Rain‐induced turbulence and air‐sea gas transfer

Abstract

[1] Results from a rain and gas exchange experiment (Bio2 RainX III) at the Biosphere 2 Center demonstrate that turbulence controls the enhancement of the air-sea gas transfer rate (or velocity) k during rainfall, even though profiles of the turbulent dissipation rate e are strongly influenced by near-surface stratification. The gas transfer rate scales with e 1 = 4 for a range of rain rates with broad drop size distributions. The hydrodynamic measurements elucidate the mechanisms responsible for the rain-enhanced k results using SF 6 tracer evasion and active controlled flux technique. High-resolution k and turbulence results highlight the causal relationship between rainfall, turbulence, stratification, and air-sea gas exchange. Profiles of e beneath the air-sea interface during rainfall, measured for the first time during a gas exchange experiment, yielded discrete values as high as 10 À2 W kg À1 . Stratification modifies and traps the turbulence near the surface, affecting the enhancement of the transfer velocity and also diminishing the vertical mixing of mass transported to the air-water interface. Although the kinetic energy flux is an integral measure of the turbulent input to the system during rain events, e is the most robust response to all the modifications and transformations to the turbulent state that follows. The Craig-Banner turbulence model, modified for rain instead of breaking wave turbulence, successfully predicts the near-surface dissipation profile at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k as it allows inferring the surface value of e fundamental to gas transfer.

Transfer Across the Air-Sea Interface

“…These studies began in the 1960s, where initial laboratory studies using O 2 invasion employed a rain simulators that had only 8-12 nozzles so only produced a few raindrops at a time, and only investigated a range of rain rates up to 17 mm h À1 (Department of Scientific and Industrial Research 1964;Banks and Herrera 1977;Banks et al 1984). In the last two decades, systematic laboratory studies examining the full range of rain rates encountered in nature have quantified the effect of rain on gas exchange (Ho et al 1997;Takagaki and Komori 2007), the interaction between rain and wind , the mechanism behind the enhancement (Ho et al 2000), the effect in saltwater Ho et al (2004); Zappa et al (2009). Furthermore, some modeling studies have been conducted to examine the potential effect of rain on air-sea CO 2 exchange Turk et al 2010).…”

“…Enhancement in k w (660) is due mostly to increased near surface turbulence, whereas bubbles play a minor role (Ho et al 2000). Experiments in saltwater demonstrate that the relationship between rain and k w (660) is the same as in freshwater, but density stratification could inhibit vertical mixing and decrease the overall gas flux (Ho et al 2004;Zappa et al 2009). …”

“…Since the profile of turbulence near the air-water interface may be complicated by the interplay between wind, waves, current shear and other processes, measurements at depth will not be representative of ε at the surface because the profile changes nonlinearly with environmental forcing. Zappa et al (2009) implement the Craig-Banner turbulence model, modified for rain instead of breaking-wave turbulence, to successfully predict the near-surface dissipation profile that varies by two orders of magnitude over the top 50 cm at the onset of the rain event before stratification plays a dominant role. This result is important for predictive modeling of k w as it allows inferring the surface value of ε fundamental to gas transfer.…”

The FuGas 2.3 Framework for Atmosphere–Ocean Coupling: Comparing Algorithms for the Estimation of Solubilities and Gas Fluxes

“…Such are the formulations proposed by Carini et al [30] or Raymond and Cole [31], accounting only for u 10 , or by Borges et al [32], adding current drag with the bottom. Meanwhile, new evidence emerged for the effects of the sea surface cool-skin and warm-layer [33][34][35][36][37][38], atmospheric stability [39,40], wave-breaking [41][42][43][44][45][46][47][48][49][50], water surface renewal [28,[51][52][53][54][55][56][57], surfactants [28,[58][59][60] and rain [61][62][63][64], just to mention a few examples from an extensive list of published works. In addition to their single influence, these factors also interact.…”

Integration of the Visible Color Spectrum and the Rough Sets Theory in the Process of Expert Knowledge Extraction

“…Color spectra have been already used in many studies to present different types of information. For example, such a scale is used in geographical research to represent the level of temperature, salinity, density, and frequency of the ocean biosphere [22]. In making medical diagnosis such a scale is used to indicate the surface plasmon resonance angle during the study of the live cell membrane [23] or in echocardiography images [24].…”