Document Type

Data Set

Publication Date

2019

Keywords

Laboratory study, spray generation, air-sea fluxes, hurricane conditions

DOI

10.17604/1qnw-sc60

Abstract

The size-dependent vertical distribution of spume particles in high wind conditions is necessary to understand their effect on air-sea fluxes of heat and momentum. The predominant focus of previous studies of spray dynamics has been on the marine environment. Spray dynamics in non-seawater bodies have not been extensively studied, and any significant differences between sea and freshwater remain unquantified. To address this gap, we have conducted the first laboratory experiment directly comparing spume concentrations above fresh and real seawater for 10-m equivalent wind speeds of 36-54 m/s. Droplets in the air above the intensely breaking wind-waves were directly observed and their distribution as functions of wind speed, height, and droplet radius was compared between the two water types. Spume droplets were imaged using a Dantec Dynamics particle image velocimetry (PIV) acquisition system modified to be used in a shadow imaging mode. A camera was positioned outside of the tank and oriented to be looking into a high intensity strobe, also mounted outside of the tank, but directly opposite the camera. For each of the vertical levels (3 total), the wind was allowed to ramp up and time (120 s) was allowed for the tank conditions to become stationary. Then at least 7 consecutive sets of 250 images were acquired for all five wind speeds. Substantially higher concentrations of seawater spume were observed as compared to freshwater across all particle sizes and wind speeds. The seawater particles’ vertical distribution was concentrated near the surface, whereas the freshwater droplets were more uniformly distributed. Seawater and freshwater height-dependent distributions exhibited different wind-speed dependences. These findings were generally unexpected and point to an unanticipated role of physiochemical processes in the spume generation mechanism which may impact spray-mediated flux parameterization over water bodies of different salinities. This dataset (.mat variable and a .m script) is associated to the above article “A Laboratory Investigation of Spume Generation in High Winds for Fresh and Seawater” by Mehta et al. (2019), submitted in JGR-Atmospheres. Specifically, this is the data used to create figures 2 through 8 in the paper.

Comments

The zip file contains:

1. .mat file named "All_variables" containing all the variables used to plot figures.

2. .m matlab script file "Master_code_for_all_figures" used to plot all figures. Note, this script runs with MatLab R2019a, for previous versions , function movmean(a,k) must be replaced with moving(a,k,'mean').

Contents: The .mat file contain all the variables used to plot figures 2 through 8 in the paper. The script to plot is self explanatory with comments highlighting what each individual section in the code does. The initial data that came from the image analysis has the following variables:

> sw/fw: Contains number concentration data for Fresh Water (fw) and Salt Water (sw) experiments (5). Each Structure is configured the same. There are elements: "nbar" and "y".

> nbar = mean number concentration, N/cm3/micron [M x 27]

> y = height above MWL in ASIST scaled by significant wave height (Hsig) for that experiment (1-5), M x 1 **note** fw has a longer profile than sw. Also, Experiment 3 (45 m/s) for fw is BAD, !!do not use data!!

> Hsig: significant wave height from UDM in ASIST [mm], see Ortiz-Suslow et al. 2016 for placement

> U10: 10-m equivalent wind speed calculated from in situ sonic winds [m/s].

> Ustar: equivalent Ustar, from U10, from Donelan et al. 2004 curve [m/s]

> dr: radius bins (or classes) used for the size spectrum [microns], spaced every 50 microns.

> All other variables in the .mat files came from these variables and can be easily tracked in the code.

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