Multiple subtropical stratospheric intrusions over Reunion Island: Observational, Lagrangian, and Eulerian numerical modeling approaches

Abstract

Signatures of multiple stratospheric intrusions were observed on simultaneous and collocated ozone and water vapor profiles retrieved by lidars and radiosondes at the Maïdo Observatory, Reunion Island (21°S, 55°E, 2160 m above sea level), during MAïdo LIdar Calibration CAmpaign in April 2013. A singular structure of the ozone vertical profile with three peaks (in excess of 90 ppbv, at ~8, ~10, and ~13 km altitude) embedded in a thick dry layer of air suggested stratospheric intrusions with multiple origins. The hypothesis is corroborated by a synoptic analysis based on re‐analyses. European Centre for Medium‐Range Weather Forecasts ERA‐Interim temporal series associated with 5 days Lagrangian back trajectories initialized on each ozone peak allows to capture their stratospheric origin. The ozone peak at the lowest altitude is associated with an irreversible tropopause folding process along the polar jet stream during an extratropical cutoff low formation. Simultaneous lidar water vapor profiles of this peak show that the anticorrelation with ozone has been removed, due to mixing processes. Back trajectories indicate that the two other ozone peaks observed at higher altitudes are associated with the dynamics of the subtropical jet stream and the lower stratosphere. The observations confirm the recent stratospheric origins. The highest ozone peak is explained by the horizontal distribution of the intrusion. Use of a Lagrangian Reverse Domain Filling model and of the Meso‐NH Eulerian mesoscale model with a passive stratospheric tracer allow to further document the stratosphere‐troposphere transport processes and to describe the detailed potential vorticity and ozone structures in which are embedded in the observed multiple stratospheric intrusions.

Long-Range Transport of Water Channelized through the Southern Subtropical Jet

“…In those three areas, the jet was deflected into two parts: a weak one towards the north, reconnecting the jet afterward, and a stronger branch reconnecting the jet after a large southern loop. Such synoptic context is similar to the situation of the multiple stratospheric intrusion events in April 2013 above the Indian Ocean, where some isentropic transport was associated with Rossby wave breakings guided by both subtropical and polar jet streams [33]. The ECMWF ERA-Interim potential vorticity (PV) field at the altitude of the cirrus cloud on 1 June 2007 between the potential temperature level of 330 and 350 K ( Figure 5), provided by the LACYTRAJ model (Figure 6b,c), reveals that when the jet is deflected abruptly, filaments of tropical air are generated that may lead to irreversible transport.…”

Validation of the Water Vapor Profiles of the Raman Lidar at the Maïdo Observatory (Reunion Island) Calibrated with Global Navigation Satellite System Integrated Water Vapor

“…The abilities of the Lidar1200 has already been successfully used to study atmospheric processes such as stratosphere-troposphere exchanges [39,60]. The data of the Lidar1200, used alone and with other measurements will bring new results on the characterization of water vapor in the troposphere, the monitoring of the water vapor in the UT/LS, the study of the exchange processes between the stratosphere and the troposphere and the validation of satellite measurements.…”

The isotopic composition of near‐surface water vapor at the Maïdo observatory (Reunion Island, southwestern Indian Ocean) documents the controls of the humidity of the subtropical troposphere

“…Several MESO‐NH simulations have been successfully performed over Reunion Island at different resolutions to study cyclone formation or pollutant transport [ Tulet and Villeneuve , ; Lesouëf et al ., , ; Jolivet et al ., ; Durand et al ., ; Sivia et al ., ; Vérèmes et al ., ]. The model was set up with four two‐way nested domains having horizontal grid spacing of 16, 8, 2, and 0.5 km and grid size of 200 × 200, 128 × 128, 128 × 128, and 192 × 160 points, respectively.…”

“…Several MESO-NH simulations have been successfully performed over Reunion Island at different resolutions to study cyclone formation or pollutant transport [Tulet and Villeneuve, 2011;Lesouëf et al, 2011Lesouëf et al, , 2013Jolivet et al, 2013;Durand et al, 2014;Sivia et al, 2015;Vérèmes et al, 2016] First, we will use the FLEXPART (FLEXible PARTicle dispersion model) Lagrangian particle dispersion model to assess air masses origin and transport pathways. We will focus on May 2015 to take advantage of the Maïdo ObservatoRy Gaz and Aerosols Ndacc Experiment (MORGANE) field campaign that started in May [Duflot et al, 2017].…”