Winter 2015

Winter 2015

Tuesday Afternoons at 4:00 PM
Thimann Lecture Hall, Room 001



January 13, 2015

Thorne Lay, UCSC

A Surge of Great Earthquakes From 2004-2014 and What We Are Learning From Them

Hosts: TBA/TBA


January 20, 2015

Rick Elphic, NASA Ames Research Center

Exploring Cold Trapped Lunar Volatiles For Fun and Profit

Hosts: TBA


January 27, 2015

Paul Hayne, JPL

The Carbon Dioxide Cycle of Mars

Hosts: TBA


February 3, 2015

Sujoy Mukhopadhyay, UC Davis

Probing early Earth environments with noble gases

Hosts: TBA


February 10, 2015

Sarah Feakins, USC

Biomarker reconstructions of vegetation and hydrology

Abstract: 

When considering the changing nature of our environment, water is a key variable shaping what is habitable and what is not, as denoted by the distribution of vegetation on the planet. The hydrogen and carbon isotopic compositions of terrestrial plant biomarkers offer powerful tools to reconstruct the nature and causes of vegetation and precipitation change. In particular the waxy coating on plant leaves and the lignin in tree wood allow us to trace both foliar and woody biomass. As a community, we’ve studied the plant synthesis of these compounds and the sedimentary archives of these biomarkers over geological time. But we still don’t know much about how these molecules are exported from plants to sediments. My talk will take you on a picturesque journey from the high Andes, down into lowland Amazonia, via the Madre De Dios River within Peru. Through large volume sampling in remote environments, we acquire unprecedented sampling resolution across a steep topographic, environmental and ecological gradient. We analyze the biomarkers of terrestrial vegetation and find they capture elevation-specific isotopic signatures. We can thus monitor the spatial and temporal integration processes in the river, and the downstream propagation of those signals. This new study provides much needed insights into the source to sink processes of terrestrial biomarkers, needed for two important objectives: 1) the spatial significance of terrestrial signals in lake and marine core sediment core reconstructions, and 2) quantification of export versus remineralization of terrestrial organic carbon from major tropical montane river systems.

Hosts: TBA


February 17, 2015

Canceled


February 24, 2015

Canceled

March 3, 2015

Angeline Pendergrass, NCAR

Changes in the distribution of rain with warming

Abstract:

How will the distribution of rainfall change in response to global warming?  Global-average rainfall increases more slowly than extreme rain rates with warming, implying a change in the shape of the rainfall distribution.  

To quantify the distribution of rain, we focus on daily precipitation accumulation from climate models.  These models have a wide range of responses to global warming, especially at the extreme end of the distribution.  In order to interpret this range of responses, we introduce two modes of change of the distribution of rain: a shift mode, where rain falls at heavier rates with no change in mean rainfall; and an increase mode, where rainfall increases by a uniform fraction at all rain rates.  These modes of change can describe the responses of the daily rainfall distribution to global warming and ENSO phases in climate models. Observations confirm the shift in response to ENSO phases.   The shift and increase modes can be interpreted in terms of the changes in moisture and vertical velocity.  

In addition to the increase and shift modes of change, some models also show a substantial increase in rainfall at the highest rain rates, which we call the extreme mode.  The difference in extreme mode across models results in a large variation in the rate of increase of extreme rainfall with warming: a range of a factor of 4 at the 99.99th percentile by the end of the century in CMIP5 simulations.

Host: Delia Santiago-Materese


March 4, 2015

(held in E&MS A340)

Angeline Pendergrass, NCAR

The rain is askew: changes in the distribution of vertical velocity with warming

Abstract:

As the planet warms, climate models predict that circulation will weaken, as rain becomes heavier and less frequent.  In this talk I’ll tell you about my work looking at the changes in circulation with warming that drive the changes in the distribution of rain discussed in my first talk.  

 With two heuristic models, we will explore how changes in vertical velocity and moisture distributions can affect the distribution of rain.  Through these models we will see that an increase in skewness, or asymmetry, of the vertical velocity distribution is crucial for explaining the change in the distribution of rain, particularly the decrease in the total number of rain events.

