Pluto's atmosphere from stellar occultations in 2012 and 2013

This is the Final Technical Report for University of Colorado's portion of the SciDAC project 'Center for Gyrokinetic Particle Simulation of Turbulent Transport.' This is funded as a multi-institutional SciDAC Center and W.W. Lee at the Princeton Plasma Physics Laboratory is the lead Principal Investigator. Scott Parker is the local Principal Investigator for University of Colorado and Yang Chen is a Co-Principal Investigator. This is Cooperative Agreement DE-FC02-05ER54816. Research personnel include Yang Chen (Senior Research Associate), Jianying Lang (Graduate Research Associate, Ph.D. Physics Student) and Scott Parker (Associate Professor). Research includes core microturbulence studies of NSTX, simulation of trapped electron modes, development of efficient particle-continuum hybrid methods and particle convergence studies of electron temperature gradient driven turbulence simulations. Recently, the particle-continuum method has been extended to five-dimensions in GEM. We find that actually a simple method works quite well for the Cyclone base case with either fully kinetic or adiabatic electrons. Particles are deposited on a 5D phase-space grid using nearest-grid-point interpolation. Then, the value of delta-f is reset, but not the particle's trajectory. This has the effect of occasionally averaging delta-f of nearby (in the phase space) particles. We are currently trying to estimate the dissipation (or effective collision operator). We have been using GEM to study turbulence and transport in NSTX with realistic equilibrium density and temperature profiles, including impurities, magnetic geometry and ExB shear flow. Greg Rewoldt, PPPL, has developed a TRANSP interface for GEM that specifies the equilibrium profiles and parameters needed to run realistic NSTX cases. Results were reported at the American Physical Society - Division of Plasma Physics, and we are currently running convergence studies to ensure physical results. We are also studying the effect of parallel shear flows, which can be quite strong in NSTX. Recent long-time simulations of electron temperature gradient driven turbulence, show that zonal flows slowly grow algebraically via the Rosenbluth-Hinton random walk mechanism. Eventually, the zonal flow gets to a level where it shear suppresses the turbulence. We have demonstrated this behavior with Cyclone base-case parameters, except with a 30% lower temperature gradient. We can demonstrate the same phenomena at higher gradients, but so far, have been unable to get a converged result at the higher temperature gradient. We find that electron ion collisions cause the zonal flows to grow at a slower rate and results in a higher heat flux. So, far all ETG simulations that come to a quasi-steady state show continued build up of zonal flow, see it appears to be a universal phenomena (for ETG). Linear and nonlinear simulations of Collisional and Collisionless trapped electron modes are underway. We find that zonal flow is typically important. We can, however, reproduce the Tannert and Jenko result (that zonal flow is unimportant) using their parameters with the electron temperature three times the ion temperature. For a typical weak gradient core value of density gradient and no temperature gradient, the CTEM is dominant. However, for a steeper density gradient (and still no temperature gradient), representative of the edge, higher k drift-waves are dominant. For the weaker density gradient core case, nonlinear simulations using GEM are routine. For the steeper gradient edge case, the nonlinear fluctuations are very high and a stationary state has not been obtained. This provides motivation for the particle-continuum algorithm. We also note that more physics, e.g. profile variation and equilibrium ExB shear flow should be significantly stabilizing, making such simulations feasible using standard delta-f techniques. This research is ongoing.

. IntroductionNine years after Pluto's flyby by New Horizons, there are still fundamental unanswered questions about Pluto's atmosphere. Here we focus on two specific plutonian mysteries. First, New Horizons revealed thin wave-like structures at global scales in the atmosphere, consistent with density perturbations previously seen in stellar occultations. It remains unclear whether these waves are orographic gravity waves initiated from winds flowing over Pluto's extensive topography or thermal tides resulting from the "breathing" of N2 ice in response to solar forcing. In addition, the impact of these waves on their climate has not yet been explored. Second, Pluto's atmospheric thermal structure measured by New Horizons [1,2] is presenting puzzling features such as: (1) a strong negative gradient between the stratosphere at 110K and the upper atmosphere at 70K, (2) a strong thermal gradient in latitude, still unexplained, and (3) a 3km-deep cold layer, which has been only partially explained.Recent studies [3] suggest that the cooling of the upper atmosphere (1) may be explained by the presence of organic hazes. However the bulk material of the haze (organic vs ice) remains unclear, and the radiative impact of the haze on the atmosphere remains to be explored in detail with 3D climate models including haze and hydrocarbon ice microphysics, and tested against available thermal emission measurements of the atmosphere. 2. The new Pluto PCMTo tackle these scientific investigations, we created a completely new-generation planetary climate model (PCM) able to simulate Pluto at high spatial resolution, with haze microphysics processes, and over the long annual timescales. This Pluto PCM is derived from the LMD Generic PCM and from the Legacy Pluto GCM [4,5,6] and therefore benefits from the recent developments from the Generic PCM such as its efficient parallelization.At the conference we will present this new tool and preliminary results regarding the impact of radiatively active hazes on Pluto's climate as well as the propagation of gravity waves in the atmosphere. AcknowledgementsThis work was supported by funding from ANR "Programme de Recherche Collaborative" 2024-2028 (ANR-23-CE49-0006).

