OH column abundance over Table Mountain Facility, California: AM‐PM diurnal asymmetry

Abstract

Observations of the OH column abundance have been made by the Fourier Transform Ultraviolet Spectrometer at the JPL Table Mountain Facility (TMF) near Los Angeles since July 1997. In the January 1998–December 2003 data set we used five OH lines to derive the OH column abundance in the atmosphere. This data set was used to quantify the OH morning/afternoon asymmetry (AMPMDA). An analysis of summer and winter data showed that the daily OH maximum occurred 26–36 minutes after solar transit. This phase lag appears to be the primary reason why OH in the afternoon is larger than at corresponding solar zenith angles in the morning throughout the year. A simple heuristic model suggests that the asymmetry is a direct consequence of the finite lifetime of OH. Comparison of the TMF data with earlier results from Fritz Peak Observatory, Colorado, by Burnett et al. reveals significant differences in the behavior of the AMPMDA between the two sites.

In situ observations of new particle formation in the tropical upper troposphere: the role of clouds and the nucleation mechanism

“…The system of differential equations for the aerosol concentrations is integrated with the VODE (Variable-coefficient Ordinary Differential Equation) solver (Brown et al, 1989). In summary, based on 1. the FLEXTRA derived estimates of temperature, relative humidity, and pressure, along a backward trajectory of air mass transport, 2. estimates of available OH (which is parameterized as a cosine of the solar zenith angle, in approximation of the diurnal cycle of OH in the troposphere after Li et al, 2005;Wang et al, 2008) and of pre-existing aerosol surface area, 3. cosmic ray induced ion production rates, calculated by a model of energetic particle transport in the Earth's atmosphere (O'Brien, 2005), which accounts for variations in cosmic ray intensity as function of latitude and altitude, 4. initial SO 2 mixing ratios of 50 pptv or 500 pptv, representing estimated minimum and maximum levels, MAIA calculates the number of aerosol particles produced in a NPF event (per cubic centimeter and second) as a function of daytime along particular air parcel trajectories intersecting with the M-55 Geophysica flight path. The diameter size range of nucleation mode particles analyzed from the MAIA simulations coincides with the diameter size range of nucleation mode particles measured by COPAS.…”

Variability of the nighttime OH layer and mesospheric ozone at high latitudes during northern winter: influence of meteorology

“…Because of the short lifetime of OH, the major variability is connected to the diurnal cycle, with maximum OH abundance roughly at noon and values very low at nighttime. This maximum moves slightly towards the afternoon with increasing altitude due to the longer chemical lifetime of OH (Li et al, 2005). Stratospheric annual and semiannual oscillations of OH are of minor importance (a few percent) and mainly follow the annual trend of ozone, water vapour and ultraviolet intensity (e.g., Canty and Minschwaner, 2002).…”

Hydroxyl in the stratosphere and mesosphere – Part 1: Diurnal variability

“…Ground-based OH column measurements also generally show larger column amounts in the afternoon compared with the morning. Mills et al (2003) found a 6% asymmetry at 45 • SZA (afternoon larger than morning) from OH column measurements at the Table Mountain Facility, which Li et al (2005) showed was due to a ∼30 min phase lag about local noon arising from the finite lifetime of HO x in the upper stratosphere and mesosphere. No seasonal differences were found in the diurnal asymmetry (Li et al, 2005).…”

“…Mills et al (2003) found a 6% asymmetry at 45 • SZA (afternoon larger than morning) from OH column measurements at the Table Mountain Facility, which Li et al (2005) showed was due to a ∼30 min phase lag about local noon arising from the finite lifetime of HO x in the upper stratosphere and mesosphere. No seasonal differences were found in the diurnal asymmetry (Li et al, 2005). On the other hand, Burnett et al (1989) obtained a similar mean OH column asymmetry favoring afternoon (7%) from Fritz Peak Observatory, but they also found large seasonal variations (∼27%) in the amplitude of the diurnal asymmetry.…”