A realistic and multi-scale dynamical study to understand thin tropical cirrus cloud life cycle

The National Science Foundation Division of Atmospheric and Geospace Sciences awarded Northwest Research Associates, Inc. $381,966 on August 15, 2026, to conduct a realistic and multi-scale dynamical study of thin tropical cirrus cloud life cycles under the Geosciences program (CFDA 47.050).

The project combines balloon observations from the STRAT-OLE-2 long-duration balloon campaigns with detailed cloud-microphysics simulations using the Community Aerosol and Radiation Model for Atmospheres (CARMA) to determine how atmospheric waves—ranging from small gravity waves to planetary-scale waves—control the formation and persistence of cirrus clouds near the tropical tropopause at 16–18 kilometers altitude. These clouds regulate water vapor entry into the stratosphere, affecting stratospheric ozone and UV protection, and influence tropical heat balance by blocking outgoing infrared radiation. The project will improve representation of these clouds and stratospheric water vapor in atmospheric models to support more reliable assessments of their effects on weather and environmental conditions, while also strengthening connections between researchers studying cirrus clouds and those studying wave dynamics.

Performance occurs in Seattle, Washington, with a completion date of July 31, 2029. Northwest Research Associates is a for-profit scientific research organization specializing in atmospheric science, space physics, and geophysical research and modeling.

Abstract

Thin cirrus clouds near the tropical tropopause, at altitudes of about 16?18 kilometers, play an important role in determining how much water vapor enters the stratosphere, which matters for several reasons including the role of humidity in determining the amount of ozone is available to protect US from harmful ultraviolet radiation. Thin cirrus clouds also matter for the heat balance of the tropics as they block outgoing infrared radiation, thereby contributing to the ambient conditions for tropical weather systems. The evolution of these clouds is strongly shaped by atmospheric waves, ranging from small, rapidly varying gravity waves (also called buoyancy waves) to much larger planetary-scale waves that produce cooling and warming over periods from minutes to several days. This project will use unique balloon observations and detailed cloud simulations to determine how these waves control the formation and persistence tropopause-level cirrus clouds. The findings will help improve the representation of these clouds and stratospheric water vapor in atmospheric models, supporting more reliable assessments of their effects on weather and environmental conditions. By linking atmospheric dynamics and cloud physics, the project will also strengthen connections between the communities of researchers studying cirrus clouds and researchers studying wave dynamics who often work in isolation from each other. This project will use balloon observations of both waves and thin cirrus clouds to determine how realistic atmospheric dynamical variability controls cloud lifecycle. The project will combine concurrent observations of clouds, temperature, humidity, aerosols, and atmospheric waves from the strat?OLE-2 long-duration balloon campaigns with detailed cloud-microphysics simulations (using the community aerosol and radiation model for atmospheres (carma)). The investigators will reproduce a well-observed cirrus event that persisted for several days in the cold phase of a large-scale tropical wave and test how the addition of smaller, higher-frequency gravity waves changes ICE formation, crystal growth, sedimentation, and cloud lifetime. The project will also examine how gravity-wave spectra vary across the tropics and how that variability affects simulated cirrus properties. Finally, the simulations will be used to estimate cloud optical properties, dehydration efficiency, and radiative effects. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the foundation's intellectual merit and broader impacts review criteria.- subawards are not planned for this award.