Fast descent routes from within or near the stratosphere to the surface at Fukuoka, Japan, studied using <sup>7</sup>Be measurements and trajectory calculations

Abstract

Abstract. By using high concentrations of 7Be as an indicator, we clarify fast descent routes from within or near the stratosphere to Earth's surface, with the study site being in Fukuoka, Japan. Most routes arise from high latitudes through the following processes. First, the descent associated with a tropopause fold occurs, followed by southward movement with slow descent at the rear side of a strong trough. Because this motion occurs along an isentropic surface, the descending air parcels nearly conserve the potential temperature. As an extension, a strong descent associated with a sharp drop in the isentropic-surface height occurs at the southern edge of the trough; this transports air parcels to low altitudes. This process involves irreversible phenomena such as filamentation and cutoff of potential vorticity. Finally, upon meeting appropriate near-surface disturbances, parcels at low altitudes are transported to Earth's surface.In some cases, parcels descend within midlatitudes. In such routes, because the potential temperature is much higher at high altitudes than at low altitudes, descent with conservation of the potential temperature is impossible, and the potential temperature decreases along the trajectories through mixing.The prevalence of the high-latitude route is explained as follows. In the midlatitude route, because parcels at high and relatively low altitudes mix, the high concentrations of 7Be included in high-altitude parcels are difficult to maintain. Therefore, for parcels to arrive at low altitudes in the midlatitude while maintaining high concentrations of 7Be, i.e., conserving the potential temperature, their area of origin should be high altitudes in high latitudes where the potential temperature is almost the same as that in the arrival area.In spring, tropopause folds are frequent in high latitudes, disturbances in the southward transport of parcels are strong, and disturbances occur by which parcels descend to the surface. Therefore, high concentrations of 7Be occur most frequently in spring.

Influence of stratospheric air masses on radiotracers and ozone over the central Mediterranean

“…Figures a–d show the mean height of the back trajectories when high values (higher than the 75th percentile) of 7 Be, 7 Be/ 210 Pb, and O 3 (the same analysis for 210 Pb is reported in the supporting information) are registered at CMN. This analysis clearly shows that high‐altitude back trajectories originating in the lower stratosphere come from the Arctic (where the tropopause is also lower due to limited convective overturning) and North America/Atlantic regions, with special strength over Greenland, whereas the lowest trajectories are coming from the lowest‐latitude regions, in agreement with Itoh and Narazaki []. It is found that high 7 Be/ 210 Pb values always match the top height in the back trajectories, pointing out once more the importance of the 7 Be/ 210 Pb activity ratio as a tracer of vertical motions in connection with STE events.…”

Modeling stratospheric intrusion and trans-Pacific transport on tropospheric ozone using hemispheric CMAQ during April 2010 – Part 1: Model evaluation and air mass characterization for stratosphere–troposphere transport

“…The global model simulation assuming the tripling of Asian anthropogenic emissions from 1985 to 2010 indicated an increase in O 3 mixing ratios by 2-6 ppbv in the western US and by 1-3 ppbv in the eastern US on a monthly mean ba-sis, with the maximum effect occurring during April-June; this increase was suggested to more than offset the benefits of 25 % domestic reduction in the western US (Jacob et al, 1999). Based on the Emission Database for Global Atmospheric Research (EDGAR) version 4.3.1, anthropogenic emissions of NO x and VOCs in China are estimated to have increased by 3.2 and 2.1 times during 1985, respectively (Crippa et al, 2016, which is generally consistent with the assumption by Jacob et al (1999).…”

The influence of mid-latitude cyclones on European background surface ozone

“…However, the direct connection between STT and peaks in groundlevel O 3 observations are generally infrequent, with only a small fraction of STT trajectories descending below the mid-troposphere (Viezee et al, 1983;Derwent et al, 1998;Eisele et al, 1999;Stohl, 2001;Škerlak et al, 2014). Air from the free troposphere is largely limited to daytime entrainment into the lowest layer of the atmosphere as the planetary boundary layer (PBL) height increases (e.g., Itoh and Narazaki, 2016;Ott et al, 2016); however, the ability for O 3 -rich air to reach the surface depends on a complex array of factors including the diurnal cycle (Itoh and Narazaki, 2016;Langford et al, 2009Langford et al, , 2012Ott et al, 2016) and the seasonal cycle of the PBL height (Langford et al, , 2017, the presence of convective mixing (Thompson et al, 1994;Eisele et al, 1999;Langford et al, 2017), and the elevation of the monitoring station, which if located within the free troposphere, especially with the nighttime collapse of the PBL, can experience direct STT (Langford et al, , 2017. The influence of the stratospheric air, although weaker by the time the air reaches the surface (Monks, 2000), can last longer in the mid-to lower troposphere if the O 3 -rich air becomes entrained in high-pressure systems behind the surface cold front and continues to subside (Danielsen, 1980;Davies and Schuepbach, 1994;Cooper et al, 2004b).…”