The Time Scales of Variability of Marine Low Clouds

Szoeke, Simon P. de; Verlinden, Kathryn L.; Yuter, Sandra E.; Mechem, David B.

doi:10.1175/jcli-d-15-0460.1

Cited by 36 publications

(32 citation statements)

References 64 publications

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“…Painemal et al , ). Similarly, studies that consider only time‐averaged behaviour (Caldwell et al , ) or mean cross‐sections across the ocean basin underappreciate the structures present in Figure , both the robust instances of upward vertical motion and, more broadly, the substantial multiscale variability in vertical motion that has been shown extends to cloud properties (de Szoeke et al , ). The ship movement of ∼10 m/s corresponds to a movement of about 2° of longitude in 6 h, consistent with the moving window average used for calculating the first term in Equation .…”

Section: Case‐studymentioning

confidence: 88%

Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

Ghate

Mechem

Cadeddu

et al. 2019

Quart J Royal Meteoro Soc

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Entrainment of warm, dry air from above the boundary layer into the cloud layer has a significant impact on stratocumulus clouds in the marine boundary layer. During the MAGIC field campaign, the Atmospheric Radiation Measurement (ARM) mobile facility was deployed aboard a container ship that made regular transects between Los Angeles, California and Honolulu, Hawaii. Observations made during MAGIC transects were collocated with observations from the Geostationary Operational Environmental Satellite (GOES‐15) and European Centre for Medium‐range Weather Forecasting (ECMWF) reanalysis model. From these data, hourly estimates of entrainment velocities in closed cellular stratocumulus cloud conditions were calculated from the mixed‐layer mass budget equation, modified to accommodate observations sampled from a moving platform. The technique is demonstrated using observations collected during Leg 15A (46 h) and then extended to 178 h of data. The average entrainment velocity was 7.83 ± 5.23 mm/s, and the average large‐scale vertical air motion at cloud top (obtained from reanalysis) was −2.56 ± 3.31 mm/s. The vertical air motion at cloud top was positive (upward) during 36 h (∼20%) with a mean of 2.68 mm/s. Entrainment velocity is highly variable and on average the MAGIC observations show no dependence of entrainment velocity on longitude or any pronounced diurnal cycle. When binned by inversion strength, the mean entrainment velocity and mean large‐scale vertical air motion mirrored each other, with both exhibiting substantial variability. Collectively, our results suggest a mean entrainment‐velocity behaviour associated with the background state, with large changes in entrainment velocity forced by strong variability in internal boundary‐layer properties like turbulence, radiation, and inversion strength. This cautions against using climatological mean estimates of entrainment velocities or neglecting instances with upward large‐scale vertical air motion.

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Section: Case‐studymentioning

confidence: 88%

Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

Ghate

Mechem

Cadeddu

et al. 2019

Quart J Royal Meteoro Soc

Self Cite

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“…Typically, a subsidence inversion is strongest over the center of the subtropical anticyclones, over cold currents (particularly the Peru Current), and over cooler than normal waters, which are subjected to enhanced upwelling in large part by trade winds on the periphery of the subtropical highs (DeSzoeke et al, 2016). The TWI becomes weaker and its base increases in height as it moves towards the west and towards the equator, as SSTs increase.…”

