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Dr. Orli Lachmy, Senior Lecturer

Contact Info

The Open University of Israel Department of Natural Sciences 1 University Road, P. O. Box 808, Raanana 43107, Israel
Office:(+972) 9-7782128 Email:orlila@openu.ac.il

Additional Information

My CRIS profile

Areas of Interest
  • Atmosphere dynamics
  • Climate variability
  • Geophysical fluid dynamics
  • Midlatitude jet streams and storm tracks

I am a senior lecturer in Earth Sciences at the Department of Natural Sciences in the Open University of Israel. I study the dynamics of the atmospheric general circulation and its role in the climate system.

I am fascinated by the atmospheric flow, which obeys simple physical rules, yet exhibits complex nonlinear behavior that is very difficult to predict. Using numerical modeling and observational analysis we are able to advance the theoretical understanding of the atmospheric general circulation dynamics and its role in the transport of energy, heat, moisture and momentum around the globe.

My research focuses on the dynamics of the midlatitude jet stream and storm tracks, which control climate and weather patterns in the midlatitudes (between 30 and 60 degrees latitude) as well as the transport of heat and moisture from the tropics to polar regions. The structure and intensity of the jet stream and storm track are expected to change in response to climate change, affecting the local patterns of precipitation and weather variability, yet there is no robust theoretical understanding of this response. My work aims at improving the theoretical understanding of this dynamical system, as part of the communal effort for improving the reliability of climate predictions.

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2023 - present
Senior lecturer (equivalent to assistant professor) at the Department of Natural Sciences, The Open University of Israel
2017 - 2023
Lecturer at the Department of Natural Sciences, The Open University of Israel.
2015 - 2017
Postdoctoral researcher under the guidance of Prof. Tiffany Shaw at the Department of Geophysical Sciences, University of Chicago.
2015
Ph.D. Atmospheric Sciences
Tel Aviv University, Tel Aviv, Israel
Topic: “Atmospheric extratropical wave-mean flow interactions
maintaining the different flow regimes of the jet stream”
Advisor: Prof. Nili Harnik
2008
M.Sc. Atmospheric Sciences
Tel Aviv University, Tel Aviv, Israel
Topic: “A wave amplitude transition in a quasi-geostrophic wavemean
flow interaction system”
Advisor: Prof. Nili Harnik
2004
B.Sc. Physics
The Hebrew University, Jerusalem, Israel

2018 Israel Science Foundation, new faculty equipment grant. Title: "High performance computer for general circulation models".

2018​  Israel Science Foundation , individual research grant. Title: " The role of midlatitude latent heating in the maintenance of the extratropical atmospheric circulation and its response to climate change".

2012 Scholarship for promoting women in science from the Israel Ministry of Science and Technology.​

2009 President and rector scholarship for excellent doctoral students, Tel Aviv University.​

2008 Graduation of M.Sc. with special distinction, Tel Aviv University.​

2006 Scholarship for excellent research students, Tel Aviv University.​

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White, I. P., Lachmy, O. and Harnik, N. (2024), Influence of a local diabatic heating  source on the midlatitude circulation, Quarterly Journal of the Royal Meteorological Society, https://doi.org/10.1002/qj.4863. 

Ghosh, S., Lachmy, O. and Kaspi, Y. (2024), The role of diabatic heating in the midlatitude atmospheric circulation response to climate change, Journal of Climate, Vol. 37, 2987-3009.  https://doi.org/10.1175/JCLI-D-23-0345.1

Garfinkel, C. I., Keller, B., Lachmy, O., White I., Gerber, E. P., Jucker, M. and Adam, O. (2024), Impact of parametrized convection on the storm track and jet stream response to global warming: Implications for mechanisms of the future poleward shift, Journal of Climate, Vol. 37, 2541-2564. 

Peles, O. and O. Lachmy (2023), Estimating the lowest latitude of baroclinic growth, Journal of the Atmospheric Sciences, Vol. 80, 1401-1414 https://doi.org/10.1175/JAS-D-22-0201.1.

Lachmy, O. (2022), The relation between the latitudinal shifts of midlatitude diabatic heating, eddy heat flux and the eddy-driven jet in CMIP6 models, Journal of Geophysical Research: Atmospheres, 127, e2022JD036556, https://doi.org/10.1029/2022JD036556. 

Messori, G., N. Harnik, E. Madonna, O. Lachmy and D. Faranda (2021), A dynamical systems characterisation of atmospheric jet regimes, Earth System Dynamics, 12, 233-251. https://doi.org/10.5194/esd-12-233-2021​.

 Lachmy, O. and Y. Kaspi (2020), The role of diabatic heating in Ferrel cell dynamics, Geophysical Research Letters, 47, e2020GL090619, https://doi.org/10.1029/2020GL090619​.​

Lachmy, O. and N. Harnik (2020), Tropospheric jet variability in different flow regimes, Quarterly Journal of the Royal Meteorological Society, Vol. 146, 327-347. doi.org/10.1002/qj.3678​

Tan Z., O. Lachmy and T. A. Shaw (2019), The sensitivity of the jet stream response to climate change to radiative assumptions, Journal of Advances in Modeling Earth Systems, 11, 934-956. https://doi.org/10.1029/2018MS001492​​. ​ 

Lachmy, O. and T. A. Shaw (2018), Connecting the energy and momentum flux response to climate change using the Eliassen and Palm relation, Journal of Climate, Vol. 31, 7401-7416. https://doi.org/10.1175/JCLI-D-17-0792.1​.​

Lachmy, O. and N. Harnik (2016), Wave and jet maintenance in different flow regimes, Journal of the Atmospheric Sciences, Vol. 73, 2465-2484. https://doi.org/10.1175/JAS-D-15-0321.1

Harnik, N., C. Garfinkel and O. Lachmy (2016), The influence of jet regimes on extreme weather events, in Dynamics and Predictability of Large-Scale, High-Impact Weather and Climate Events 2, 79. Edited by J. Li, R. Swinbank, H. Volkert and R. Grotjahn, Cambridge University Press.

