The Imprint of the Southern Annular Mode on Black Carbon AOD in the Western Cape Province

Abstract

This study examines the relationship between variations of the Southern Annular Mode (SAM) and black carbon (BC) at 550 nm aerosol optical depth (AOD) in the Western Cape province (WC). Variations of the positive (negative) phase of the SAM are found to be related to regional circulation types (CTs) in southern Africa, associated with suppressed (enhanced) westerly wind over the WC through the southward (northward) migration of Southern Hemisphere mid-latitude cyclones. The CTs related to positive (negative) SAM anomalies induce stable (unstable) atmospheric conditions over the southwestern regions of the WC, especially during the austral winter and autumn seasons. Through the control of CTs, positive (negative) SAM phases tend to contribute to the build-up (dispersion and dilution) of BC in the study region because they imply dry (wet) conditions which favor the build-up (washing out) of pollutant particles in the atmosphere. Indeed, recent years with an above-average frequency of CTs related to positive (negative) SAM anomalies are associated with a high (low) BC AOD over southwesternmost Africa.

Causal discovery of drivers of surface ozone variability in Antarctica using a deep learning algorithm

“…For example, Thompson et al 57 argue that changes in AAO (forced by changes in GHGs concentration and stratospheric ozone depletion) has resulted in cooling over the east Antarctica and enhanced sea spray over the adjoining marine areas. Similarly, Ibebuchi et al 58 show that the long-term trend in AAO is responsible for variability of black carbon (an important component of AOD) over the southern mid-latitude, especially over the south western Africa. All stations included for causal analysis in this study are situated in East Antarctica (except Arrival Heights which lies at the foothold of Trans-Antarctic mountain range receiving a large amount of Katabatic outflow from the high altitude Antarctic plateau), and air parcel transport to these stations spend considerable amount of time over the adjoining marine areas.…”

Patterns of atmospheric circulation in Western Europe linked to heavy rainfall in Germany: preliminary analysis into the 2021 heavy rainfall episode

“…The clustering technique used in classifying the circulation types (CTs) in Western Europe is the fuzzy obliquely rotated T-mode (i.e., variable is time series and observation is grid points) principal component analysis (PCA). The method has been successfully applied to separate wetting and drying signals in southern Africa, investigate their teleconnections, and the impact of radiative heating on the signals (e.g., Ibebuchi 2021a, b, c, d;Ibebuchi and Paeth 2021). Obliquely rotated T-mode PCA has been widely applied in classifying circulation patterns in Europe (e.g., Huth et al 2008).…”