[Grad-postdoc-assn] ATOC colloquium on Friday, October 14 at 11am MT

Thu Oct 13 20:50:06 MDT 2022

Hi everyone,

A reminder that we will hold the next ATOC colloquium on *Friday, October
14 at 11am MT over Zoom and in SEEC S228*. This week's colloquium will a
trio of conference-length presentations from *ATOC graduate student, Becca
Baiman, as well as NCAR ASP Postdoctoral Scholars, Hristo Chipilski and
Carlos Martinez*.* The zoom login information and abstracts for each
talk are provided below. Please join us for coffee and conversation
beginning at 10:45am MT and stay afterwards for a lunch catered by Illegal
Pete's.*

We look forward to seeing you tomorrow!

-The ATOC Colloquium Committee

_________________________________________________

*A Circumpolar View of Synoptic Drivers of Atmospheric Rivers Reaching
Antarctica*
Becca Baiman (ATOC)

Despite being rare events, atmospheric rivers (ARs) influence variability
in surface mass balance of the Antarctic ice sheet. Therefore, identifying
the environmental factors that produce high-impact ARs over Antarctica may
allow us to better understand changes to the surface mass balance of
Antarctica in the future and how this will influence total ice sheet mass
balance. Here, we attempt to provide a circumpolar view of AR-favorable
synoptic environments by constructing longitudinal profiles of 500-hPa
geopotential height anomalies during AR events. We then create a catalog of
analog, non-AR environments that most closely match the geopotential height
distribution during AR time steps. The subsequent analysis compares the
geopotential height anomaly profiles from timesteps with and without ARs
(1) to identify what conditions result in ARs versus no ARs, given a
similar environment (2) to connect the variability of AR environments to
the variability of their impacts on Antarctica.

*Invertible Neural Networks for Nonlinear Ensemble Filtering*

*Hristo Chipilski (NCAR ASP)*

*Operational data assimilation (DA) methods used for initializing Earth
system models are based on restrictive linear-Gaussian assumptions that can
produce large analysis biases and subsequent degradation of the forecast
performance. Here, I will exploit the mathematical structure of invertible
neural networks to address this problem. Specifically, I will derive a new
nonlinear ensemble DA method which shows superior performance over the
classical ensemble Kalman filter (EnKF) for a challenging toy problem.*

*An Evaluation of the Seasonal Hydroclimate of the Caribbean within CESM
and other CMIP6 Models*
Carlos Martinez (NCAR ASP)

The Caribbean and Central America hydroclimate is understudied and complex
in part due to its data sparsity, varied topographies, and multi-faceted
interactions with tropical and mid-latitude forcings. Recent work developed
a refined and comprehensive understanding of the observed hydroclimate that
has yet to be explored in global circulation models. This study
investigates the simulation of the Caribbean hydroclimate using a suite of
station and gridded observational datasets, the Community Earth System
Model (CESM) high resolution (0.25x0.25°), version 1-LE & (large ensemble)
and 2-LE (0.9x1.25°), and CMIP6HighResMIP experiments. The climatologies
(1983-2014) of the annual rainfall cycle and total moisture fluxes, and
climatological regressions of SSTs, sea-level pressure (SLP), and
zonal/meridional low-level winds onto indices of seasonal Caribbean
rainfall totals are calculated to investigate inter-model differences.
Generally, fully coupled CESM and CMIP6 simulations underestimate
precipitation across the Caribbean, with some improvements using
high-resolution (<0.5°) simulations. The underestimations are largest
during the Early-Rainy Season (ERS; mid-April to mid-June). Precipitation
biases in AMIP experiments are smaller, regardless of their spatial
resolution, suggesting precipitation is improved when observed SST is used.
A moisture divergence bias associated with a stronger/west-displaced North
Atlantic Subtropical High (NASH), and a weaker / southern displaced
Intertropical Convergence Zone (ITCZ) suggest a contribution from regional
and large-scale dynamics in CESM and CMIP6 to the dry bias. The findings
emphasize the importance of higher-resolution models for simulating the
hydroclimate in the Caribbean, highlight the complex small-to-large scale
interactions that need to be addressed in global circulation models to
accurately simulate the regions' hydroclimate, and provide implications for
future climate projection and prediction studies.
__________________________________________________

*Zoom login Information:*

*Topic: ATOC Colloquium*
*Time: Friday, Oct. 14 at 11am MT*

*Join Zoom Meeting*
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-- 
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(he/him)
Administrator

Advanced Study Program
Education, Engagement and Early-Career Development
National Center For Atmospheric Research
*phone: 303.497.1607*
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