Abstract

This study investigates the influence of major Sudden Stratospheric Warming (SSW) events on
precipitable water vapor (PWV) and rainfall variability over the equatorial–low latitude region of Africa.
GNSS-derived PWV data from four stations; Djibouti (DJIG), Ambo (ABOO), Lagos (ULAG), and
Libreville (NLKG), were analyzed alongside ERA5 reanalysis rainfall data and MERRA-2 stratospheric
temperature and zonal wind fields for the 2016/2017 and 2017/2018 SSW events. PWV was retrieved
from GNSS observations using Precise Point Positioning (PPP) techniques, and the analysis was
conducted within a phase-based framework, classifying each event into ascending (AP), mature (MP),
and descending (DP) phases. Results show that SSW events exhibit clear stratospheric signatures,
including rapid temperature increases (~50–60 K) and zonal wind reversals, consistent with major
warming criteria. These disturbances are associated with a distinct tropospheric response. During the
AP, PWV is suppressed across all stations, accompanied by weak and sporadic rainfall. In the MP, both
PWV and rainfall increase significantly, with PWV reaching ~50–60 mm and rainfall peaking at ~40–
55 mm/day, indicating strong coupling between moisture availability and convective processes. During
the DP, PWV remains elevated, while rainfall becomes more variable, reflecting a lagged and weakened
coupling. Coastal stations (ULAG and NLKG) consistently exhibit higher PWV and rainfall due to
enhanced oceanic moisture supply. The results further demonstrate that while elevated PWV is a
necessary condition for rainfall, it is not sufficient, as precipitation depends on favorable dynamical and
thermodynamic conditions, including vertical motion and atmospheric instability. This study provides
new GNSS-based observational evidence of phase-dependent stratosphere and troposphere coupling in
the African sector and highlights the importance of integrating PWV observations into regional weather
forecasting and climate modeling.

Key words: Sudden Stratospheric Warming; Precipitable water vapor; Equatorial and Low Latitude; Stratosphere and Troposphere Coupling