Tropospheric O3 distribution over the Indian Ocean during spring 1995 evaluated with a chemistry-climate model

An analysis of tropospheric O 3 over the Indian Ocean during spring 1995 is presented based on O 3 soundings and results from the chemistry-general circulation model ECHAM (European Centre Hamburg Model). The ECHAM model is nudged towards actual meteorology using ECMWF analyses, to enable a direct comparison between model results and in situ observations. The model reproduces observed CO levels in different air mass categories. The model also reproduces the general tendencies and the diurnal variation in the observed surface pressure, although the amplitude of the diurnal variation in the amplitude is underestimated. The model simulates the general O 3 tendencies as seen in the sonde observations. Tropospheric O 3 profiles were characterized by low surface concentrations (< 10 ppbv), mid-tropospheric maxima (60-100 ppbv, between 700-250 hPa) and upper-tropospheric minima (< 20 ppbv, between 250-100 hPa). Large-scale upper tropospheric O 3 minima were caused by convective transport of O 3 -depleted boundary layer air in the Inter Tropical Convergence Zone (ITCZ). Similarly, an upper tropospheric O 3 minimum was caused by cyclone Marlene south of the ITCZ. The mid-tropospheric O 3 maxima were caused by transport of polluted African air. The ECHAM model appears to overestimate surface O 3 levels, and does not reproduce the diurnal variations very well This could be related to unaccounted multiphase O 3 destruction mechanisms involving low level clouds and aerosols, and missing halogen chemistr

Ozonesonde Observations in the Equatorial Eastern Pacific : The Shoyo-Maru Survey

We have conducted GPS radiosonde and ozonesonde observations on board the research vessel "Shoyo-Maru" in the equatorial eastern Pacific. These observations took place in September and October 1999 as a part of the Soundings of Ozone and Water in the Equatorial Region (SOWER)/Pacific mission. The mean profile of ozone is similar to that for the dry season (September to October) at San Cristóbal, Galápagos (0.9°S, 89.6°W ) located in the equatorial eastern Pacific. The mean tropospheric ozone concentration is about 40 ppbv with a maximum in the mid-troposphere. Compared with the mean profile during the dry season at Watukosek, Indonesia (7.5°S, 112.6°E), this mid-tropospheric maximum is larger, and a sharp increase of ozone below the tropopause begins at a lower altitude for the Shoyo-Maru pro fi le. We frequently observed layers in which ozone and humidity are highly anti-correlated. These layers have vertical scales from several kilometers to several hundred meters. Horizontal scales of these layers are roughly 1000 km, which may correspond to time scales of about 2 days, since the vessel sailed about 500 km/day. These layers are related to northerly winds, which bring in wet and ozone-poor air from the inter-tropical convergence zone situated in the northern side of the main cruise track. Similar layers were observed in ozone pro fi les at San Cristóbal and Watukosek, mostly during the dry season, suggesting the existence of layers advected without vertical mixing

Ozonesonde climatology between 1995 and 2009: description, evaluation and applications

Abstract. An ozone climatology based on ozone soundings for the last 15 years has been constructed for model evaluation and comparisons to other observations. Vertical ozone profiles for 41 stations around the globe have been compiled and averaged for the years 1980–1994 and 1995–2009. The climatology provides information about the median and the width of the ozone probability distribution function, as well as interannual variability of ozone between 1995 and 2009, in pressure and tropopause-referenced altitudes. In addition to single stations, regional aggregates are presented, combining stations with similar ozone characteristics. The Hellinger distance is introduced as a new diagnostic to compare the variability of ozone distributions within each region and used for model evaluation purposes. This measure compares not only the mean, but also the shape of distributions. The representativeness of regional aggregates is discussed using independent observations from surface stations and MOZAIC aircraft data. Ozone from all of these data sets show an excellent agreement within the range of the interannual variability, especially if a sufficient number of measurements are available, as is the case for West Europe. Within the climatology, a significant longitudinal variability of ozone in the troposphere and lower stratosphere in the northern mid- and high latitudes is found. The climatology is used to evaluate results from two model intercomparison activities, HTAP for the troposphere and CCMVal2 for the tropopause region and the stratosphere. HTAP ozone is in good agreement with observations in the troposphere within their range of uncertainty, but ozone peaks too early in the Northern Hemisphere spring. The strong gradients of ozone around the tropopause are less well captured by many models. Lower stratospheric ozone is overestimated for all regions by the multi-model mean of CCMVal2 models. Individual models also show major shortcomings in reproducing the shape of ozone probability distribution functions in various regions and different altitudes, which might have significant implications for the radiative budgets in those models. </jats:p