The Origin of Tropospheric Air Masses and related transport processes infer from FTIR measurements and Model Simulations in Western Pacific Region and South America

Abstract

<p>The Western Pacific Region has some of the highest sea surface temperatures in the world, described as the Tropical Warm Pool (TWP). It plays a major role in the troposphere-stratosphere exchange and, the chemical composition in the TWP will greatly affect that in the Tropical Tropopause Layer (TTL) and therefore the stratosphere. The FTIR station in Koror, Palau (7.5°N, 134°E) is the only FTIR site in the Warm Pool, which was installed as part of the EU-project StratoClim in 2016. The FTIR station in Paramaribo, Suriname (5.8°N, 55°W) was established as part of the EU-program STAR in 2004. The measurement site in Burgos, Philippines (18.5°N, 120.65°E) (Velazco et al., 2017a) just beside the Warm Pool was installed in 2016. Our analysis of FTIR methane measurements at Palau from 11/2018 – 06/2021 and at Suriname from 01/2017 – 05/2021 with the GEOS-Chem model simulations give some insights into transport processes and the origin of air mass in the TWP. The NDACC retrieved CH<sub>4</sub> has good sensitivity to the troposphere and stratosphere. Tropospheric and stratospheric X<sub>CH4</sub> are analyzed separately based on the FTIR measurements. Simulations of CH<sub>4</sub> from the GEOS-Chem model are used to be compared with the measurements from two tropical sites. The position of the Chemical Equator (Hamilton et al., 2008) calculated from the GEOS-Chem model simulations and FLEXPART are used to investigate the seasonal variations of the CH<sub>4</sub> measurements from FTIR.</p>

Properties of Cirrus Cloud Observed over Koror, Palau (7.3°N, 134.5°E), in Tropical Western Pacific Region

“…In this layer, the trace gases such as O 3 and CO also show a large vertical gradient [78,79], which implies the need for a higher upper limit of the TTL as the air eventually transits into the lower stratosphere. Even though this is the most concise definition incorporating most previous research on this topic [80,81], the exact level of LHCO is difficult to quantify compared with the thermal tropopause CPT/LRT, and varies in different places and seasons. Thus, this study will use the CPT definition to give a picture of the upper TTL region above Palau, as can be seen in Section 3.4.…”