Collaborative Research: Characterizing Atmospheric Tropical-waves of the Lower Stratosphere with Reel-down Atmospheric Temperature Sensing for Strateole-2--RATS Chasing CATS!

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This award supports the continued participation of the Principal Investigators (PIs) in the Strateole-2 field campaign, organized by the French space agency (CNES, for Centre National d'Etudes Spatiales) and the Laboratory for Dynamic Meteorology (LMD) at the University of Paris-Saclay. The campaign makes observations of the tropical tropopause layer (TTL), the layer of the atmosphere from roughly 14km to 18km between the tropical troposphere and stratosphere, using balloons designed to float at a constant altitude for flights of up to 3 months. The balloons are launched from the Seychelles and float around the equator just above the top of the TTL or in the lower stratosphere at an altitude near 20km. Strateole-2 was planned as a set of three deployments, a preliminary engineering deployment with 8 balloon flights followed by two science deployments with 20 flights each. The first two deployments took place in 2019 and 2021 and funds for the PIs' participation in these deployments were provided through AGS-1642277. The third deployment is scheduled to begin in October 2025. Funds provided here support the development and deployment of a new instrument with the acronym RATS, for Reel-down Atmospheric Temperature Sensor. Roughly speaking RATS is a thermometer lowered on a long tether below a balloon gondola which contains a second thermometer. The difference in temperature between the two thermometers can be used to detect gravity waves, atmospheric waves similar to ocean surface waves only they can propagate vertically as well as horizontally. RATS can detect gravity waves because the up and down motions of the waves cause cooling and warming, thus the difference in temperature between two appropriately separated thermometers can record the passage of a wave. The title of the proposal refers to the use of the RATS thermometers for the Characterization of Atmospheric Tropical waves of the lower Stratosphere (CATS). Motivation for the work comes from the role of gravity waves in driving the Quasi-Biennial Oscillation (QBO), the reversal in zonal wind direction over the equator that begins in the upper stratosphere and descends to the tropopause over a period slightly longer than two years. The QBO matters for subseasonal weather prediction because it has been linked to modes of climate variability that influence weather around the world. Models used for weather prediction have difficulty capturing the QBO, in part because the waves that drive it have wavelengths that are smaller than typical model grid spacings, particularly in the vertical. RATS can detect waves with vertical wavelengths between 2 and 30 times the distance between the two thermometers, which is set to either 200m or 300m to capture wavelengths from 400m to 6km or 600m to 9km. The longer wavelengths can be resolved by operational models and thus compared with the model output while the shorter ones are unresolved. The award covers the development of the RATS hardware, which includes a Lower Measuring Unit (LMU) containing a thermometer (developed by CNES) along with an RS41 radiosonde sensor module (from Vaisala) to measures temperature, humidity, and pressure, and a GPS receiver for determining position. The LMU is raised and lowered using a spool and pulley system that allows it to be docked to the gondola for launch and reeled down when the balloon reaches its flight altitude. The gondola contains a second thermometer along with a barometer and GPS receiver. The work is of societal interest given the prospects for better long-range weather predictions through improved representation of the wave driving of the QBO. The Strateole-2 field campaign involves collaborations with two operational weather prediction centers, thereby providing a connection from research to operations. All field campaign data is made available to the global research community to pursue additional research topics on TTL physics and dynamics. 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.