Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D65: Statistical and Nonlinear Physics of Earth and its ClimateFocus
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Sponsoring Units: GPC GSNP Chair: Mara Freilich; Hussein Aluie, Dept. of Mechanical Engg, University of Rochester. Laboratory for Laser Energetics, Rochester, NY, USA. Room: Room 414 |
Monday, March 6, 2023 3:00PM - 3:36PM |
D65.00001: The ocean’s global overturning circulation and climate: from observations to process understanding Invited Speaker: Lynne Talley The ocean’s prominent partnership in climate has been evident for more than a century. Its sea surface temperature (SST) is its principal physical component that affects the atmosphere. Processes setting the observed SST distribution are myriad, and include not just air-sea heat exchange but also the ocean’s lateral and vertical circulation, turbulence distribution, and stratification. And also for more than a century, it has been understood that the ocean has a global scale overturning circulation, in which dense cold waters sink to depth at higher latitudes and rise to the surface wherever they can be forced to do so. This circulation exerts strong controls on ocean stratification, and hence affects large-scale SST variations. This in turn affects where the ocean is best poised to absorb and store excess (anthropogenic) heat. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D65.00002: Global Energy Spectrum of the General Oceanic Circulation Hussein Aluie, Benjamin A Storer, Michele Buzzicotti, Hemant Khatri, Stephen Griffies Advent of satellite altimetry brought into focus the pervasiveness of mesoscale eddies O(100)km in size, which are the ocean’s analogue of weather systems and are often regarded as the spectral peak of kinetic energy (KE). Yet, understanding of the ocean’s spatial scales has been derived mostly from Fourier analysis in small "representative" regions that cannot capture the vast dynamic range at planetary scales. Here, we use a coarse-graining method to analyze scales much larger than what had been possible before. Spectra spanning over three decades of length-scales reveal the Antarctic Circumpolar Current as the spectral peak of the global extra-tropical circulation, at ≈104 km, and a previously unobserved power-law scaling over scales larger than 103 km. A smaller spectral peak exists at ≈300 km associated with mesoscales, which, due to their wider spread in wavenumber space, account for more than 50% of resolved surface KE globally. Seasonal cycles of length-scales exhibit a characteristic lag-time of ≈40 days per octave of length-scales such that in both hemispheres, KE at 102 km peaks in spring while KE at 103 km peaks in late summer. These results provide a new window for understanding the multiscale oceanic circulation within Earth’s climate system, including the largest planetary scales. |
Monday, March 6, 2023 3:48PM - 4:24PM |
D65.00003: The multi-scale physics of ocean spray aerosols generation by breaking waves and bursting bubbles Invited Speaker: Luc Deike Physical processes at the ocean-atmosphere interface have a large effect on climate and weather by controlling the transfer of momentum and mass. Without wave breaking, transport between the ocean and the atmosphere is through slow conduction and molecular diffusion, while wave breaking is a transitional process from laminar to turbulent flow. When waves are breaking, the surface experiences dramatic changes, with sea spray ejection in the atmosphere and air entrainment into the ocean water. In this talk I will discuss recent efforts towards improving our understanding and modeling of ocean spray aerosol production through a multi-scale approach. Ocean spray aerosol impact climate through radiative processes and while acting as cloud condensation nuclei. We combine detailed laboratory experiments and numerical simulations on turbulent multiphase flows, including wave breaking, bubble break-up in turbulence and spray production by bubble bursting together with a statistical description of breaking waves to develop a general theoretical framework. This framework aims to account for the very large range of scales involved in the process, from wave statistics scales of order of km, O(1m-1km), to wave breaking dynamics, O(1-10m), air bubble entrainment, bubble dynamics in turbulence and finally bubble bursting at the first surface, O(microns to mm). The resulting ocean spray aerosols emissions are evaluated globally and are in remarkable agreement with field observations, without being adjusted to match any existing datasets, in terms of magnitude of sea salt emissions and size distribution. The remarkable coherence between the model and observations of sea salt emissions therefore strongly supports the mechanistic approach and paves the way for improved modeling of atmospheric processes controlled by aerosols of oceanic origin. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D65.00004: Statistics of breaking wave fields with a multilayer numerical framework Jiarong Wu, Stephane Popinet, Luc Deike Wave breaking is a distinct feature of ocean surface waves at moderate to high wind speeds. They generate widely observable whitecaps and greatly enhance the air-sea gas exchange and upper ocean mixing. Wave breaking is highly nonlinear, intermittent in space and time, and multi-scale as the underlying wave spectrum is; these features create difficulties for both analytical and numerical models. We simulate an ensemble of phase-resolved breaking wave fields in the physical space, where strong non-linearities including wave breaking are modeled despite no surface overturning. This is achieved using a novel multi-layer framework, which generalizes the single-layer Saint-Venant system into a multi-layer and non-hydrostatic formulation of the Navier-Stokes equations. The modeled wave fields show statistics of breaking that are in good agreement with field measurements. We propose a scaling of the breaking statistics solely based on wave properties and discuss the implications for previous empirical formulations. