Hydroxyl in the stratosphere and mesosphere – Part 1: Diurnal variability 1Department of Physics, New Mexico Institute of Mining and Technology, Socorro, USA
02 Feb 2011
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
3University of Edinburgh, Edinburgh, UK
Received: 09 Aug 2010 – Published in Atmos. Chem. Phys. Discuss.: 28 Sep 2010Abstract. Diurnal variations in hydroxyl (OH) in the stratosphere and mesosphere are
analyzed using measurements from the Aura Microwave Limb Sounder (MLS). The
primary driver for OH diurnal variations is the ultraviolet actinic flux
that initiates the photochemical production of reactive hydrogen species.
The magnitude of this flux is governed largely by changes in solar zenith
angle (SZA) throughout the day, and OH diurnal variations are well approximated
by an exponential function of the secant of SZA. Measured OH concentrations are
fit to a function of the form exp[−βsec(SZA)], where the parameter
β is a function of altitude. We examine the magnitude of β and
show that it is related to the optical depths of ultraviolet absorption by
ozone and molecular oxygen. Values of β from SLIMCAT model
simulations show the same vertical structure as those from MLS and the
average level of agreement between model and measurements is 6%. The
vertical profile of β from MLS can be represented by a simple
analytic formulation involving the ozone and water vapor photodissociation
rates. This formulation is used to infer the altitude dependence of the
primary production mechanisms for OH: the reaction of excited-state atomic
oxygen with water vapor versus the direct photodissociation of water vapor.
Revised: 19 Jan 2011 – Accepted: 20 Jan 2011 – Published: 02 Feb 2011
Citation: Minschwaner, K., Manney, G. L., Wang, S. H., and Harwood, R. S.: Hydroxyl in the stratosphere and mesosphere – Part 1: Diurnal variability, Atmos. Chem. Phys., 11, 955-962, doi:10.5194/acp-11-955-2011, 2011.