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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.

September 18, 2019

calendar_today Reconciling Predictability and Uncertainties in Seasonal Predictions and Future Projections of Tropical Cyclone Activity

person Lunchtime Seminar - Lunchtime Seminar Series - Gan Zhang (AOS)

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

Improvements of dynamic models have transformed long-range predictions of tropical cyclone (TC) activity, and these improvements also open up new paths for exploring the predictability and uncertainties for such predictions. The first part of this talk focuses on the future projection of TC activity on the regional scale. The regional projection is currently considered highly uncertain because of uncertainties related to the large-scale environmental changes. Here we focus on some future environmental changes that are relatively robustly simulated by CMIP5 models but received little attention among TC researchers. Such environmental changes include a weakening of extratropical eddy activity and a poleward shift of midlatitude westerlies. Using idealized regional simulations, we show that a dramatic suppression of extratropical weather variability may profoundly affect TC activity in the subtropics, including the storm frequency and their movement. Using more realistic global large-ensemble simulations, we show that potential future changes in extratropical circulation with global warming could affect TC propagation. The findings may have important implications for populated coastal regions outside the tropics, where TC-related risks are relatively low in the current climate. The second part of this talk investigates the seasonal predictability of TC activity and pathways to improve dynamic prediction systems. Using the ensemble hindcasts by GFDL's FLOR prediction system, we show that TC activity in coastal regions and/or at higher latitudes is sensitive to uncertainties of initial conditions. Our analysis also suggests that the seasonal predictability of regional and basin-wide TC activity might be higher than the skill that has been realized by pre-existing FLOR prediction systems. Using idealized prediction experiments, we show that the gap might be narrowed by reducing ocean biases or improving the initialization of land-atmosphere components. With improved simulations of the large-scale atmospheric environment in the tropics and/or the extratropics, the skill gains of seasonal TC prediction are statistically significant. The promising findings suggest new research opportunities and will help with the design of next-generation prediction systems of TC activity.

September 19, 2019

calendar_today Turbulence, Convection and Clouds in Global Atmospheric Models: The Unified EDMF Approach

person Formal Seminar (approved) - Formal Seminar - Joao Teixeira (JPL)

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

The parameterization of turbulent and convective mixing in global atmospheric models has been a major challenge in weather and climate research for several decades. In particular, different parameterizations are used, and patched together often artificially, for different types of convection: dry or moist, in the boundary layer or in the full troposphere. The Eddy-Diffusivity (ED) approach has been relatively successful in representing the properties of neutral and stable boundary layers and surface layers in general. The Mass-Flux (MF) approach, on the other hand, has been used for the parameterization of shallow and deep moist convection. In this presentation, an approach based on an optimal combination of the ED and MF parameterizations (EDMF) is discussed in detail as a solution for the full unification of the parameterizations of turbulent and convective mixing in atmospheric models. In particular, we will present results from a new multi-plume stochastic EDMF parameterization that fully unifies the representation of convection in weather and climate models: One single parameterization that represents the effects of dry, shallow and deep moist convection in the atmosphere.

September 25, 2019

calendar_today Evaluating Last Interglacial Constraints on Future Antarctic Ice-Sheet Mass Losses with a Supervised Machine Learning Technique

person Lunchtime Seminar - Lunchtime Seminar Series - Daniel Gilford (Rutgers University)

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

Antarctic ice loss has accelerated in recent decades, and its contributions to global sea level rise could be as high as ~1 meter by the end of the century. But deep uncertainties in ice-sheet physics make it difficult to produce robust projections of sea level rise. The lack of agreement among experts and poor constraints on ice-sheet model parameters exemplify this ambiguity. Past warm periods provide useful analog climates where sea levels were much higher than present, but these paleoclimate estimates are themselves deeply uncertain. It is critical to assess the efficacy of paleoclimate estimates constraining future Antarctic ice-sheet mass losses to (1) improve future projections of sea level rise and (2) inform paleoclimate research and observational goals. Here we use Gaussian Process regression to develop a statistical "emulator" designed to mimic the behavior of an ice-sheet model. Gaussian process modeling is a non-parametric supervised machine learning technique which maps inputs (e.g. ice-sheet model parameters) to target outputs (e.g. sea-level contributions from Antarctica) with explicit quantification of model uncertainties. Emulation is applied over the last interglacial (LIG; a warm period ~125,000 years ago) and a future high greenhouse gas emissions scenario, and is trained on ice-sheet model ensembles constructed by varying the parameters of maximum rate of ice-cliff loss and the coefficient of ice-shelf hydrofracturing. Emulated projections are calibrated with various LIG constraints on Antarctic sea level contributions to find the likely configurations of model parameterizations. Using a Bayesian approach, we quantify uncertainties in future projections from the ice-sheet model if the LIG estimated contributions were well-known. Results also show how specific assumptions about the LIG period (such as those used in past studies) can influence future projections, and highlight the importance of continued observational efforts. POC: Pu Lin.

