The Lagrangian structure of ozone mini-holes and potential vorticity anomalies in the Northern Hemisphere

Abstract

Abstract. An ozone mini-hole is a synoptic-scale area of strongly reduced column total ozone, which undergoes a growth-decay cycle in association with baroclinic weather systems. The tracks of mini-hole events recorded during the TOMS observation period over the Northern Hemisphere provide a database for building anomaly fields of various meteorological parameters, following each mini-hole center in a Lagrangian sense. The resulting fields provide, for the first time, a complete mean Lagrangian picture of the three-dimensional structure of typical ozone mini-holes in the Northern Hemisphere. Mini-holes are shown to be associated with anomalous warm anticyclonic flow in the upper troposphere and cold cyclonic anomalies in the middle stratosphere. Ascending air columns occur upstream and descent downstream of the mini-hole centers. Band-pass filtering is used to reveal the transient synoptic nature of miniholes embedded within larger scale circulation anomalies. Significant correlations between ozone and Ertel's potential vorticity on isentropes (IPV) both near the tropopause and in the middle stratosphere are shown and then utilized by reconstructing the Lagrangian analysis to follow local IPV anomalies instead of ozone minima. By using IPV as a proxy for ozone, the geopotential anomaly dipolar structure in the vertical characteristic of mini-holes is shown to result from a superposition of two largely independent dynamical components, stratospheric and tropospheric, typically operating on different time scales. Hence, ozone mini-holes may be viewed primarily as phenomena of coincidence.

Atmospheric Blocking Signatures in Total Ozone and Ozone Miniholes

“…Some authors apply absolute fixed TOC thresholds lower than 300 DU , 225 DU (Petzoldt 1999;Brö nnimann and Hood 2003) or 220 DU (Bojkov and Balis 2001). Alternative definitions employ relative values such as the standard deviation (Koch et al 2005;Antó n et al 2008) or timevariant thresholds lower than the monthly or the annual mean by some quantity between 70 and 80 DU (James 1998;Krzyscin 2002;Iwao and Hirooka 2006). Additional considerations are mandatory regarding the location and characteristic scales of ozone miniholes.…”

“…These transient and localized events of reduced ozone were called ozone miniholes (Newman et al 1988). They are frequently observed from late autumn to early spring at extratropical latitudes of both hemispheres (e.g., Peters et al 1995;James 1998;Hood et al 2001), in close spatial correlation to the storm-track region and the jet stream (Orsolini et al 1998). Though their scale and duration are considerably smaller than those of the polar ozone hole, ozone miniholes can enhance UV radiation over populated areas (e.g., Semane et al 2002;Orsolini et al 2003;Antó n et al 2007Antó n et al , 2008 and hence, can cause adverse effects on human health and ecosystems, particularly at low to middle summer latitudes.…”

“…Recent studies suggest an increasing frequency of winter-spring ozone miniholes over the Euro-Atlantic sector since at least the 1980s, particularly during the 1990s (e.g., James 1998;Hood et al 1999;Bojkov and Balis 2001), which may account for up to one-third of the observed TOC trend in the 408-658N latitudinal belt (Reid et al 2000). Regional dynamical changes seem to have contributed partially to this increase (Brö nnimann and Hood 2003), in agreement with the effects of the North Atlantic Oscillation (NAO) on the ozone minihole frequency (Orsolini and Limpasuvan 2001).…”

A model study of the January 2006 low total ozone episode over Western Europe and comparison with ozone sonde data

“…Taking the =450 K level assures that in the lower altitude compartment, which comprised certainly the lower stratosphere and not yet the mid-stratosphere, the influences of the lifting of the tropopause and the advection of low-latitude air masses were included and that in the upper altitude compartment the effect of the polar vortex displacement was included. In addition, James and Peters (2002) reported the average limit of the influence of the polar vortex during low total ozone epidsodes to be around 70 hPa over Western and Middle Europe.…”

“…Under such conditions, a displacement of the polar vortex will lead to low total ozone columns over regions normally not affected by severe chemical ozone destruction in the stratosphere. These two dynamic processes can be superimposed, leading to severe low total ozone column values (Petzoldt, 1999;James and Peters, 2002). In-situ chemical ozone destruction in the column within the timescale of such very low total ozone episodes is assumed to be negligible (e.g., Hood et al, 2001).…”