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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.

February 21, 2019

calendar_today Recent strengthening of the tropical Pacific zonal SST gradient is a dynamically consistent response to rising greenhouse gases

person Formal Seminar (approved) - Formal Seminar - Richard Seagar (Lamont, Columbia University)

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

As exemplified by El Nino, the tropical Pacific Ocean strongly influences regional climates and their variability worldwide. It also regulates the rate of global temperature rise in response to rising greenhouse gases (GHGs). The tropical Pacific Ocean response to rising GHGs impacts all of the world's population. State-of-the-art climate models predict that positive radiative forcing reduces the west-to-east warm-to-cool sea surface temperature (SST) gradient across the equatorial Pacific. In nature, however, the gradient has strengthened in recent decades as GHG concentrations have risen sharply. This stark discrepancy between models and observations has troubled the climate research community for two decades. Here, by returning to the fundamental dynamics and thermodynamics of the tropical ocean-atmosphere system, and avoiding sources of model bias, we show that a parsimonious formulation of tropical Pacific dynamics yields a response that is consistent with observations and attributable to rising GHGs. We use the same dynamics to show that the erroneous warming in state-of-the-art models is a consequence of their cold bias in the equatorial cold tongue. The failure of state-of-the-art models to capture the correct response introduces critical error into their projections of climate change in the many regions sensitive to tropical Pacific SSTs.

February 27, 2019

calendar_today Decadal variability and predictability in the Southern Ocean - implications for interpreting recent observed trends

person Lunchtime Seminar - Lunchtime Seminar Series - Liping Zhang (CICS-P)

access_time 12:00 pm - 1:00 pm

place Location: Smagorinsky Seminar Room

While decadal variability and predictability in the North Atlantic and North Pacific have received considerable attention, there has been less work on decadal variability and predictability in the Southern Ocean. As shown previously, a coherent mode of decadal to centennial variability exists in multiple climate models. The mechanism involves a multidecadal accumulation of heat in the subsurface of the Southern Ocean, which is then rapidly discharged through intense oceanic convection when the accumulation of subsurface heat reduces the stratification of the water column. The release of this accumulated subsurface heat can have considerable regional scale climatic impacts, along with substantial impacts on ocean heat uptake. Using a large suite of perfect predictability experiments, in concert with long control simulations, we show that this variability has a high degree of predictability. We present further results that show this type of variability may play an important role for interpreting recently observed trends of sea ice and temperature in the Southern Ocean. Specifically, observed trends over the last several decades resemble a particular phase of this variability in which reduced oceanic convection leads to subsurface warming and surface cooling, with associated increases in sea ice extent. This phase of natural variability may substantially contribute to observed decadal trends, working in concert with other factors.

February 28, 2019

calendar_today Are we deadlocked on the problem of parameterizing microphysics?

person Formal Seminar (approved) - Formal Seminar - Hugh Morrison (NCAR)

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

Current microphysics schemes in cloud, weather, and climate models exhibit deficiencies that are due in part to their simplified representation of a complex natural state, and in part due to a fundamental lack of understanding of microphysical processes. Although there have been many advancements, there is little evidence that increasing sophistication of schemes results in convergence on the “truth”. For example, model solution spread using different bin microphysics schemes (explicitly evolving the particle size distributions) is similar to that using different bulk schemes in recent model intercomparison studies. Two key challenges will be discussed: 1) numerical implementation, and 2) fundamental uncertainty of the underlying process rates and parameters. The recently-developed Lagrangian “super-particle” method helps to address the former, and I will advocate for its use in process-level microphysical modeling. In this approach, the cloud and precipitation particle populations are represented by a sub-sampling of point particles that follow Lagrangian trajectories in the modeled flow. However, like all approaches, the microphysical process rates and parameters using the “super-particle” method still have large uncertainties, especially for the ice phase. These uncertainties arise from the fact that there is no benchmark set of governing microphysical equations, combined with the inherent challenge of directly observing process rates. To address these inevitable uncertainties and constrain process rates rigorously with the wealth of indirect observations now available (e.g., satellite and ground-based remote sensing), the incorporation of Bayesian statistics directly into schemes is proposed. This idea will be discussed in the context of a novel probabilistic bulk parameterization framework called the Bayesian Observationally-constrained Statistical-physical Scheme (BOSS). BOSS combines existing, though inherently limited, process level microphysical knowledge with flexible process rate formulations and parameters trained to observations through Bayesian inference. Using a raindrop size distribution (DSD) normalization method that relates DSD moments to one another via generalized power series, generalized multivariate power expressions are derived for the microphysical process rates as functions of a set of prognostic DSD moments in BOSS. The approach is flexible and can utilize any number and combination of prognostic moments and any number of terms in the process rate formulations. This means that both uncertainty in parameter values and structural uncertainty associated with the process rate formulations can be investigated systematically, which is not possible using traditional schemes. I will discuss results using a Monte Carlo Markov Chain sampler within the BOSS framework to constrain microphysical process rates and parameters directly with “synthetic” observations.