Pluto's atmosphere is cold and hazy. Recent observations have shown it to be much colder than predicted theoretically, suggesting an unknown cooling mechanism. Atmospheric gas molecules, particularly water vapour, have been proposed as a coolant; however, because Pluto's thermal structure is expected to be in radiative-conductive equilibrium, the required water vapour would need to be supersaturated by many orders of magnitude under thermodynamic equilibrium conditions. Here we report that atmospheric hazes, rather than gases, can explain Pluto's temperature profile. We find that haze particles have substantially larger solar heating and thermal cooling rates than gas molecules, dominating the atmospheric radiative balance from the ground to an altitude of 700 kilometres, above which heat conduction maintains an isothermal atmosphere. We conclude that Pluto's atmosphere is unique among Solar System planetary atmospheres, as its radiative energy equilibrium is controlled primarily by haze particles instead of gas molecules. We predict that Pluto is therefore several orders of magnitude brighter at mid-infrared wavelengths than previously thought-a brightness that could be detected by future telescopes.

Measurements of ice temperature to depths of 30–40 m. are given for a number of points on the ice sheet in MacRobertson Land. Variations of mean surface temperature with elevation and with latitude, and the temperature gradients below a depth of 15 m. are compared with results from other parts of Antarctica and from Greenland. Explanations of negative temperature gradients near the surface of ice sheets are reviewed, and an equation derived by Robin is checked against the measurements following its recent justification from conduction theory. Surface ice velocities necessary for development of the observed temperature gradients are computed, and these values are then compared with ice velocities estimated independently from flow measurements at the coast and continuity considerations. It is found that, if negative gradients are attributed solely to the Robin effect, improbably high ice velocities are called for, and so climatic change is reconsidered. Some evidence of secular warming in Antarctica is mentioned and a recent numerical solution of the conduction equation for the surface-warming case is described. It is concluded that the measured temperature profiles can be explained reasonably by climatic amelioration.

Measurements of ice temperature to depths of 30–40 m. are given for a number of points on the ice sheet in MacRobertson Land. Variations of mean surface temperature with elevation and with latitude, and the temperature gradients below a depth of 15 m. are compared with results from other parts of Antarctica and from Greenland. Explanations of negative temperature gradients near the surface of ice sheets are reviewed, and an equation derived by Robin is checked against the measurements following its recent justification from conduction theory. Surface ice velocities necessary for development of the observed temperature gradients are computed, and these values are then compared with ice velocities estimated independently from flow measurements at the coast and continuity considerations. It is found that, if negative gradients are attributed solely to the Robin effect, improbably high ice velocities are called for, and so climatic change is reconsidered. Some evidence of secular warming in Antarctica is mentioned and a recent numerical solution of the conduction equation for the surface-warming case is described. It is concluded that the measured temperature profiles can be explained reasonably by climatic amelioration.

The wind and temperature data collected from the Radiosonde over Hyderabad (17.2N, 78.20E) for the years 2010 and 2011 have been consolidated. The results in the form of monthly mean values provide reliable reference wind profiles and temperatures profiles for tropospheric and stratospheric heights up to 40km. The zonal and meridional Wind profiles as well as temperature profiles are calculated and presented in graphical forms. A change in wind direction and velocity has been noticed in zonal wind. Investigation in the dynamics of the lower atmosphere would be helpful in better planning for Aerodynamic Technology.

