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GFDL Events & Seminars

Visitors without GFDL affiliation attending seminars or other organized events must present government or university issued photo ID or two other forms of identification to gain access to the facility. If an acceptable ID cannot be provided, the Visitor will not be allowed access. If access is granted, the Visitor must sign in and be given a Visitor Badge. The Visitor Badge expires immediately after the seminar.

August 12, 2020

calendar_today AMOL/GFDL Science Connections Workshop

person Meeting - AMOL/GFDL Science Connections Workshop

access_time 9:30 am - 12:00 pm

place Location: Other (see event description)

This is a virtual workshop. Meeting ID meet.google.com/xmj-jxdj-joo Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪551 263 193 0390#‬

August 12, 2020

calendar_today AMOL/GFDL Science Connections Workshop

person Meeting - AMOL/GFDL Science Connections Workshop

access_time 1:00 pm - 3:00 pm

place Location: Other (see event description)

This is a virtual workshop. Meeting ID meet.google.com/xmj-jxdj-joo Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪551 263 193 0390#‬

August 13, 2020

calendar_today AMOL/GFDL Science Connections Workshop

person Meeting - AMOL/GFDL Science Connections Workshop

access_time 9:30 am - 12:00 pm

place Location: Other (see event description)

This is a virtual workshop. Meeting ID meet.google.com/ggw-nagf-cia Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪194 997 614 8158#‬

August 13, 2020

calendar_today AMOL/GFDL Science Connections Workshop

person Meeting - AMOL/GFDL Science Connections Workshop

access_time 1:00 pm - 3:00 pm

place Location: Other (see event description)

This is a virtual workshop. Meeting ID meet.google.com/ggw-nagf-cia Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪194 997 614 8158#‬

August 13, 2020

calendar_today Please see Description for Titles of both Presentations

person Informal Seminar - Summer Intern Presentations-Avery Barnett / Surabhi Biyani (Grinnel College and University of Washington)

access_time 12:00 pm - 12:30 pm

place Location: Other (see event description)

Join with Google Meet meet.google.com/acw-rudu-cnf Join by phone ?(US) +1 617-675-4444? PIN: ?152 910 743 6312?# 12:00pm-12:30pm: Presenter: Avery Barnett - Grinnel College Host: Brandon Reichl Program: CIMES Title: Validation of WAVEWATCH III Simulations under Hurricanes in Shallow and Deep Water. Abstract: The validation of surface wave models in shallow water under hurricanes remains a difficult task due to the limited number of observations taken in this regime. In this study we utilize airborne SRA observations of the hurricane wave field under three hurricanes (Hurricane Irene, 2011; Hurricane Ingrid, 2013; and Hurricane Karen, 2013) and use this data to assess the skill of wave simulations from NOAA's surface wave model WAVEWATCH III. This dataset includes several examples of observed wave spectra in shallow water conditions (

August 13, 2020

calendar_today Detecting and projecting changes in U.S. precipitation extremes

person Informal Seminar - Surabhi Biyani (University of Washington / CIMES)

access_time 12:30 pm - 1:00 pm

place Location: Other (see event description)

Join with Google Meet meet.google.com/acw-rudu-cnf Join by phone ‪(US) +1 617-675-4444‬ PIN: ‪152 910 743 6312‬# no abstract provided

August 14, 2020

calendar_today Theory and hierarchical modeling of tropical and extratropical cyclones

person Special Event - Tsung-Lin Hsieh - FPO Defense (GFDL)

access_time 10:00 am - 12:00 pm

place Location: Other (see event description)

Aspects of tropical and extratropical cyclone dynamics and their relationships with the climate are investigated. Theoretical advances are made in the development of analytical approximations verified in model experiments designed with hierarchical levels of process representation. Starting with the quasi-geostrophic theory, a new regime of solutions is investigated, which challenges the classical theories of wave-mean flow interaction. The results show the emergence of surface easterlies in the baroclinic zone, as opposed to the Earth-like surface westerlies, in the parameter space where the quasi-linear approximation of the large-scale midlatitude circulation breaks down. With an increased level of complexity, a theory is developed to connect the convection-scale moist dynamics with the synoptic-scale circulation of a mature baroclinic cyclone. Verified in a quasi-steady simulation of a moist baroclinic cyclone, the theory establishes limits within which a rescaling of nonhydrostatic dynamics improves the representation of convection in global climate models. A diagnostic theory is developed to explain the frequency of tropical cyclones simulated in global climate models. The complex relationship between the cyclone frequency and the large-scale circulation is simplified by decomposing the cyclone development process. A hierarchy of model experiments are conducted to isolate specific processes and to evaluate the corresponding components in the theory. The theory is applied to realistic simulations of historical and future climates, as well as observational tropical cyclone records. Physical interpretations are established regarding the diversity of tropical cyclone simulations across models and the projected frequency in response to various global warming perturbations. Meeting ID meet.google.com/xpm-eymx-rpu Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪570 173 102 3988#‬

