Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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- 44 - Sensitivity in Calculation of Turbulent Fluxes over Sea to the State of the Surface Waves Anna Rutgersson, Ann-Sofi Smedman and Björn Carlsson Department of Earth Sciences, Meteorology, Uppsala University, Uppsala, Sweden. anna.rutgersson@geo.uu.se 1. Introduction It has been shown in numerous investigations, from the Baltic Sea as well as other regions that the state of the waves influences the overlying atmosphere. Relatively recently it was found that also the situation with long waves (swell) changes the structure of the atmosphere. This has been seen and shown for many atmospheric parameters in Smedman et al. (1999), Rutgersson et al. (2001) and other investigations. In numerical wave models the process of including also swell effects is now starting and has been shown to be of importance for surface fluxes (Kudryavtsev and Makin, 2003). To find out if the effect of swell is so important that it should be included in atmospheric and ocean models we are investigating the sensitivity of turbulent fluxes in different models to wave effects. 2. Methods The specific situation of interest here is the situation where we have long waves (or swell). Then the waves are not locally generated by the wind, but have travelled from other regions. These situations have been shown to occur frequently over the Baltic Sea (Rutgersson et al., 2001). In Guo Larsén et al., (2003a and b) and Rutgersson et al., (2001) new values for the dimensionless gradients as well as transfer coefficients for heat and momentum have been determined for the situation when we have long waves. In Figure 1 the non-dimensional wind gradient (Φm) φ m ∂U zκ = ∂z u * at 10 and 26 meters is shown when swell is present. Data is from the Östergarnsholm-site in the Baltic Sea. As is clear from the figure the gradients differ significantly from the expected value (represented by the solid line). Effect of changed in transfer coefficients and gradients are investigated when calculating the surface fluxes from bulkformulations. Bulk-formulations are frequently used when estimating surface fluxes in different types of databases (ship data, satellite data and also in gridded synoptic databases). Thus, if waves influence surface fluxes calculated by bulk-formulations is of great importance to know when determining for example heat and water budgets over the Baltic Sea. In most models transfer coefficients are calculated with assumptions based on previous knowledge of air-sea interaction. It is possible to assume that the wave effect is smaller in a model, since models tend to adjust themselves to a changed parameterisation. The sensitivity is investigated in a ocean process-oriented model, PROBE-Baltic covering the Baltic Sea (Omstedt and Axell, 2003) and forced with gridded meteorological data. The regional climate model RCA (Rummukainen et al., 2001) is used for limited periods to investigate the possible results of introducing wave-effects in surface fluxes in a regional climate model-system covering the Baltic Sea region. Figure 1. Non-dimensional wind gradient at 10 and 26 metres for the situation when swell is present (filled symbols). The solid lines represent the expected gradients for different values of the atmospheric stability (z/L). 3. Results Since there generally exist no information about the state of the waves in most models it is not possible to include a full description of the wave effects, but we are instead investigating the sensitivity of the models to possible wave effects. This is important to know before starting to couple to an ocean wave model. In Figure 2 the surface stress is calculated using a bulk-formulation developed for the situation with swell (red-dashed curve) and a state-of-theart bulk-formulation not including wave effects (blue-solid curve). The period is one with very well developed swell and the red curve thus agrees well with the measured surface stress (green pluses). It is here interesting to note that the blue curve is about 40% larger that the red and would thus give an overestimation of the flux using ordinary bulk methods with about 40%. This is expected to be larger than for sensible and latent heat fluxes.
Figure 2. Surface stress from two days in September 1995. Pluses are directly measured surface stress, red-dashed line is calculated using a revised bulk-formulation valid for swell and blue-solid line is calculated a generally used bulkformulation. References Guo Larsén, X., and Smedman, A.-S., Impact of waves on air-sea exchange of sensible heat in the Baltic Sea. Submitted to Q. J. R. Meteorol. Soc., 2003a Guo Larsén, X., Makin, V. and Smedman, A.-S., Impact of waves on the sea drag: measurements in the Baltic Sea and a model interpretation. Submitted to The Global Atmosphere and Ocean System., 2003b Kudryavstev, V. N. and Makin, V. K., Impact of Swell on marine Atmospheric Boundary Layer, Submitted to J. Phys. Ocean., 2003 Omstedt, A. and L., Axell. Modeling the variations of salinity and temperature in the large Gulfs of the Baltic Sea. Continental Shelf Research, 23, 265-294, 2003 Rummukainen, M., J. Räisänen, B. Bringfelt, A. Ullerstig, A. Omstedt, U. Willen, U. Hansson and C. Jones. A regional climate model for northern Europe – model description and results from the downscaling of two GCM control simulations. Climate Dyn., 2001 Rutgersson, A., Smedman, A.-S., Högström, U., Use of conventional stability parameters during swell, J. Geophys. Res., 106 , 27,117-27,134., 2001 Smedman, A., Högström, U., Bergström, H., Rutgersson, A., Kahma, K., and H. Pettersson, A case-study of air-sea interaction during swell conditions, J. Geophys. Res, 104, 25,833-25,851, 1999 - 45 -
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Fourth Stu
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Preface The 4 th Study</str
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- I - Table of Abstracts Title Auth
Page 9 and 10: - III - Sensitivity in Calculation
Page 11 and 12: - V - Parameter Estimation of the S
Page 13 and 14: - VII - The Realism of the ECHAM5.2
Page 15 and 16: Adam, W. K. .......................
