Fig. 2From: GNSS brings us back on the ground from ionospherea Quasi-biennial oscillation (QBO) and b tropopause height respond to El Niño-Southern Oscillation (ENSO) observed by the FORMOSAT-3/COSMIC (F3/C) radio occultation (RO) technique. A band-pass filter with the cutoff period ranging from 18 to 34 months is applied to extract the QBO component from the RO temperature averaged within 5° N–5° S at each pressure level. b The departure of tropopause height from its mean annual cycle. The monthly tropopause height is averaged over the Niño 3.4 area (5° N–5° S, 120°–170° W). c Red and blue (exceeding the threshold of ± 0.5 °C) on the Oceanic Niño Index (ONI) indicates the ENSO warm and cold phases, respectivelyBack to article page