ALBERT

Description: Knowledge of solar wind conditions at Mars is often necessary to study the planet's magnetospheric and ionospheric dynamics. With no continuous upstream solar wind monitor at Mars, studies have used a variety of methods to measure or predict Martian solar wind conditions. In situ measurements, when available, are preferred, but can often be limited in continuity or scope, and so studies have also utilized solar wind proxies, spacecraft flybys, and Earth-Mars alignment to provide solar wind context. Despite the importance of solar wind knowledge and the range of methods used to provide it, the use of solar wind models remains relatively unutilized. This study uses the WSA-ENLIL + Cone solar wind model to calculate solar wind parameters at Mars’ orbital location to provide a new approach to determining solar wind conditions at Mars. Comparisons of the model results with observations by the MAVEN spacecraft indicate that the WSA-ENLIL + Cone model can forecast solar wind conditions at Mars as accurately as it has predicted them historically at the Earth, although at Mars the model systematically mispredicts solar wind speed and density, likely a result of magnetogram calibration. Particular focus is placed on modeling the early March 2015 ICMEs that interacted with Mars. Despite the complexity of the ICMEs, the model accurately predicted the speed and arrival time of the ICME-driven interplanetary shock, although it underpredicted other solar wind parameters. These results suggest that solar wind models can be used to provide the necessary general context of the heliospheric conditions to planetary studies.

Description: Multipoint observations from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on board Mars Express and the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission reveal a dynamic response of the Martian ionosphere to abrupt variations in the upstream solar wind plasma. On 2 February 2017, MAVEN, located upstream from the Martian bow shock, encountered a CIR-related interplanetary shock with a sudden enhancement in the dynamic pressure. MARSIS, operating in the upper ionosphere at ∼478 km altitudes and ∼78 ∘ solar zenith angles, observed a sharp increase in the local magnetic field magnitude ∼1 min after the shock passage at MAVEN. The time lag is roughly consistent with the expected propagation time of a pressure pulse from the bow shock to the upper ionosphere at the fast magnetosonic speed. Subsequently, remote soundings recorded disturbed signatures of the topside ionosphere below Mars Express.

Description: The response of Mars to the major space weather events called Interplanetary Coronal Mass Ejections (ICMEs) is of interest for both general planetary solar wind interaction studies and related speculations on their evolutionary consequences-especially with respect to atmosphere escape. Various particle and field signatures of ICMEs have been observed on Phobos-2, Mars Global Surveyor (MGS), Mars Express (MEX), and now MAVEN. Of these, MAVEN's combined instrumentation and orbit geometry is particularly well-suited to characterize both the event drivers and their consequences. However, MAVEN has detected only moderate disturbances at Mars due in large part to the general weakness of the present solar cycle. Nevertheless, the strongest event observed by MAVEN in March 2015 provides an example illustrating how further insights can be gained from available models. Here we first look more closely at what previously run BATS-R-US MHD simulations of the combined MAVEN observations tell us about the March 2015 event consequences. We then use analogous models to infer those same responses, including magnetic field topology changes and ionospheric consequences, to a hypothetical extreme ICME at Mars based on STEREO-A measurements in July 2012. The results suggest how greatly enhanced, yet realistic, solar wind pressure, magnetic field, and convection electric field combine to produce strong magnetospheric coupling with important consequences for upper atmosphere and ionosphere energization.

