Observation of the surface horizontal thermohaline variability at mesoscale to submesoscale in the north‐eastern subtropical Atlantic Ocean

Abstract

The seasonal variability of the surface horizontal thermohaline structure is investigated in the north-eastern Atlantic Surface Salinity Maximum (SSM) at length scales from five to hundreds of kilometers, i.e., at submesoscale to mesoscale. The near-surface temperature and salinity data from merchant ship thermosalinograph (TSG) transects across the Atlantic are used to compute the horizontal temperature, salinity and density fluctuations, and the density ratio. During late winter in the north-eastern SSM, thermohaline compensation is observed for wavelengths from 5 km to more than 200 km; in spite of large and sharp surface thermohaline fronts, a weak density surface horizontal gradient is observed. Temperature and salinity exhibit an energetic spectra in k 22 slope scale between 20-100 km scale and a steeper slope at shorter wavelengths, while density spectra exhibit lower energy level with a clear k 23 slope below 20 km, consistent with interior quasigeostrophic turbulence. During summer in the north-eastern SSM, salinity and temperature gradients are no longer compensated due to strong atmospheric heating of the upper ocean. In comparison with winter, the surface density spectrum is enhanced with a flatter slope between k 22 and k 21 between 5 and 20 km.

Ship-Based Contributions to Global Ocean, Weather, and Climate Observing Systems

“…Ships can also measure the multiple, simultaneous parameters needed to adjust observations measured at various sensor heights to a common reference height or depth. The high horizontal resolution of ship measurements also resolves sub-footprint processes, helping to interpret and validate the satellite measurements (e.g., Kolodziejczyk et al, 2015b;Boutin et al, 2018).…”

“…The global network of ship-based TSG measurements (Figure 6) has enormously increased our ability to study variations in ocean salinity. Ongoing projects managing flowthrough water data include SAMOS, the U.S. Rolling Deck to Repository 4 , Global Ocean Surface Underway Data (GOSUD; Kolodziejczyk et al, 2015b), Ferryboxes (Petersen, 2014) 5 , and the Surface Ocean Carbon Observing NETwork (Wanninkhof, 2019). Although profiles of surface temperature and salinity are available at single points through Argo (Roemmich et al, 2009;Riser et al, 2016), conductivity-temperature-depth (CTD) casts (e.g., Talley et al, 2016), and moorings (McPhaden et al, 1998;Bourlès et al, 2008), only TSGs on ships, drifters, and autonomous surface vessels provide the capability to measure high-horizontal salinity variations in frontal and sub-mesoscale structures (e.g., Kolodziejczyk et al, 2015a).…”

Singularity Power Spectra: A Method to Assess Geophysical Consistency of Gridded Products—Application to Sea-Surface Salinity Remote Sensing Maps

“…Indeed, in situ data and satellite products likely have different spatial and temporal sampling characteristics, potentially hindering the use of in situ data to verify the spatial and temporal consistency of satellite-derived fields. An in situ observation, e.g., derived from in situ data are between -1 and -3 [Kolodziejczyk et al, 2015b;Cole et al, 2010;Cole and Rudnick, 2012]. Dispersion in the spectral slope value of a product, depending on the region under study [Reynolds and Chelton, 2010], can be the consequence et al, 2008a;Turiel et al, 2009], for extracting additional information about the spatial variability from salinity products, including climatology, model output, in situ reanalysis and remote sensing analyses.…”

Multi-sensor in situ observations to resolve the sub-mesoscale features in the stratified Gulf of Finland, Baltic Sea

“…Based on remote sensing altimeter data, it is shown that sea level wavenumber spectra also correspond well to the surface quasi-geostrophic theory (Le Traon et al, 2008). In a recent study, Kolodziejczyk et al (2015) showed that if the surface density is analyzed then the −2 spectral slope is obtained in summer conditions when the salinity and temperature variations do not compensate each other (in north-eastern subtropical Atlantic Ocean). We have used temperature data to estimate potential energy wavenumber spectra assuming that mostly temperature determines the density in the upper layer (including the seasonal thermocline) in the Gulf of Finland in summer.…”