In this talk I will also share with you my vision for studying the changes in rain: its mean, its distribution in frequency and intensity as well as in space.  I will highlight what is known, what I’ve learned about rain and how it can change at global scales by focusing on atmospheric radiation and statistics, and where the next frontiers are.  Looking ahead, there is still work to be done strengthening this global-scale understanding, and also building on it to increase our knowledge about regional precipitation change by incorporating dynamical perspectives.


March 10, 2015

Nicole Feldl, Caltech

Global change from the spatial pattern of feedbacks

Abstract: Uncertainty in the spatial pattern of climate change is dominated by divergent predictions among climate models. Model differences are closely linked to their representation of climate feedbacks, that is, the additional radiative fluxes that are caused by changes in clouds, water vapor, surface albedo, and other factors, in response to an external climate forcing. Progress in constraining this uncertainty is therefore predicated on understanding how patterns of individual climate feedbacks aggregate into a regional and global climate response. Here a new framework is presented for evaluating the spatial pattern of surface warming. The links between feedbacks, atmospheric heat transport, and temperature response are investigated in a range of simulations, from simple moist energy-balance models to state-of-the-art general circulation models. The results offer insights for understanding fundamental features of the Earth’s climate response, such as Arctic-amplified warming, and how uncertainty in feedback patterns drives uncertainty in the patterns of temperature response.

Host: Karla Knudson


March 11, 2015

(held in E&MS A340)

Nicole Feldl, Caltech

Coupling between climate feedbacks and tropical circulation

Abstract: Recent advances have demonstrated how regional climate feedbacks can be used to characterize the spatial pattern of warming in terms of contributions from feedbacks, atmosphere and ocean heat transport, and the radiative forcing due to increasing greenhouse gas concentrations. Fundamentally, feedbacks represent the energetics of the climate system; imbalances will affect heat flux between latitudes. In the tropics, the primary way the atmosphere modulates energy transport is by changing the mean meridional circulation--either the position of the Intertropical Convergence Zone, associated with the ascending branch of the Hadley cell, or the strength of the circulation. Idealized experiments in an aquaplanet simulation will be used to systematically test the effect of disabling individual feedbacks, with the goal of establishing causal relationships. By analyzing the coupled feedback-circulation system, the results offer insights into understanding both climate sensitivity and the response of tropical precipitation in a warmer world.


March 17, 2015

Tianle Yuan, NASA

Volcanically induced A-bombs through cloud physics

Abstract: Anthropogenic aerosols, tiny airborne particles, affect the Earth’s energy balance. In particular, their interactions with clouds constitute the leading uncertainty in quantifying climate drivers. Since direct simulation of aerosol-cloud interactions is numerically intractable, observational investigations are acutely needed. However, attribution of aerosol influence and cloud adjustments pose huge challenge to observational studies. Moreover, most previous studies only examined aerosol-cloud interactions for shallow clouds. Here with the state-of-the-art satellite data we overcome these challenges and explore a new frontier by investigating deep convective clouds’ response to aerosols. This is achieved with an ideal natural experiment that is set up by a volcano. The Anatahan Volcano injects a modest amount of sulfur dioxides to the atmosphere. They are turned into sulfate aerosols and ingested by maritime convective clouds, which dramatically enhances lightning activity by hundreds of percent. A chain of physical processes propagating upscales from changes in tiny aerosol particles is responsible. Results here push into new frontiers and, indeed, cloud physics from the volcanically induced aerosol ‘lightning bombs’ have interesting applications for Earth system studies.

Host: Mikael Witte


March 18, 2015

(held in E&MS A340)

Tianle Yuan, NASA

Observing interactions and feedbacks among aerosols, clouds and climate from above
 
Abstract: Satellite data are increasingly being used to tackle a range of problems in climate science. They offer unprecedented global view of the climate system from above. This provides revolutionary opportunities to study interactions and feedbacks among aerosols, clouds and climate dynamics. These interactions and feedback processes have major implications for human induced climate change as well as paleoclimate studies. Here major challenges in using satellite data and methods to overcome them are discussed with a few examples with an emphasis on aerosol-cloud interactions. Having a physically sound conceptual picture and appropriate ways to reconstruct satellite data are helpful. Using current satellite observations, it is also possible to shed light on paleoclimate studies by identifying critical feedback processes in biogeochemical cycle and atmosphere-ocean coupling involving dust and clouds. Such connections between the past and the present create fascinating opportunities to combine proxy data and current satellite data to tackle a range of issues.