The Influence of Preexisting Stratification and Tropical Rain Modes on the Mixed Layer Salinity Response to Rainfall

Iyer, Suneil; Drushka, Kyla

doi:10.1029/2021jc017574

Cited by 8 publications

(14 citation statements)

References 69 publications

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Section: Rl Statistics From 2d Forcing Experimentssupporting

confidence: 90%

“…As there are few cases of RLs forming over strong upper ocean stratification at wind speeds above 6 m s −1 , wind speed bins in Figure 10 only extend to 6 m s −1 . This result conforms to the idealized model experiments of Iyer and Drushka (2021a) that revealed larger salinity anomalies and delayed mixing in the upper ocean when rain falls on a stably stratified upper ocean compared to rain falling on a well-mixed upper ocean. 𝐴𝐴 N 2 𝑇𝑇 within rain layers (RLs) binned column-wise by max rain rate from 30 min prior to 30 min after RL formation, and row-wise by mean wind speed over the interval of 1 hr prior to 6 hr after RL formation.…”

Section: Rl Duration Frequency and Intensitysupporting

confidence: 89%

“…A challenge in using atmospheric model output as forcing data to compile RL statistics arises when assessing RL behavior many hours after formation. Idealized experiments allow for assessment of RL characteristics from single impulse rain rates (Drushka et al., 2016 ) or an idealized evolution of rain and wind‐based on observations (Iyer & Drushka, 2021a ). Forcing GOTM with WRF output provides complex and realistic atmospheric forcing conditions which aids understanding of RL duration, frequency, intensity, and size.…”

Section: Discussionmentioning

confidence: 99%

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Rain‐Induced Stratification of the Equatorial Indian Ocean and Its Potential Feedback to the Atmosphere

et al. 2022

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Surface freshening through precipitation can act to stably stratify the upper ocean, forming a rain layer (RL). RLs inhibit subsurface vertical mixing, isolating deeper ocean layers from the atmosphere. This process has been studied using observations and idealized simulations. The present ocean modeling study builds upon this body of work by incorporating spatially resolved and realistic atmospheric forcing. Fine‐scale observations of the upper ocean collected during the Dynamics of the Madden‐Julian Oscillation field campaign are used to verify the General Ocean Turbulence Model (GOTM). Spatiotemporal characteristics of equatorial Indian Ocean RLs are then investigated by forcing a 2D array of GOTM columns with realistic and well‐resolved output from an existing regional atmospheric simulation. RL influence on the ocean‐atmosphere system is evaluated through analysis of RL‐induced modification to surface fluxes and sea surface temperature (SST). This analysis demonstrates that RLs cool the ocean surface on time scales longer than the associated precipitation event. A second simulation with identical atmospheric forcing to that in the first, but with rainfall set to zero, is performed to investigate the role of rain temperature and salinity stratification in maintaining cold SST anomalies within RLs. Approximately one third, or 0.1°C, of the SST reduction within RLs can be attributed to rain effects, while the remainder is attributed to changes in atmospheric temperature and humidity. The prolonged RL‐induced SST anomalies enhance SST gradients that have been shown to favor the initiation of atmospheric convection. These findings encourage continued research of RL feedbacks to the atmosphere.

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Section: Rl Statistics From 2d Forcing Experimentssupporting

confidence: 90%

Section: Rl Duration Frequency and Intensitysupporting

confidence: 89%

Section: Discussionmentioning

confidence: 99%

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Rain‐Induced Stratification of the Equatorial Indian Ocean and Its Potential Feedback to the Atmosphere

et al. 2022

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“…Therefore, we suggest the existence of another, but very shallow, freshwater lens. A freshwater lens can persist for hours or days under lower wind speed conditions (Drushka et al, 2019;Iyer & Drushka, 2021a;Price, 1979;Reverdin et al, 2012Reverdin et al, , 2021Thompson et al, 2019). Moulin et al (2021) reported that most of the 28 freshwater lenses were observed at wind speeds of less than 5 m s −1 .…”

