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

We 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.