The horizontal temperature gradients in the tropical free troposphere are generally assumed to be weak. We show with ERA5 data that substantial zonal virtual temperature (Tυ) gradients persist climatologically in the tropical free troposphere and investigate their causes. The gradients change seasonally: Tυ at 500 hPa over the equatorial western Pacific Ocean (EWP) is usually much warmer (up to 3 K) than that over the equatorial central Pacific Ocean (ECP) during December–February (DJF), while the temperature differences between EWP and ECP are much smaller during June–August (JJA). During DJF, Tυ gradients over the Pacific prevail throughout the entire free troposphere, especially in the upper troposphere near 300 hPa. We find that the associated hydrostatic pressure gradients are mainly balanced by the nonlinear terms in the momentum equation, in particular via zonal wind advection. Strong zonal winds occur near the equator in boreal winter, transporting zonal momentum so as to balance the pressure gradient force. The zonal winds are due to large-scale equatorial waves, excited by a heating pattern that is relatively symmetric about the equator. In boreal summer, the large-scale equatorial waves are less active in the Pacific region due to a more asymmetric temperature pattern, so the zonal momentum advection and Tυ gradients are both much weaker. The results point to an important role of the nonlinear terms in the tropical balanced dynamics, stressing the need for an improved theoretical understanding and modeling framework of the tropical atmosphere that includes these nonlinear terms, or their net effect.

Diurnal CO variations in the Venus mesophere from CO microwave spectra

<p>We show with ERA5 reanalysis data that substantial zonal virtual temperature gradients, on monthly time scales, exist in the tropical free troposphere. The strength of the temperature gradients changes seasonally: the Equatorial Western Pacific Ocean (EWP) is usually much warmer than the Equatorial Central Pacific Ocean (ECP) during December-January-February (DJF), while ECP becomes slightly warmer than EWP during June-July-August (JJA). During DJF, the virtual temperature gradients in the Pacific prevail throughout the entire free troposphere, and are most pronounced in the upper troposphere near 300hPa. We find that the free-tropospheric temperature gradients are related to the pressure gradients, while the pressure gradient force is mainly balanced by the nonlinear terms in the momentum equation---zonal wind advection. Strong zonal winds occur near the equator in January, transporting momentum zonally and balancing the pressure gradient force. The reason that strong zonal winds occur is that vigorous large-scale equatorial waves are excited due to the heating pattern being more symmetric to the equator. In July, the large-scale equatorial waves are less active in the Pacific Ocean. No strong zonal wind exists to sustain the pressure gradient as well as temperature gradient to develop. As a result, the virtual temperature distributions are much more uniform. The results point out the important role of the nonlinear terms in the tropical balanced dynamics on monthly time scales, stressing the need of an improved theoretical understanding and modeling framework of the tropical atmosphere by including the nonlinear terms in the dynamical balance.</p>

A non‐LTE radiative transfer model for the population of the CO(1) vibrational state in the middle atmosphere is presented. Radiative transfer is treated by using the Curtis matrix method. The transmittances needed for the Curtis matrix have been computed by using the GENLN2 line‐by‐line radiance/transmittance code. A study of the radiative and collisional processes and atmospheric parameters that affect the population of CO(1) populations has been performed. We find that the tropospheric kinetic temperature and CO abundance profiles play an important role through radiative coupling in the population of mesospheric CO(1) at night‐time. During the day, the solar flux and the mesospheric CO abundance are the main factors determining the CO vibrational temperature in the mesosphere. Non‐thermal collisions with the atmospheric N2(1) are also shown to be important for the daytime population of CO(1) in that region. The consequences of these results for the retrieval of CO abundances from the remote sensing of radiance at 4.7 μm are discussed.

Ambient temperature interference (ATI) is a concern that has not been adequately addressed in studies of coupled water and heat transport in unsaturated soil. Our objectives were to detect ATI, minimize it, and obtain nonisothermal, steady‐state temperature and moisture profiles with minimum ATI. Two soils, a sand and a silty clay loam (sicl), were packed into cylindrical cells with uniform moisture. Temperature gradients were imposed by making one end warmer (40, 23, or 19°C) than the other end (1 or 9°C). Steady‐state temperature profile data were obtained for various cell configurations and ambient temperatures. The configuration showing least ATI was a 2.5‐cm‐diam., 5‐cm‐long cell, with 8 cm radial insulation. Longer cells of the same basic design or with less insulation had greater ATI, as did a larger diameter cell (4 cm diam. and 14 cm long). All tests (sand at 0.049 m 3 m −3 moisture; sicl at 0.049 and 0.146 m 3 m −3 ) using lowest ATI cells produced concave upward temperature profiles. In contrast, the larger diameter cell (sicl, high ATI) had concave downward profiles. Water redistribution into the cooler half of cells was more pronounced with sand (>90%) than sicl. Cells exhibiting low ATI appear to provide more consistent and meaningful soil temperature and moisture profiles than had previously been obtainable.

