Assessment of SCATSat‐1 Scatterometer Winds on the Upper Ocean Simulations in the North Indian Ocean

Abstract

are the dominant modes of intraseasonal oscillation (ISO) in the tropical ocean. These processes are described by the 30-90 days fluctuations of low-level winds and convection over the Indian Ocean (IO) and propagating from the equator to the southeast Asian region. Strong intraseasonal variability of sea surface temperature (SST) during MISO events in the tropical IO is well established and modulated by air-sea interactions, which is confirmed by both observational studies (Duvel & Vialard, 2007;Sengupta & Ravichandran, 2001) as well as modeling studies (Achuthavarier & Krishnamurthy, 2011;Fu et al., 2002). Additionally, mixed layer depth (MLD), barrier layer thickness (BLT), and salinity stratification influence the amplitude of SST in intraseasonal variability (Li et al., 2017). Strong intraseasonal SST variability is associated with shallower MLD (Sengupta Abstract The performance of a new scatterometer SCATSat-1 winds with TropFlux on simulating the upper oceanic processes is analyzed over the northern Indian Ocean (IO) using Regional Ocean Modeling System (ROMS). The nutrient, phytoplankton, zooplankton, and detritus (NPZD) ecosystem model are included for studying the postcyclonic responses on biophysical parameters during three cyclones of different intensities (Maarutha, Mora, and Ockhi) in 2017. The SCATSat-1 (TropFlux) winds showed that skill scores are higher than 0.85 (0.66), and RMSEs are less than 0.48 (1.96) m s −1 with RAMA and OMNI buoy observations. Two SCATSat-1 wind experiments, one with 1/4° (SS-E) and other regridded wind to 1° (SSR-E), are compared with the simulation by TropFlux air-sea fluxes available at 1° (TF-E). Seasonal variability of simulated oceanic parameters in SS-E and SSR-E showed marginal improvement than TF-E as compared with observations. However, SSHA variability associated with downwelling Kelvin waves along the Bay of Bengal coast and southward east India coastal current (EICC) during postmonsoon is better simulated in SCATSat-1 experiments. All experiments showed observed intraseasonal oscillations (30-90 days) with higher variability in thermocline than upper layers at RAMA locations over the equator. On western (eastern) equatorial IO, the signals are stronger during boreal winter (premonsoon) and summer (monsoon). Drop in temperature up to 2.5°C during cyclonic events is reasonably better captured in SS-E and SSR-E than TF-E due to better accuracy in SCATSat-1 winds. During cyclones, surface chlorophyll attained a peak after 5-10 days of cyclone passage in SCATSat-1 winds experiments and satellite observations. Plain Language Summary Wind plays an important role in driving the surface circulation of the ocean. Therefore, winds with reasonable accuracy are required to simulate the ocean processes at different timescales through numerical modeling. The ocean simulations are useful for studying oceanic processes and air-sea interaction. The study evaluated the performance of a scatterometer wind and a reanalysis wind. The validations with satellite and in situ observat...

Characterization of Tropical Cyclone Intensity Using the HY-2B Scatterometer Wind Data

“…Satellite scatterometers generally provide high-quality vector winds over the global ocean surface, such that they have been widely used in the study of TC structure and location [10][11][12][13]. Notably the Ku-band pencil-beam scatterometers, such as SeaWinds onboard QuikSCAT [14], OSCAT onboard the Indian Oceansat-2 [15] and SCATSat-1 satellites [16], and HSCAT on the Chinese HY-2 satellite series [17], are with wide observation swaths of ~1800 km, making them more likely to acquire the entire TC structure in a single overpass than the C-band fixed fan-beam scatterometers, e.g., Advanced Scatterometers (ASCAT) onboard the MetOp satellite series [18]. However, due to signal saturation in the (co-polarized) radar backscatter measurements, both C-and Ku-band scatterometer extreme wind speeds show large errors.…”