Abstract Polar vortices are common planetary-scale flows that encircle the pole in the middle or high latitudes and are observed in most of the solar system’s planetary atmospheres. The polar vortices on Earth, Mars, and Titan are dynamically related to the mean meridional circulation and exhibit a significant seasonal cycle. However, the polar vortex’s characteristics vary between the three planets. To understand the mechanisms that influence the polar vortex’s dynamics and dependence on planetary parameters, we use an idealized general circulation model with a seasonal cycle in which we vary the obliquity, rotation rate, and orbital period. We find that there are distinct regimes for the polar vortex seasonal cycle across the parameter space. Some regimes have similarities to the observed polar vortices, including a weakening of the polar vortex during midwinter at slow rotation rates, similar to Titan’s polar vortex. Other regimes found within the parameter space have no counterpart in the solar system. In addition, we show that for a significant fraction of the parameter space, the vortex’s potential vorticity latitudinal structure is annular, similar to the observed structure of the polar vortices on Mars and Titan. We also find a suppression of storm activity during midwinter that resembles the suppression observed on Mars and Earth, which occurs in simulations where the jet velocity is particularly strong. This wide variety of polar vortex dynamical regimes that shares similarities with observed polar vortices, suggests that among exoplanets there can be a wide variability of polar vortices.
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Polar vortex crystals: Emergence and structure
Vortex crystals are quasiregular arrays of like-signed vortices in solid-body rotation embedded within a uniform background of weaker vorticity. Vortex crystals are observed at the poles of Jupiter and in laboratory experiments with magnetized electron plasmas in axisymmetric geometries. We show that vortex crystals form from the free evolution of randomly excited two-dimensional turbulence on an idealized polar cap. Once formed, the crystals are long lived and survive until the end of the simulations (300 crystal-rotation periods). We identify a fundamental length scale, L γ = ( U / γ ) 1 / 3 , characterizing the size of the crystal in terms of the mean-square velocity U of the fluid and the polar parameter γ = f p / a p 2 , with f p the Coriolis parameter at the pole and a p the polar radius of the planet.
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- Award ID(s):
- 2048583
- NSF-PAR ID:
- 10333264
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 119
- Issue:
- 17
- ISSN:
- 0027-8424
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The need for operational models describing the friction factor
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ABSTRACT Relaxation dynamics of PVDF blended with a random zwitterionic copolymer (
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null (Ed.)This paper mathematically characterizes the tiny feasible regions within the vast 6D rotation–translation space in a full molecular replacement (MR) search. The capability to a priori isolate such regions is potentially important for enhancing robustness and efficiency in computational phasing in macromolecular crystallography (MX). The previous four papers in this series have concentrated on the properties of the full configuration space of rigid bodies that move relative to each other with crystallographic symmetry constraints. In particular, it was shown that the configuration space of interest in this problem is the right-coset space Γ\ G , where Γ is the space group of the chiral macromolecular crystal and G is the group of rigid-body motions, and that fundamental domains F Γ\ G can be realized in many ways that have interesting algebraic and geometric properties. The cost function in MR methods can be viewed as a function on these fundamental domains. This, the fifth and final paper in this series, articulates the constraints that bodies packed with crystallographic symmetry must obey. It is shown that these constraints define a thin feasible set inside a motion space and that they fall into two categories: (i) the bodies must not interpenetrate, thereby excluding so-called `collision zones' from consideration in MR searches; (ii) the bodies must be in contact with a sufficient number of neighbors so as to form a rigid network leading to a physically realizable crystal. In this paper, these constraints are applied using ellipsoidal proxies for proteins to bound the feasible regions. It is shown that the volume of these feasible regions is small relative to the total volume of the motion space, which justifies the use of ellipsoids as proxies for complex proteins in MR searches, and this is demonstrated with P 1 (the simplest space group) and with P 2 1 2 1 2 1 (the most common space group in MX).more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1073/pnas.2120486119
