Eli Tziperman, ocean, atmosphere, and climate dynamics

Ocean, Atmosphere, and Climate Dynamics

Introduction

Our research deals with ocean, atmosphere and climate dynamics, trying to understand physical processes that affect Earth's climate on time scales of a few years to millions of years. Climate variability results from a rich set of nonlinear, sometime chaotic, physical interactions of the oceans, atmosphere and at times the biosphere as well. Some of the very basic questions in this research area are still unanswered. E.g., why were there ice ages, why is El Niño difficult to predict, what future warming can we expect in a century, how can we understand specific observed features of past warm climates millions of years ago and what can they teach us about the future. These open challenges makes this a fascinating field to work in for those of us with an interest in applying physical and mathematical principles to the study of the natural world. In addition, climate is, of course, a research area with practical aspects directly affecting our life, creating an engaging combination of a scientific challenge and societal relevance. We normally use both simplified mathematical models of a given climate phenomenon to understand the mechanisms in question in detail, together with realistic state-of-the-art simulations for testing ideas developed using simpler models.

Please follow the links below for examples of our research activities.

El Niño

El Niño is a large-scale surface warming of the Pacific Ocean every 3–6 years that lasts a few months and dramatically affects weather and climate world wide; for further intro, see wikipedia. Some of the questions we worked on:

Irregularity

Why is El Niño irregular and therefore difficult to predict?
More

Westerly wind bursts

These occur in the Equatorial Pacific, last one to two weeks and strongly amplify major El Niño events. What role do they play? What causes them? (With Ian Eisenman, Minmin Fu)
More

Seasonality

Why does El Niño peak toward the end of the calendar year? (With Eli Galanti)
More

The Atlantic Meridional Overturning Circulation (AMOC) and large scale ocean dynamics

The oceans play a dominant role in long-term climate change and interannual climate variability. AMOC is a significant player in much of this. Following are a few examples of related questions we worked on:

Is AMOC close to a tipping point?

Much is said about AMOC collapsing in a warmer climate. We have examined its potential proximity to a tipping point (bifurcation) using box models and an ocean circulation model.

AMOC variability

One possible explanation for AMOC oscillations is that these are damped linear oscillations forced by weather noise. This can involve interesting non-normal dynamics and transient amplification (with Steve Griffies, Laure Zanna).

What sets the basic stratification of the oceans?

Munk (1969) noted that the vertical ocean temperature profile is exponential, yet his explanation runs into observational constraints. The ventilated thermocline theory must prescribe the ocean stratification. What physical processes control this stratification and how? (With Madeline Miller, Xiaoting Yang)

More: [1, 2, 3]

Water mass transformation

Significant insights may be gained by studying air-sea heat and fresh water fluxes as a function of the surface density. This work extended Walin's work in temperature space (with Kevin Speer).

More: [1, 2, 3]

Past climates

Ice ages

The 100 kyr glacial cycles are the strongest climate variability over the past million years, yet we still do not understand why they occur, what determines their period, why CO₂ changes by 50% during each cycle, etc. We proposed a "sea ice switch" mechanism and explored various other aspects (with Hezi Gildor, Yossi Ashkenazy).

Hothouse climates (Eocene, 50 Myr)

Dramatic evidence shows that interior continental temperatures did not fall below freezing for millions of years in places that routinely see −40 °C every winter now. We proposed a convective Arctic cloud feedback and a low continental cloud feedback to try to explain this (with Dorian Abbot, Tim Cronin).

Warm climate (Pliocene, 2–5 Myr)

This is the nearest past analog of a future climate change. Among the issues we addressed: there may have been a permanent El Niño, California was much wetter, and coastal upwelling may have shut down. Lots of potential lessons for future climate change (with Nathan Arnold, Madeline Miller, Minmin Fu).

Snowball Earth

Earth has frozen over a couple of times 600–700 Myr ago, each event lasting million of years. We have examined a possible ocean bacteria-driven initiation mechanism, studied the ocean circulation and ice flow over a snowball ocean (with Yossi Ashkenazy).

Abrupt (past) climate change

Dansgaard–Oeschger and Heinrich events during the last ice age involved dramatic temperature and ice volume changes. We proposed sea ice changes were involved and examined their mechanism (with Hezi Gildor, Roiy Sayag, Yohai Kaspi).

Attribution of extreme events

Can we rapidly attribute individual extreme weather events to anthropogenic climate change by fitting the observed record to an extreme value distribution? (With Peter Sherman and Peter Huybers).

More: [1]

Stronger Madden-Julian oscillation and more frequent Sudden Stratospheric Warmings

We explored the mechanism of the expected strengthening of the MJO, a major tropical atmospheric variability mode, and how that might affect stratospheric warming events (with Nathan Arnold and Wanying Kang).

More: [MJO intensification: 1, 2, 3; SSW increase: 4, 5, 6]

North Atlantic Oscillation and Arctic Oscillation

These two climate variability modes are essentially identical today, we showed them to potentially decouple in a warmer future climate (with Claudia Pasquero and Mostafa Hamouda).

More: [1]

Cryosphere

Sea ice dynamics

Sea ice is a major climate player, and its cover in both polar areas is characterized by a complex and continuously changing distribution of floe sizes from centimeters to hundreds of km. We developed a model for the floe size and thickness distribution allowing to represent this complexity in global climate models (with Chris Horvat).

Ice streams

Ice streams in Antarctica cover merely 10% of the surface, yet accounts for about 90% of the ice sheet discharge, with a similar role in Greenland and in past ice sheets. They likely played a role in the dramatic climate shifts during ice ages and will play a role in a warmer future climate. Their dynamics are still not completely understood (with Roiy Sayag, Alex Robel).

Icy moons (Europa)

Europa, Jupiter's moon, and some other solar system icy moons have subsurface oceans that may support life. We studied their global ice flow, examined the role of salinity and formulated consistent upper and lower ocean boundary conditions. We suggested an ocean current mechanism for an asynchronous rotation of Europa's icy shell (with Yossi Ashkenazy).