Detection of stratospheric ozone intrusions by windprofiler radars

Abstract

Stratospheric ozone attenuates harmful ultraviolet radiation and protects the Earth's biosphere. Ozone is also of fundamental importance for the chemistry of the lowermost part of the atmosphere, the troposphere. At ground level, ozone is an important by-product of anthropogenic pollution, damaging forests and crops, and negatively affecting human health. Ozone is critical to the chemical and thermal balance of the troposphere because, via the formation of hydroxyl radicals, it controls the capacity of tropospheric air to oxidize and remove other pollutants. Moreover, ozone is an important greenhouse gas, particularly in the upper troposphere. Although photochemistry in the lower troposphere is the major source of tropospheric ozone, the stratosphere-troposphere transport of ozone is important to the overall climatology, budget and long-term trends of tropospheric ozone. Stratospheric intrusion events, however, are still poorly understood. Here we introduce the use of modern windprofiler radars to assist in such transport investigations. By hourly monitoring the radar-derived tropopause height in combination with a series of frequent ozonesonde balloon launches, we find numerous intrusions of ozone from the stratosphere into the troposphere in southeastern Canada. On some occasions, ozone is dispersed at altitudes of two to four kilometres, but on other occasions it reaches the ground, where it can dominate the ozone density variability. We observe rapid changes in radar tropopause height immediately preceding these intrusion events. Such changes therefore serve as a valuable diagnostic for the occurrence of ozone intrusion events. Our studies emphasize the impact that stratospheric ozone can have on tropospheric ozone, and show that windprofiler data can be used to infer the possibility of ozone intrusions, as well as better represent tropopause motions in association with stratosphere-troposphere transport.

A re-evaluated Canadian ozonesonde record: measurements of the vertical distribution of ozone over Canada from 1966 to 2013

“…For example, ozonesonde measurements show impact on near-surface ozone concentrations of intrusions of ozone from the lower stratosphere (e.g. He et al, 2011;Hocking et al, 2007) and the inter-continental transport of tropospheric ozone and its precursor species (Oltmans et al, 2006(Oltmans et al, , 2010. Canadian ozonesondes have also provided essential information on the nature of Arctic stratospheric ozone loss (Manney et al, 2011;Fioletov et al, 1997;Kerr et al, 1993), of Arctic surface depletion events Bottenheim et al, 2002), and of the global circulation of ozone (Lin et al, 2015;Bönisch et al, 2011;Pan et al, 2009), as well as of tropospheric sources and budgets (Emmons et al, 2015;Parrington et al, 2012;Walker et al, 2010Walker et al, , 2012Macdonald et al, 2011;Thompson et al, 2007;Tarasick et al, 2007).…”

Study of Stratosphere‐troposphere exchange events of ozone in India and Greece using ozonesonde ascents

“…Diffusive and convective transports cause exchange of air between the boundary layer and the free troposphere, carrying ozone and its precursors to higher altitudes (Roelofs and Lelieveld, 2000). An important and significant natural source of ozone in the troposphere is downward transport of stratospheric ozone (Holton et al, 1995;Hocking et al, 2007), called STE of ozone and is related to the stratospheric circulation called the Brewer-Dobson circulation. The mechanisms leading to STE from the lowermost stratosphere to the troposphere are tropopause folds, cut-off lows and quasi adiabatic transport along isentropic surfaces (Vaughan, 1988;Holton et al, 1995).…”

Transport and Distribution of Short-lived Climate Pollutants in the Himalaya

“…Between December 29, 2015 and January 7, 2016, twenty nine ozonesondes were launched from the city of Pokhara (28.12°N, 83.58°E, 800 m asl, population of 400,000) situated in a valley about 30 km from the Himalayan range (Table 1 altitude from ±5% to ±10% and precision varied from ±3% to ±5% (Smith, et al, 2007). Pressure offsets were corrected using the geopotential height and GPS altitude from the radiosonde.…”

“…The maximum temperature in Pokhara ranges from 13.2 °C in January to 25. altitude from ±5% to ±10% and precision varied from ±3% to ±5% (Smith, et al, 2007). Pressure offsets were corrected using the geopotential height and GPS altitude from the radiosonde.…”

“…Radiosonde observations over the Tibetan Plateau (TP) reveal a high frequency (~80% of all profiles) of multiple thermal tropopauses during winter . Stable potential temperature (hereafter referred to as theta) and low RH over the Tibetan Plateau during winter can potentially enhance the downward transport of O3 rich dry eddies of stratospheric origin as a part of BrewerDobson circulation (Chen et al, 2013;Bracci et al, 2012;Hocking et al, 2007). Model calculations, surface observations, and back trajectories suggest that stratospheric intrusions in the Himalayan region occur most frequently during winter and early spring Chen et al 2013).…”