Advances in simulating atmospheric variability with the ECMWF model: From synoptic to decadal time-scales

2008 ◽  
Vol 134 (634) ◽  
pp. 1337-1351 ◽  
Author(s):  
Peter Bechtold ◽  
Martin Köhler ◽  
Thomas Jung ◽  
Francisco Doblas-Reyes ◽  
Martin Leutbecher ◽  
...  
Keyword(s):  
Time Scales ◽  
Atmospheric Variability ◽  
Ecmwf Model

scholarly journals Tropical and Extratropical Controls of Gulf of California Surges and Summertime Precipitation over the Southwestern United States

2016 ◽  
Vol 144 (7) ◽  
pp. 2695-2718 ◽  
Author(s):  
Salvatore Pascale ◽  
Simona Bordoni
Keyword(s):  
Time Scales ◽  
Gulf Of California ◽  
Dominant Role ◽  
Principal Component ◽  
North American Monsoon ◽  
Atmospheric Variability ◽  
Near Surface ◽  
The North ◽  
Precipitation Anomalies ◽  
The Relationship

Abstract In this study ERA-Interim data are used to study the influence of Gulf of California (GoC) moisture surges on the North American monsoon (NAM) precipitation over Arizona and western New Mexico (AZWNM), as well as the connection with larger-scale tropical and extratropical variability. To identify GoC surges, an improved index based on principal component analyses of the near-surface GoC winds is introduced. It is found that GoC surges explain up to 70% of the summertime rainfall over AZWNM. The number of surges that lead to enhanced rainfall in this region varies from 4 to 18 per year and is positively correlated with annual summertime precipitation. Regression analyses are performed to explore the relationship between GoC surges, AZWNM precipitation, and tropical and extratropical atmospheric variability at the synoptic (2–8 days), quasi-biweekly (10–20 days), and subseasonal (25–90 days) time scales. It is found that tropical and extratropical waves, responsible for intrusions of moist tropical air into midlatitudes, interact on all three time scales, with direct impacts on the development of GoC surges and positive precipitation anomalies over AZWNM. Strong precipitation events in this region are, however, found to be associated with time scales longer than synoptic, with the quasi-biweekly and subseasonal modes playing a dominant role in the occurrence of these more extreme events.

How Important Is Air–Sea Coupling in ENSO and MJO Evolution?

2009 ◽  
Vol 22 (11) ◽  
pp. 2958-2977 ◽  
Author(s):  
Matthew Newman ◽  
Prashant D. Sardeshmukh ◽  
Cécile Penland
Keyword(s):  
Time Scales ◽  
Evolution Operator ◽  
Power Spectra ◽  
Dynamical Evolution ◽  
Atmospheric Variability ◽  
Basic Premise ◽  
Strongly Coupled ◽  
Dominant Period ◽  
Linear Inverse Model ◽  
Daily Time

Abstract The effect of air–sea coupling on tropical climate variability is investigated in a coupled linear inverse model (LIM) derived from the simultaneous and 6-day lag covariances of observed 7-day running mean departures from the annual cycle. The model predicts the covariances at all other lags. The predicted and observed lag covariances, as well as the associated power spectra, are generally found to agree within sampling uncertainty. This validates the LIM’s basic premise that beyond daily time scales, the evolution of tropical atmospheric and oceanic anomalies is effectively linear and stochastically driven. It also justifies a linear diagnosis of air–sea coupling in the system. The results show that air–sea coupling has a very small effect on subseasonal atmospheric variability. It has much larger effects on longer-term variability, in both the atmosphere and the ocean, including greatly increasing the amplitude of ENSO and lengthening its dominant period from 2 to 4 years. Consistent with these results, the eigenvectors of the system’s dynamical evolution operator also separate into two distinct, but nonorthogonal, subspaces: one governing the nearly uncoupled subseasonal dynamics and the other governing the strongly coupled longer-term dynamics. These subspaces arise naturally from the LIM analysis; no bandpass frequency filtering need be applied. One implication of this remarkably clean separation of the uncoupled and coupled dynamics is that GCM errors in anomalous tropical air–sea coupling may cause substantial errors on interannual and longer time scales but probably not on the subseasonal scales associated with the MJO.

