall anthropogenic forcing of the climate, in which the Twomey effect plays a fundamental role. Satellite-based estimates of the Twomey effect are especially challenging, mainly due to the difficulty in disentangling aerosol effects on cloud droplet number concentration (&lt;em&gt;N&lt;/em&gt;&lt;sub&gt;d&lt;/sub&gt;) from possible confounders. By combining multiple satellite observations and reanalysis, this study investigates the impacts of a) updraft, b) precipitation, c) retrieval errors, as well as (d) vertical co-location between aerosol and cloud, on the assessment of&amp;#160;&lt;em&gt;N&lt;/em&gt;&lt;sub&gt;d&lt;/sub&gt;-toaerosol sensitivity (&lt;em&gt;S&lt;/em&gt;) in the context of marine warm (liquid) clouds. Our analysis suggests that&amp;#160;&lt;em&gt;S&lt;/em&gt;&amp;#160;increases remarkably with both cloud base height and cloud geometric thickness (proxies for vertical velocity at cloud base), consistent with stronger aerosol-cloud interactions at larger updraft velocity. In turn, introducing the confounding effect of aerosol&amp;#8211;precipitation interaction can artificially amplify&amp;#160;&lt;em&gt;S&lt;/em&gt;&amp;#160;by an estimated 21 %, highlighting the necessity of removing precipitating clouds from analyses on the Twomey effect. It is noted that the retrieval biases in aerosol and cloud appear to underestimate&amp;#160;&lt;em&gt;S&lt;/em&gt;, in which cloud fraction acts as a key modulator, making it practically difficult to balance the accuracies of aerosol&amp;#8211;cloud retrievals at aggregate

Journal article

Montagud-Camps V, Hellinger P, Verdini A, Papini E, Franci L, Matteini L, Landi Set al., 2022,

Quantification of the cross-helicity cascade with Karman-Howarth-Monin and Spectral transfer equations

<jats:p>&lt;p&gt;Spectral transfer equations allow to &amp;#160;quantify the value of the energy flux of a turbulent flow across concentric shells in Fourier space. Karman-Howarth-Monin equations serve as a complement to the Spectral Transfer analysis, since they &amp;#160;quantify &amp;#160;as well the energy transfer rate of turbulence across scales via third-order structure functions, but also provide information on the directionality of the flux. We have extended the use of these methods to study the cascade of cross-helicity and compare it to the energy cascade &amp;#160;in 3D compressible MHD simulations. Our results show that the cross-helicity cascade reaches stationarity after the energy cascade, thus indicating a slower turbulence development for this invariant. Once fully developed, the cross-helicity cascade matches the main features of the energy one.&lt;/p&gt;</jats:p>

Journal article

Woolley T, Matteini L, Horbury TS, Bale SD, Laker R, Woodham LD, Stawarz JEet al., 2022,

Linking In-situ Magnetic and Density Structures in the Low Latitude Slow Solar Wind to Solar Origins

<jats:p>&lt;p&gt;To date, Parker Solar Probe has completed ten solar encounters and measured a wealth of in-situ data down to heliocentric distances of ~13 solar radii. This data provides a novel opportunity to investigate the near-Sun environment and understand the young slow solar wind. Typically, the slow solar wind observed in the inner heliosphere is split into an Alfvenic and a non-Alfvenic component. The Alfvenic slow wind is thought to originate from overexpanded coronal hole field lines, whereas the non-Alfvenic slow wind could originate from active regions, transient events, or reconnection at the tips of helmet streamers. In this work, we find structures associated with non-Alfvenic slow wind in the low latitude wind measured by Parker Solar Probe. We identify at least two distinct types of structure using magnetic field magnitude, electron pitch angle distributions, and electron number density. After statistically analysing these structures, with a focus on their plasma properties, shape, and location with respect to the heliospheric current sheet, we link them to solar origins. We find structures that are consistent with the plasma blobs seen previously in remote sensing observations.&lt;/p&gt;</jats:p>

Journal article

Maffei S, Livermore P, Mound J, Eggington J, Eastwood J, Sanchez S, Freeman Met al., 2022,

The future evolution of the auroral zones

<jats:p>&lt;p&gt;The auroral zones indicate the locations on the Earth&amp;#8217;s surface where, on average, it is most likely to spot aurorae as a consequence of increased solar activity. The shape of the auroral zones and, similarly, the geographical locations most vulnerable to extreme space weather events are modulated by the geomagnetic field of internal origin. As the latter evolves in time, the formers will be subject to variations on the same timescales.&lt;/p&gt;&lt;p&gt;From available geomagnetic field forecasts (which provide an estimate of the future evolution of the geomagnetic field of internal origin) we derive AACGM latitudes and estimate the future evolution of the auroral zones. The novel aspect of this technique is that we make use of all available Gauss coefficients to produce the forecasts, while the majority of present techniques estimate the location of the auroral zones based on the dipolar coefficients only. Our results show that, while the shift of the geomagnetic dipole axis has a first order contribution, higher order Gauss coefficients contribute significantly to the location and shape of the auroral zones.&lt;/p&gt;&lt;p&gt;The same technique is then extended to estimate the future location of the geographical location that would be, on average, most exposed to extreme space weather event. We find that the space-weather related risk will not change significantly for the UK over the next 50 years. For the Canadian provinces of Quebec and Ontario, however, we predict a significant increase in the risk associated to extreme solar activity.&lt;/p&gt;</jats:p>

Journal article

Ben-Yami M, Oetjen H, Brindley H, Cossich W, Lajas D, Maestri T, Magurno D, Raspollini P, Sgheri L, Warwick Let al., 2022,

Emissivity retrievals with FORUM's end-to-end simulator: challenges and recommendations

