# Oceanography

Senior Lecturer
Head of the academic committee of the Hebrew University Climate Science Center (HUCS)
972-2-6586514
Room 307 North
In my group we study the large-scale dynamics of the atmosphere and oceans and the interactions between them, with emphasis on tropical climate dynamics. We aim to improve our understanding of variations in the present and past climates, and the governing dynamic and thermodynamic mechanisms that drive them. We also strive to mediate between theoretical and applied geophysical practices, by developing tools and methods for applications such as bias reduction in climate models, interpretation of paleo records, and quantification of variations of the tropical rain belt.

The theoretical tools we use include idealized models of the atmosphere and oceans which are amenable to mathematical analysis, an idealized general circulation model (FMS), as well as the analysis of comprehensive climate models (e.g., CMIP and PMIP models). We also aim to anchor the research in observations. To handle the large variety of observational and modeling datasets, we use a software tool called GOAT (Geophysical Observation Analysis Tool).

Current research projects include:

• Idealised coupled cloud-ocean-atmosphere models
• The effect of continent distribution on tropical climate
• The relation of the atmospheric energy budget and tropical precipitation
• Origin and nature of the double ITCZ bias
• Variations of the tropical rain belt in the present and past climates
• Relating the Hadley cell strength to the atmospheric energy budget

## Amotz Agnon

Professor
972-2-65-84743
amotz@mail.huji.ac.il
Room 216 South

#### Interests:

Earthquake geology and mechanics, mid-ocean ridge and ophiolite dynamics, geo-archaeology, sea-level change and glaciation.

## natalie chernihovski

natalie.chernihovsk@mail.huji.ac.il

## Hezi Gildor

Professor
972-2-6584393
hezi.gildor@mail.huji.ac.il
Room 312 North

Interests:

physical oceanography (ocean mixing and stirring, internal waves, density currents...), modern and paleo climate dynamics, interaction between biota and climate.

## Gil lapid

gilapid@gmail.com

## Yoav lindemann

yoav.lindemann@mail.huji.ac.il

## Nathan Paldor

Professor
972-2-65-84924
nathan.paldor@mail.huji.ac.il
Room 301 North

My research interests encompass the fundamentals of atmospheric and oceanic dynamics. The complex whirling of eddies of all sizes, the majestic major ocean currents or jet streams in the atmosphere are all examples of large scale dynamical features of the ever evolving fluids that move on the surface of the rotating spherical earth. The amount of fluid (be it gas in the atmosphere or saline water in the ocean) that are transported by these flows is too large for us to grasp at first glance. The Gulf Stream transports about 100 million tons of water every second from low latitudes to the mid-latitudes along the eastern coast of North America; about 3,000 times the amount of water flowing down the Niagara Falls. The Subtropical Jet Stream in the atmosphere transports about half-a-million tons of air (recall that the density of air is about 1/1000 that of water) around the earth from west to east at altitudes of about 10 km and speeds of the order of 100-150 km/h. The existence of the Subtropical Jet Stream enables the Israeli Airline El-Al to fly non-stop from Los-Angeles to Tel-Aviv, which it does in the opposite direction quite seldom. In my Geophysical Fluid Dynamics (GFD) research I attempt to define the exact physical origin of certain fluid dynamical phenomena and to provide exact theoretical descriptions of their observed features (such as the way they change with time and space). I also attempt to highlight the geophysical ramifications of their presence.

In recent years I developed a theory of non-harmonic (also described as Trapped) waves of Geophysical Fluid Dynamics based on the formulation of a time-independent, Schrodinger eigenvalue equation for zonally propagating wave of the Rotating Shallow Water Equations (AKA Laplace Tidal Equations). The energy levels of the eigenvalue equation provide explicit expressions for the phase speeds of the waves and the associated eigenfunctions describe the meridional amplitude structure of the various waves. This formulation is relevant to many physical settings including the mid-latitude f-/$$\beta-$$ plane, the equatorial $$\beta-$$plane and the spherical Earth. In particular, this formulation provided, for the first time, explicit expressions for the dispersion relations of Planetary (Rossby) waves and Inertia-Gravity (Poincare) waves on the spherical Earth (i.e. a rotating sphere but without the centrifugal acceleration. In additon to providing approximate, but highly accurate expressions for Planetary and Inertia-Gravity waves on the spherical earth the formulation of the  Schrodinger eigenvalue equation has provided a clear demonstration that Yanai wave (AKA the mixed Rossby-Gravity mode) exists on a sphere but for different reasons than on the equatorial $$\beta-$$plane: In the latter this wave exists only because the second westward propagating wave is associated with singular zonal velocity while on a sphere the approximate solution by the Schrodinger equation yields an unacceptable (complex) phase speed near the gravity wave phase speed.

In contrast to the planar theories where Kelvin waves exist as additional modes to Inertia-Gravity waves (e.g. modes in which one velocity component vanishes identically so the other velocity and the height fields solve the three scalar Rotating Shallow water Equations) on a sphere these waves do not exist at all but the eastward propagating Inertia-Gravity n=0 mode is nearly non-dispersive.

These theoretical advances enabled the construction of test cases for the dynamical cores of global scale General Circulation Models and the explicit expressions have also been applied in the interpretation of satellite borne observations of Sea Surface Height Anomalies in the Indian Ocean south of Australia where the nearly zonal coast provides the "wall" at which the waves are Trapped.

My book entitled “Shallow Water Waves on the Rotating Earth” which was published by Springer in 2015 provides the details of this unified approach to the known waves of Geophysical Fluid Dynamics

My updated list of publications

## Yeala Shaked

Associate Professor
972-8-6360139
yeala.shaked@mail.huji.ac.il
Room 16 South

Research Interests

As a marine biogeochemist, my interest revolves around the interactions between organisms and their environment, with emphasis on trace metal bioavailability to phytoplankton and redox transformations. I am intrigued by the fact that microorganisms, striving to acquire nutrients and protect themselves from external stressors, actively modify their chemical milieu and in turn influence the biogeochemical cycles of trace and major elements in the ocean. I study fundamental processes and mechanisms by combining field and laboratory measurements and experiments.

Ongoing and future projects:

• Dust as a source of iron to Trichodesmium, a globally significant phytoplankton
• Bioavailability of iron to phytoplankton

Get in touch: yeala.shaked@mail.huji.ac.il