Significant wave height is an important parameter for characterizing ocean surface waves. With the development of remote sensing technology, satellite radar altimetry has become an essential tool for obtaining significant wave height estimations. However, its measurement only covers the satellite track on the ground and cannot be applied to large regions or areas. In this study, we obtained significant wave height from the Hai Yang-2A (HY-2A) radar altimeter and sea surface wind speed at a 10-m height from the HY-2A microwave scatterometer for October 2013, and then proposed a wind-wave relationship model for the South China Sea using linear/nonlinear regression analysis at high/low wind speeds (0 to 40 m s-1). By comparison with two other windwave models and validation with HY-2A observations in November 2013, our results show that the proposed wind-wave relationship model is credible, and at low wind speed exhibited good consistency with the wind-wave model from in-situ observations. According to the proposed model, significant wave height from the HY-2A microwave scatterometer-retrieved wind speed and ocean wind wave analysis during the "1329" Typhoon Krosa were successfully obtained and determined. Data coverage of the computed significant wave height was far wider than that of the satellite radar altimeter observations and demonstrated development of typhoon wave fields over a large region. Overall, this study and proposed model provide useful information for the analysis and forecast of typhoon waves and potential storm surge disasters.

Hourly sea surface temperature (SST) retrieved from Himawari-8 by the Japan Aerospace Exploration Agency (H8-SST/JAXA, latest version 1.2) is becoming an important data source for data merging as well as for resolving diurnal variation (DV). However, the spatial and temporal variation of the errors for the full disk is still unclear. In this article, two years of H8-SSTs/JAXA are validated against in situ measurements from iQuam2. In general, H8-SSTs/JAXA shows small biases between −0.11 and −0.03 K with root mean square error (RMSE) between 0.58 and 0.73 K. The spatial distributions of the errors reveal the following patterns: 1) a small median bias close to 0.1 K and RMSE of 0.4-0.6 K comparing to drifters are found at satellite zenith angle (SZA) 0°-35°; 2) negative biases (∼−0.3 K) are detected at SZA s 35°-58°; and 3) larger positive biases exceeding 0.3 K are also found along the viewing boundaries. The temporal variations of the errors show that 1) there is no prominent seasonal variation; 2) the amplitude of the DV of the errors is only ∼0.1 K for the statistical of all matchups, and 3) the maximum errors appears in the morning rather than in the noon. The statistics will be used in future work for DV analysis and merging purposes.

Abstract:The validation of sea surface temperature (SST) retrieved from the new sensor Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-Orbiting Partnership (S-NPP) Satellite is essential for the interpretation, use, and improvement of the new generation SST product. In this study, the magnitude and characteristics of uncertainties in S-NPP VIIRS SST produced by the Naval Oceanographic Office (NAVO) are investigated. The NAVO S-NPP VIIRS SST and eight types of quality-controlled in situ SST from the National Oceanic and Atmospheric Administration in situ Quality Monitor (iQuam) are condensed into a Taylor diagram. Considering these comparisons and their spatial coverage, the NAVO S-NPP VIIRS SST is then validated using collocated drifters measured SST via a three-way error analysis which also includes SST derived from Moderate Resolution Imaging Spectro-radiometer (MODIS) onboard AQUA. The analysis shows that the NAVO S-NPP VIIRS SST is of high accuracy, which lies between the drifters measured SST and AQUA MODIS SST. The histogram of NAVO S-NPP VIIRS SST root-mean-square error (RMSE) shows normality in the range of 0-0.6˝C with a median of~0.31˝C. Global distribution of NAVO VIIRS SST shows pronounced warm biases up to 0.5˝C in the Southern Hemisphere at high latitudes with respect to the drifters measured SST, while near-zero biases are observed in AQUA MODIS. It means that these biases may be caused by the NAVO S-NPP VIIRS SST retrieval algorithm rather than the nature of the SST. The reasons and correction for this bias need to be further studied.

Understanding aerosols optical properties over the oceans is vital for enhancing our knowledge of aerosol effects on climate and pollutant transport between continents. In this study, the characteristics of aerosol optical thickness (AOT) at 500 nm (τ500nm), Ångström exponent for the wavelength pair 440–870 nm (α) and volume size distribution (VSD), are presented and analyzed over the East China seas based on the observations at four AERONET sites during 1999–2019. The main results are: (1) the mean τ500nm (α) value ranged from 0.31 to 0.36 (1.17–1.31); (2) the distribution of τ500nm (α) is similar to a log-normal distribution with a right-skewed long tail larger than 0.5 (closer to the normal distribution); (3) large AOT (τ500nm>0.6) was frequently observed in summer (June and July) and spring (March to May), followed by autumn and winter; (4) all aerosol types were observed, and urban/industrial aerosols and mixed types were dominant throughout the period. The atmospheric column aerosol was characterized by a bimodal lognormal size distribution with a fine mode at effective radius, Reff = 0.16 ± 0.01 μm, and coarse mode at Reff = 2.05 ± 0.1 μm.