Lachmy, O. and N. Harnik (2014), The transition to a subtropical jet regime and its maintenance, Journal of the Atmospheric Sciences, Vol. 71, 1389-1409.https://doi.org/10.1175/JAS-D-13-0125.1

Lachmy, O. and N. Harnik (2009), A wave amplitude transition in a quasi-linear model with radiative forcing and surface drag, Journal of the Atmospheric Sciences, Vol. 66, 3479-3490. https://doi.org/10.1175/2009JAS3157.1

Research

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The interaction between the storm tracks and the subtropical jet

​The subtropical jet is a band of fast eastward winds in the upper tropospheric subtropics, driven by advection of angular momentum from the tropics by the Hadley circulation cell. Though the subtropical jet is not driven by the midlatitude eddies that form the storm tracks, these two components of the flow are strongly coupled. We study how the interaction between the subtropical jet and the storm tracks affects their properties.
One aspect of this interaction is the effect of the subtropical jet on the baroclinicity - the instability that leads to the growth of midlatitude eddies - and on the lowest latitude of baroclinic growth. We found that the Eady growth rate, often used as the measure of baroclinicity, underestimates the lowest latitude of baroclinic growth. In contrast, supercriticality (the inverse of the Charney number) - a different measure of baroclinicity - captures well the observed lowest latitude of baroclinic growth.

See this paper, which compares the estimated and observed lowest latitude of baroclinic growth.

The effect of latent heating on the general circulation of the atmosphere 

Latent heat release associated with midlatitude storms is an important component of the midlatitude heat budget. Latent heating, radiative cooling, meridional and vertical heat fluxes as well as adiabatic heating or cooling due to the mean vertical wind are the major components of the heat budget. Since adiabatic cooling and heating by the vertical motion of air is related to the location of the mean circulation cells, any change in the heat budget affects the general circulation of the atmosphere. In collaboration with prof. Yohai Kaspi​, we study the midlatitude heat budget and the effect of latent heating on the structure of the Ferrel cell, the jet stream and the storm tracks and the relations between them.
 
This effect was studied using observations, CMIP6 models and an idealized model, to investigate its role in the midlatitude circulation response to climate change. 

The response of the atmospheric circulation to climate change 

​Climate models generally predict a poleward shift of the eddy driven jet stream in response to increased greenhouse gas concentration. However, there is a large spread in the jet shift between different models and the physical reasons for this shift are not fully understood. The storm tracks associated with the eddy driven jet are also expected to shift poleward in response to climate change. Several theories have been proposed to explain the storm track shift and the eddy driven jet shift, yet there is no complete theory that connects the latitudes of the storm track and eddy driven jet.

 

In collaboration with Prof. Tiffany Shaw​ we have studied the connection between the latitudes of the storm track and eddy driven jet using the Eliassen and Palm relation, which connects the eddy energy and momentum fluxes. We found that differences in the climatological mean flow can lead to opposite eddy driven jet shifts, while the poleward storm track shift is more robust. The analysis of the terms in the Eliassen and Palm relation showed that the eddy phase speed and the response of the mean flow to climate change are not necessary for predicting the eddy driven jet shift, given the eddy energy flux response. 

See this publication.


Flow regimes of the atmospheric jet stream

​The atmospheric jet stream appears sometimes as a region of strong zonal winds concentrated at the upper tropospheric subtropics, referred to as the subtropical jet, and sometimes it appears as a meandering band of winds in the midlatitudes, associated with surface westerlies, known as the eddy driven jet. The two types of jets sometimes merge to a single jet and sometimes separate. The dominant type of jet depends on the location, season and year. 
 

In my PhD research with Prof. Nili Harnik​ we have revealed the mechanisms that control the regime transition between the subtropical, merged and eddy driven jet states in an idealized configuration. Our ongoing work is concerned with the dynamics that control changes in the variability characteristics of the jet as it transitions between the different regimes. 

This work is summarized in three publications, focusing on the subtropical jet maintenance, the maintenance of all three regimes, and the transition in the jet variability properties.

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  • Head of the Earth Sciences field in the Department of Natural Sciences 

  • Academic responsibility for the courses: "Physical Climatology", "Introduction to Meteorology", "Synoptic Meteorology Laboratory", "The Climate Change Problem", "Atmospheric Chemistry", "Introduction to Geophysics", Introduction to Environmental Sciences".​


  • Development of courses: "Physical Climatology", "The Climate Change Problem", "Introduction to Environmental Sciences".

Group members

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Ian White (joint supervision with Nili Harnik, Tel-Aviv University)

Oren Peles

​Soumik Ghosh (joint supervision with Yohai Kaspi, Weizmann Institude of Science)

Student / Postdoc / Research assistant oppotunities

M.Sc. and Ph.D. student as well as postdoc or research assistant opportunities are available in my group. For more details please send me an e-mail to: orlila@openu.ac.il.

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