scholarly journals How Has Subtropical Stratocumulus and Associated Meteorology Changed since the 1980s?*

2015 ◽  
Vol 28 (21) ◽  
pp. 8396-8410 ◽  
Author(s):  
C. Seethala ◽  
Joel R. Norris ◽  
Timothy A. Myers
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Meteorological Parameters ◽  
Cloud Amount ◽  
Sea Surface ◽  
Independent Effect ◽  
Multilinear Regression ◽  
Low Level ◽  
Observational Uncertainty ◽  
Inversion Strength

Abstract The importance of low-level cloud feedbacks to climate sensitivity motivates an investigation of how low-level cloud amount and related meteorological conditions have changed in recent decades in subtropical stratocumulus regions. Using satellite cloud datasets corrected for inhomogeneities, it is found that during 1984–2009 low-level cloud amount substantially increased over the northeastern Pacific, southeastern Pacific, and southeastern Atlantic; decreased over the northeastern Atlantic; and weakly increased over the southeastern Indian Ocean subtropical stratocumulus regions. Examination of meteorological parameters from four reanalyses indicates that positive trends in low-level cloud amount are associated with cooler sea surface temperature, greater inversion strength, and enhanced cold-air advection. The converse holds for negative trends in low-level cloud amount. A multilinear regression model based on these three meteorological variables reproduces the sign and magnitude of observed cloud amount trends in all stratocumulus regions within the range of observational uncertainty. Changes in inversion strength have the largest independent effect on cloud trends, followed by changes in advection strength. Changes in sea surface temperature have the smallest independent effect on cloud trends. Differing signs of cloud trends and differing contributions from meteorological parameters suggest that observed changes in subtropical stratocumulus since the 1980s may be due to natural variability rather than a systematic response to climate change.

On the Relationships between Subtropical Clouds and Meteorology in Observations and CMIP3 and CMIP5 Models*

2015 ◽  
Vol 28 (8) ◽  
pp. 2945-2967 ◽  
Author(s):  
Timothy A. Myers ◽  
Joel R. Norris
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Cloud Fraction ◽  
Sea Surface ◽  
Radiative Effect ◽  
Low Level ◽  
Temperature Advection ◽  
Cloud Radiative Effect ◽  
High Level ◽  
The Relationship

Abstract Climate models’ simulation of clouds over the eastern subtropical oceans contributes to large uncertainties in projected cloud feedback to global warming. Here, interannual relationships of cloud radiative effect and cloud fraction to meteorological variables are examined in observations and in models participating in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5, respectively). In observations, cooler sea surface temperature, a stronger estimated temperature inversion, and colder horizontal surface temperature advection are each associated with larger low-level cloud fraction and increased reflected shortwave radiation. A moister free troposphere and weaker subsidence are each associated with larger mid- and high-level cloud fraction and offsetting components of shortwave and longwave cloud radiative effect. It is found that a larger percentage of CMIP5 than CMIP3 models simulate the wrong sign or magnitude of the relationship of shortwave cloud radiative effect to sea surface temperature and estimated inversion strength. Furthermore, most models fail to produce the sign of the relationship between shortwave cloud radiative effect and temperature advection. These deficiencies are mostly, but not exclusively, attributable to errors in the relationship between low-level cloud fraction and meteorology. Poor model performance also arises due to errors in the response of mid- and high-level cloud fraction to variations in meteorology. Models exhibiting relationships closest to observations tend to project less solar reflection by clouds in the late twenty-first century and have higher climate sensitivities than poorer-performing models. Nevertheless, the intermodel spread of climate sensitivity is large even among these realistic models.

scholarly journals U.S. West Coast Surface Heat Fluxes, Wind Stress, and Wind Stress Curl from a Mesoscale Model

2005 ◽  
Vol 133 (11) ◽  
pp. 3202-3216 ◽  
Author(s):  
T. Haack ◽  
S. D. Burk ◽  
R. M. Hodur
Keyword(s):  
Relative Humidity ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Wind Stress ◽  
Mesoscale Model ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Wind Stress Curl ◽  
Low Level

