Studies of turbulence in the surface layer over water (Lough Neagh). Part I. Instrumentation, programme, profiles

<jats:title>Abstract</jats:title><jats:p>Instrumentation is described which has been used over a body of deep water, with fetches of 8 km to 22 km, to provide (i) vertical profiles of mean wind <jats:italic>u</jats:italic>, potential temperature ø and specific humidity <jats:italic>q</jats:italic> from the water surface to 16 m height and (ii) turbulent fluctuations of temperature and of the longitudinal and vertical components of wind and hence the vertical fluxes of momentum and sensible heat.</jats:p><jats:p>Logarithmic wind profiles in near‐neutral conditions lead to a drag‐coefficient <jats:italic>C</jats:italic><jats:sub><jats:italic>D</jats:italic></jats:sub> of the water surface as a function of the wind speed <jats:italic>u</jats:italic><jats:sub>10</jats:sub> at 10 m height given by 10<jats:sup>3</jats:sup> <jats:italic>C</jats:italic><jats:sub><jats:italic>D</jats:italic></jats:sub> = 0.36 + 0.10<jats:italic>u</jats:italic><jats:sub>10</jats:sub> (3 m s<jats:sup>−1</jats:sup> < <jats:italic>u</jats:italic><jats:sub>10</jats:sub> < 16 m s<jats:sup>−1</jats:sup>). Corresponding bulk transfer coefficients for heat and water vapour are not distinguishably different from <jats:italic>C</jats:italic><jats:sub><jats:italic>D</jats:italic></jats:sub> in the observed range of <jats:italic>u*z<jats:sub>0</jats:sub>/ν</jats:italic> < 10<jats:sup>2</jats:sup> (conventional nomenclature).</jats:p><jats:p>An analysis, following Webb (1970), of profiles in stable conditions (0 < Ri<jats:sub>4</jats:sub> ≤ 0.16) lends support to the utility of the log‐linear form. Using the Monin‐Oboukhov relation ∂<jats:italic>X</jats:italic>/∂<jats:italic>z</jats:italic> = <jats:italic>X</jats:italic>*ø (<jats:italic>z</jats:italic>/<jats:italic>L</jats:italic>)/(<jats:italic>kz</jats:italic>) where × is either <jats:italic>u, ø</jats:italic>, or <jats:italic>q</jats:italic> and taking ø(<jats:italic>z</jats:italic>/<jats:italic>L</jats:italic>) = 1 + α <jats:italic>z</jats:italic>/<jats:italic>L</jats:italic>, so that <jats:italic>z/L</jats:italic> = Ri/(1− α Ri), we find α ≃ 6. In unstable conditions (0 > Ri<jats:sub>4</jats:sub> ≥ −0.6) the profile shape factor <jats:italic>S</jats:italic><jats:sub><jats:italic>x</jats:italic></jats:sub> = (<jats:italic>X</jats:italic><jats:sub>4</jats:sub> − <jats:italic>X</jats:italic><jats:sub>1</jats:sub>)/(<jats:italic>X</jats:italic><jats:sub>16</jats:sub> − <jats:italic>X</jats:italic><jats:sub>1</jats:sub>) is greater for ø than for <jats:italic>u</jats:italic>, implying ø<jats:sub><jats:italic>H</jats:italic></jats:sub> < ø<jats:sub><jats:italic>M</jats:italic></jats:sub> (K<jats:sub>H</jats:sub> > <jats:italic>K</jats:italic><jats:sub><jats:italic>M</jats:italic></jats:sub>) but <jats:italic>S</jats:italic><jats:sub><jats:italic>q</jats:italic></jats:sub> has less well defined behaviour. The data on <jats:italic>S</jats:italic><jats:sub><jats:italic>u</jats:italic>,ø</jats:sub> are not inconsistent with ø<jats:sub><jats:italic>M</jats:italic></jats:sub> = (1 − 16 z/L)<jats:sup>−1/4</jats:sup>, ø<jats:sub>H</jats:sub> = ø<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/tex2gif-stack-1.gif" xlink:title="urn:x-wiley:00359009:media:QJ49709841711:tex2gif-stack-1" />, as proposed by Dyer and Hicks (1970) and others but the shape factor is very insensitive to the numerical factor multiplying <jats:italic>z/L</jats:italic> in these relations.</jats:p><jats:p>Analysis of the measurements of turbulent fluctuations and derived fluxes will be presented in later papers.</jats:p>