Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA)- Work Package 1
Work Package 1 addresses the Interaction of the Southern Ocean with the Atmosphere and the research will be conducted by the National Oceanography Centre (NOC), the British Antarctic Survey (BAS), the Plymouth Marine Laboratory (PML) and the Centre for Polar Observation and Modelling(CPOM).
To address Q1, WP1 will make and use new observations (T1, T4) of surface fluxes and their controlling parameters to better constrain the exchanges of heat and carbon across the surface of the Southern Ocean. This will be conducted across a range of conditions: the open ocean, partially ice-covered regions such as leads (cracks) and polynyas, and solid pack-ice.
New instruments will be tested for the measurement of air-sea-ice gas fluxes using laser absorption spectroscopy on RRS James Clark Ross, and to assess their capability to provide accurate surface flux observations. Within this assessment, a comparison with cavity ring-down spectrometer CO2 flux measurements from aircraft flights in a range of surface conditions will be included. An autonomous system integrating sensors, data logging and flux analysis processing will be developed for ORCHESTRA, and for future use on ships of opportunity. A system to quality control historical surface flux and flux-related data from research vessels will also be developed and analysis of existing observations made in the unique conditions of the Southern Ocean will be made.
ORCHESTRA will integrate the new and existing observations to critically assess current state of the art fields of flux and flux-related parameters in atmospheric and oceanic reanalyses, used widely to force ocean models. An assessment of new Earth Observation (EO) measurements and products (T5) that may more accurately represent the surface parameters that control air-sea exchange will be done. Measurement, sampling and structural uncertainties in flux parameterisations will be determined from direct flux measurements, including those made directly by ORCHESTRA. Tests on whether existing parameterisations are suitable for calculating air-sea exchange under the extreme Southern Ocean conditions will be done, with improved parameterisations to be proposed depending on the achieved results.
The sensitivity of heat and carbon fluxes in ocean-only models to realistic uncertainty in both forcing fields and flux parameterisations will be assessed via an adjoint modelling approach (T9). Perturbation experiments will quantify the impact of uncertainty in surface forcing on the model estimates of the ocean state and key processes (T8). The air-sea-ice fluxes of heat, momentum and CO2 in the climate and Earth System simulations (T7) will be assessed at both high and low resolution using observations and uncertainty estimates from ORCHESTRA. These assessments will be used to understand flux-related biases in the UK Earth System Model (UK-ESM), important in reducing the unrealistically warm Southern Ocean near-surface temperatures seen in this and other models.