Atmospheric and Oceanic Origins of Tropical Precipitation Variability

2017 ◽  
Vol 30 (9) ◽  
pp. 3197-3217 ◽  
Author(s):  
Jie He ◽  
Clara Deser ◽  
Brian J. Soden
Keyword(s):  
Time Scales ◽  
Ocean Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Noise Spectrum ◽  
Precipitation Variability ◽  
Ocean Dynamics ◽  
Atmospheric Variability ◽  
Tropical Precipitation ◽  
Summer Hemisphere

The intrinsic atmospheric and ocean-induced tropical precipitation variability is studied using millennial control simulations with various degrees of ocean coupling. A comparison between the coupled simulation and the atmosphere-only simulation with climatological sea surface temperatures (SSTs) shows that a substantial amount of tropical precipitation variability is generated without oceanic influence. This intrinsic atmospheric variability features a red noise spectrum from daily to monthly time scales and a white noise spectrum beyond the monthly time scale. The oceanic impact is inappreciable for submonthly time scales but important at interannual and longer time scales. For time scales longer than a year, it enhances precipitation variability throughout much of the tropical oceans and suppresses it in some subtropical areas, preferentially in the summer hemisphere. The sign of the ocean-induced precipitation variability can be inferred from the local precipitation–SST relationship, which largely reflects the local feedbacks between the two, although nonlocal forcing associated with El Niño–Southern Oscillation also plays a role. The thermodynamic and dynamic nature of the ocean-induced precipitation variability is studied by comparing the fully coupled and slab ocean simulations. For time scales longer than a year, equatorial precipitation variability is almost entirely driven by ocean circulation, except in the Atlantic Ocean. In the rest of the tropics, ocean-induced precipitation variability is dominated by mixed layer thermodynamics. Additional analyses indicate that both dynamic and thermodynamic oceanic processes are important for establishing the leading modes of large-scale tropical precipitation variability. On the other hand, ocean dynamics likely dampens tropical Pacific variability at multidecadal time scales and beyond.

scholarly journals Intrinsic Variability of Sea Level from Global Ocean Simulations: Spatiotemporal Scales

2015 ◽  
Vol 28 (10) ◽  
pp. 4279-4292 ◽  
Author(s):  
Guillaume Sérazin ◽  
Thierry Penduff ◽  
Sandy Grégorio ◽  
Bernard Barnier ◽  
Jean-Marc Molines ◽  
...  
Keyword(s):  
Sea Level ◽  
Time Scales ◽  
General Circulation ◽  
Spatial Scales ◽  
Full Range ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Atmospheric Variability ◽  
Low Frequencies

Abstract In high-resolution ocean general circulation models (OGCMs), as in process-oriented models, a substantial amount of interannual to decadal variability is generated spontaneously by oceanic nonlinearities: that is, without any variability in the atmospheric forcing at these time scales. The authors investigate the temporal and spatial scales at which this intrinsic oceanic variability has the strongest imprints on sea level anomalies (SLAs) using a ° global OGCM, by comparing a “hindcast” driven by the full range of atmospheric time scales with its counterpart forced by a repeated climatological atmospheric seasonal cycle. Outputs from both simulations are compared within distinct frequency–wavenumber bins. The fully forced hindcast is shown to reproduce the observed distribution and magnitude of low-frequency SLA variability very accurately. The small-scale (L < 6°) SLA variance is, at all time scales, barely sensitive to atmospheric variability and is almost entirely of intrinsic origin. The high-frequency (mesoscale) part and the low-frequency part of this small-scale variability have almost identical geographical distributions, supporting the hypothesis of a nonlinear temporal inverse cascade spontaneously transferring kinetic energy from high to low frequencies. The large-scale (L > 12°) low-frequency variability is mostly related to the atmospheric variability over most of the global ocean, but it is shown to remain largely intrinsic in three eddy-active regions: the Gulf Stream, Kuroshio, and Antarctic Circumpolar Current (ACC). Compared to its ¼° predecessor, the authors’ ° OGCM is shown to yield a stronger intrinsic SLA variability, at both mesoscale and low frequencies.

scholarly journals Internal Atmospheric Variability and Interannual-to-Decadal ENSO Variability in a CGCM

2009 ◽  
Vol 22 (9) ◽  
pp. 2335-2355 ◽  
Author(s):  
Sang-Wook Yeh ◽  
Ben P. Kirtman
Keyword(s):  
Time Scales ◽  
General Circulation ◽  
General Circulation Models ◽  
Tropical Pacific ◽  
Frequency Noise ◽  
Atmospheric Variability ◽  
Enso Variability ◽  
Ensemble Strategy ◽  
The Tropics ◽  
The Impact

