Abstract: The harmonic method was employed to analyze the diurnal variation of different types marine aquaculture water under different weather conditions (sunny, partly cloudy, cloudy and overcast), based on the water temperature data of aquaculture pond and cage embayment in Ningbo from 2010 to 2013. The results showed that: (1) two and three order harmonic models could well simulate water temperature variations of aquaculture pond and cage embayment, respectively. The absolute error of temperature simulation for different types marine aquaculture water were all at a low level (aquaculture pond: hourly 0.24-0.31℃, maximum 0.2-0.24℃, minimum 0.11-0.15℃,cage embayment: hourly 0.1-0.15℃, maximum 0.06-0.1℃, minimum 0.06-0.08℃ ). (2) Harmonic simulation error with significant diurnal variation was higher in daytime and lower in nighttime, the harmonic method simulation on the trend of water temperature variation in overcast day was worse than that in other weather conditions. (3) Water temperature diurnal variation of aquaculture pond had two cycles with 24 hours and 12 hours, and 24 hours cycle contributed the highest proportion. Water temperature diurnal variation of cage embayment had 12 hours, 24 hours and 6hr periods, and the proportion of 12 hours and 24 hours was higher than that of 6 hours. From sunny to cloudy day, the proportion of 12 hours and 24 hours was almost equal, while the proportion of 24 hours cycle significantly decreased in overcast day. We propose that the harmonic method provides a good proxy for simulating and quantitatively analyzing the diurnal variation of aquaculture pond water and cage embayment water, which provides an important reference for water temperature refinement forecast.

Key words: Aquaculture pond, Cage embayment, Water temperature, Different weather, Harmonic analysis