Abstract
This paper addresses the subject of inter-annual variability of the tropical precipitable water vapor (PWV) derived from 18 years of global navigation satellite system (GNSS) observations. Non-linear trends of retrieved GNSS PWV were investigated using the singular spectrum analysis (SSA) along with various climate indices. For most of the analyzed stations (~49%) the GNSS PWV anomaly was related to the El Niño Southern Oscillation (ENSO), although its influence on the PWV variability was not homogeneous. The cross-correlations coefficient values estimated between the Multivariate ENSO Index (MEI) and PWV were up to 0.78. A strong cross-correlation was also found for regional climate pattern expressed through CAR, DMI, HAW, NPGO, TNA and TSA indices. A distinct agreement was also found when instead of climate indices, the local sea surface temperature was examined (average correlation 0.60). The SSA method made it also possible to distinguish small-scale phenomena that affect PWV, such as local droughts or wetter rainy seasons. The overall nature of the investigated changes was also verified through linear trend analysis. In general, not a single station was characterized by a negative trend and its weighted mean value, calculated for all stations was equal to 0.08 ± 0.01 mm/year.
Highlights
The tropical region is a major center of atmospheric convection, accompanied by significant latent heat release [1]
This paper addressed the subject of inter-annual long-term variability of the tropical
This paper addressed the subject of inter-annual long-term variability of the tropical precipitable water vapor (PWV) derived from global navigation satellite system (GNSS) observations
Summary
The tropical region is a major center of atmospheric convection, accompanied by significant latent heat release [1]. Since precipitation rates are the largest in the global tropics, so is the amount of latent heat transferred to the atmosphere. Variability in the tropical water vapor impacts global circulation patterns. The equatorial humidity changes resulting from, e.g., El Niño–Southern Oscillation (ENSO), which is the most prominent year-to-year climate fluctuation on Earth [4], has a strong impact on tropical weather and climate [5,6,7]. Long-term, reliable monitoring of water vapor variability in the tropics is an important task in understanding global climate, especially considering the fact that water vapor is characterized by the single highest positive feedback on the surface temperature [11,12,13,14] and dominates the effect of the Earth’s surface temperature increase [15]
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