Composition and physical properties of the Asian Tropopause Aerosol Layer and the North American Tropospheric Aerosol Layer

Abstract

Recent studies revealed layers of enhanced aerosol scattering in the upper troposphere and lower stratosphere over Asia (Asian Tropopause Aerosol Layer (ATAL)) and North America (North American Tropospheric Aerosol Layer (NATAL)). We use a sectional aerosol model (Community Aerosol and Radiation Model for Atmospheres (CARMA)) coupled with the Community Earth System Model version 1 (CESM1) to explore the composition and optical properties of these aerosol layers. The observed aerosol extinction enhancement is reproduced by CESM1/CARMA. Both model and observations indicate a strong gradient of the sulfur-to-carbon ratio from Europe to the Asia on constant pressure surfaces. We found that the ATAL is mostly composed of sulfates, surface-emitted organics, and secondary organics; the NATAL is mostly composed of sulfates and secondary organics. The model also suggests that emission increases in Asia between 2000 and 2010 led to an increase of aerosol optical depth of the ATAL by 0.002 on average which is consistent with observations. Key Points The Asian Tropopause Aerosol Layer is composed of sulfate, primary organics, and secondary organics The North American Tropospheric Aerosol Layer is mostly composed of sulfate and secondary organics Aerosol Optical Depth of Asian Tropopause Aerosol Layer increases by 0.002 from 2000 to 2010

Variability and evolution of the midlatitude stratospheric aerosol budget from 22 years of ground-based lidar and satellite observations

“…The influence of the Asian monsoon on the composition of the lower stratosphere at OHP -as suggested by our analysis -implies that the increase in ATAL AOD reported by Vernier et al (2015) and Yu et al (2015) should also be reflected in OHP lidar observations. Indeed, after the removal of volcanically perturbed data, we observe a doubling of LS partial AOD since 1998 in late summer and early fall, i.e., in phase with the ATAL signal detected at OHP.…”

“…Analysis of nonvolcanic fraction of data suggests that the annual cycle of midlatitude background stratospheric aerosol is largely driven by remote (tropical) processes: convective cross-tropopause transport of clean air (Vernier et al, 2011c) during southern summer and polluted air from the Asian monsoon (Randel et al, 2010;Vernier et al, 2015;Yu et al, 2015) during northern summer, both followed by poleward transport. Although this interpretation appears consistent, alternative contributors should also be considered.…”

“…Meanwhile, recent studies report a measurable increase in nonvolcanic components of aerosol within the Asian Tropopause Aerosol Layer (ATAL), occurring during the northern summer above the Asian monsoon Yu et al, 2015). Accurate long-term measurements are indispensable to quantify the human-induced change in stratospheric aerosol.…”

Investigation of the aerosol–cloud–rainfall association over the Indian summer monsoon region

“…Therefore, another possible pathway through which meteorological covariability can influence our correlation analysis over the ISMR is due to the positive association between the magnitude of the Asian tropopause aerosol layer and AOD. However, the tropopause aerosol layer pathway results in insignificant enhancements of AOD during JJAS by ∼ 0.01-0.02 over south Asia compared to the observed climatological mean AOD (∼ 0.6) (Vernier et al, 2015;Yu et al, 2015). Thus, contributions of the Asian tropopause aerosol layer to the observed positive gradients (Fig.…”

Potential impact of carbonaceous aerosol on the upper troposphere and lower stratosphere (UTLS) and precipitation during Asian summer monsoon in a global model simulation

“…(Li et al, 2005; In panels (a, c, d, e, f) the tropopause is averaged over the same region where the field parameter is averaged. Park, 2006;Fu et al, 2006;Park et al, 2008Park et al, , 2009Randel et al, 2010;Fadnavis et al, 2013Fadnavis et al, , 2014Fadnavis et al, , 2015 and aerosols (Tobo et al, 2007;Vernier et al, 2011;Thomason and Vernier, 2013;Yu et al, 2015) in the ASM anticyclone. Figure 3b exhibits the distribution of seasonal (June-September) mean carbonaceous aerosols (BC and OC together) from CTRL simulation in the anticyclone (∼ 100 hPa).…”