Spring 2015

Spring 2015

Tuesday Afternoons at 4:00 PM
Natural Science Annex 101

March 31, 2015

Dan Li, Princeton

Towards urban sustainability under a changing climate

Abstract: Cities are emerging as the nexus of water, energy, and health challenges in this century and beyond. A better understanding of urban microclimate within the context of global climate change has important implications for addressing many urban environmental issues and for achieving urban sustainability. In this presentation, efforts towards understanding interactions between urbanization and global climate change will be described. First, synergies between urban heat islands and heat waves will be examined using observational data, numerical simulations and an analytical model. Second, development and evaluation of urban representations in global climate and earth systems models will be presented. Other challenges including advancing in our understanding of urban-atmosphere interactions, multi-scale climate simulations, and integrating new environmental sensing technologies with numerical simulations will be discussed.

Hosts:Daniel Killam

April 1, 2015

Dan Li, Princeton

(held in E&MS A340 at 11:30 AM)

Monin-Obukhov Similarity Theory: A new perspective on an old topic

Abstract: Land-atmosphere interactions ​and air-sea interactions are largely regulated by turbulence in the atmospheric surface layer, which spans from the surface to about 50-100 m above the surface. As compared to turbulent boundary layers in lab experiments that are often only subject to the shear force, turbulence in the atmospheric surface layer is constantly affected by the buoyancy force resulting from surface heating and cooling. As a result, many turbulence theories, when applied to the atmospheric surface layer, need to be expanded to consider buoyancy effects. A case in point is the stability correction functions for momentum and heat that are used to account for buoyancy-induced distortions to the logarithmic profiles for mean velocity and temperature, respectively. These stability correction functions are the centerpiece of the Monin-Obukhov Similarity Theory (hence they are also called Monin-Obukhov similarity functions) and are used in almost all numerical weather and climate models. Monin and Obukhov postulated that these stability correction functions can be only determined from experimental data, and many field campaigns such as the famous Kansas experiment have been conducted ever since to determine these stability correction functions. Theories that explain the shape of these stability correction functions are currently lacking. In this presentation, a co-spectral theory will be proposed to link these macroscopic relations that describe the mean flow (e.g., the stability correction functions) to the micro-states of turbulent kinetic and potential energy distributions, as measured by their spectra. It will be shown that the universality of Monin-Obukhov similarity functions is largely inherited from the universality of the Kolmogorov-Obukhov-Corrsin laws for turbulence spectra in the inertial subrange.

April 7, 2015

Simon Klemperer, Stanford University

Tibet: geophysical and geochemical interpretations of the lithospheric architecture of the India/Asia collision


Tibet is the result of Earth's greatest continental collision.  But we cannot yet with any certainty do a material balance between Indian crust entering the collision zone, and the Indian crust being subducted into the mantle, underthrust beneath Tibet, or accreted to the upper-plate thrust sheets of the Himalaya.  Nor can we with confidence describe the geometry of the Indian lithosphere beneath the Asian plate nor map its northern limit.  Over 20 years of broadband and some active-source seismology on the Plateau has produced a generation of seismologists who all "know" the answers, except that we all believe different things.  As many other papers on petrology and geochemistry of Neogene igneous rocks have sought to explain the state of the mantle - at least as it was at the time those rocks were erupted or intruded, typically ≥10 Myr bp, which in a system evolving at cm/yr may provide little constraint on today's lithospheric geometry.   I will present new near-vertical reflection and broadband seismic data acquired in the Himalaya and southern Tibet, and new noble-gas measurements on geothermal systems, that support the cartoon below and inform my understanding about ways India approaches southern Tibet: underthrusting fully, faces insurmountable troubles!

Hosts: Eli Silver/Jared Kluesner

April 14, 2015

Da Yang, UC Berkeley

The Madden-Julian Oscillation

Abstract: The Madden-Julian Oscillation (MJO) is a pattern of intense rainfall and associated planetary-scale circulations in the tropical atmosphere, with a recurrence interval of 30-90 days. Although the MJO was first discovered 40 years ago, it is still a challenge to simulate the MJO in general circulation models (GCMs), and even with simple models it is difficult to agree on the basic mechanisms. This deficiency is mainly due to our poor understanding of moist convection—deep cumulus clouds and thunderstorms, which occur at scales that are smaller than the resolution elements of the GCMs. Moist convection is the most important mechanism for transporting energy from the ocean to the atmosphere. Success in simulating the MJO will improve our understanding of moist convection and thereby improve weather and climate forecasting. In this presentation, I will combine observation, modeling, and theory to address the following questions. What is the nature of the MJO? What determines its propagation speed and horizontal scale? How does the MJO respond to climate changes? Our findings challenge previous paradigms, which average over the small scales and focus on the large-scale structure of the MJO. Our findings point to ways for improving the climate models.