Abstract Monthly averages of numerical model fields are beneficial for depicting patterns in surface forcing such as sensible and latent heat fluxes, wind stress, and wind stress curl over data-sparse ocean regions. Grid resolutions less than 10 km provide the necessary mesoscale detail to characterize the impact of a complex coastline and coastal topography. In the present study a high-resolution mesoscale model is employed to reveal patterns in low-level winds, temperature, relative humidity, sea surface temperature as well as surface fluxes, over the eastern Pacific and along the U.S. west coast. Hourly output from successive 12-h forecasts are averaged to obtain monthly mean patterns from each season of 1999. The averages yield information on interactions between the ocean and the overlying atmosphere and on the influence of coastal terrain forcing in addition to their month-to-month variability. The spring to summer transition is characterized by a dramatic shift in near-surface winds, temperature, and relative humidity as offshore regions of large upward surface fluxes diminish and an alongshore coastal flux gradient forms. Embedded within this gradient, and the imprint of strong summertime topographic forcing, are small-scale fluctuations that vary in concert with local changes in sea surface temperature. Potential feedbacks between the low-level wind, sea surface temperature, and the wind stress curl are explored in the coastal regime and offshore waters. In all seasons, offshore extensions of colder coastal waters impose a marked influence on low-level conditions by locally enhancing stability and reducing the wind speed, while buoy measurements along the coast indicate that sea surface temperatures and wind speeds tend to be negatively correlated.

scholarly journals Are paleoclimate model ensembles consistent with the MARGO data synthesis?

2011 ◽  
Vol 7 (2) ◽  
pp. 775-807 ◽  
Author(s):  
J. C. Hargreaves ◽  
A. Paul ◽  
R. Ohgaito ◽  
A. Abe-Ouchi ◽  
J. D. Annan
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Temperature Data ◽  
Sea Surface ◽  
Data Synthesis ◽  
The North ◽  
Weak Evidence ◽  
Observational Uncertainty ◽  
Model Ensembles ◽  
Surface Temperature Data

Abstract. We investigate the consistency of various ensembles of model simulations with the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) sea surface temperature data synthesis. We discover that while two multi-model ensembles, created through the Paleoclimate Model Intercomparison Projects (PMIP and PMIP2), pass our simple tests of reliability, an ensemble based on parameter variation in a single model does not perform so well. We show that accounting for observational uncertainty in the MARGO database is of prime importance for correctly evaluating the ensembles. Perhaps surprisingly, the inclusion of a coupled dynamical ocean (compared to the use of a slab ocean) does not appear to cause a wider spread in the sea surface temperature anomalies, but rather causes systematic changes with more heat transported north in the Atlantic. There is weak evidence that the sea surface temperature data may be more consistent with meridional overturning in the North Atlantic being similar for the LGM and the present day, however, the small size of the PMIP2 ensemble prevents any statistically significant results from being obtained.

scholarly journals The role of the meridional sea surface temperature gradient in controlling the Caribbean low‐level jet

2017 ◽  
Vol 122 (11) ◽  
pp. 5903-5916 ◽  
Author(s):  
Tito Maldonado ◽  
Anna Rutgersson ◽  
Rodrigo Caballero ◽  
Francesco S. R. Pausata ◽  
Eric Alfaro ◽  
...  
Keyword(s):  
Temperature Gradient ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Low Level ◽  
Sea Surface Temperature Gradient ◽  
Low Level Jet ◽  
The Caribbean ◽  
Surface Temperature Gradient

Low-Level Cloud Variability over the Equatorial Cold Tongue in Observations and Models

2007 ◽  
Vol 20 (8) ◽  
pp. 1555-1570 ◽  
Author(s):  
David K. Mansbach ◽  
Joel R. Norris
Keyword(s):  
Boundary Layer ◽  
Surface Temperature ◽  
Climate Models ◽  
Cloud Amount ◽  
Global Climate Models ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Cold Tongue ◽  
Multilinear Regression ◽  
Near Surface ◽  
Low Level

Abstract Examination of cloud and meteorological observations from satellite, surface, and reanalysis datasets indicates that monthly anomalies in low-level cloud amount and near-surface temperature advection are strongly negatively correlated on the southern side of the equatorial Pacific cold tongue. This inverse correlation occurs independently of relationships between cloud amount and sea surface temperature (SST) or lower tropospheric static stability (LTS), and the combination of advection plus SST or LTS explains significantly more interannual cloud variability in a multilinear regression than does SST or LTS alone. Warm anomalous advection occurs when the equatorial cold tongue is well defined and the southeastern Pacific trade winds bring relatively warm air over colder water. Ship meteorological reports and soundings show that the atmospheric surface layer becomes stratified under these conditions, thus inhibiting the upward mixing of moisture needed to sustain cloudiness against subsidence and entrainment drying. Cold anomalous advection primarily occurs when the equatorial cold tongue is weak or absent and the air–sea temperature difference is substantially negative. These conditions favor a more convective atmospheric boundary layer, greater cloud amount, and less frequent occurrence of clear sky. Examination of output from global climate models developed by the Geophysical Fluid Dynamics Laboratory (GFDL) and the National Center for Atmospheric Research (NCAR) indicates that both models generally fail to simulate the cloud–advection relationships observed on the northern and southern sides of the equatorial cold tongue. Although the GFDL atmosphere model does reproduce the expected signs of cloud-advection correlations when forced with prescribed historical SST variations, it does not consistently do so when coupled to an ocean model. The NCAR model has difficulty reproducing the observed correlations in both atmosphere-only and coupled versions. This suggests that boundary layer cloud parameterizations could be improved through better representation of the effects of advection over varying SST.

