Observed Trend in the Trade Wind Inversion Height and a Possible Dynamic Constraint on its Equatorward Slope

The trade wind inversion refers to the lower-tropospheric temperature inversion that extends equatorward from the oceanic subtropical anticyclones. The inversion base slopes upward towards the equator, and along the way, there is a well-documented transition from widespread marine stratocumulus to clumps of cumulus clouds. This equatorward slope of the trade wind inversion emerges as a critical parameter influencing subtropical cloud distribution and the Earth's radiative budget.

In this ongoing work, we estimate trends in the trade wind inversion height at selected locations within the Atlantic and eastern Pacific using 40 years of radiosonde data. We find that the inversion base has shifted upward in the atmosphere. This is consistent with ocean surface warming and the weakening of the Hadley circulation. However, preliminary results also indicate that the annual-mean equatorward slope of the inversion has not changed appreciably over the past 40 years. In other words, the upward shift in the inversion is relatively uniform .

To account for this observation, we invoke the theory of dynamical adjustment of the inversion as proposed by Schubert et al. (1995). To the extent that these preliminary results hold under additional scrutiny, we hypothesize that the dynamical adjustment constrains the inversion slope to a critical value. That is, local changes in the inversion height are homogenized by dynamical adjustment, and its equatorward slope remains the same even as the inversion base is rising.

Reference

Schubert, W. H., P. E. Ciesielski, C. Lu, and R. H. Johnson, 1995: Dynamical Adjustment of the Trade Wind Inversion Layer. J. Atmos. Sci., 52, 2941–2952