, Atmospheric Measurement Techniques, Vol: 15, Pages: 1755-1777, ISSN: 1867-1381

Spectral emissivity is a key property of the Earth's surface, of which only very few measurements exist so far in the far-infrared (FIR) spectral region, even though recent work has shown that the FIR is important for accurate modelling of the global climate. The European Space Agency's 9th Earth Explorer, FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will provide the first global spectrally resolved measurements of the Earth's top-of-the-atmosphere (TOA) spectrum in the FIR. In clear-sky conditions with low water vapour content, these measurements will provide a unique opportunity to retrieve spectrally resolved FIR surface emissivity. In preparation for the FORUM mission with an expected launch in 2027, this study takes the first steps towards the development of an operational emissivity retrieval for FORUM by investigating the sensitivity of the emissivity product of a full spectrum optimal estimation retrieval method to different physical and operational parameters. The tool used for the sensitivity tests is the FORUM mission's end-to-end simulator. These tests show that the spectral emissivity of most surface types can be retrieved for dry scenes in the 350–600 cm−1 region, with an absolute uncertainty ranging from 0.005 to 0.01. In addition, the quality of the retrieval is quantified with respect to the precipitable water vapour content of the scene, and the uncertainty caused by the correlation of emissivity with surface temperature is investigated. Based on these investigations, a road map is recommended for the development of the operational emissivity product.

Journal article

Saboya E, Zazzeri G, Graven H, Manning AJ, Michel SEet al., 2022,

Continuous CH4 and delta(CH4)-C-13 measurements in London demonstrate under-reported natural gas leakage

, Atmospheric Chemistry and Physics, Vol: 22, Pages: 3595-3613, ISSN: 1680-7316

Top-down greenhouse gas measurements can be used to independently assess the accuracy of bottom-up emission estimates. We report atmospheric methane (CH4) mole fractions and δ13CH4 measurements from Imperial College London from early 2018 onwards using a Picarro G2201-i analyser. Measurements from March 2018 to October 2020 were compared to simulations of CH4 mole fractions and δ13CH4 produced using the NAME (Numerical Atmospheric-dispersion Modelling Environment) dispersion model coupled with the UK National Atmospheric Emissions Inventory, UK NAEI, and a global inventory, the Emissions Database for Global Atmospheric Research (EDGAR), with model spatial resolutions of ∼ 2, ∼ 10, and ∼ 25 km. Simulation–measurement comparisons are used to evaluate London emissions and the source apportionment in the global (EDGAR) and UK national (NAEI) emission inventories. Observed mole fractions were underestimated by 30 %–35 % in the NAEI simulations. In contrast, a good correspondence between observations and EDGAR simulations was seen. There was no correlation between the measured and simulated δ13CH4 values for either NAEI or EDGAR, however, suggesting the inventories' sectoral attributions are incorrect. On average, natural gas sources accounted for 20 %–28 % of the above background CH4 in the NAEI simulations and only 6 %–9 % in the EDGAR simulations. In contrast, nearly 84 % of isotopic source values calculated by Keeling plot analysis (using measurement data from the afternoon) of individual pollution events were higher than −45 ‰, suggesting the primary CH4 sources in London are actually natural gas leaks. The simulation–observation comparison of CH4 mole fractions suggests that total emissions in London are much higher than the NAEI estimate (0.04 Tg CH4 yr−1) but close to, or slightly lo

Journal article

Reville V, Fargette N, Rouillard AP, Lavraud B, Velli M, Strugarek A, Parenti S, Brun AS, Shi C, Kouloumvakos A, Poirier N, Pinto RF, Louarn P, Fedorov A, Owen CJ, Genot V, Horbury TS, Laker R, O'Brien H, Angelini V, Fauchon-Jones E, Kasper JCet al., 2022,

Flux rope and dynamics of the heliospheric current sheet Study of the Parker Solar Probe and Solar Orbiter conjunction of June 2020

, Astronomy and Astrophysics: a European journal, Vol: 659, Pages: 1-14, ISSN: 0004-6361

Context. Solar Orbiter and Parker Solar Probe jointly observed the solar wind for the first time in June 2020, capturing data from very different solar wind streams: calm, Alfvénic wind and also highly dynamic large-scale structures.Context. Our aim is to understand the origin and characteristics of the highly dynamic solar wind observed by the two probes, particularly in the vicinity of the heliospheric current sheet (HCS).Methods. We analyzed the plasma data obtained by Parker Solar Probe and Solar Orbiter in situ during the month of June 2020. We used the Alfvén-wave turbulence magnetohydrodynamic solar wind model WindPredict-AW and we performed two 3D simulations based on ADAPT solar magnetograms for this period.Results. We show that the dynamic regions measured by both spacecraft are pervaded by flux ropes close to the HCS. These flux ropes are also present in the simulations, forming at the tip of helmet streamers, that is, at the base of the heliospheric current sheet. The formation mechanism involves a pressure-driven instability followed by a fast tearing reconnection process. We further characterize the 3D spatial structure of helmet streamer born flux ropes, which appears in the simulations to be related to the network of quasi-separatrices.

Journal article

Ukhorskiy AY, Sorathia KA, Merkin VG, Crabtree C, Fletcher AC, Malaspina DM, Schwartz SJet al., 2022,

Cross-scale energy cascade powered by magnetospheric convection

, SCIENTIFIC REPORTS, Vol: 12, ISSN: 2045-2322

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Journal article

Reville V, Velli M, Panasenco O, Tenerani A, Shi C, Badman ST, Bale SD, Kasper JC, Stevens ML, Korreck KE, Bonnell JW, Case AW, Dudok de Wit T, Goetz K, Harvey PR, Larson DE, Livi R, Malaspina DM, MacDowall RJ, Pulupa M, Whittlesey PLet al., 2022,