Modified Refractivity-Based Lifted Index Using Exact Formula for Lifted Condensation Level

Abstract

Temperature is responsible for the rise of air parcels in the atmosphere, which in turn impairs the transmission of electromagnetic waves. Therefore, atmospheric stability is a function of the temperature of the rising and sinking air parcel with respect to the environmental air temperature at the lifted condensation level (LCL). Refractivity-based lifted index (RLI), a stability index model, uses an approximate LCL value. This study modifies the RLI using the exact formula of the LCL to obtain a precise modified refractivity-based lifted index (MRLI) model for the computation of refractivity-based atmospheric stability profiles. Two years (2020–2021) reanalysis data of atmospheric parameters (temperature, relative humidity and atmospheric pressure) were obtained from European Centre for Medium-Range Weather Forecasts (ECMWF) satellite for Lagos (6.6018° N, 3.3515° E), Abuja (9.0765° N, 7.3986° E) and Yola (9.2095° N, 12.4782° E) at 500–1000 hPa. RLI and MRLI were analysed at four synoptic hours (0, 6, 12, and 18 h) Local Time (LT). The trend shows that when RLI is negative, MRLI is negative; when RLI becomes less negative, MRLI is less negative, except in some cases where a significant amount of water vapour is observed at 500 hPa. Furthermore, a higher negative MRLI value indicates more environmental moisture and is supportive of convective activity, which implies an unstable atmosphere. MRLI has higher night-time (18–0 h LT) values compared to the daytime (6–12 h LT) due to low temperature and high humidity. Also, MRLI negative value decreases as the altitude increases with seasonal averages of − 97, − 86, and − 83 N-units over Lagos, Abuja, and Yola, respectively. A strong positive relationship was observed between MRLI and RLI, with correlation coefficients of 0.99999 for Lagos, 0.99823 for Abuja, and 0.99765 for Yola. MRLI attempts to lower the approximation error exhibited by RLI values for dry season months over Abuja and Yola.