scholarly journals Characterizing Observed Midtopped Cloud Regimes Associated with Southern Ocean Shortwave Radiation Biases

2014 ◽  
Vol 27 (16) ◽  
pp. 6189-6203 ◽  
Author(s):  
Shannon Mason ◽  
Christian Jakob ◽  
Alain Protat ◽  
Julien Delanoë
Keyword(s):  
Southern Ocean ◽  
High Latitude ◽  
Model Evaluation ◽  
Climate Models ◽  
Evaluation Studies ◽  
Ocean Model ◽  
Satellite Observations ◽  
Shortwave Radiation ◽  
Cloud Regime ◽  
Cloud Regimes

Abstract Clouds strongly affect the absorption and reflection of shortwave and longwave radiation in the atmosphere. A key bias in climate models is related to excess absorbed shortwave radiation in the high-latitude Southern Ocean. Model evaluation studies attribute these biases in part to midtopped clouds, and observations confirm significant midtopped clouds in the zone of interest. However, it is not yet clear what cloud properties can be attributed to the deficit in modeled clouds. Present approaches using observed cloud regimes do not sufficiently differentiate between potentially distinct types of midtopped clouds and their meteorological contexts. This study presents a refined set of midtopped cloud subregimes for the high-latitude Southern Ocean, which are distinct in their dynamical and thermodynamic background states. Active satellite observations from CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) are used to study the macrophysical structure and microphysical properties of the new cloud regimes. The subgrid-scale variability of cloud structure and microphysics is quantified within the cloud regimes by identifying representative physical cloud profiles at high resolution from the radar–lidar (DARDAR) cloud classification mask. The midtopped cloud subregimes distinguish between stratiform clouds under a high inversion and moderate subsidence; an optically thin cold-air advection cloud regime occurring under weak subsidence and including altostratus over low clouds; optically thick clouds with frequent deep structures under weak ascent and warm midlevel anomalies; and a midlevel convective cloud regime associated with strong ascent and warm advection. The new midtopped cloud regimes for the high-latitude Southern Ocean will provide a refined tool for model evaluation and the attribution of shortwave radiation biases to distinct cloud processes and properties.

scholarly journals A Hybrid Cloud Regime Methodology Used to Evaluate Southern Ocean Cloud and Shortwave Radiation Errors in ACCESS

2015 ◽  
Vol 28 (15) ◽  
pp. 6001-6018 ◽  
Author(s):  
Shannon Mason ◽  
Jennifer K. Fletcher ◽  
John M. Haynes ◽  
Charmaine Franklin ◽  
Alain Protat ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Climate Models ◽  
Global Climate ◽  
Evaluation Studies ◽  
Global Climate Models ◽  
Shortwave Radiation ◽  
Extratropical Cyclones ◽  
Hybrid Cloud ◽  
Cloud Parameterization ◽  
Cloud Regimes

AbstractA deficit of shortwave cloud forcing over the Southern Ocean is persistent in many global climate models. Cloud regimes have been widely used in model evaluation studies to make a process-oriented diagnosis of cloud parameterization errors, but cloud regimes have some limitations in resolving both observed and simulated cloud behavior. A hybrid methodology is developed for identifying cloud regimes from observed and simulated cloud simultaneously.Through this methodology, 11 hybrid cloud regimes are identified in the ACCESS1.3 model for the high-latitude Southern Ocean. The hybrid cloud regimes resolve the features of observed cloud and characterize cloud errors in the model. The simulated properties of the hybrid cloud regimes, and their occurrence over the Southern Ocean and in the context of extratropical cyclones, are evaluated, and their contributions to the shortwave radiation errors are quantified.Three errors are identified: an overall deficit of cloud fraction, a tendency toward optically thin low and midtopped cloud, and an absence of a shallow frontal-type cloud at high latitudes and in the warm fronts of extratropical cyclones.To demonstrate the utility of the hybrid cloud regimes for the evaluation of changes to the model, the effects of selected changes to the model microphysics are investigated.

scholarly journals Origins of the Solar Radiation Biases over the Southern Ocean in CFMIP2 Models*

