The diurnal variability of precipitable water vapor derived from GPS tropospheric path delays over the Eastern Mediterranean

Abstract

The study of the diurnal variations of the total water vapor amount in an atmospheric column, also known as Precipitable Water Vapor (PWV) or Integrated Water Vapor (IWV), is highly significant in meteorology and climatology studies, yet very limited due to insufficient spatial and temporal in situ measurements. Nowadays, Global Navigation Satellite System (GNSS) ground receivers are used along with retrieval techniques in order to conduct high sample rate PWV estimations. Here, we present the annual and seasonal PWV diurnal cycles extracted from the Survey Of Israel Active Permanent Network (SOI-APN) GNSS receivers in the Eastern Mediterranean region. The data period spans from 5 to 21 years, ensuring its suitability for studying the PWV annual and seasonal mean diurnal variations. We particularly focus on the summer months (JJA), where the Mediterranean Sea Breeze (MSB) plays a dominant role in transporting humidity inland. For most stations, the diurnal amplitude in summer is the highest compared to the seasonal mean (4%–21%), followed by spring, autumn and winter (2%–4%). The PWV in the coastal stations peaks at 6–7 UTC while the northernmost highland station peaks at 8 UTC and the southernmost at 14 UTC indicating frontal MSB propagation from the coastline eastward inland combined with northern winds enhancement due to Coriolis force. Moreover, for most stations, the PWV peak hour is correlated with the distance from the Mediterranean Sea shore, substantiating the MSB's role as a key driver of the PWV diurnal variability during summer months. The PWV minimum values in the coastal stations occurs between 14 UTC and 19 UTC while in the highland stations it varies from 17 to 00 UTC. The coastal stations' PWV amplitude, compared to the daily mean, is around 1 mm while the highland stations amplitude is 2–3 mm. In addition, a strong correlation between the PWV diurnal cycle and the atmospheric Mixing Layer Height (MLH) diurnal variations is found using ceilometer data, suggesting that the MLH modulates the PWV, however this conclusion requires further research. Finally, using harmonic analysis with the PWV diurnal variations in summer, reveals that the diurnal and the semidiurnal modes account for ~95% of the sub-daily variance in 19 out of 21 GNSS stations