August 18, 2020

calendar_today How can we use idealized model configurations to attempt to constrain cloud feedbacks?

person Informal Seminar - AOS Summer Workshop on Cloud Climate Feedbacks w/Timothy Cronin (Princeton University)

access_time 12:00 pm - 1:00 pm

place Location: Other (see event description)

Abstract: I will talk about three angles of attack on questions tied to this broad subject that my work has recently pursued. First, how does convective aggregation affect climate sensitivity? Simulations of radiative-convective equilibrium in a long-channel geometry were found to have a somewhat realistic distribution of large-scale dynamical regimes (Cronin & Wing, 2017). This prompted us to look at how clouds and circulation change with surface temperature, and how these affect climate feedbacks. Using a novel approximate radiative kernel methodology, we found that cloud feedbacks are small and positive, but that the overall climate sensitivity is lower in the channel configuration with aggregated convection than a smaller domain with disaggregated convection. Second, precipitation efficiency has been found to be a key parameter controlling cloud feedbacks in global climate models - can we constrain it and the direction of its change with warming in idealized simulations? We found that precipitation efficiency tends to increase with surface warming in small-domain simulations, mostly due to increasing cloud water content and the nonlinearity of precipitation formation by autoconversion (Lutsko & Cronin, 2018). Third, how do SST patterns influence cloud feedbacks? I will describe simulations of "Mock-Walker cells'' forced by sinusoidal patterns in long-channel geometry; preliminary results suggest that cloud feedbacks are much more strongly positive when the SST contrast between warm and cold pools is weak (El Nino-like) than when it is strong (La Nina-like). POC: Elizabeth Yankovsky

August 18, 2020

calendar_today Cloud feedbacks, climate sensitivity, and observational constraints

person Informal Seminar - AOS Summer Workshop on Cloud Climate Feedback with Mark Zelinka (Princeton University )

access_time 3:00 pm - 4:00 pm

place Location: Other (see event description)

Abstract: In the plenary talk I will discuss the causes of higher climate sensitivity in the latest state-of-the- art CMIP6 Earth system models relative to their predecessors in CMIP5. Taken as a whole, these latest models are more sensitive primarily because they have stronger amplifying cloud feedbacks, particularly in the extratropics, where low clouds become less extensive and less reflective as the planet warms. This stronger positive cloud feedback arises due to changes in model physics and may be related to improved representation of cloud phase. Given the continued importance of low cloud feedback in driving uncertainty in climate sensitivity across climate models and between model generations, I will then discuss ongoing work that is attempting to constrain the global marine low cloud feedback using satellite observations of how low cloud properties respond to individual cloud-controlling factors. This work indicates that the observed sensitivity of low clouds to their meteorological controls is incompatible with very high or very low values of climate sensitivity. POC: Elizabeth Yankovsky

August 19, 2020

calendar_today Mixed-Phase Clouds and Extratropical Cloud Optical Depth Feedback: their Importance for Climate Sensitivity and Arctic Amplification

person Informal Seminar - AOS Summer Workshop on Cloud Climate Feedback with Ivy Tan (Princeton University)

access_time 12:00 pm - 1:00 pm

place Location: Other (see event description)

Abstract: I'll start by motivating the need to better represent mixed-phase clouds in climate models, and their ramifications for the extratropical cloud optical depth feedback, which has been linked to the higher climate sensitivity of the CMIP6 models but yet whose sign is currently uncertain. Using the emergent constraint approach, I will present a unique method that uses satellite observations to decompose the contributions from clouds to the feedback categorized by their thermodynamic phase. Using this as guidance, I will discuss the extent to which shifts from stratocumulus to cumulus clouds contribute to a positive extratropical cloud optical depth feedback based on the recent satellite record. This will be followed by an analysis of the role of ice nucleation in the feedback based on version 5 of NASA's Goddard Earth Observing System (GEOS-5) model. Finally, observational constraints on the cloud optical depth feedback are proposed based on lessons learned about the importance of the representation of cloud microphysical properties for large-scale feedback. POC: Elizabeth Yankovsky

