Instrument: Coastal Ocean Lagrangian Float

 COOL float

A COastal Ocean Lagrangian (COOL) float measures compass angle, pressure, and temperature and is constructed from a glass pipe 2.2 m long and with an outer diameter of 9.5 cm. The float consists of the glass pipe, electronics, a volume changer (VOCHA) located within the float, vanes and a compass, a pinger and either a compressee or drop weight. The COOL float is based on the previously designed isopycnal f/h float (Rossby et al., 1994). Glass was used since it has a very small thermal expansion coefficient. Thus, the float will remain on the same density surface even if the temperature and salinity of the water changes but its density doesn't. If a water parcel is displaced vertically, it will either expand or compress due to the change in pressure and not change its potential density. Since the glass float is less compressible than seawater, it will not follow this water parcel. Therefore, a compressee is added to the float to match the float's compressibility to that of seawater. The COOL float has a volume changer (VOCHA) in it to allow the float to follow a water parcel whose density is changing. However, in our short test deployments, we only used the VOCHA for calibration purposes (described later). Eight vanes at a angle to the horizontal and a compass were added to the isopycnal f/h to make the COOL float. As water flows vertically past the float, the vanes will make the float rotate. Measuring the rotation rate with a compass inside the float will provide a measure of the vertical velocity past the float. If the float is isobaric (that is, the float will remain at a constant pressure; it does not have a compressee), the vertical velocity past the float will be mainly due to the vertical velocity of internal waves. However, vanes on the isopycnal COOL float will make it respond to diapycnal velocities instead of vertical velocities. That is, the float will measure only the amount of water flowing past the float whose density is changing.