BOW-TIE

Beobachtung von Ozean und Wolken – Das Trans ITCZ Experiment
(Translation: ocean and cloud observation - the trans-ITCZ experiment)

Lead PIs: Daniel Klocke, Julia Windmiller, Bjorn Stevens (MPI-M), Marcus Dengler (GEOMAR)

The goal of BOW-TIE is to investigate how processes on the scale of convective storms, and their interaction with the ocean, impact the properties of the Atlantic Intertropical Convergence Zone (ITCZ). Focusing on storm-scale processes is motivated by current research which suggests their crucial role for the mesoscale dynamics in the ITCZ which in turn appears important for understanding its large-scale structure and subsequent links to global circulation patterns.

To link the storm-scale processes to the large-scale ITCZ ship-board measurements are used, with repeated crossings of the ITCZ, linking detailed vertical profiling of the atmosphere and ocean to long-standing buoy measurements through the PIRATA array. This pattern will have weak sea-surface temperature gradients for the western and strong gradients for the eastern leg.

Important tasks will be to obtain vertically resolved cross-sections of the ITCZ, through the upper ocean, and the surrounding thermodynamic and dynamic conditions. Measurements will include atmospheric and oceanic measurements, with more intensive measurements of the ocean and atmosphere boundary layers; these will allow us to also investigate the atmosphere-ocean coupling on the scale of the storm systems.

Main measurements will include precipitation, cloud profiles, humidity profiles, wind profiles, surface wind speeds and direction, sea-surface temperature and upper ocean measurements of temperature, currents speed and direction, and salinity. As a related component, the campaign will explore cloud microphysical development and aerosol-cloud interactions in the exceptionally clean conditions of the inner ITCZ, as these are thought to influence the surface energy budget and hence air-sea coupling. Together these measurements will provide a benchmark for storm-resolving models and help to determine why they lead to an improved representation of the tropical circulation systems.

Trajectory of the FS METEOR during the BOW-TIE campaign.

Through the US fundet project PICCOLO (Process investigation of clouds and convective organization over the tropical ocean) FS Meteor is equiped with the Sea-Going Polarimetric (SEA-POL) C-Band radar of the Colorado State University (CSU) for BOW-TIE.