August 19, 2020

calendar_today Tropical SST Contrast in a Warmer Climate: Radiation, Cloud and Circulation Interactions

person Informal Seminar - AOS Summer Workshop on Cloud Climate Feedback with Dennis Hartmann (Princeton University)

access_time 2:00 pm - 3:00 pm

place Location: Other (see event description)

Abstract: The Tropical SST contrast is an important subject in climate sensitivity and climate impacts research. A brief history of such studies will be given, followed by an investigation employing the GFDL AM2 GCM in Tropic World configuration, Slab Ocean, No Rotation, Uniform Insolation. In this configuration SST contrasts naturally develop in response to aggregation of convection and the development of a large-scale circulation connecting the warm & convecting, and cooler & subsiding regions. As the SST is raised from current to warmer tropical values, the SST contrast at first increases and then decreases. The solutions also oscillate about their equilibrium SST difference, and these oscillations can be used as a probe to investigate the mechanisms of the oscillation. A draft paper is available here: Hartmann, D.L., B.D. Dygert, Q. Fu and P.N. Blossey, 2020: The Warming Physics of the Tropic World: Part 1 Mean State JAMES, submitted link here. A draft Part 2 on the cycles may be submitted and available by the time of the workshop. POC: Elizabeth Yankovsky

August 20, 2020

calendar_today A walk in the cloud: Facilitating climate research using Amazon Web Services

person Informal Seminar - Summer Intern Presentation - Natalie O'Leary (Princeton University)

access_time 11:00 am - 11:30 am

place Location: Other (see event description)

no abstract provided. Connection Info: meet.google.com/kjc-ddtx-ows Join by phone ‪(US) +1 617-675-4444‬ PIN: ‪422 801 607 9334‬#

August 21, 2020

calendar_today Panel Discussion

person Informal Seminar - AOS Summer Workshop on Cloud Climate Feedback Panel Discussion (Princeton University)

access_time 3:00 pm - 4:15 pm

place Location: Other (see event description)

Connection Information: Meeting ID meet.google.com/fmz-kued-ieh Phone Numbers (‪US‬) ‪+1 617-675-4444‬ PIN: ‪383 745 440 1267#‬

August 28, 2020

calendar_today Modeling and parameterizing submesoscale turbulence in dense Arctic flows

person Informal Seminar - Elizabeth Yankovsky - FPO Defense (Princeton University)

access_time 9:30 am - 12:00 pm

place Location: Other (see event description)

Dense gravity currents forced by surface buoyancy loss over continental shelf regions are important contributors to subsurface and abyssal ventilation throughout the World Ocean, yet remain challenging to model accurately. In this thesis, we present idealized experiments of rotating terrain-following gravity currents employing the nonhydrostatic MITgcm in z coordinates and the hydrostatic GFDL-MOM6 in z* and isopycnal coordinates. In the highest-resolution simulations, the dense flow undergoes geostrophic adjustment and forms bottom- and surface-intensified jets. The density front along the topography combined with geostrophic shear initiates submesoscale symmetric instability (SI), which leads to onset of secondary shear instability, dissipation of geostrophic energy, and irreversible mixing. We explore the impact of vertical coordinate, resolution, and parameterization of shear-driven mixing on water mass transformation. In isopycnal coordinates, limited vertical resolution in abyssal regions leads to inadequate representation of mixing. We develop and implement a parameterization for SI-driven turbulence to mediate this issue. The scheme is based on identifying unstable regions through a balanced Richardson number criterion and slumping the isopycnals towards a balanced state. A fraction of the potential energy released by the slumping is passed to the shear mixing parameterization, so that potential energy extracted from the geostrophic flow by SI is converted to kinetic energy and used for vertical mixing. Such a scheme becomes crucial as ocean models move towards resolving mesoscale eddies and fronts but not the submesoscale phenomena they host. In the final thesis component, we examine how state-of-the-art global ocean models currently represent water transformation processes in the Arctic. We consider a 1/4 degree and analogous 1/8 degree model and find that ventilation by overflows as well as transformation of the warm, salty Atlantic inflow both contribute to creating highly dense waters in the Eurasian shelves. The 1/8 degree model performs better in capturing transient dense flows emanating from polynyas around coastal islands such as Novaya Zemlya; the 1/4 degree model marginally resolves overflows but has an overly diffuse vertical structure. As a next step in bridging our idealized process studies with the global simulations, we will perform regional mesoscale-resolving modeling with our SI parameterization to further constrain Arctic ventilation pathways.