March 6, 2019

calendar_today Tropospheric ozone inter-annual variability and extreme events

person Lunchtime Seminar - Lunchtime Seminar Series - Alex Zhang (CICS-P)

access_time 12:00 pm - 1:30 pm

place Location: Smagorinsky Seminar Room

Better knowledge on how well current global climate-chemistry models represent the inter-annual variabilities (IAVs) and extremes of tropospheric ozone (O3) as well as their driving factors is with great importance for understanding and predicting long-term O3 trends with models. Here we explore the IAVs of tropospheric O3 in the northern hemisphere simulated with multiple chemistry-climate models participating in the Chemistry-Climate Model Initiative phase 1 (CCMI-1) and assess the models’ performances of simulating the O3 extremes during extreme weather conditions in the U.S. We find that the examined models have diverse performances on simulating the tropospheric O3 IAVs with or without observational constraints and all models underestimate O3 anomalies during heat waves over the past three decades. Using intensive field measurements and the latest AM4 and GEOS-Chem at high resolutions, we specifically investigate the IAVs and sources of springtime O3 in the western U.S. and find that background O3 is the key driver of O3 IAV there with STT O3 dominating the background O3. Our findings have advanced the knowledge of the abilities and deficiencies of current climate-chemistry models in representing the IAVs and extremes of tropospheric O3.

April 18, 2019

calendar_today Aerosol impacts on marine biogeochemistry

person Formal Seminar (approved) - Formal Seminar - Adina Paytan (Institute of Marine Sciences, UC Santa Cruz)

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

Atmospheric deposition of trace elements and nutrients to the ocean can significantly modify seawater chemistry and influence oceanic productivity. However, mounting evidence suggests that the response of phytoplankton to atmospheric deposition depends on the chemical composition of the aerosols and varies across different phytoplankton species. Responses are also different depending on oceanographic setting and season. To determine if and how nutrients and metals from atmospheric deposition influence phytoplankton community structure in the Ocean we analyzed nutrient (nitrogen and phosphorous) and metal (Fe, Cu, Zn, Ni) concentrations in marine aerosols and tested how these constituents impact phytoplankton. This is done using incubation experiments with natural phytoplankton assemblages with different sources and amounts of aerosol or pure nutrients and metal additions. Laboratory-based culture experiments with phytoplankton from different taxonomic groups helped identify species that were most sensitive to aerosol additions. Variance in utilization of nutrients and susceptibility to metal toxicity was identified among different taxa, suggesting that aerosol deposition could potentially alter patterns of marine primary production and phytoplankton community structure. In addition, input of bioaerosols can also affect phytoplankton communities and should be considered. Changes in atmospheric deposition and aerosol composition that are impacted from natural and anthropogenic change could therefore have effects on ocean chemistry and productivity with potential feedbacks to the carbon cycle. Host: Lori Sentman

May 8, 2019

calendar_today GFDL Poster Expo

person Special Event - GFDL Poster Expo

access_time 1:00 pm - 4:00 pm

place Location: Smagorinsky Seminar Room

GFDL Poster Expo

June 27, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

July 11, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

July 18, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

July 25, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

August 1, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

August 8, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD

August 15, 2019

calendar_today TBD

person Formal Seminar (approved) - Formal Seminar

access_time 2:00 pm - 3:00 pm

place Location: Smagorinsky Seminar Room

TBD