# An axisymmetric limit for the width of the Hadley cell on planets with large obliquity and long seasonality

## TL;DR

This paper investigates the limits of Hadley cell width on planets with extreme obliquity and seasonality, using theoretical and numerical methods to identify the dominant factors influencing circulation patterns.

## Contribution

It introduces an axisymmetric theoretical framework and GCM simulations to determine how the thermal Rossby number and rotation rate control Hadley cell characteristics on diverse planets.

## Key findings

- Rotation rate critically influences Hadley cell width and position.
- Thermal Rossby number governs the circulation's behavior.
- Results explain the observed circulation features on Mars and Titan.

## Abstract

Hadley cells dominate the meridional circulation of terrestrial atmospheres. The Solar System terrestrial atmospheres, Venus, Earth, Mars and Titan, exhibit a large variety in the strength, width and seasonality of their Hadley circulation. Despite the Hadley cell being thermally driven, in all planets, the ascending branch does not coincide with the warmest latitude, even in cases with very long seasonality (e.g., Titan) or very small thermal inertia (e.g., Mars). In order to understand the characteristics of the Hadley circulation in case of extreme planetary characteristics, we show both theoretically, using axisymmetric theory, and numerically, using a set of idealized GCM simulations, that the thermal Rossby number dictates the character of the circulation. Given the possible variation of thermal Rossby number parameters, the rotation rate is found to be the most critical factor controlling the circulation characteristics. The results also explain the location of the ascending branch on Mars and Titan.