This thesis consists of three parts, each related to the use of tracer measurements todiagnose the small-scale structure and mechanisms by which air is transported, bothvertically and horizontally, in the lower stratosphere.
1. I demonstrate that the isotopic composition of water vapor can diagnose rapid convectivetransport across the tropopause. I use data from the space shuttle- and balloon-borneFourier transform solar occultation spectrometers ATMOS (Atmospheric TraceMOlecule Spectrometer) and Mark-IV to reconstruct the mean deuterium isotopic compositionof water entering the stratosphere. Initial δD is -670 per mil (33% of deuteratedwater retained). I construct a one-dimensional model simulating isotopic fractionationduring 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 ofthe uppermost troposphere. The observed stratospheric δD is then far heavier than modeleddepletions under most conditions. I conclude that the observations can be matchedonly by substantial evaporation of lofted condensate or by ascent in highly-supersaturatedconditions, and infer that mean stratospheric air must have experienced rapid convectionto at least near-tropopause altitudes. This study serves to demonstrate that the isotopiccomposition of water vapor is a valuable tracer that can be used to constrain mechanismsof stratosphere-troposphere transport.
2. I use in-situ tunable diode laser measurements of CO, H_2O, and N_2O taken overFairbanks, AK to show rapid transport by streamers of air in the lower stratosphere. Iwas 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 latitudein 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 contradictionto 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 isstrongly seasonal, in agreement with previous trajectory results, but with a longer periodof activity. I conclude that the tropopause transition layer extends to 420 K Ɵ, and thattransport 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 aircraftplatforms. I initiated and led an effort to design and build an instrument capableof 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 onenear-infrared laser sources. Light is injected into a 94-pass Herriott cell for a total of 94meters 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 isotopomersof water vapor, and methane, are detected in a single scan, allowing improvedaccuracy 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 canprovide a versatile tool for t racer measurements in the tropopause region.
