Transport of Water Vapor from Tropical Cyclones to the Upper Troposphere

Tair Plotnik,Colin Price,Joydeb Saha,Anirban Guha

doi:10.3390/atmos12111506

Abstract

This paper investigates the influence of tropical cyclones on water vapor concentrations in the upper atmosphere above these storms. We use independent data sets of tropical storm intensity, water vapor and lightning activity to investigate this relationship. Water vapor in the upper troposphere is a key greenhouse gas, with direct impacts on surface temperatures. Both the amount and altitude of water vapor impact the radiative balance and the greenhouse effect of the atmosphere. The water vapor enters the upper troposphere through deep convective storms, often associated with lightning activity. The intensity of the lightning activity represents the intensity of the convection in these storms, and hence the amount of water vapor transported aloft. In this paper, we investigate the role of tropical cyclones on the contribution of water vapor to the upper atmosphere moistening. Tropical cyclones are the largest most intense storms on Earth and can last for up to two weeks at a time. There is also evidence that the intensity of tropical cyclones is increasing, and will continue to increase, due to global warming. In this study we find that the maximum moistening of the upper atmosphere occurs at the 200 hPa level (~12 km altitude), with a lag of 1–2 days after the maximum sustained winds in the tropical cyclone. While the water vapor peaks after the maximum of the storm intensity, the lightning activity peaks before the maximum intensity of the storms, as shown previously. We show here that the absolute amount of water vapor in the upper troposphere above tropical storms increases linearly with the intensity of the storms. For every 10 hPa decrease in the minimum pressure of tropical storms, the specific humidity increases around 0.2 g/kg at the 200 hPa level.

Highlights

One of the key elements controlling Earth’s climate is tropospheric water vapor that has direct effects as a greenhouse gas, as well as indirect effects through the interaction with clouds, aerosols, and tropospheric chemistry
Using the data described above a 3D empirical model of each storm was created to investigate the link between the SH at different atmospheric levels, lightning activity and the maximum intensity of the storms
We focused on the impact of tropical cyclones on the concentrations of water vapor in the upper troposphere

Summary

Introduction

One of the key elements controlling Earth’s climate is tropospheric water vapor that has direct effects as a greenhouse gas, as well as indirect effects through the interaction with clouds, aerosols, and tropospheric chemistry. The link between lightning and upper tropospheric water vapor has been studied before [10,11] showing a lag of approximately 24 h between the lightning activity and the increase in UTWV. Tropical cyclones develop out of tropical disturbances within the Intertropical Convergence Zone (ITCZ) [12], a region that marks the thermal “equator” of the planet, and is associated with deep convection, thunderstorms and heavy rainfall. In these regions, a combination of dynamic and thermodynamic parameters support the development of tropical cyclones, such as low-level convergence, vorticity, low wind shear, high humidity, atmospheric instability, and warm sea surface temperatures (SSTs) above 26 ◦C. Three data sets were used in this study: Tropical cyclone intensity data defined by the maximum sustained winds or minimum pressure in the storm; lightning discharge data within 5 degrees or the eye of the storm; and specific humidity data in the upper atmosphere within 5 degrees of the eye of the storm

Tropical Cyclone Winds

Lightning Data

Specific Humidity in the Upper Troposphere

Results