Abstract The interactive ensemble coupling strategy has been developed specifically to determine how noise due to internal atmosphere dynamics impacts climate variability within the context of coupled general circulation models (CGCMs). In this study the authors investigate the impact of internal atmospheric variability on the ENSO variability using four CGCM simulations. In the control simulation, the interactive ensemble strategy is applied globally, thereby reducing the noise at the air–sea interface at each ocean grid point. In the second and third CGCM simulations, the interactive ensemble strategy is applied locally in the extratropics versus the tropics only, respectively. In addition, those results were compared with a standard CGCM. The results suggest that tropical internal atmospheric variability strengthens the interannual-to-decadal ENSO variability and leads to a broader spectral peak. However, the noise due to internal atmospheric dynamics plays different roles when the interannual and decadal ENSO variability is considered separately. There are noise-induced changes in the SST–zonal wind stress feedbacks from interannual to decadal time scales. The tropical atmospheric internal variability largely modifies the frequency as opposed to the amplitude of the ENSO variability on interannual time scales. In contrast, tropical internal atmospheric variability is effective in forcing decadal ENSO variability, resulting in a significant decrease of decadal ENSO amplitude in the central tropical Pacific in a CGCM when the noise is reduced. The authors argue that the decadal ENSO variability is directly affected by the low-frequency noise over the western part of the tropical Pacific in a linear sense. On the other hand, the impact of extratropical atmospheric noise on the ENSO variability is weaker than the noise in the tropics.

scholarly journals On the Coupling between Barotropic and Baroclinic Modes of Extratropical Atmospheric Variability

2018 ◽  
Vol 75 (6) ◽  
pp. 1853-1871 ◽  
Author(s):  
Lina Boljka ◽  
Theodore G. Shepherd ◽  
Michael Blackburn
Keyword(s):  
Time Scales ◽  
Feedback Mechanism ◽  
Wave Activity ◽  
Life Cycles ◽  
Heat Fluxes ◽  
Mean Flow ◽  
Atmospheric Variability ◽  
Modes Of Variability ◽  
Momentum Fluxes ◽  
Baroclinic Modes

Abstract The baroclinic and barotropic components of atmospheric dynamics are usually viewed as interlinked through the baroclinic life cycle, with baroclinic growth of eddies connected to heat fluxes, barotropic decay connected to momentum fluxes, and the two eddy fluxes connected through the Eliassen–Palm wave activity. However, recent observational studies have suggested that these two components of the dynamics are largely decoupled in their variability, with variations in the zonal mean flow associated mainly with the momentum fluxes, variations in the baroclinic wave activity associated mainly with the heat fluxes, and essentially no correlation between the two. These relationships are examined in a dry dynamical core model under different configurations and in Southern Hemisphere observations, considering different frequency bands to account for the different time scales of atmospheric variability. It is shown that at intermediate periods longer than 10 days, the decoupling of the baroclinic and barotropic modes of variability can indeed occur as the eddy kinetic energy at those time scales is only affected by the heat fluxes and not the momentum fluxes. The baroclinic variability includes the oscillator model with periods of 20–30 days. At both the synoptic time scale and the quasi-steady limit, the baroclinic and barotropic modes of variability are linked, consistent with baroclinic life cycles and the positive baroclinic feedback mechanism, respectively. In the quasi-steady limit, the pulsating modes of variability and their correlations depend sensitively on the model climatology.

LVSEM: Past Present and Future

1990 ◽  
Vol 48 (1) ◽  
pp. 364-365
Author(s):  
James B. Pawley
Keyword(s):  
Field Emission ◽  
Line Width ◽  
Time Scales ◽  
Silicon Oxide ◽  
Beam Current ◽  
High Brightness ◽  
High Beam ◽  
Fixed Charges ◽  
Beam Voltage ◽  
Deposited Metal

Past: In 1960 Thornley published the first description of SEM studies carried out at low beam voltage (LVSEM, 1-5 kV). The aim was to reduce charging on insulators but increased contrast and difficulties with low beam current and frozen biological specimens were also noted. These disadvantages prevented widespread use of LVSEM except by a few enthusiasts such as Boyde. An exception was its use in connection with studies in which biological specimens were dissected in the SEM as this process destroyed the conducting films and produced charging unless LVSEM was used.In the 1980’s field emission (FE) SEM’s came into more common use. The high brightness and smaller energy spread characteristic of the FE-SEM’s greatly reduced the practical resolution penalty associated with LVSEM and the number of investigators taking advantage of the technique rapidly expanded; led by those studying semiconductors. In semiconductor research, the SEM is used to measure the line-width of the deposited metal conductors and of the features of the photo-resist used to form them. In addition, the SEM is used to measure the surface potentials of operating circuits with sub-micrometer resolution and on pico-second time scales. Because high beam voltages destroy semiconductors by injecting fixed charges into silicon oxide insulators, these studies must be performed using LVSEM where the beam does not penetrate so far.

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