On the interaction of Jupiter's Great Red Spot and zonal jet streams

In this paper, Jupiter's Great Red Spot (GRS) is used to determine properties of the Jovian atmosphere that cannot otherwise be found. These properties include the potential vorticity of the GRS and its neighboring jet streams, the shear imposed on the GRS by the jet streams, and the vertical entropy gradient (i.e., Rossby deformation radius). The cloud cover of the GRS, which is often used to define the GRS's area and aspect ratio, is found to differ significantly from the region of the GRS's potential vorticity anomaly. The westward-going jet stream to the north of the GRS and the eastward-going jet stream to its south are each found to have a large potential vorticity ``jump''. The jumps have opposite sign and as a consequence of their interaction with the GRS, the shear imposed on the GRS is reduced. The east-west to north-south aspect ratio of the GRS's potential vorticity anomaly depends on the ratio of the imposed shear to the strength of the anomaly. The aspect ratio is found to be $\approx$2:1, but without the opposing jumps it would be much greater. The GRS's high-speed collar and quiescent interior require that the potential vorticity in the interior be approximately half that in the collar. No other persistent geophysical vortex has a significant minimum of potential vorticity in its interior and laboratory vortices with such a minimum are unstable.Comment: Manuscript accepted to Journal of the Atmospheric Sciences, March 2007. v2: minor stylistic changes (after journal proof reading

Vertical Processes and Resolution Impact Ice Shelf Basal Melting: A Multi-Model Study

Understanding ice shelf–ocean interaction is fundamental to projecting the Antarctic ice sheet response to a warming climate. Numerical ice shelf–ocean models are a powerful tool for simulating this interaction, yet are limited by inherent model weaknesses and scarce observations, leading to parameterisations that are unverified and unvalidated below ice shelves. We explore how different models simulate ice shelf–ocean interaction using the 2nd Ice Shelf–Ocean Model Intercomparison Project (ISOMIP+) framework. Vertical discretisation and resolution of the ocean model are shown to have a significant effect on ice shelf basal melt rate, through differences in the distribution of meltwater fluxes and the calculation of thermal driving. Z-coordinate models, which generally have coarser vertical resolution in ice shelf cavities, may simulate higher melt rates compared to terrain-following coordinate models. This is due to the typically higher resolution of the ice–ocean boundary layer region in terrain following models, which allows better representation of a thin meltwater layer, increased stratification, and as a result, better insulation of the ice from water below. We show that a terrain-following model, a z-level coordinate model and a hybrid approach give similar results when the effective vertical resolution adjacent to the ice shelf base is similar, despite each model employing different paradigms for distributing meltwater fluxes and sampling tracers for melting. We provide a benchmark for thermodynamic ice shelf–ocean interaction with different model vertical coordinates and vertical resolutions, and suggest a framework for any future ice shelf–ocean thermodynamic parameterisations

Vertical processes and resolution impact ice shelf basal melting: A multi-model study

Understanding ice shelf–ocean interaction is fundamental to projecting the Antarctic ice sheet response to a warming climate. Numerical ice shelf–ocean models are a powerful tool for simulating this interaction, yet are limited by inherent model weaknesses and scarce observations, leading to parameterisations that are unverified and unvalidated below ice shelves. We explore how different models simulate ice shelf–ocean interaction using the 2nd Ice Shelf–Ocean Model Intercomparison Project (ISOMIP+) framework. Vertical discretisation and resolution of the ocean model are shown to have a significant effect on ice shelf basal melt rate, through differences in the distribution of meltwater fluxes and the calculation of thermal driving. Z-coordinate models, which generally have coarser vertical resolution in ice shelf cavities, may simulate higher melt rates compared to terrain-following coordinate models. This is due to the typically higher resolution of the ice–ocean boundary layer region in terrain following models, which allows better representation of a thin meltwater layer, increased stratification, and as a result, better insulation of the ice from water below. We show that a terrain-following model, a z-level coordinate model and a hybrid approach give similar results when the effective vertical resolution adjacent to the ice shelf base is similar, despite each model employing different paradigms for distributing meltwater fluxes and sampling tracers for melting. We provide a benchmark for thermodynamic ice shelf–ocean interaction with different model vertical coordinates and vertical resolutions, and suggest a framework for any future ice shelf–ocean thermodynamic parameterisations. © 2020 The Author

Dramatic Change in Jupiter's Great Red Spot from Spacecraft Observations

Jupiter's Great Red Spot (GRS) is one of its most distinct and enduring features. Since the advent of modern telescopes, keen observers have noted its appearance and documented a change in shape from very oblong to oval, confirmed in measurements from spacecraft data. It currently spans the smallest latitude and longitude size ever recorded. Here we show that this change has been accompanied by an increase in cloud/haze reflectance as sensed in methane gas absorption bands, increased absorption at wavelengths shorter than 500 nanometers, and increased spectral slope between 500 and 630 nanometers. These changes occurred between 2012 and 2014, without a significant change in internal tangential wind speeds; the decreased size results in a 3.2 day horizontal cloud circulation period, shorter than previously observed. As the GRS has narrowed in latitude, it interacts less with the jets flanking its north and south edges, perhaps allowing for less cloud mixing and longer UV irradiation of cloud and aerosol particles. Given its long life and observational record, we expect that future modeling of the GRS's changes, in concert with laboratory flow experiments, will drive our understanding of vortex evolution and stability in a confined flow field crucial for comparison with other planetary atmospheres

Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1)

Coupled ice sheet–ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet–ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions - notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods - taking a secondary role. © 2020 Wolters Kluwer Medknow Publications. All rights reserved

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role

Experimental protocol for sea level projections from ISMIP6 stand-alone ice sheet models

Projection of the contribution of ice sheets to sea level change as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form of simulations from coupled ice sheet–climate models and stand-alone ice sheet models, overseen by the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). This paper describes the experimental setup for process-based sea level change projections to be performed with stand-alone Greenland and Antarctic ice sheet models in the context of ISMIP6. The ISMIP6 protocol relies on a suite of polar atmospheric and oceanic CMIP-based forcing for ice sheet models, in order to explore the uncertainty in projected sea level change due to future emissions scenarios, CMIP models, ice sheet models, and parameterizations for ice–ocean interactions. We describe here the approach taken for defining the suite of ISMIP6 stand-alone ice sheet simulations, document the experimental framework and implementation, and present an overview of the ISMIP6 forcing to be used by participating ice sheet modeling groups

Future Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets

Projections of the sea level contribution from the Greenland and Antarctic ice sheets (GrIS and AIS) rely on atmospheric and oceanic drivers obtained from climate models. The Earth System Models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) generally project greater future warming compared with the previous Coupled Model Intercomparison Project phase 5 (CMIP5) effort. Here we use four CMIP6 models and a selection of CMIP5 models to force multiple ice sheet models as part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We find that the projected sea level contribution at 2100 from the ice sheet model ensemble under the CMIP6 scenarios falls within the CMIP5 range for the Antarctic ice sheet but is significantly increased for Greenland. Warmer atmosphere in CMIP6 models results in higher Greenland mass loss due to surface melt. For Antarctica, CMIP6 forcing is similar to CMIP5 and mass gain from increased snowfall counteracts increased loss due to ocean warming