Page 17 and 18: - 1 - Activities of the GEWEX Hydro
Page 19 and 20: eference site archive (Cabauw, Neth
Page 21 and 22: - 5 - Remote Sensing of Atmospheric
Page 23 and 24: minute averages around the satellit
Page 25 and 26: - 9 - Precipitation Type Statistics
Page 27 and 28: - 11 - Assimilation of New Land Sur
Page 29 and 30: Multichannel Microwave Radiometer f
Page 31 and 32: output has been processed in an equ
Page 33 and 34: height dependence of the Z-R-relati
Page 35 and 36: - 19 - CERES and Surface Radiation
Page 37 and 38: - 21 - Coastal Wind Mapping from Sa
Page 39 and 40: - 23 - Clouds and Water Vapor over
Page 41 and 42: - 25 - Broadband Cloud Albedo from
Page 43 and 44: - 27 - Observation of Clouds and Wa
Page 45 and 46: shows a ground-track of the vessel
Page 47 and 48: - 31 - Determination and Comparison
Page 49 and 50: - 33 - Spatial Variability of Snow
Page 51 and 52: - 35 - EVA-GRIPS: Regional Evaporat
Page 53 and 54: - 37 - LITFASS-2003 - A Land Surfac
Page 55 and 56: -39- Calibrated Surface Temperature
Page 57 and 58: - 41 - The Marine Boundary Layer -
Page 59: - 43 - Characteristics of the Atmos
Page 63 and 64: During the experiment the water was
Page 65 and 66: While the number of smallest drops
Page 67 and 68: SCANDIA will not be supported any l
Page 69 and 70: - 53 - Relationships Between Precip
Page 71 and 72: - 55 - Analysis of the Role of Atmo
Page 73 and 74: - 57 - Meteorological Peculiarities
Page 75 and 76: Baltic Sea Inflow Events Jan Piechu
Page 77 and 78: - 61 - The Different Baltic Inflows
Page 79 and 80: - 63 - Observations of Turbulent Ki
Page 81 and 82: - 65 - The Influence of Synoptic Si
Page 83 and 84: -67- Improved Method for the Determ
Page 85 and 86: -69- The Helicopter-Borne Turbulenc
Page 87 and 88: - 71 - CEOP Reference Site Data fro
Page 89 and 90: - 73 - The BALTEX Hydrological Data
Page 91 and 92: - 75 - Hydrological and Hydrochemic
Page 93 and 94: -77- Sea-level Monitoring at MARNET
Page 95 and 96: 1 0.8 0.6 0.4 0.2 GO(CLD-M) ERA40 S
Page 97 and 98: Figure 2. Monhly mean values of lat
Page 99 and 100: In the case of an ideal fit, the co
Page 101 and 102: - 85 - Influence of Atmospheric For
Page 103 and 104: The largest inter-annual variabilit
Page 105 and 106: References Andrejev, O, Sokolov, A.
Page 107 and 108: On the other hand, if the stratific
Page 109 and 110: Cyberska 1989, Cyberska and Krzymin
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- 95 - Continental-Scale Water-Bala
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- 97 - ICTS (Inter-CSE Transferabil
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The subsurface flow calculation is
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functions only data with higher qua
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- 103 - Modelling the Impact of Ine
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- 105 - Objective Calibration of th
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- 107 - Validation of Boundary Laye
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- 109 - Simulated Dynamical Process
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spreads along isobaths (fig.2). As
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than the precipitation pattern of J
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Figure 2. Long-term variability in
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obvious from temperature charts. Ho
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shortening of the winter seasons by
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Maximum 5 day precipitation (mm) Nu
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scale parameters the correlation be
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similar: the locations of main mini
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- 127 - Storminess on the Western C
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- 129 - Trends in Wind Speed over t
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- 131 - Wind Energy Prognoses for t
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- 133 - Detection of Climate Change
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Figure 3. Cross section of salinity
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of 35 m/s up to 3 hours. Data on wi
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Figure 2. Time series of Mean Sea L
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- 141 - Calculation and Forecast of
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- 143 - An Overview of Long-Term Ti
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- 145 - Baltic Sea Saltwater Inflow
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- 147 - Significance of Feedback in
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Lindström, G., Johansson, B., Pers
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- 151 - Air-Sea Fluxes Including Mo
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- 153 - The Realism of the ECHAM5.2
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- 155 - Figure 3. Accumulated total
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Figure 2. Example for Fourier decom
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Figure1. Modeled percent volume cha
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conditions even more challenging th
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surface heat fluxes close to zero.
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- 165 - Figure 1. Modeled seasonal
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- 167 - Present-Day and Future Prec
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- 169 - Extreme Precipitation on a
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at the stations Pärnu (Estonia) an
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6. Results There are many possible
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and vegetation, and to derive the h
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The structure of water bodies cadas
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Figure 1. The area of Gdańsk subje
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- 181 - Climate and Water Resources
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- 183 - Generating Synthetic Daily
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The evapotranspiration is affected
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Model parameters and coefficients:
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3. Hydrodynamic model of nutrient l
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No. 15: Minutes of 8 th Meeting of
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Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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