Description: Normal solar wind flows and intense solar transient events interact directly with the upper Martian atmosphere due to the absence of an intrinsic global planetary magnetic field. Since the launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, there are now new means to directly observe solar wind parameters at the planet's orbital location for limited time spans. Due to MAVEN's highly elliptical orbit, in situ measurements cannot be taken while MAVEN is inside Mars' magnetosheath. To model solar wind conditions during these atmospheric and magnetospheric passages, this research project utilized the solar wind forecasting capabilities of the WSA-ENLIL+Cone model. The model was used to simulate solar wind parameters which included magnetic field magnitude, plasma particle density, dynamic pressure, proton temperature, and velocity during a four Carrington rotation-long segment. An additional simulation that lasted 18 Carrington rotations was then conducted. The precision of each simulation was examined for intervals when MAVEN was in the upstream solar wind, i.e., with no exospheric or magnetospheric phenomena altering in situ measurements. It was determined that generalized, extensive simulations have comparable prediction capabilities as shorter, more comprehensive simulations. Generally, this study aimed to quantify the loss of detail in long-term simulations and to determine if extended simulations can provide accurate, continuous upstream solar wind conditions when there is a lack of in situ measurements.

Description: Solar energetic particles (SEPs) can precipitate directly into the atmospheres of weakly magnetized planets, causing increased ionization, heating, and altered neutral chemistry. However, strong localized crustal magnetism at Mars can deflect energetic charged particles and reduce precipitation. In order to quantify these effects, we have developed a model of proton transport and energy deposition in spatially varying magnetic fields, called Atmospheric Scattering of Protons and Energetic Neutrals (ASPEN). We benchmark the model's particle tracing algorithm, collisional physics, and heating rates, comparing against previously published work in the latter two cases. We find that energetic non-relativistic protons precipitating in proximity to a crustal field anomaly will primarily deposit energy at either their stopping altitude or magnetic reflection altitude. We compared atmospheric ionization in the presence and absence of crustal magnetic fields at 50° S and 182° E during the peak flux of the 29 October 2003 “Halloween storm” SEP event. The presence of crustal magnetic fields reduced total ionization by ~30% but caused ionization to occur over a wider geographic area.

Description: [1]  The radial alignment of ACE and Ulysses in February 2004 and August 2007 provided us with unprecedented opportunities to study the radial evolution of planar magnetic structures in 3 corotating interaction regions (CIRs). The in-situ observations are compared with results from an analytical and a numerical model of CIRs (Lee, 2000; Odstrcil, 2003). We find that: 1) All 3 CIRs' meridional tilt retained its North/South orientation at ACE and Ulysses, but the evolution was not systematic. Further, the model results of CIR meridional tilt do not agree with observations. 2) All 3 CIRs rotated azimuthally with the Parker spiral as expected, however model results only describe this behavior quantitatively for 1 CIR. 3) For all 3 CIRs, the solar wind deflection angles were predicted by the coupled solar corona-solar wind models, Wang-Sheely-Arge (WSA)-Enlil and MHD Around a Sphere (MAS)-Enlil, but neither model reproduced the observed planar magnetic structures. 4) The WSA-Enlil results of azimuthal magnetic field orientation are in better agreement with observations than those based on the MAS-Enlil. We suggest that the evolution of meridional tilt from ACE to Ulysses did not agree with projections because the parent coronal holes were highly structured. We also suggest that observations of azimuthal tilt do not agree with the model results because the models may underestimate transverse flows, whereas in reality, these flows could affect the observed azimuthal tilt of the CIR. The local orientation of PMSs within CIRs may also be distorted by transients, but their effect is unclear.

Description: Solar energetic particle (SEP) event modeling has gained renewed attention in part because of the availability of a decade of multipoint measurements from STEREO and L1 spacecraft at 1 AU. These observations are coupled with improving simulations of the geometry and strength of heliospheric shocks obtained by using coronagraph images to send erupted material into realistic solar wind backgrounds. The STEREO and ACE measurements in particular have highlighted the sometimes surprisingly widespread nature of SEP events. It is thus an opportune time for testing SEP models, which typically focus on protons ~1-100 MeV, toward both physical insight to these observations and potentially useful space radiation environment forecasting tools. Some approaches emphasize the concept of particle acceleration and propagation from close to the Sun, while others emphasize the local field line connection to a traveling, evolving shock source. Among the latter is the previously introduced SEPMOD treatment, based on the widely-accessible and well-exercised WSA-ENLIL-cone model. SEPMOD produces SEP proton time profiles at any location within the ENLIL domain. Here we demonstrate a SEPMOD version that accommodates multiple, concurrent shock sources occurring over periods of several weeks. The results illustrate the importance of considering longer-duration time periods and multiple CME contributions in analyzing, modeling, and forecasting SEP events.