Hosts: JP O'Brien

April 15, 2015

Da Yang, UC Berkeley

(held in E&MS A340 at 11:30 AM)

Moist convection, building blocks of the tropical climate system

Abstract: Moist convection—thunderstorms—is a fundamental process on Earth, yet it is one of the most difficult processes to model and one of the least well understood. Moist convection accounts for more than half of the vertical heat transfer in the lower atmosphere. Its interaction with atmospheric flows forms the basis of a spectrum of atmospheric phenomena across wide temporal and spatial scales, including mesoscale cloud clusters, synoptic scale convectively coupled waves, planetary scale Madden-Julian Oscillations (MJOs), and the global scale rainfall distribution.

In this presentation, I will discuss the interaction between the short-lived tropical transients (MJOs and equatorial waves) and the mean climate state. In particular, I will address how the MJO and equatorial waves respond to climate changes, and how they in turn shape the mean climate state. This is achieved by simulating convection in a wide range of climates with a super-parameterized climate model. Such models are the next-generation climate models and replace the traditional representation of moist convection by explicitly resolving cloud systems within each grid cell. Moist convection is therefore represented more accurately. By addressing these topics, we can advance our understanding of moist convection, and thereby improve our ability to forecast climate changes.

Hosts: JP O'Brien

April 21, 2015

George Hilley, Stanford University

Randomness and Order in Branched Channel Networks

Hosts: Claire Masteller/Jon Perkins

April 28, 2015

Mara Brady, California State University, Fresno

Exploring challenges and opportunities in recognizing the signature of sea level, tectonic subsidence, and sediment supply in the stratigraphic record: a comparison of field-based and model-generated data from carbonate sedimentary records

Abstract: Over Phanerozoic time scales, sedimentary records from the tectonically-stable interiors of continents versus their subsiding margins are dramatically thinner and assumed to be relative incomplete, with more numerous gaps caused by erosion and non-deposition. However, this assumption need not be true for the shorter time scales over which the preserved sedimentary record accumulated on the continental interior, or craton.  Using original field-collected data, this study compares Middle-Upper Devonian carbonate-dominated sedimentary and fossil records from Iowa (cratonic interior) and Nevada (continental margin) to evaluate whether the cratonic record is (1) miniaturized, i.e. thinner, but equally complete; (2) comparable in thickness and quality where the sedimentary record is preserved, but certain portions of the record are notably absent, i.e. omitted or truncated; or (3) so invariably preserved that the stratigraphic packages and skeletal concentrations are qualitatively different compared to the contemporaneous continental margin record.

To explore insights gained from the field, we use a previously-developed, one-dimensional forward model to generate stratigraphic columns. Knowing the true history underlying each model run, we can test the sensitivity of the resultant stratigraphy to variation in subsidence and sedimentation rates, while maintaining the same eustatic sea level curve. The model results lead to new questions that can direct future field studies. Overall, this approach can inform similar investigations in other carbonate, siliciclastic and non-marine records, especially over stratigraphic scales finer than the temporal resolution typically afforded by numerical ages and correlation techniques.

Host: Matthew Clapham/Marko Manojlovic

May 5, 2015

Erin Pettit, University of Alaska

Pathways for Escape: The search for the mechanisms driving Blood Falls "outburst flood" events

Abstract: Blood Falls is the supraglacial expression of episodic releases of brine from a unique subglacial and englacial brine hydrological system within Taylor Glacier, a cold polar glacier in the McMurdo Dry Valleys, Antarctica. Evidence from ground penetrating radar, GPS, time lapse imagery, and passive seismics suggest how glacier flow and fracture interact with the subglacial brine hydrological system to create a pathway and trigger for brine outburst floods.

Jill Mikucki, The University of Tennessee, Knoxville

MIDGE: An interdisciplinary quest for the source of 'Blood Falls' on the Taylor Glacier, Antarctica

Hosts: Slawek Tulaczyk/Neil Foley

May 12, 2015

Roland Burgmann, UC Berkeley

Periodic Crustal Deformation and Seismicity

Host: Lingling Ye

May 19, 2015

Jim Gill

Changbaishan Volcano on the China/N. Korea border: large eruptions, geo-politics, and geochemistry

Host:Cara Vennari

May 26, 2015

Thure Edward Cerling, University of Utah

African Environments of Human Evolution: The Isotope Evidence

Abstract: Stable isotopes are the basis for understanding modern climate, ecology, and diet; likewise, they can be used to understanding the history of climate, ecology, and animal diets through geological time. In this lecture I will discuss how we use these natural tracers to understand the context of human evolution in Africa over the past 4 million years. Using isotopes, we can reconstruct the nature of the vegetation on the landscape, estimate temperatures and precipitation, and put constraints on animal diets including early humans.

Host: Paul Koch/Leslie Petrie

May 27, 2015

(held in E&MS A340 at 11:00 AM)

Thure Edward Cerling, University of Utah

HAIR: History of Animals using Isotope Records

Abstract: In this lecture, the History of Animals using Isotope Records (HAIR), I will explore how natural abundances of stable isotopes are recorded in animal tissues. The isotopes ratios of hydrogen, carbon, nitrogen, oxygen and sulfur are used in studies of wildlife ecology, animal physiology, and forensics. Seasonal diet change and migration are just two examples of how stable isotopes provide new insights into animal behavior.

Host: Paul Koch/Leslie Petrie