Sudden increase in the total ozone density due to secondary ozone peaks and its effect on total ozone trends over Korea

Abstract

Total column ozone (TCO) amounts observed by the Dobson spectrophotometer from 1985 to 2008 in Seoul and vertical ozone profiles obtained with the ozonesonde from 1995 to 2007 in Pohang were used to investigate the relationship between the occurrence of Secondary Ozone Peak (SOP) in the Upper Troposphere/Lower Stratosphere (UT/LS) layer and the enhancement in TCO over the Korean Peninsula. Based on Hybrid Single-Particle, Lagrangian Integrated Trajectory (HYSPLIT) simulations, the advection of a northern mid-latitudinal ozone-rich airmass from the northwest is closely related to SOP occurrences, which consequently lead to enhancements in the amount of ozone in both the UT/LS and the total column at stations in Korea. In addition, both the frequency of the northwesterly advection and the northern mid-latitudinal ozone amount are revealed to affect the amount of ozone in the UT/LS and total column by up to 7 DU. The relationship between the SOP occurrence frequency and the long-term TCO trend was investigated with observed data collected in all seasons. The UT/LS ozone enhancements, which are largely affected by SOP occurrences, are considered to be positively related to the TCO trend from 1985 to 2008 over the Korean Peninsula.

Introduction

Stratospheric ozone plays an important role in absorbing UV radiation from the sun and preserving human health and global biological systems. Furthermore, ozone is an important heating source in the stratosphere (Manabe and Moller, 1961). Since the discovery of the ozone hole in Antarctica (Chubachi, 1984, Farman et al., 1985), the stratospheric ozone trend and its recovery have been one of the most important global issues in the fields of climate and environmental science. For this reason, extensive studies of ozone have been carried out in order to evaluate the global ozone variation with data measured both at ground and satellite-based platforms (e.g., Stolarski et al., 1991, Fioletov et al., 2002). These investigations have also focused on local (e.g., Cho et al., 1994, Cho et al., 2003, Tarasick et al., 1995, Kim et al., 2005) and global ozone trends (e.g., Fishman et al., 1990, Fioletov et al., 2002, Ziemke et al., 2005).

Total column ozone variations are known to be associated with the changes in solar activity (e.g., Angell, 1989, Zerefos et al., 2001, Harris et al., 2003) and natural oscillations (e.g., Angell and Kroshover, 1973, Rood, 1986). After removing these effects, the trend of residuals which were derived from the total column ozone (TCO) was considered to be the ozone layer trend (e.g., Reinsel et al., 1981, Reinsel and Tiao, 1987). However, tropospheric ozone has recently been found to be affected by natural oscillations such as the arctic oscillation (Creilson et al., 2005), and the Stratosphere-Troposphere Exchange (STE) (Kim et al., 2002) in the mid-latitude regions. A previous investigation by Kim et al. (2002) revealed that STE of ozone over Korea is associated with upper trough and surface high pressure system, where downward fluxes of ozone can occur between 100 and 500 h Pa. STE of ozone has a large influence on the vertical ozone profile in the upper troposphere. Hwang et al. (2007) suggested that the subsidence of stratospheric airmass is related to the formation of the Secondary Ozone Peak (SOP) in the Upper Troposphere/Low Stratosphere (UT/LS) over East Asia. Rossby wave breaking induces the intrusion of stratospheric (or tropospheric) ozone, which causes one or several ozone peaks in ozone profiles (Lemoine, 2004).

Hwang et al. (2007) reported that the characteristics of SOP, defined as the maximum in the ozone profile limited to the altitude range of 9–16 km, have the peak with the higher partial pressure in the case of more than one maximum, and found that the frequency of SOP occurrence increased from 1995 to 2004 based on Halogen Occultation Experiment (HALOE) and ozonesonde observations in Pohang, Korea. Using ozonesonde and SAGE II data since 1969 and 1985, respectively, Lemoine (2004) found that two types of advection resulted in SOP in the UT/LS. The highest SOP occurrence frequency was observed during the period from March through May in Uccle, Europe. It was revealed that the SOP occurrence frequency was highly correlated with the seasonal cycle of TCO in Uccle. Lemoine (2004) used data from February to May to show that STE has a large influence on high-latitudinal TCO changes and also potentially affect long-term ozone trends. However, the effect of SOP formation on TCO trends for East Asia has yet to be investigated.

In the present work, the investigation was conducted, for the first time, to identify the relationship between TCO trends and SOP occurrence in the UT/LS layer at stations in the Korean Peninsula by quantifying enhanced amounts of TCO due to SOP events over a long period. In addition, the mechanisms of SOP formation are examined based on Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) simulations. The effects of the SOP occurrence frequency on the seasonal characteristics of UT/LS ozone and the TCO amount are also investigated.