# Review on the Role of GNSS Meteorology in Monitoring Water Vapor for Atmospheric Physics
## 4 Spatio-Temporal Analysis
### Asia  
**China. ** [PERSON] et al. [91] investigated the spatial, seasonal and diurnal distribution of water vapor for three years (2004-2007). The region with the highest IWV was the South-East, with a strong annual cycle (amplitude of \(\sim\)15 mm), while the lowest IWV was found in the North-West region, with a smaller annual cycle (amplitude of \(\sim\)4 mm). Mean diurnal cycle amplitude was found to be 0.7 mm. The spatial distribution was dependent on latitude, topography, season and monsoon. [PERSON] et al. [92] studied midsummer diurnal variations over 18 stations around the Poyang Lake during three year period (2015-2018). Diurnal IWV typically peaks at 1200-2000 Local Solar Time (LST). Air temperature diurnal cycle was reported to be likely behind the IWV diurnal cycle. The semi-diurnal cycle was found to account for about 50% of variance contribution. Tibetan Plateau is a region of high interest in China, specially because of its role in the summer monsoon. [PERSON] et al. [93] studied the premonsoon and monsoon diurnal variability at the station of Lhasa in this region. Premosoon minima and maxima occurred at 1800 and 0400 LST, respectively, while, in the monsoon period, these were displaced to 1500 and 2300 LST. This result shows that water vapor is affected by local circulation. It also indicates the usefulness of GNSS for studying the IWV daily cycle and recommends the addition of more stations to the Plateau in order to study moisture transport in the region. **Japan. ** [PERSON] and [PERSON] [94] studied the diurnal variability in 5 GNSS stations and the other three radiosonde stations. The maximum was found around 1800-2000 LST, some hours later than in China. [PERSON] et al. [95] also analyzed the diurnal variations in central Japan during August 2000, which found the maximum at the same hours. The moisture transport was found to cause the differences in phase of the diurnal cycle of IWV among different locations. **Sumatra. ** [PERSON] et al. [96] presented the diurnal variation in the island of Sumatra, and found a distinct diurnal cycle. [PERSON] et al. [97] used data from the Sumatran GNSS array to study the diurnal cycle of water vapor. The Madden-Julian oscillation (MJO) was found to impact on the diurnal cycle, appearing smaller in both the daily mean and the amplitude of the diurnal cycle during the suppressed phase relative to the developing/active MJO phase. The evening/nighttime peaks of IWV offshore appeared later during the suppressed phase of the MJO compared to its active phase (from 1900 LST in the active phase to 2200 LST in the suppressed phase). **South Korea. ** [PERSON] and [PERSON] [98] estimated the trend over 5 stations of South Korea (2000-2009) as 0.11 mm year\({}^{-1}\). They also calculated seasonal trends for summer (0.16 mm year\({}^{-1}\)), winter (0.04 mm year\({}^{-1}\)), spring (0.05 mm year\({}^{-1}\)), and autumn (\(-\)0.14 mm year\({}^{-1}\)). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Work** & **Year** & **N** & **Start** & **End** & **Region** & **Type** & **Value** \\ \hline
[94] & 2001 & 5 & 1999-07 & 1999-08 & Japan & Diurnal & max: 1900 \\ \hline
[99] & 2002 & 54 & 1996-01 & \multirow{2}{*}{2000-12} & \multirow{2}{*}{North America (US)} & \multirow{2}{*}{Diurnal} & max: 1000–1400 (winter) and \\  & & & & & & & midafternoon-midnight \\ \cline{1-1} \cline{5-6}  & & 17 & 1993-08 & & Scandinavia (Sweden) & Trends & 0.15 \\ \hline
[101] & 2007 & 2 & 1998-01 & 2006-12 & Africa (South Africa) & Trends & non-significant \\ \hline
[95] & 2008 & 6 & 2000-08 & 2000-08 & Japan & Diurnal & max: 1900, min: noon \\ \hline
[102] & \multirow{2}{*}{2009} & 32 & 1996-01 & \multirow{2}{*}{2005-12} & Baltic (Finland, Latvia, Sweden) & Diurnal & - \\ \cline{1-1} \cline{5-6}  & & & & & & Seasonal & \\ \cline{1-1} \cline{5-6}  & & & & & & & 1800–2100 UT \\ \hline
[98] & 2010 & 5 & 2000-01 & 2009-12 & SouthKorea & Trends & 0.11 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of spatio-temporal studies.