Abstract
Water vapor transport affects regional precipitation and climate change. The measurement of precipitable water (PW) and water vapor flux (WVF) is of great importance for the study of precipitation and water vapor transport. This study presented a new method of computing PW and estimating WVF using the water vapor vertical column density (VCD) and profile retrieved from multi-axis differential optical absorption spectroscopy (MAX-DOAS), combined with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 wind profiles. We applied our method to MAX-DOAS observations in the coastal (Qingdao) and inland (Xi’an) cities of China from June 2019 to May 2020 and compared the results to the ERA5 reanalysis datasets. Good agreement with ERA5 datasets was found; the correlation coefficient (r) of the PW and the zonal and meridional WVFs were r ≥ 0.92, r = 0.77, and r ≥ 0.89, respectively. The comparison results showed the feasibility and reliability of estimating PW and WVF using MAX-DOAS. Then, we analyzed the seasonal and diurnal climatology of the PW and WVFs in Qingdao and Xi’an. The results indicated that the seasonal and diurnal variations of the PW in the two cities were similar. The zonal water vapor transport of the two cities mainly involved eastward transport, Qingdao’s meridional water vapor mainly involved southward transport, and that of Xi’an mainly involved northward transport. The WVFs of the two cities were higher in the afternoon than in the morning, which may be related to wind speed. The results also indicated that the WVF transmitting belts appeared at around 2 and 1.4 km above the surface in Qingdao and around 2.8, 2.6, 1.6, and 1.0 km above the surface in Xi’an. Before precipitation, the WVF transmitting belt moved from near the ground to a high level, reaching its maximum at about 2 km, and the PW and meridional vertically integrated WVF increased. Finally, the sources and transports of water vapor during continuous precipitation and torrential rain were analyzed according to a 24 h backward trajectory. The air mass from the southeast accounted for more than 84% during continuous precipitation in Xi’an, while the air mass from the ocean accounted for more than 75% during torrential rain in Qingdao and was accompanied by a high-level ocean jet stream. As an optical remote sensing instrument, MAX-DOAS has the advantages of high spatiotemporal resolution, low cost, and easy maintenance. The application of MAX-DOAS to meteorological remote sensing provides a better method for evaluating the PW and WVF.
Highlights
Water vapor is the most important greenhouse gas in nature and plays a vital role in cloud formation, precipitation, and the atmospheric radiation budget [1]
We compared the water vapor flux (WVF) with the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 WVFs and found good during the continuous precipitation period in vapor results mainly only cameindicated from the agreement
Using MAX-DOAS and wind radar to perform these measurements and reduce the errors caused in Section 2.5.2 is our research goal
Summary
Water vapor is the most important greenhouse gas in nature and plays a vital role in cloud formation, precipitation, and the atmospheric radiation budget [1]. Tropospheric water vapor flux (WVF) is an important parameter in water cycles and an important factor affecting energy balance. Continuous observation of this parameter can reflect changes in the regional hydrological climate [8,9,10,11]. The water vapor concentration is greatly affected by transportation, local water vapor evaporation, and condensation [1]. To understand the climatic characteristics of regional precipitation and atmospheric water cycles, the measurement of PW and WVF is extremely important, especially in the lower troposphere. The water vapor concentration is usually higher in the lower atmosphere, and high concentrations are the most important for evaluating the condensation and transportation of water vapor
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