October 2, 2019

calendar_today Response of Subtropical Stationary Waves and Hydrological Extremes to Climate Warming in Boreal Summer

person Lunchtime Seminar - Lunchtime Seminar Series - Jiacan Yuan (Rutgers University)

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

Inland hydrological extremes (droughts and extreme rainfall events) can cause enormous economic loss and threaten lives. Observations show the frequency of hydrological extremes has increased significantly during recent decades. The increase can, to a large extent, be explained by a warming climate. Here we find subtropical stationary waves in the atmosphere, which emerge as alternating subtropical high-pressure systems and monsoon low-pressure systems, can act as an important bridge connecting the frequency of regional hydrological extremes with global warming. We first investigate multiple reanalysis products in the period of 1979-2013. A robust positive trend in the subtropical stationary-wave amplitude (SWA) is observed during this period. These changes are found to be coupled with the changes in precipitation amount and frequency of hydrological extremes over the subtropical regions. We then examine the past and future responses of SWA to increasing climate forcing using 31 CMIP5 GCMs. The results indicate that the SWA is likely to intensify in a warming climate, and a positive SWA trend is at least partially driven by increasing external forcing. The results about interannual relationships between SWA and hydrological-extreme frequency suggest that high SWA is related to increased heavy-rainfall day frequency over South Asia, the Indochinese Peninsula, and southern China (SA-EA), and to increased dry-spell-day frequency over the northwestern and central United States (NUS) and southern United States and Mexico (SUS-MEX). These relationships could be explained as circulation anomalies associated with SWA providing persistent weather conditions that favor the occurrence of hydrological extremes over these regions. The projected amplification of SWA, combined with the relationships between SWA and frequency of hydrological extremes, partially explain the projected increases in frequency of dry-spells over NUS and SUS-MEX and in frequency of heavy-rainfall days over SA-EA in a warming climate.

October 16, 2019

calendar_today Progress in quantifying the effective radiative forcing due to aerosol-cloud interactions

person Lunchtime Seminar - Lunchtime Seminar Series - Johannes Quaas

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

The effective radiative forcing due to aerosol-cloud interaction, ERFaci, is composed of the radiative forcing due to aerosol-cloud interactions, RFaci (Twomey effect) that is the immediate response of cloud albedo to an increase in droplet number concentration, Nd. Previous satellite-based quantifications of this effect were hampered by deficiencies in the retrieval of aerosol and also Nd. The talk will firstly discuss progress in this regard, which leads to a stronger estimated RFaci than previous satellite-based approaches. The other component of ERFaci is in the cloud adjustments. These can be split into adjustments of cloud fraction, f, and liquid water path, L. In terms of the latter, statistical relationships between L and Nd show on average negative adjustments of L (a positive forcing component). In turn, the analysis of ship-, volcano- and industry tracks leads to an estimated small overall effect on L; these results are trustworthy since a cause-effect relation is assured. In terms of the f adjustment, the current results point to an increase in cloud fraction at larger Nd. It is unclear which processes lead to this result. The talk will also briefly discuss how cloud-resolving simulations may help to better understand the remaining uncertainties. In the last part, a brief discussion will be presented on initial steps towards an estimate of the response of cirrus to anthropogenic aerosols. POC: Leo Donner or Yi Ming

November 13, 2019

calendar_today Scorched Earth: Ecosystem-Atmosphere Interactions Exacerbate Climate Penalty on Air Pollution in Europe

person Lunchtime Seminar - Lunchtime Seminar Series - Meiyun Lin

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

TBD

November 22, 2019

calendar_today Dr. Kikuro Miyakoda Symposium

person Special Event - Dr. Kikuro Miyakoda Symposium

access_time 12:00 pm - 5:00 pm

place Location: Smagorinsky Seminar Room

Dr. Kikuro Miyakoda Symposium will highlight Kikuro's life achievements in the world of Science. A memorial coordinated by his Daughter will be in the morning.

December 3, 2019

calendar_today To be provided

person Informal Seminar - Informal Seminar Schedule - Laura Wilcox (University of Reading, UK)

access_time 10:30 am - 11:30 am

place Location: Smagorinsky Seminar Room

To be provided

December 4, 2019

calendar_today TBD

person Lunchtime Seminar - Lunchtime Seminar Series -Nathaniel Johnson (GFDL)

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

TBD

December 5, 2019

calendar_today Eddy Saturation

person Informal Seminar - Navid Constantinou (Australian National University)

access_time 10:30 am - 11:30 am

place Location: 317 Seminar Room

Eddy Saturation