Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1478 Introducing Surface Gravity Waves into Earth System Models LICHUAN WU ACTA UNIVERSITATIS UPSALIENSIS ISSN 1651-6214 ISBN 978-91-554-9822-1 UPPSALA urn:nbn:se:uu:diva-314760 2017 Dissertation presented at Uppsala University to be publicly examined in Axel Hambergsalen, Villavägen 16, Uppsala, Wednesday, 12 April 2017 at 10:00 for the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty examiner: Dr Peter Janssen (European Centre for Medium-Range Weather Forecasts). Abstract Wu, L. 2017. Introducing Surface Gravity Waves into Earth System Models. Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1478. 50 pp. Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9822-1. Surface gravity waves alter the turbulence of the bottom atmosphere and the upper ocean. Accordingly, they can affect momentum flux, heat fluxes, gas exchange and atmospheric mixing. However, in most state-of-the-art Earth System Models (ESMs), surface wave influences are not fully considered or even included. Here, applying surface wave influences into ESMs is investigated from different aspects. Tuning parameterisations for including instantaneous wave influences has difficulties to capture wave influences. Increasing the horizontal resolution of models intensifies storm simulations for both atmosphere-wave coupled (considering the influence of instantaneous wave-induced stress) and stand-alone atmospheric models. However, coupled models are more sensitive to the horizontal resolution than stand-alone atmospheric models. Under high winds, wave states have a big impact on the sea spray generation. Introducing a wave-state-dependent sea spray generation function and Charnock coefficient into a wind stress parameterisation improves the model performance concerning wind speed (intensifies storms). Adding sea spray impact on heat fluxes improves the simulation results of air temperature. Adding sea spray impact both on the wind stress and heat fluxes results in better model performance on wind speed and air temperature while compared to adding only one wave influence. Swell impact on atmospheric turbulence closure schemes should be taken into account through three terms: the atmospheric mixing length scale, the swell-induced momentum flux at the surface, and the profile of swell-induced momentum flux. Introducing the swell impact on the three terms into turbulence closure schemes shows a better performance than introducing only one of the influences. Considering all surface wave impacts on the upper-ocean turbulence (wave breaking, Stokes drift interaction with the Coriolis force, Langmuir circulation, and stirring by non-breaking waves), rather than just one effect, significantly improves model performance. The non- breaking-wave-induced mixing and Langmuir circulation are the most important terms when considering the impact of waves on upper-ocean mixing. Accurate climate simulations from ESMs are very important references for social and biological systems to adapt the climate change. Comparing simulation results with measurements shows that adding surface wave influences improves model performance. Thus, an accurate description of all important wave impact processes should be correctly represented in ESMs, which are important tools to describe climate and weather. Reducing the uncertainties of simulation results from ESMs through introducing surface gravity wave influences is necessary. Keywords: Surface gravity waves, Air-sea interaction, Earth-System Model, Atmospheric mixing, Upper-ocean turbulence Lichuan Wu, Department of Earth Sciences, LUVAL, Villav. 16, Uppsala University, SE-75236 Uppsala, Sweden. © Lichuan Wu 2017 ISSN 1651-6214 ISBN 978-91-554-9822-1 urn:nbn:se:uu:diva-314760 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-314760) Dedicated to my family and friends 仅以d文.给我的¶º和朋Ë们 List of papers This thesis is based on the following papers, which are referred to in the text by their Roman numerals. I Wu, L., Sproson, D., Sahlée, E., Rutgersson, A. (2017). Surface wave impact when simulating mid-latitude storm development. Journal of Atmospheric and Oceanic Technology, 34(1), 233–248. doi: 10.1175/JT ECH-D-16-0070.1. II Wu, L., Rutgersson, A., Sahlée, E., Larsén, X.G. (2015). The impact of waves and sea spray on modelling storm track and development. Tellus. Series A, Dynamic meteorology and oceanography, 67, 27967. doi: 10.3402/tellusa.v67.27967. III Wu, L., Rutgersson, A., Sahlée, E., Larsén, X.G. (2016). Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere- wave model. Journal of Geophysical Research: Oceans, 121(7), 4633– 4648. doi: 10.1002/2015JC011576. IV Wu, L., Rutgersson, A., Nilsson, E. (2017). Atmospheric boundary layer turbulence closure scheme for wind-following swell conditions. Journal of the Atmospheric Sciences (Under review). V Wu, L., Rutgersson, A., Sahlée, E. (2015). Upper-ocean mixing due to surface gravity waves. Journal of Geophysical Research: Oceans, 120(12), 8210–8228. doi: 10.1002/2015JC011329. Reprints were made with permission from the publishers. In the above listed papers, I was responsible for the model developments, experimental designs, numerical modelling, analysis of the results and writing of the papers. In Paper I, D. Sproson contributed to the model development and experimental design. The other co-authors contributed to discussions about the ideas of the studies, giving feedback to the results, writing the manuscripts and sharing measurements. In addition, I have contributed to the following journal papers during my PhD study, which are not appended to this thesis. Wu, L., Hristov T., Rutgersson, A. (2017). Vertical profile of spectrum- integrated wave-coherent momentum flux and variances (submitted). Jeworrek, J., Wu, L., Christian D., Rutgersson, A. (2017). Character- istics of Convective Snow Bands along the Swedish East Coast. Earth System Dynamics (In press). doi:10.5194/esd-2016-43. Cai, Y., Wen Y., Wu, L., Zhou C., Zhang F. (2017). Impact of wave breaking on upper-ocean turbulence. Journal of Geophysical Research: Oceans (In press). doi: 10.1002/2016JC012654. Wen, Y., Geng, X., Wu, L., Yip, T.L., Huang, L., Wu, D. (2017). Green routing design in short seas. Int. J. Shipping and Transport Logistics (In press). doi: 10.1504/IJSTL.2017.10002963. Wu, L., Wen, Y., Zhou C., Xiao, C., Zhang, J. (2014). Modeling the Vul- nerability of Waterway Networks. Journal of waterway, port, coastal, and ocean engineering 140(4): 04014012. doi: 10.1061/(ASCE)WW.1 943-5460.0000238. Contents 1 Introduction .................................................................................................. 9 2 Background ................................................................................................ 12 2.1 Monin-Obukhov similarity theory ................................................ 12 2.2 Turbulence closure schemes .......................................................... 13 2.2.1 K-theory ........................................................................... 13 2.2.2 E − l model ...................................................................... 14 2.2.3 MYNN model .................................................................. 14 2.2.4 k − e Model ...................................................................... 15 3 Parameterisations with wave influences ................................................... 16 3.1 Wave-induced stress ....................................................................... 16 3.1.1 Wave spectra model ......................................................... 16 3.1.2 Parameterisation .............................................................. 17 3.2 Sea spray influences ....................................................................... 18 3.2.1 Wind stress ....................................................................... 18 3.2.2 Heat flux ........................................................................... 20 3.3 Swell impact on atmospheric mixing ............................................ 20 3.3.1 E − l model ...................................................................... 20 3.3.2 MYNN model .................................................................. 21 3.4 Wave impact on upper-ocean turbulence ...................................... 22 3.4.1 Breaking waves ................................................................ 22 3.4.2 Stokes drift ....................................................................... 23 3.4.3 Non-breaking waves ........................................................ 23 4 Models and data ......................................................................................... 25 4.1 Coupled models .............................................................................. 25 4.2 1D models ....................................................................................... 25 4.3 Measurements ................................................................................. 26 5 Results ........................................................................................................ 27 5.1 Influence of instantaneous waves .................................................. 27 5.2 Influence of horizontal resolution ................................................. 30 5.3 Influence of sea spray .................................................................... 30 5.4