Section: Temperature and Cloud Responsementioning

confidence: 99%

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

et al. 2017

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Abstract. Reducing insolation has been proposed as a geoengineering response to global warming. Here we present the results of climate model simulations of a unique Geoengineering Model Intercomparison Project Testbed experiment to investigate the benefits and risks of a scheme that would brighten certain oceanic regions. The National Center for Atmospheric Research CESM CAM4-Chem global climate model was modified to simulate a scheme in which the albedo of the ocean surface is increased over the subtropical ocean gyres in the Southern Hemisphere. In theory, this could be accomplished using a stable, nondispersive foam, comprised of tiny, highly reflective microbubbles. Such a foam has been developed under idealized conditions, although deployment at a large scale is presently infeasible. We conducted three ensemble members of a simulation (G4Foam) from 2020 through to 2069 in which the albedo of the ocean surface is set to 0.15 (an increase of 150 %) over the three subtropical ocean gyres in the Southern Hemisphere, against a background of the RCP6.0 (representative concentration pathway resulting in +6 W m −2 radiative forcing by 2100) scenario. After 2069, geoengineering is ceased, and the simulation is run for an additional 20 years. Global mean surface temperature in G4Foam is 0.6 K lower than RCP6.0, with statistically significant cooling relative to RCP6.0 south of 30 • N. There is an increase in rainfall over land, most pronouncedly in the tropics during the June-July-August season, relative to both G4SSA (specified stratospheric aerosols) and RCP6.0. Heavily populated and highly cultivated regions throughout the tropics, including the Sahel, southern Asia, the Maritime Continent, Central America, and much of the Amazon experience a statistically significant increase in precipitation minus evaporation. The temperature response to the relatively modest global average forcing of −1.5 W m −2 is amplified through a series of positive cloud feedbacks, in which more shortwave radiation is reflected. The precipitation response is primarily the result of the intensification of the southern Hadley cell, as its mean position migrates northward and away from the Equator in response to the asymmetric cooling.

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“…Meridional modes in these two regions are thought to be analogous given their interaction with the ITCZ and their colocation with oceanic upwelling (Xie and Philander 1994;Chiang and Vimont 2004). Recent studies show that this meridional-mode-like SST variability is influenced by positive cloud radiative feedback, which enhances the persistence of SST variability (Smirnov and Vimont 2012;Evan et al 2013;Bellomo et al 2014bBellomo et al , 2015Zhang et al 2014;de Szoeke et al 2016). Previous studies also implicitly assume that local anomalous ocean heat transport is not essential for the WES feedback because it occurs in model configurations that do not have interactive ocean dynamics (Chiang and Vimont 2004;Vimont 2010;Smirnov and Vimont 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Positive shortwave cloud radiative feedback on northeast subtropical SST has been identified extensively in observations and models (Klein and Hartmann 1993;Norris and Leovy 1994;Burgman et al 2008;Clement et al 2009;Evan et al 2013;Zhang et al 2014;Bellomo et al 2014aBellomo et al , b, 2015de Szoeke et al 2016;Burgman et al 2017;Myers et al 2018a, b), though only one other study has assessed how much subtropical SST variability depends on cloud radiative feedback (Brown et al 2016). The feedback occurs through climatologically cool SST coinciding with the descending branch of the Hadley circulation, high atmospheric stability, a strong temperature inversion-all of which contribute to the formation of boundary layer stratocumulus cloud decks (Klein and Hartmann 1993;Norris 1998).…”

Section: Introductionmentioning

confidence: 99%

Contributions of atmospheric and oceanic feedbacks to subtropical northeastern sea surface temperature variability

2019

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Previous studies show that the dominant mode of variability in the Northeastern subtropical Pacific and Atlantic are analogous. Most attention has been given to the wind-evaporation-sea surface temperature (WES) feedback, but more recent studies suggest that clouds and ocean play a role. Here, it is shown that, while the mode of variability is similar, the quantitative role of clouds and ocean are different. Using Community Earth System Model, version 1.2, cloud feedbacks and interactive ocean dynamics are disabled separately to diagnose the relative contributions of each to sea surface temperature (SST) variability in subtropical northeastern ocean basins. Results from four experiments show that the relative contributions from WES and cloud radiative feedback depend on the role of the ocean. Positive cloud radiative feedback is evident in both basins but has less impact on SST variance in the Atlantic than in the Pacific. The reason for this is that ocean processes strongly damp SST anomalies in the Pacific and weakly enhance SST anomalies in the Atlantic. When cloud feedbacks are disabled, ocean processes become a larger driver of SST variability in the Atlantic. In line with previous studies, the Northeast Pacific SST variability may be understood as a white-noise-forced linear stochastic system with positive feedback from cloud and damping by latent heat flux and ocean processes, while Atlantic SST is driven partially by variations in ocean circulation and requires vertical mixing for rendition. Between these two regions, different ocean dynamics lead to different roles for atmospheric feedbacks but still result in similar patterns of SST variability.

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The Time Scales of Variability of Marine Low Clouds

Cited by 36 publications

References 64 publications

Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

The G4Foam Experiment: global climate impacts of regional ocean albedo modification

Contributions of atmospheric and oceanic feedbacks to subtropical northeastern sea surface temperature variability

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