Stratospheric Imaging of Polar Mesospheric Clouds: A New Window on Small-Scale Atmospheric Dynamics

TL;DR

This paper introduces a novel observational method using stratospheric balloon images of polar mesospheric clouds to study small-scale atmospheric turbulence and instabilities at altitudes around 82 km.

Contribution

It provides the first detailed images of turbulence structures at sub-20 meter scales in the mesosphere, offering new insights into atmospheric dynamics.

Findings

Revealed turbulence structures at scales < 20 m

Identified the smallest turbulence scales observable in the atmosphere

Demonstrated the effectiveness of balloon-based optical imaging for atmospheric studies

Abstract

Instabilities and turbulence extending to the smallest dynamical scales play important roles in the deposition of energy and momentum by gravity waves throughout the atmosphere. However, these dynamics and their effects have been impossible to quantify to date due to lack of observational guidance. Serendipitous optical images of polar mesospheric clouds at ~82 km obtained by star cameras aboard a cosmology experiment deployed on a stratospheric balloon provide a new observational tool, revealing instability and turbulence structures extending to spatial scales < 20 m. At 82 km, this resolution provides sensitivity extending to the smallest turbulence scale not strongly influenced by viscosity: the "inner scale" of turbulence, $l_0\sim$10($\nu^3$/$\epsilon$)$^{1/4}$. Such images represent a new window into small-scale dynamics that occur throughout the atmosphere but are impossible to observe in such detail at any other altitude. We present a sample of images revealing a range of dynamics features, and employ numerical simulations that resolve these dynamics to guide our interpretation of several observed events.