Tracers of rapid transport in the lower stratosphere

• Main Author: Moyer, Elisabeth Jeanne Bailey
• Format: Thesis
• Language: English
• Published: California Institute of Technology 2001
• Subjects: Planetary Sciences; Planetary Science and Environmental Engineering; Arctic; Fairbanks
• Online Access: https://dx.doi.org/10.7907/snq4-db56; https://resolver.caltech.edu/CaltechTHESIS:02122013-103240444

This thesis consists of three parts, each related to the use of tracer measurements to diagnose the small-scale structure and mechanisms by which air is transported, both vertically and horizontally, in the lower stratosphere. 1. I demonstrate that the isotopic composition of water vapor can diagnose rapid convective transport across the tropopause. I use data from the space shuttle- and balloon-borne Fourier transform solar occultation spectrometers ATMOS (Atmospheric Trace MOlecule Spectrometer) and Mark-IV to reconstruct the mean deuterium isotopic composition of water entering the stratosphere. Initial δD is -670 per mil (33% of deuterated water retained). I construct a one-dimensional model simulating isotopic fractionation during ascent to the tropopause and demonstrate that for all but the most rapid ascent. virtually all deuterated water is stripped from an air parcel in the last few kilometers of the uppermost troposphere. The observed stratospheric δD is then far heavier than modeled depletions under most conditions. I conclude that the observations can be matched only by substantial evaporation of lofted condensate or by ascent in highly-supersaturated conditions, and infer that mean stratospheric air must have experienced rapid convection to at least near-tropopause altitudes. This study serves to demonstrate that the isotopic composition of water vapor is a valuable tracer that can be used to constrain mechanisms of stratosphere-troposphere transport. 2. I use in-situ tunable diode laser measurements of CO, H_2O, and N_2O taken over Fairbanks, AK to show rapid transport by streamers of air in the lower stratosphere. I was part of a team that used ALIAS and JPL-H2O, two tunable diode laser spectrometers built by the Webster group of the Jet Propulsion Laboratory, to obtain data in the upper troposphere and lower stratosphere on 21 ER-2 flights between April and September, 1991, during the POLARIS (Photochemistry of Ozone Loss in the Arctic Region In Summer) mission. I use this dataset to identify episodes of rapid polewards advection in the lowermost stratosphere in which filaments of air move from tropics to 65 N latitude in weeks. I find that the lowermost stratosphere is a region of intense filamentary activity, but that tropical filamentation is absent above the 420 K surface, in contradiction to the results of previous trajectory simulations. Individual filaments extend from the “overworld” stratosphere to the local tropopause, showing that the boundary between “overworld and “middleworld” is not a true dynamical barrier. The filamentation is strongly seasonal, in agreement with previous trajectory results, but with a longer period of activity. I conclude that the tropopause transition layer extends to 420 K Ɵ, and that transport in this layer is coupled to changes in the tropospheric subtropical jet. 3. I describe the design and construction of a new lightweight open-path tunable-diode- laser instrument for measurements of water, vapor isotopic composition from aircraft platforms. I initiated and led an effort to design and build an instrument capable of resolving transport issues such as those mentioned in (1). WISP (Water Isotope SPectrometer) is a 3-channel tunable-diode-laser spectrometer, with two mid-infrared and one near-infrared laser sources. Light is injected into a 94-pass Herriott cell for a total of 94 meters of pathlength. The expected threshold sensitivity is a few parts in 10^5 absorption. Detection of HDO has an expected SNR >10 up to near-tropopause altitudes. All isotopomers of water vapor, and methane, are detected in a single scan, allowing improved accuracy as common systematics drop out of the ratio. I led the integration of the instrument on NASA’s WB-57 aircraft as part of the ACCENT mission. The instrument can provide a versatile tool for t racer measurements in the tropopause region.