scholarly journals Modulation of the sea-surface temperature in the Southeast Pacific by the atmospheric low-level coastal jet

2013 ◽  
Vol 118 (9) ◽  
pp. 3979-3998 ◽  
Author(s):  
Xiaodong Hong ◽  
Shouping Wang ◽  
Teddy R. Holt ◽  
Paul J. Martin ◽  
Larry O'Neill
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Low Level ◽  
Coastal Jet ◽  
Southeast Pacific

scholarly journals SIGNATURE OF THE CLIMATE CHANGE IN THE SOUTH CASPIAN BASIN AND COASTAL AREA

2019 ◽  
Vol 47 (5) ◽  
pp. 12-25
Author(s):  
Parvin Ghafarian ◽  
Sahar Tajbakhsh
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Caspian Sea ◽  
Meteorological Parameters ◽  
Sea Surface ◽  
Maximum Temperature ◽  
The South ◽  
South Caspian Basin ◽  
Increasing Trend

The climate change is the main issue in recent decades. Marine and coastal areas are deeply affected by climate change. To investigate the effect of climate change in the southern coast of the Caspian Sea, the variations of main meteorological parameters such as anomaly of minimum and maximum temperature, precipitation, sea surface temperature and, also the frequency of foggy, hazy and dusty days are examined in a 40-year period from 1979 to 2018 (anomalies with respect to the 1981–2010 baseline). The results of the study showed that the significant increasing trend in temperature in all stations that located in industrial and urban area. There is no significant change in precipitation due to complex structure of this parameter in the South Caspian Sea areas. The lake effect and topography play as a key role in generation of precipitation than large scale systems. Also there is highly significant increasing trend of sea surface temperature in South Caspian Sea which is a result of the effects of global warming in that region. There is also an increase in the occurrence of the rare dust phenomenon in that area. The increasing trend of hazy days was observed in all areas, particularly in industrial zones that can affect some meteorological parameters.

High sensitivity of seasonal tropical precipitation to local sea-surface temperature

2020 ◽  
Author(s):  
Robin Chadwick ◽  
Peter Good ◽  
Christopher Holloway ◽  
John Kennedy ◽  
Jason Lowe ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Climate Model ◽  
Sea Surface ◽  
Climate Projections ◽  
Office Work ◽  
Shallow Convection ◽  
Seasonal Forecasts ◽  
Tropical Precipitation ◽  
Observational Uncertainty

<p>Seasonal mean tropical precipitation at any location is controlled by a tangle of local and remote effects, including influences from SSTs across the globe. This, along with uncertainty in precipitation observations, and extremely limited observations of atmospheric circulation, makes understanding the relevant physics challenging. Climate model precipitation biases persisting across multiple generations of models point towards stubborn gaps in understanding and reduce confidence in seasonal forecasts and climate projections.  This includes the 'double ITCZ problem': excessive rainfall in the southern tropical Pacific, first reported in 1995.  Model ITCZs also tend to be too wide.</p><p>Our study shows that in the real world, the sensitivity of tropical precipitation to local sea surface temperature is high, associated with strong shallow circulations.  This rests on a novel analysis of observations, unpicking local and remote controls on precipitation, and navigating a path through observational uncertainty.  Models with appropriate sensitivity to local sea surface temperature, perform well across many conditions.  Improvements in this sensitivity from the fifth to the sixth model intercomparison project are small, highlighting the need for new understanding.  By further linking model biases to shallow convection, our results highlight a target process for focused research: accelerating improvements in seasonal forecasts through to multi-decadal climate projections.</p><p>Wider Met Office work linking precipitation evaluation between climate, seasonal and weather timescales will also be summarised.</p>

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