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Tropical Dynamics

Research on tropical dynamics has evolved thanks to an Israeli-Indian research grant with Prof. Jai Sukhatme. It focuses on multiple scale interactions and the role of tropical waves in shaping the large scale variability. So far we have examined how stochastic small scale forcing (order 100km) can excite a red spectrum through a turbulent upscale cascade, alongside tropical modes, in a moist shallow water model. We find that an upscale cascade (with a -5/3 slope) is excited whenever vorticity anomalies are excited, with moisture facilitating the excitation of vorticity from moisture or heigh anomalies. We are currently examining the role of moisture in driving the model to a state of superrotation. In its dry version, we find spontaneous transitions between sub- and super- rotation (Figure 1).

Other questions we have examined include: What is the role of moisture-coupling (via latent heat release) in shaping the circulation in a tropical planet (uniform solar heating and SSTs)? What is the role of tropical waves in driving the Hadley circulation?

Past work has also examined the balance at the top of tropical cyclones. 

Figure 1: Latitude-time plot of the zonal mean zonal wind in a dry shallow water model forced by small-scale stochastic forcing. Red is eastward flow (Superrotation, when on the equator), blue is westward (sub-rotation when on the equator).

Select publications:

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Submitted/in preparation:

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Thakur, ABS, J. Sukhatme, and N. Harnik. 2024: Investigating the role of tropical and extra-tropical waves in the Hadley circulation via present-day Earth-like to globally uniform SST forcing. Revision under review, Q J R Meteorol Soc.

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Published:

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Schröttle, J., Suhas, D., Harnik, N. and Sukhatme, J. (2022), Turbulence and equatorial waves in moist and dry shallow-water flow, excited through mesoscale stochastic forcing. Q J R Meteorol Soc. 148, 599–619.

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Suhas, D.L., Sukhatme, J. & Harnik, N.(2021) Dry and moist atmospheric circulation with uniform sea-surface temperature. Q J R Meteorol Soc, 1– 22. 

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Cohen, Y., Durden, S. L., Harnik, N., & Heifetz, E.: 2019. Relating Observations of Gradient Nonbalance at the Top of Hurricanes With Their Warm Core Structures. Geophys. Res. Lett., 46, 11510– 11519.   Selected for Editor’s Highlight

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Cohen, Y.,  N. Harnik, E. Heifetz, D. S. Nolan, D Tao, and F Zhang, 2017: On the Violation of Gradient Wind Balance at the top of Tropical Cyclones, Geophys. Res. Lett. 44, 8017–8026.

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Adam, O. and N. Harnik, 2013: Idealized annually averaged Macroturbulent Hadley Circulation in a Shallow Water Model. J. Atmos. Sci., 70, 284-302.

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