National Aeronautics and Space Administration

Sea Level Rise Seminar
Speaker: Ted Scambos (Univ Colorado)
Title: The Threat From Thwaites: Doomsday or Dud?

This is an on-line, virtual presentation only. Please consult with event host Patrick Alexander for connection details.

Abstract:
Results of the 150-researcher, 7-year International Thwaites Glacier Collaboration (ITGC) have set a stage for future field, satellite, and modeling research in the region. Related work continues with remote sensing evaluations of ongoing changes and further analysis of the extensive onshore and offshore data sets.


The ITGC advanced bathymetric, oceanographic, and glaciological mapping of the entire Thwaites basin and much of the adjacent Dotson-Crosson ice shelf system as well. Sediment core analysis indicates that both Thwaites and Pine Island began an accelerated pace of retreat in the mid-1940s, although the system appears to have been in balance as late as the 1970s. Earlier retreat of the system in the mid-Holocene Optimum brought the glacier elevation to 35 meters below the present level (in one region), but slowly declining temperatures since the Optimum allowed it to recover.

Rapid fracturing and acceleration of the Thwaites Eastern Ice Shelf (TEIS) appears to be a result of thinning and periodic interaction with the faster-moving main glacier trunk and the Thwaites Western Ice Tongue (TWIT, now mostly broken up) and increased shearing to the point of lateral rupture of a shear zone bounding the northern limit of the shelf.

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GISS Lunch Seminar
Speaker: Nithin Allwayin (Stony Brook University)
Title: Warm cloud microphysical processes and their implications for model representations: insights from digital in-line holography, large eddy simulations, and remote sensing

This is a hybrid presentation, presented both in-person and on-line. Please consult with event host Joseph Kelly for connection details if you wish to virtually attend.

Abstract:
A cloud droplet begins its journey with aerosol activation, undergoes condensation and coalescence growth, and is eventually removed through precipitation or evaporation. Over their lifecycle, the droplets evolve across several orders of magnitude in size and mass. This complexity can only be captured in part when representing them in climate models and often requires idealizations and assumptions. I'll examine some of these processes and assumptions using airborne digital holography, large eddy simulations (LES), and satellite observations, and discuss their implications for warm-cloud parameterizations. I'll begin with holographic observations of locally narrow cloud droplet populations forming regions of characteristic distributions. Broader gamma-like distributions, commonly used in models, emerge after averaging these characteristic distributions. Idealized LESs reproduces some of this structure but remains more uniform than observations of real clouds.

Next, I'll discuss why evaporation from entrainment looks predominantly inhomogeneous in cumulus clouds, where some droplets evaporate completely, and why this matters for model representations. I'll then move on to drizzle, using the first spaceborne Doppler observations from EarthCARE to examine regime-dependent partitioning of microphysical properties in warm clouds. I'll conclude by discussing rapidly evolving convective systems and how Multi-sensor Agile Adaptive Sampling (MAAS) can capture their evolution, resolve thermal structures and turbulence, and provide targeted observations for model evaluation.

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