Air-Sea Flux Measurements over the Southern Ocean David James Tupman Submitted in accordance with the requirements for the degree of Doctor of Philosophy The University of Leeds School of Earth and Environment August 2013 The candidate confirms that the work submitted is his own and that appropriate credit has been given where reference has been made to the work of others. This copy has been supplied on the understanding that it is copyright material and that no quotation from the thesis may be published without proper acknowledgement. - 1 - Acknowledgements I would primarily like to thank Ian Brooks for supervision, guidance, and comments throughout the period of study, and the rest of the air-sea interaction group at ICAS. Thanks to all at NOC and BAS who contributed to the WAGES project, but particularly to Margaret Yelland and John Prytherch for many useful discussions and comments. Many thanks of course to all at ICAS who made my time at Leeds and working life there so enjoyable. - 2 - Abstract The Waves, Aerosol, and Gas Exchange Study (WAGES) collected 18 months of near-continuous and autonomous turbulent air-sea flux estimates from the research vessel RRS James Clark Ross. Supporting meteorological and sea-state measurements were also made, with the objective of improving air-sea flux parameterisations. Making turbulence measurements from a ship is technically challenging, due to bias caused by platform motion and airflow distortion. Typically, visual inspection of individual turbulence spectra is needed to quality control eddy covariance flux estimates; for WAGES the sheer volume of data motivated the development of an automated quality control method, to be performed on individual flux cospectra. The application of these tests allowed a robust relationship between the 10 m wind speed and the neutral drag coefficient to be developed, which had previously not been achieved with ship-based covariance measurements alone. This parameterisation is toward the higher end of the range of accepted values, and indicates some wind speed dependence of the Charnock parameter, rather than it being a constant. A detailed investigation of turbulent flow distortion was made; insights into the physics were gained, and a novel correction method for motion-correlated flow distortion was developed and validated. Two major modes of motion-correlated flow distortion of the turbulence were found: one correlated to the pitch, acknowledge in the literature; a second and more powerful mode correlated to the rate of change of the pitch, not acknowledged in any publication. The quality control and bias correction techniques developed for the momentum fluxes were transferred to a preliminary investigation of the sensible and latent heat fluxes. The uncertainty in the latent heat transfer coefficient was reduced considerably by use of the new techniques; however the sensible heat fluxes were dominated by noise, so discarded. The methods and corrections developed in this thesis could be used to re- analyse the turbulent flux measurements from many ship-based campaigns; improving our understanding of the physics of air-sea exchange without need for additional expensive measurements. - 3 - Contents Acknowledgements ...............................................................................................- 2 - Abstract..................................................................................................................- 3 - Contents .................................................................................................................- 4 - Figures....................................................................................................................- 7 - Tables ...................................................................................................................- 12 - 1 Introduction................................................................................................- 13 - 2 Literature Review ......................................................................................- 18 - 2.1 The atmospheric surface layer above an infinite flat surface............................... - 18 - 2.1.1 Qualitative description of the surface layer .................................................. - 18 - 2.1.2 Quantitative surface layer relationships........................................................ - 22 - 2.1.3 Turbulence Spectra ....................................................................................... - 27 - 2.2 Wave influences on the surface layer................................................................... - 31 - 2.2.1 Stress and turbulent spectra .......................................................................... - 34 - 2.2.2 Vertical wind profile..................................................................................... - 40 - 2.2.3 Effects on TKE terms.................................................................................... - 42 - 2.3 Airflow distortion................................................................................................. - 43 - 2.4 Flux parameterisations ......................................................................................... - 45 - 2.4.1 Wind speed dependence................................................................................ - 45 - 2.4.2 Sea State influence........................................................................................ - 51 - 2.5 Literature review summary .................................................................................. - 54 - 3 WAGES.......................................................................................................- 55 - 3.1 Overview .............................................................................................................. - 55 - 3.1.1 Transition from HiWASE to WAGES.......................................................... - 55 - 3.2 Instrumentation..................................................................................................... - 57 - 3.2.1 Flux instrumentation ..................................................................................... - 57 - 3.2.2 Meteorology and sea state sensors................................................................ - 61 - 3.2.3 Data Logging ................................................................................................ - 63 - 3.3 Post-cruise processing.......................................................................................... - 64 - 3.3.1 Conversion into Matlab compatible files...................................................... - 65 - 3.3.2 Spike removal ............................................................................................... - 66 - - 4 - 3.3.3 Synchronisation of flux sensors.................................................................... - 67 - 3.3.4 Motion Correction......................................................................................... - 68 - 3.3.5 Rotation into the streamline frame of reference ........................................... - 74 - 3.3.6 Choice of time series length.......................................................................... - 77 - 3.3.7 Mean temperature and relative humidity ...................................................... - 79 - 3.3.8 Calculation of mean conditions .................................................................... - 82 - 3.3.9 Calculation of fluxes..................................................................................... - 85 - 3.4 Quality control...................................................................................................... - 86 - 3.4.1 Major events and data losses......................................................................... - 86 - 3.5 Flux Results.......................................................................................................... - 95 - 3.6 Summary ............................................................................................................ - 102 - 4 Automated spectral quality control........................................................- 104 - 4.1 Common contamination types............................................................................ - 105 - 4.2 Overview ............................................................................................................ - 108 - 4.3 Kaimal form fitting............................................................................................. - 110 - 4.4 Motion contamination ........................................................................................ - 111 - 4.4.1 Ship motion frequency band detection ....................................................... - 111 - 4.4.2 Motion contamination and interpolation..................................................... - 113 - 4.5 High frequency contamination........................................................................... - 117 - 4.6 Cospectral peak frequency rejection .................................................................. - 119 - 4.7 Relative wind direction restrictions.................................................................... - 121 - 4.8 General quality test............................................................................................. - 124 - 4.9 Results ................................................................................................................ - 126 - 4.10 Summary........................................................................................................