Articles | Volume 15, issue 13
Research article
08 Jul 2015
Research article |  | 08 Jul 2015

Characterisation of J(O1D) at Cape Grim 2000–2005

S. R. Wilson

Abstract. Estimates of the rate of production of excited oxygen atoms due to the photolysis of ozone (J(O1D)) have been derived from radiation measurements carried out at Cape Grim, Tasmania (40.6° S, 144.7° E). The individual measurements have a total uncertainty of 16 % (1σ). These estimates agree well with model estimates of clear-sky photolysis rates. Observations spanning 2000–2005 have been used to quantify the impact of season, clouds and ozone column amount. The annual cycle of J(O1D) has been investigated via monthly means. These means show an interannual variation (monthly standard deviation) of 9 %, but in midsummer and midwinter this reduces to 3–5 %. Variations in solar zenith angle and total column ozone explain 86 % of the observed variability in the measured photolysis rates. The impact of total column ozone, expressed as a radiation amplification factor (RAF), is found to be ~ 1.53, in agreement with model estimates. This ozone dependence explains 20 % of the variation observed at medium solar zenith angles (30–50°). The impact of clouds results in a median reduction of 30 % in J(O1D) for the same solar zenith angle range. Including estimates of cloudiness derived from long-wave radiation measurements resulted in a statistically significant fit to observations, but the quality of the fit did not increase significantly as measured by the adjusted R2.

Short summary
Measurements of the photolysis rates which drive production of OH from ozone are reported for Cape Grim, a "clean-air" site in the southern midlatitudes. This remote maritime site sits in the Southern Ocean, a region of the globe which is little studied. From the 6 years of data the dependence of this photolysis on solar zenith angle and stratospheric ozone is determined. Included with the reported values is an estimate of the uncertainties in these measurements.
Final-revised paper