Spatiotemporal Variability of Rainfall and Surface Salinity in the Eastern Pacific Fresh Pool: A Joint In Situ and Satellite Analysis During the SPURS‐2 Field Campaign

Abstract

AbstractWe perform a statistical characterization of the 2016–2017 SPURS‐2 field campaign in situ data and coincident satellite data spanning 8°–12°N, 120°–130°W to quantify the spatial and temporal scales of variability of rain and near‐surface salinity in the Eastern Pacific Fresh Pool. Observations of rain rate and near‐surface to surface salinity are obtained from ships, moorings, autonomous platforms, and satellite remote sensing: Integrated Multi‐satellitE Retrievals for GPM (IMERG); and Soil Moisture Active Passive (NASA SMAP L3 V5). The integral length and time scales of rain and near‐surface salinity vary seasonally. In the rainy season (August–October) when the Intertropical Convergence Zone (ITCZ) migrates over the SPURS‐2 study site, the integral time scales of rain were about 30–60 min and those of near‐surface salinity were closer to that of the rain, 1–2 days, indicating forcing by rain. Meanwhile, the zonal integral length scale of in situ near‐surface salinity was twice as large as the meridional scale (50 vs. 20 km), consistent with the ITCZ's zonally‐propagating and ‐organized rain features. The magnitude and seasonal variation of the sea surface salinity integral time scale were not captured by SMAP since the rainy ITCZ‐period scales were smaller than SMAP resolution (70 km, 8‐day running mean). In the dry season (February–May), the in situ rain integral time scale reduced to less than 30 min while that of the near‐surface salinity increased to 1–5 days, the ocean mesoscale. IMERG overestimated the rain integral time scale by a factor of two to ten in both seasons.