Large-Scale State and Evolution of the Atmosphere and Ocean during PISTON

The first field campaign of the Propagation of Intra-Seasonal Tropical Oscillations (PISTON) project took place, over two months beginning mid-August 2018, in the north-western Tropical Pacific, north of Palau. The primary platform for the PISTON 2018 campaign was the R/V Thomas G. Thompson, outfitted with a large suite of instruments for observing the atmosphere and upper ocean. In this presentation we will discuss the large-scale setting in which the PISTON observations occurred, in order to provide context for the observations themselves. Using the in situ PISTON field data along with historical and remotely sensed data sets, we will summarize the state and evolution of the atmosphere and ocean in the PISTON area and the surrounding region, and interpret them in terms of identifiable modes of variability.

In the atmosphere, PISTON was characterized by periods of easterly low-level winds and westward-propagating synoptic-scale disturbances, interspersed with periods of strong low-level westerlies associated with tropical cyclones. Tropical cyclone activity was strong during PISTON overall, while the most common modes of intraseasonal variability – the Madden-Julian oscillation and Boreal Summer Intraseasonal Oscillation –
were inactive for much of the field campaign. The ocean data provide distinct cases of the oceanic conditions present during the tropical cyclone activity, including changes in the mixed layer and salinity stratification.