2014 ◽  
Vol 27 (1) ◽  
pp. 41-56 ◽  
Author(s):  
A. Bodas-Salcedo ◽  
K. D. Williams ◽  
M. A. Ringer ◽  
I. Beau ◽  
J. N. S. Cole ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Southern Ocean ◽  
Climate Models ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Leading Role ◽  
Cloud Properties ◽  
Daily Data ◽  
Cloud Regime ◽  
Cloud Regimes

Abstract Current climate models generally reflect too little solar radiation over the Southern Ocean, which may be the leading cause of the prevalent sea surface temperature biases in climate models. The authors study the role of clouds on the radiation biases in atmosphere-only simulations of the Cloud Feedback Model Intercomparison Project phase 2 (CFMIP2), as clouds have a leading role in controlling the solar radiation absorbed at those latitudes. The authors composite daily data around cyclone centers in the latitude band between 40° and 70°S during the summer. They use cloud property estimates from satellite to classify clouds into different regimes, which allow them to relate the cloud regimes and their associated radiative biases to the meteorological conditions in which they occur. The cloud regimes are defined using cloud properties retrieved using passive sensors and may suffer from the errors associated with this type of retrievals. The authors use information from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar to investigate in more detail the properties of the “midlevel” cloud regime. Most of the model biases occur in the cold-air side of the cyclone composite, and the cyclone composite accounts for most of the climatological error in that latitudinal band. The midlevel regime is the main contributor to reflected shortwave radiation biases. CALIPSO data show that the midlevel cloud regime is dominated by two main cloud types: cloud with tops actually at midlevel and low-level cloud. Improving the simulation of these cloud types should help reduce the biases in the simulation of the solar radiation budget in the Southern Ocean in climate models.

scholarly journals The Surface Downwelling Solar Radiation Surplus over the Southern Ocean in the Met Office Model: The Role of Midlatitude Cyclone Clouds

2012 ◽  
Vol 25 (21) ◽  
pp. 7467-7486 ◽  
Author(s):  
A. Bodas-Salcedo ◽  
K. D. Williams ◽  
P. R. Field ◽  
A. P. Lock
Keyword(s):  
Southern Ocean ◽  
Optical Depth ◽  
Radiative Properties ◽  
Shortwave Radiation ◽  
Radiative Fluxes ◽  
Cloud Properties ◽  
Cloud Regime ◽  
New Diagnosis ◽  
Cloud Regimes

The authors study the role of clouds in the persistent bias of surface downwelling shortwave radiation (SDSR) in the Southern Ocean in the atmosphere-only version of the Met Office model. The reduction of this bias in the atmosphere-only version is important to minimize sea surface temperature biases when the atmosphere model is coupled to a dynamic ocean. The authors use cloud properties and radiative fluxes estimates from the International Satellite Cloud Climatology Project (ISCCP) and apply a clustering technique to classify clouds into different regimes over the Southern Ocean. Then, they composite the cloud regimes around cyclone centers, which allows them to study the role of each cloud regime in a mean composite cyclone. Low- and midlevel clouds in the cold-air sector of the cyclones are responsible for most of the bias. Based on this analysis, the authors develop and test a new diagnosis of shear-dominated boundary layers. This change improves the simulation of the SDSR through a better simulation of the frequency of occurrence of the cloud regimes in the cyclone composite. Substantial biases in the radiative properties of the midtop and stratocumulus regimes are still present, which suggests the need to increase the optical depth of the low-level cloud with moderate optical depth and cloud with tops at midlevels.

scholarly journals Variability in the mechanisms controlling Southern Ocean phytoplankton bloom phenology in an ocean model and satellite observations

2017 ◽  
Vol 31 (5) ◽  
pp. 922-940 ◽  
Author(s):  
Tyler Rohr ◽  
Matthew C. Long ◽  
Maria T. Kavanaugh ◽  
Keith Lindsay ◽  
Scott C. Doney
Keyword(s):  
Southern Ocean ◽  
Phytoplankton Bloom ◽  
Ocean Model ◽  
Satellite Observations

scholarly journals Ocean processes at the Antarctic continental slope

2014 ◽  
Vol 372 (2019) ◽  
pp. 20130047 ◽  
Author(s):  
Karen J. Heywood ◽  
Sunke Schmidtko ◽  
Céline Heuzé ◽  
Jan Kaiser ◽  
Timothy D. Jickells ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Continental Shelf ◽  
Continental Slope ◽  
Climate Models ◽  
Water Mass ◽  
Ocean Model ◽  
Shelf Break ◽  
Small Scale ◽  
Exchange Processes ◽  
The Antarctic

