GEOGRAPHY

The study reveals the processes and mechanisms of Haihao and its synergistic phenomena


January 7, 2021 “Haihao” photo Courtesy of the research group

The satellite observed the changes in ocean surface temperature, chlorophyll concentration and sea surface roughness caused by Haihao

On January 7, 2021, the sea surface of the Yellow Sea in Qingdao was like a “pot”, and a large area of white clouds rose on the vast sea, and under the morning sun, it was like a fairyland, a rare spectacle known as the “Haihao” phenomenon.

Li Xiaofeng, a researcher at the Institute of Oceanography of the Chinese Academy of Sciences, conducted a comprehensive observation and analysis of the thermodynamic, biological and kinetic processes related to the Haihao phenomenon by fusing several satellite data in orbit, and accurately simulated the phenomenon by using the regional marine meteorological coupling model (ROMS-WRF). The study found that the upwelling induced by the strong cold snap in winter compensated for the loss of heat in the upper layers of the ocean due to the sharp drop in temperature, making the maximum sea temperature difference of the day reach nearly 20 degrees Celsius. Under the huge sea temperature difference and the corresponding interaction, the rapid evaporation of seawater, so that the water vapor near the sea surface is close to saturation, which is the main reason for the “Haihao” phenomenon. Recently, the results of the study were published in the Journal of Atmospheric Sciences, an academic journal of the American Meteorological Society.

According to Li Xiaofeng, the occurrence of the “Haihao” phenomenon is dominated by thermal instability factors, rather than driven by dynamic factors. Thermodynamic instability promotes the evaporation of surface seawater. The emergence of the “Haihao” phenomenon usually requires two conditions: “condensation nucleus” and “temperature difference”.

The team embedded the Chemical Aerosol Radiation Transport Module (GOCART) in the coupled model to find that 0.5-1.5 sea salt particles were released into the low-altitude atmosphere as the main condensation nucleus with the evaporation process, which promoted the formation of “Haihao”, which also increased the PM2.5 content of the day by 50%.

In addition, in view of the special rough texture characteristics of the sea surface presented by the “Haihao” phenomenon, the research team developed a novel image analysis method – SAR cell type length algorithm. The results show that the farther the offshore line, the stronger the atmospheric instability, so that the underlying atmospheric convection continues to develop and form a larger texture structure of sea surface cells. (Source: China Science Daily, Liao Yang, Li Hezhao)

Related Paper Information: https://doi.org/10.1175/JAS-D-22-0065.1



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