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D65.00005: Prospects for estimating Transient Climate Response to Greenhouse Gases using the Fluctuation Dissipation Theorem William Collins One of the core metrics for climate change is the steady-state increase in global surface air temperature with doubled concentrations of CO2 known as the Equilibrium Climate Sensitivity (ECS). Best estimates of ECS remain uncertain to factors of O(3) despite intensive research since the first comprehensive assessment of global warming due to CO2 over forty years ago (Charney et al., NAP, 1979). The large range in ECS propagates into projections of the future physical state of the climate system, and it introduces considerable incertitude into policy responses designed to mitigate global warming. The uncertainty in ECS stems largely from multiscale and multiphysics feedbacks introduced by components of the climate system, especially by clouds and the cryosphere, for which we lack first-principles theories. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D65.00006: Simpson's Law and the Water Vapor Feedback Nadir Jeevanjee The 2021 Nobel prize in physics was awarded in part to Suki Manabe for the first credible calculation of Earth's climate sensitivity, including a proper treatment of the water vapor feedback which doubles that sensitivity. This talk will demonstrate how the strength of this water vapor feedback can be tied to a basic property of water vapor radiative transfer known as "Simpson's Law". Consideration of Simpson's Law allows for a quantitative, analytical estimate of the strength of the water vapor feedback, consistent with Manabe's early work as well as recent work employing satellite observations and a hierarchy of climate models. |
Monday, March 6, 2023 5:00PM - 5:36PM |
D65.00007: Conservation laws for atmospheric dynamics with clouds Invited Speaker: Samuel N Stechmann Clouds and rainfall are among the most challenging aspects of weather and climate. In addition to difficulties in observing and simulating clouds, there is a large gap in our theoretical understanding of atmospheric dynamics with clouds versus without clouds (i.e., of moist fluid dynamics versus dry fluid dynamics). Here, I will present some recent work toward closing this gap by defining basic principles of geophysical fluid dynamics (GFD) that hold even in the presence of phase changes of water. In particular, I will present cloudy versions of the conservation principles of energy and potential vorticity, the latter of which is a cloudy extension of the classic Kelvin circulation theorem. |
Monday, March 6, 2023 5:36PM - 5:48PM |
D65.00008: Observation of Waves in the Climate System with Nontrivial Topology John B Marston, Ziyan Zhu, Weixuan Xu, Jung-Eun Lee, Baylor Fox-Kemper The rotation of the earth breaks time-reversal and parity symmetries in an opposite sense north and south of the equator, leading to a topological origin for certain atmospheric and oceanic equatorial waves. Away from the equator the shallow water and stably-stratified primitive equations exhibit Poincaré-gravity waves that have nontrivial topology as evidenced by a phase singularity in frequency-wavevector space. This non-trivial topology then predicts, via the principle of bulk-boundary correspondence, the existence of two equatorial waves along the equatorial interface, the Kelvin and Yanai waves. To verify the nontrivial topology of Poincaré-gravity waves, we examine ERA5 reanalysis data and study cross-correlations between the wind velocity and geopotential height of the mid-latitude stratosphere at the 50 hPa height, and find the predicted vortex and anti-vortex in the phase of the correlations at the high frequencies of the waves. By contrast, lower frequency planetary waves are found to have trivial topology. These results demonstrate a new way to understand of waves in the stratosphere, and provides a new qualitative tool for the investigation of waves in other components of the climate system. |
Monday, March 6, 2023 5:48PM - 6:00PM |
D65.00009: Impacts of changing storm characteristics in a stochastic model for dryland vegetation pattern formation Mary Silber, Punit Gandhi In various drylands around the globe vegetation can be self-organized into striking stripe patterns, where vegetation alternates with bare soil over kilometer scales. These banded patterns are oriented transverse to a gentle slope of the terrain, of 0.5-2% grade. Models, as well as early observational studies, suggest these patterns exist because of positive feedbacks between the vegetation distribution and the soil water distribution that follows a rare rain storm. For example, there is enhanced infiltration of storm water in the vegetated regions compared to the bare ones, in part due to the increased surface roughness caused by the vegetation, which slows any overland water flow. We compare different models for the soil water re-distribution process on a gentle hillslope, following a rain storm, to investigate how that depends on precipitation characteristics such as typical storm depth and storm intensity, both of which are likely to be altered by climate change. Storm variability is captured as well through use of a simple stochastic rainfall model. Our modeling focus is on determining when an abrupt change in rainfall characteristics might lead to loss of vegetation bands, or even a complete collapse of this vulnerable dryland ecosystem. |
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