The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system.

scholarly journals Controlling high-latitude Southern Ocean convection in climate models

2015 ◽  
Vol 86 ◽  
pp. 58-75 ◽  
Author(s):  
Achim Stössel ◽  
Dirk Notz ◽  
F. Alexander Haumann ◽  
Helmuth Haak ◽  
Johann Jungclaus ◽  
...  
Keyword(s):  
Southern Ocean ◽  
High Latitude ◽  
Climate Models ◽  
Ocean Convection

Trends in the CERES Dataset, 2000–13: The Effects of Sea Ice and Jet Shifts and Comparison to Climate Models

2014 ◽  
Vol 27 (6) ◽  
pp. 2444-2456 ◽  
Author(s):  
Dennis L. Hartmann ◽  
Paulo Ceppi
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Climate Models ◽  
Radiant Energy ◽  
Shortwave Radiation ◽  
Radiative Energy ◽  
Cmip5 Models ◽  
Model Intercomparison ◽  
Sea Ice Extent ◽  
Intercomparison Project

Abstract The Clouds and the Earth’s Radiant Energy System (CERES) observations of global top-of-atmosphere radiative energy fluxes for the period March 2000–February 2013 are examined for robust trends and variability. The trend in Arctic ice is clearly evident in the time series of reflected shortwave radiation, which closely follows the record of ice extent. The data indicate that, for every 106 km2 decrease in September sea ice extent, annual-mean absorbed solar radiation averaged over 75°–90°N increases by 2.5 W m−2, or about 6 W m−2 between 2000 and 2012. CMIP5 models generally show a much smaller change in sea ice extent over the 1970–2012 period, but the relationship of sea ice extent to reflected shortwave is in good agreement with recent observations. Another robust trend during this period is an increase in reflected shortwave radiation in the zonal belt from 45° to 65°S. This trend is mostly related to increases in sea ice concentrations in the Southern Ocean and less directly related to cloudiness trends associated with the annular variability of the Southern Hemisphere. Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) produce a scaling of cloud reflection to zonal wind increase that is similar to trend observations in regions separated from the direct effects of sea ice. Atmospheric Model Intercomparison Project (AMIP) model responses over the Southern Ocean are not consistent with each other or with the observed shortwave trends in regions removed from the direct effect of sea ice.

Mean circulation and hydrography in the Ross Sea sector, Southern Ocean: representation in numerical models

2010 ◽  
Vol 22 (5) ◽  
pp. 533-558 ◽  
Author(s):  
Graham J. Rickard ◽  
Malcolm J. Roberts ◽  
Michael J.M. Williams ◽  
Alistair Dunn ◽  
Murray H. Smith
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Climate Models ◽  
Ross Sea ◽  
Numerical Models ◽  
Ocean Model ◽  
Shelf Circulation ◽  
Circumpolar Current ◽  
Mean Circulation ◽  
The Antarctic

AbstractThree models were used to look at the Southern Ocean Ross Sea sector circulation and hydrography. Two were climate models of low (1°) to intermediate resolution (1/3°), and one was an operational high resolution (1/10°) ocean model. Despite model differences (including physics and forcing), mean and monthly variability aspects of off-shelf circulation are consistently represented, and could imply bathymetric constraints. Western and eastern cyclonic gyral systems separated by shallow bathymetry around 180°E redistributing water between the wider Southern Ocean and the Ross Sea are found. Some model seasonal gyral transports increase as the Antarctic Circumpolar Current transport decreases. Model flows at 900 m at the gyral eastern end compare favourably with float data. On-shelf model depth-averaged west–east flow is relatively consistent with that reconstructed from longline fishing records. These flows have components associated with isopycnal gradients in both light and dense waters. The climate models reproduce characteristic isopycnal layer inflections (‘V’s) associated with the observed Antarctic Slope Front and on-shelf deep water formation, and these models transport some 4 Sv of this bottom water northwards across the outer 1000 m shelf isobath. Overall flow complexity suggests care is needed to force regional Ross Sea models.