Section: Response Of δS and δT During Precipitation Events And Frontsmentioning

confidence: 99%

Temperature and Salinity Anomalies in the Sea Surface Microlayer of the South Pacific During Precipitation Events

et al. 2023

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We present the results of salinity (ΔS) and temperature (ΔT) anomalies in the sea surface microlayer (SML) in relation to the underlying mixed bulk water (bulk). Several light to moderate rain events were recorded in the southern Pacific near Fiji using our remotely operated catamaran. Precipitation and evaporation drive freshwater fluxes across the sea surface (i.e., the SML) and are the most essential processes of the hydrologic cycle. However, measurements of the SML during precipitation are rare, but necessary to fully understand freshwater exchange at the air‐sea interface. Here we show that freshwater can mix rapidly with the bulk water through wind‐induced mixing, as ΔS and ΔT show a clear dependence on wind speed. At high wind speeds (5.1–11.6 m s−1), anomalies approach zero (ΔS = −0.02 ± 0.49 g kg−1, ΔT = −0.09 ± 0.46°C) but can reach ΔS = 1.00 ± 0.20 g kg−1 and ΔT = −0.37 ± 0.09°C at lower wind speeds (0–2 m s−1). We find shallow freshwater lenses and fronts, likely caused by past rainfall, with ΔS and ΔT of up to −1.11 g kg−1 and 1.77°C, respectively. Our observations suggest that freshwater lenses can be very shallow (<1 m depth) and missed by conventional measurements. In addition, the temperature and salinity in the SML respond to freshwater fluxes instantaneously. It highlights the role of the SML in a mechanistic understanding of the fate of freshwater over the ocean and, therefore, the global hydrologic cycle.

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“…Rainfall also covaries with and depends on various other atmospheric variables, for example the wind, air temperature, humidity, and properties of clouds (Rickenbach and Rutledge 1998;Tokay et al 1999;Masunaga et al 2005;Jin et al 2018;Stephens et al 2019;Iyer and Drushka 2021a), which also influence the downwelling shortwave and longwave radiation at the sea surface. As a consequence of the variable multitude of changes to the atmosphere and ocean that occur with rain and the intermittency of strong rain events, the characteristics of the surface atmosphere and upper ocean during rain events vary considerably in space and time and how the upper ocean responds to a rain event is not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Rain Impacts on the Surface Atmosphere and Upper Ocean in the Central Equatorial Pacific

Whitt

2022

Journal of Physical Oceanography

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The impacts of rainy days (> 24 mm) on the physics of the surface atmosphere and upper ocean are characterized in the central Pacific Ocean (140-170°W) on the equator, where deep-cycle turbulence substantially influences the sea-surface temperature and air-sea heat flux on diurnal and longer timescales. Here, rainfall is relatively weak on average (1-3 mm/day), and enough rain to substantially alter the diurnal cycle of upper-ocean buoyancy only occurs on the order of once in 100 days, albeit more frequently to the west and during El Niño and boreal winter. Rainy days are associated with multiple systematic changes in the surface atmosphere, but the freshwater and the reduction in daily downwelling shortwave radiation (by ∼ 50 W/m2) are co-dominant and drive systematic changes in the ocean during and the day after the rainy day. These two drivers explain ensemble average reductions in the upper-ocean salinity −0.12 psu at 1 m) and temperature (−0.16°C at 1 m) and increases in buoyancy (+0.0005 m/s2 at 1 m), which are typically confined to a shallow fresh/warm mixing layer of order 10 m thick in the daytime. At deeper depths, the intrinsic ocean temperature, salinity, and velocity variability make it challenging to extract an ensemble average response to rainy days in observations, but some examples from observations and large eddy simulations suggest that rainfall can significantly reduce the vertical extent and heat flux in the deep-cycle turbulence, although the bulk energetics and buoyancy flux of the turbulence are not necessarily modified by rain.

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The Influence of Preexisting Stratification and Tropical Rain Modes on the Mixed Layer Salinity Response to Rainfall

Abstract: Introduction and BackgroundThe inter-tropical convergence zone (ITCZ) is characterized by frequent rain events, which produce intermittent near-surface salinity anomalies (

Cited by 8 publications

References 69 publications

Rain‐Induced Stratification of the Equatorial Indian Ocean and Its Potential Feedback to the Atmosphere

Rain‐Induced Stratification of the Equatorial Indian Ocean and Its Potential Feedback to the Atmosphere

Temperature and Salinity Anomalies in the Sea Surface Microlayer of the South Pacific During Precipitation Events

Rain Impacts on the Surface Atmosphere and Upper Ocean in the Central Equatorial Pacific

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