Sea-land total ozone differences from TOMS: GHOST effect

Mean global TOMS (Total Ozone Mapping Spectrometer) ozone data, averaged in time, reveals persistent year-to-year differences in total ozone between c ontinents and oceans. This feature has been named GHOST (global hidden ozon e structures from TOMS). During Northern Hemisphere summer it can be seen w ithin the latitudinal belt between 40 degreesS and 50 degreesN. The most pr onounced land-sea difference in total ozone with values of up to 18 Dobson units is observed between latitudes 35 degreesN and 40 degreesN. The gradie nts associated with the coastlines are stronger in summer, when transient p lanetary wave activity decreases, but is still observable in the winter per iod. The Iberian Peninsula has been selected as a case study to examine the effect of each possible contribution quantitatively. It has been found tha t the truncation of the lower tropospheric column due to the topography exp lains 26% of the land-sea differences, while permanent differences in tropo pause height distribution can account for a further 8%. After these "correc tions" other structures remain. Additional contributions due to the TOMS to tal ozone retrieval algorithm artifact (absorbing aerosol distribution) are also explored. After considering the optical depths and absorbance of aero sols above the Iberian Peninsula, the remaining 66% is compatible with the presence of UV-absorbing aerosols whose effects may not be correctly accoun ted for in the TOMS retrieval algorithm.