Description: ABSTRACT During Intensive Observation Period 13 (15–16 October 2012) of the first Special Observing Period of the Hydrological cycle in the Mediterranean Experiment (HyMeX), Southern Italy (SI) was affected by two consecutive heavy precipitation events (HPEs). Both HPEs were associated with multi-cell V-shaped retrograde regeneration mesoscale convective systems (MCSs). The life cycle of two MCSs in connection with their dynamic and thermodynamic environments were analysed using a combination of ground-based, airborne and spaceborne observations and numerical simulations. Rain gauges revealed that heavy precipitation occurred in two phases: the first one from 1300 to 1700 UTC (35 mm h −1 ) was caused by a V-shaped system initiating over the Tyrrhenian Sea in the early morning of 15 October. Convection was triggered by the low-level convergence between the south-westerlies ahead of an upper-level trough positioned over south-eastern France and very moist southerlies from the Strait of Sicily. The convection was favoured by high convective available potential energy (1500 J kg −1 ) resulting from warm and moist conditions at low levels associated with high sea surface temperatures in the Sicily Channel. In addition, humidity at mid-level was enriched by the presence of an elevated moisture plume from tropical Africa, favouring the efficiency of the convection to produce more precipitation. The second phase of heavy precipitation (2300 UTC on 15 October to 0200 UTC on 16 October, 34 mm h −1 ) was caused by a MCS initiating over Algeria around 1300 UTC, which subsequently traveled over the Strait of Sicily toward Sicily and SI. Convection was maintained by the combination of large low-level moisture contents and a marked convergence ahead of the cold front. Unlike other MCSs forming in the same region earlier on that day, this huge V-shaped system did affect SI because the strong upper-level flow progressively veered from southwesterly to south-southwesterly.

Description: ABSTRACT During Intensive Observation Period 15a (20 October 2012) of the first Special Observation Period of the Hydrological cycle in the Mediterranean Experiment, north-eastern Spain experienced heavy precipitation (130 mm in 24 h) associated with a retrograde regeneration mesoscale convective system (MCS) developing in the exit region of the Ebro River Valley (ERV). The life cycle of the MCS that brought intense hourly rainfall (34 mm) from the foothill of Iberian Plateau to the central Pyrenees, as well as the detailed structure of moist marine flow upstream, were analysed using a combination of ground-based, airborne and space-borne observations as well as model analyses. Over the Balearic Sea, the south-westerlies along the north-eastern flank of a surface low converged with south-easterlies from north Africa, creating a near surface moisture tongue in the region of the Balearic Islands, and a southeast-northwest oriented convergence line within a cloud cluster advecting from northern Africa. Airborne lidar measurements, acquired upstream of the ERV, evidenced water vapour mixing ratios in excess of 15 g kg −1 in the marine atmospheric boundary layer. In the mid-level (700 hPa), the presence of an elevated moisture plume from tropical Africa contributed for about one third to the large moisture content present over the western Mediterranean Sea. In this moist environment, the MCS was initiated over the orography of the north-eastern tip of the Iberian plateau, due to the combined influence of the approaching convergence line ahead of the surface low and the convergence resulting from weak north-westerlies channeled in the ERV and the easterlies impinging on the coastal range. After the initiation phase, the MCS further developed over the foothill of Iberian Plateau and moved into the ERV and along the southern flank of the Pyrenees, thanks to the penetration of the warm and moist maritime south-easterly flow through the narrow gap between the north-eastern part of the Iberian Plateau and the Catalan coastal range.