Using land-based stations for air–sea interaction studies

Abstract

In situ measurements representing the marine atmosphere and air-sea interaction are taken at ships, buoys, stationary moorings and land-based towers, where each observation platform has structural restrictions. Air-sea fluxes are often small, and due to the limitations of the sensors, several corrections are applied. Land-based towers are convenient for long-term observations, but one critical aspect is the representativeness of marine conditions. Hence, a careful analysis of the sites and the data is necessary. Based on the concept of flux footprint, we suggest defining flux data from land-based marine micrometeorological sites in categories depending on the type of land influence: 1. CAT1: Marine data representing open sea, 2. CAT2: Disturbed wave field resulting in physical properties different from open sea conditions and heterogeneity of water properties in the footprint region, and 3. CAT3: Mixed land-sea footprint, very heterogeneous conditions and possible active carbon production/consumption. Characterization of data would be beneficial for combined analyses using several sites in coastal and marginal seas and evaluation/comparison of properties and dynamics. Aerosol fluxes are a useful contribution to characterizing a marine micrometeorological field station; for most conditions, they change sign between land and sea sectors. Measured fluxes from the land-based marine station € Ostergarnsholm are used as an example of a land-based marine site to evaluate the categories and to present an example of differences between open sea and coastal conditions. At the € Ostergarnsholm site the surface drag is larger for CAT2 and CAT3 than for CAT1 when wind speed is below 10 m/s. The heat and humidity fluxes show a distinctive distinguished seasonal cycle; latent heat flux is larger for CAT2 and CAT3 compared to CAT1. The flux of carbon dioxide is large from the coastal and land-sea sectors, showing a large seasonal cycle and significant variability (compared to the open sea sector). Aerosol fluxes are partly dominated by sea spray emissions comparable to those observed at other open sea conditions.

The FuGas 2.5 Updated for the Effects of Surface Turbulence on the Transfer Velocity of Gases at the Atmosphere–Ocean Interface

“…Several explanations have been advanced for the swell interference in the transfer velocities. The older and larger waves have been demonstrated as having a direct interaction with the atmosphere, and as interfering in the properties of the shorter wind-waves that often regulate the turbulence and air-flow over the sea-surface [77][78][79]. The interference of swell was demonstrated to be stronger with lower winds, steeper waves and/or when opposing the wind direction [50,51,54], which was precisely our case.…”

“…Simultaneously, we measured the atmospheric and oceanic variables related with turbulence and commonly used in formulations estimating gas transfer velocities. The surveys took place in the Baltic Sea during May 2014 and May to September 2015, with data sampled at the atmospheric tower at Östergarnsholm (57 • 27 N, 18 • 59 E), and with the Submersible Autonomous Moored Instrument (SAMI-CO 2 ) 1 km away and the Directional Waverider (DWR) 3.5 km away, both south-eastward from the tower [7,12,45,[77][78][79]. The vertical CO 2 fluxes measured by E-C were averaged over 30 min bins, and subject to the Webb-Pearman-Leuning (WPL) correction [80].…”

“…For the u * estimates, we used only the wind data without flow distortion from land or from our own atmospheric tower (80 • < wind direction < 220 • ). For an extensive description of the data processing, quality control and selection of data from open sea sectors, we refer to Nilsson et al [78] and Rutgersson et al [79]. Furthermore, time sequences with abrupt changes in wind properties were discarded, assuming that the homogeneity of conditions had been severely violated.…”

Cyanobacteria net community production in the Baltic Sea as inferred from profiling &lt;i&gt;p&lt;/i&gt;CO&lt;sub&gt;2&lt;/sub&gt; measurements

“…Meteorological observations were provided by the ICOS flux tower (Fig. 1b) located on the southernmost tip of the Island of Östergarnsholm (57.43010°N, 18.98415°E;Rutgersson et al, 2020). Atmospheric pCO 2 was recorded with an atmospheric profile system (AP200, Campbell Scientific, Logan, USA) mounted with a CO 2 /H 2 O gas analyzer (LI-840A, LI-COR Biosciences, Lincoln, USA).…”

Looking for an Offshore Low-Level Jet Champion among Recent Reanalyses: A Tight Race over the Baltic Sea

“…The Östergarnsholm measurement station is a meteorological research site located at the southern tip of a small (approximately 2 km 2 ), flat island 4 km east of Gotland (e.g., [34,35]). The site is part of the ICOS (Integrated Carbon Observatory System) and includes, among other things, a 30-m-high land-based tower with high-frequency measurements and a continuous-wave scanning LiDAR, Z300 ZX LiDARs, modified to measure up to 300 m and store raw data [36].…”