scholarly journals Southern Ocean Cloud and Aerosol data: a compilation of measurements from the 2018 Southern Ocean Ross Sea Marine Ecosystems and Environment voyage

2020 ◽  
Author(s):  
Stefanie Kremser ◽  
Mike Harvey ◽  
Peter Kuma ◽  
Sean Hartery ◽  
Alexia Saint-Macary ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Climate Models ◽  
Dimethyl Sulfide ◽  
Prediction Models ◽  
Climate Model ◽  
Ross Sea ◽  
Evaluation Studies ◽  
Weather Prediction ◽  
Data Sets

Abstract. Due to its remote location and extreme weather conditions, atmospheric in situ measurements are rare in the Southern Ocean. As a result, aerosol-cloud interactions in this region are poorly understood and remain a major source of uncertainty in climate models. This, in turn, contributes substantially to persistent biases in climate model simulations, numerical weather prediction models and reanalyses. It has been shown in previous studies that in situ and ground-based remote sensing measurements across the Southern Ocean are critical for complementing satellite data sets due to the importance of boundary layer and low-level cloud processes. These processes are poorly sampled by satellite-based measurements which are typically obscured by near-continuous overlying cloud cover observed in this region. In this work we present a comprehensive set of ship-based aerosol and meteorological observations collected on the TAN1802 voyage of R/V Tangaroa across the Southern Ocean, from Wellington, New Zealand, to the Ross Sea, Antarctica. The voyage was carried out from 8 February to 21 March, 2018. Many distinct, but contemporaneous, data sets were collected throughout the voyage. The compiled data sets include measurements from a range of instruments, such as (i) meteorological conditions at the sea surface and profile measurements; (ii) the size and concentration of particles; (iii) trace gases dissolved in the ocean surface such as dimethyl sulfide and carbonyl sulfide; (iv) and remotely sensed observations of low clouds. Here, we describe the voyage, the instruments, data processing, and provide a brief overview of some of the data products available. We encourage the scientific community to use these measurements for further analysis and model evaluation studies, in particular, for studies of Southern Ocean clouds, aerosol and their interaction. The data sets presented in this study are publicly available at https://doi.org/10.5281/zenodo.4060237 (Kremser et al. 2020).

scholarly journals Major Characteristics of Southern Ocean Cloud Regimes and Their Effects on the Energy Budget

2011 ◽  
Vol 24 (19) ◽  
pp. 5061-5080 ◽  
Author(s):  
John M. Haynes ◽  
Christian Jakob ◽  
William B. Rossow ◽  
George Tselioudis ◽  
Josephine Brown
Keyword(s):  
Southern Ocean ◽  
Large Scale ◽  
Climate Models ◽  
Satellite Observation ◽  
Radiative Heating ◽  
Radiation Balance ◽  
Heating Rates ◽  
Cloud Systems ◽  
Low Cloud ◽  
Cloud Regimes

Clouds over the Southern Ocean are often poorly represented by climate models, but they make a significant contribution to the top-of-atmosphere (TOA) radiation balance, particularly in the shortwave portion of the energy spectrum. This study seeks to better quantify the organization and structure of Southern Hemisphere midlatitude clouds by combining measurements from active and passive satellite-based datasets. Geostationary and polar-orbiter satellite data from the International Satellite Cloud Climatology Project (ISCCP) are used to quantify large-scale, recurring modes of cloudiness, and active observations from CloudSat and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to examine vertical structure, radiative heating rates, and precipitation associated with these clouds. It is found that cloud systems are organized into eight distinct regimes and that ISCCP overestimates the midlevel cloudiness of these regimes. All regimes contain a relatively high occurrence of low cloud, with 79% of all cloud layers observed having tops below 3 km, but multiple-layered clouds systems are present in approximately 34% of observed cloud profiles. The spatial distribution of regimes varies according to season, with cloud systems being geometrically thicker, on average, during the austral winter. Those regimes found to be most closely associated with midlatitude cyclones produce precipitation the most frequently, although drizzle is extremely common in low-cloud regimes. The regimes associated with cyclones have the highest in-regime shortwave cloud radiative effect at the TOA, but the low-cloud regimes, by virtue of their high frequency of occurrence over the oceans, dominate both TOA and surface shortwave effects in this region as a whole.

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