A Plea for the Study of Spiciness

Seminar by Prof. Niklas Schneider from International Pacific Research Center and Department of Oceanography University of Hawaiʻi at Mānoa

09 December 2022
KST 10:00 – 11:00

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

The evolution of thermal anomalies in the ocean are key to climate fluctuations such as El Nino and longer term decadal variability. Away from the surface, the propagation of thermal and accompanying haline anomalies are governed by wave processes and advection. A representation in terms of spiciness and density separates the processes and is useful to explore underlying dynamics.

Spiciness quantifies contrasts between cool and fresh or hot and salty (spicy) ocean waters of the same density. Traditionally this property has been used to determine double-diffusive stability of a water column, a small-scale process. Here, we will review the use of spiciness in the study large-scale air-sea interaction and climate variability. We focus of the upper ocean where the pressure dependence of sea water’s thermal and haline expansion coefficients can be neglected.   Spiciness and density form an alternate pair of variables to describe the two component nature of sea water. These variables have distinct dynamics. Density is dynamically active through impacts on horizontal pressure gradients. For time scales longer than inertial, its is governed by potential vorticity conservation and associated (Rossby) waves. Spiciness, on the other hand, is dynamically inactive and evolves as a passive tracer. Examples from observations and numerical simulations show these distinct properties and will be discussed. In particular, we will explore why spiciness may be effective at decadal time scales. 

Once spiciness anomalies return to the air-sea interface, the atmosphere responds to associated impact of surface temperature only. It is insensitive to changes of surface salinity. This potentially results in a rearrangement of the coupled upper-ocean atmosphere system. Large ensemble simulations conducted at ICCP are perfectly suited to study these processes.