Operational strategy to stabilize lithium metal anodes by applied thermal gradient

Turbulent transport and zonal flow (ZF) dynamics in the mixed kinetic ballooning mode (KBM) and ion temperature gradient (ITG) mode dominated turbulence states are analyzed by gyrokinetic simulations based on the experimental observations of KBMs in the HL-2A Internal Transport Barrier (ITB) plasmas with weak magnetic shear configuration. Results have shown that KBMs and ITGs are the main candidates for turbulent transport and the inclusion of fast ions (FIs) can destabilize both instabilities, which is resulted by the decrease of ballooning parameter αMHD hence reduced Shafranov shift stabilization due to the negative FI density gradient, making them more unstable according to the ŝ-αMHD diagram. In addition, the ITGs are suppressed by both dilution and finite-β stabilization effects caused by FIs. Nonlinear simulations excluding the effects of FIs indicate that the transport is minimum at βe=βeexp as the turbulence predominated by ITGs is strongly suppressed by the nonlinear electromagnetic (EM) stabilization and enhancement of ZFs. However, the transport is further increased with β e although the ZFs become stronger due to the transition from ITG to KBM dominated turbulence state. The presence of FIs can modify the relation between ZF shearing rate and β e. The transport level is insensitive to β e when βe⩽βeexp but increases significantly because of the KBM destabilization. Meanwhile, the ZF amplitude reaches maximum at βe=βeexp whereas it suffers an erosion at higher values, implying that the plasma might be a self-organized critical state owning to the interactions among ZFs, KBMs and FI effects hence setting the plasma β around β exp. The results have also provided a possible explanation that the destabilization of EM turbulence is responsible for the ion heat transport stiffness under weak magnetic shear configurations in the off-axis neutral beam injection heated ITB plasmas on HL-2A.

Effects of hydrogeological and climate change on the subsurface thermal regime in the Sendai Plain

This thesis aims at enhancing our fundamental understanding of the East Asian summer monsoon (EASM), and mechanisms implicated in its climatology in present-day and warmer climates. We focus on the most prominent feature of the EASM, i.e., the so-called Meiyu-Baiu (MB), which is characterized by a well-defined, southwest to northeast elongated quasi-stationary rainfall band, spanning from eastern China to Japan and into the northwestern Pacific Ocean in June and July. We begin with an observational study of the energetics of the MB front in present-day climate. Analyses of the moist static energy (MSE) budget of the MB front indicate that horizontal advection of moist enthalpy, primarily of dry enthalpy, sustains the front in a region of otherwise negative net energy input into the atmospheric column. A decomposition of the horizontal dry enthalpy advection into mean, transient, and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection. Numerical simulations in which the Tibetan Plateau (TP) is either retained or removed show that the TP influences the stationary enthalpy flux, and hence the MB front, primarily by changing the meridional stationary eddy velocity, with reinforced southerly wind on the northwestern flank of the north Pacific subtropical high (NPSH) over the MB region and northerly wind to its north. Changes in the longitudinal thermal gradient are mainly confined to the near downstream of the TP, with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended MB region. Similar mechanisms are shown to be implicated in present climate simulations in the Couple Model Intercomparison Project - Phase 5 (CMIP5) models. We find that the spatial distribution of the EASM precipitation simulated by different models is highly correlated with the meridional stationary eddy velocity. The correlation becomes more robust when energy fluxes into the atmospheric column are considered, consistent with the observational analyses. The spread in the area-averaged rainfall amount can be partially explained by the spread in the simulated globally-averaged precipitation, with the rest primarily due to the lower-level meridional wind convergence. Clear relationships between precipitation and zonal and meridional eddy velocities are observed. Finally, the response of the EASM to greenhouse gas forcing is investigated at different time scales in CMIP5 model simulations. The reduction of radiative cooling and the increase in continental surface temperature occur much more rapidly than changes in sea surface temperatures (SSTs). Without changes in SSTs, the rainfall in the monsoon region decreases (increases) over ocean (land) in most models. On longer time scales, as SSTs increase, rainfall changes are opposite. The total response to atmospheric CO^2 forcing and subsequent SST warming is a large (modest) increase in rainfall over ocean (land) in the EASM region. Dynamic changes, in spite of significant contributions from the thermodynamic component, play an important role in setting up the spatial pattern of precipitation changes. Rainfall anomalies over East China are a direct consequence of local land-sea contrast, while changes in the larger-scale oceanic rainfall band are closely associated with the displacement of the larger-scale NPSH. Numerical simulations show that topography and SST patterns play an important role in rainfall changes in the EASM region.