HR: 1340h
AN: A43A-0868    [Abstracts]
TI: Mesospheric HCN, N₂O, and CO: Measurements and Implications for Dynamics and Chemistry
AU: * Sandor, B J
EM: sandor@spacescience.org
AF: Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, United States
AU: Clancy, R T
EM: clancy@spaceScience.org
AF: Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, United States
AB: We present contemporaneous, colocated, ground-based observations of N₂O (upper stratosphere), HCN (lower mesosphere), and CO (upper mesosphere). Of these, 50-70 km HCN data are unique, and of interest for understanding lower mesospheric chemistry. Reaction with OH is a primary sink for HCN, suggesting HCN abundances may be useful in studies of lower mesospheric hydrogen (HO_x) chemistry. Measured increases with altitude of both HCN [Jaramillo et al., 1988] and CH₃CN [Livesey et al., 2001; 2004] in the stratosphere are not understood, in that neither has a known stratospheric source. Chemical conversion of HCN to/from CH₃CN is not supported by model studies [Brasseur et al., 1985], but the CN bond in each molecule suggests that studying the chemistry of one will shed light on the other. Global measurements of stratospheric N₂O and upper mesospheric CO have been used in many previous studies as indicators of large scale atmospheric transport, N₂O moving upward from the troposphere, and CO downward from the thermosphere. HCN is analogous to N₂O, in that each is produced in the troposphere, then transported upward as (nearly) inert species, until reaching an altitude where photochemical destruction begins. Because HCN persists to higher altitudes than does N₂O, it is a candidate for studies of large scale lower mesospheric transport, analogous to N₂O in studies of the statosphere. We compare local N₂O, HCN, and CO abundances for what they may indicate about bulk transport across the full altitude range 40-100 km, and discuss HCN as a candidate for future global studies of lower mesospheric transport. Ground-based observations of the 266 GHz HCN, 226 GHz N₂O, and 230 GHz CO lines were made over the period 1998-2002, using the 12-meter telescope at Kitt Peak AZ [a facility of NSF, operated by the Univ. of Arizona Steward Observatory, under loan agreement with NRAO]. These are passive observations of rotational LTE emission lines. Frequency switching is used to remove the lower atmospheric background, and altitudes of the measured species are derived from shape of each pressure broadened line.
DE: 0340 Middle atmosphere: composition and chemistry
DE: 0341 Middle atmosphere: constituent transport and chemistry (3334)
DE: 3319 General circulation (1223)
DE: 3332 Mesospheric dynamics
DE: 3334 Middle atmosphere dynamics (0341, 0342)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting