The Role of Radiative Interactions in Tropical Cyclone Development under Realistic Boundary Conditions

2020 ◽  
pp. 1-38
Author(s):  
Bosong Zhang ◽  
Brian J. Soden ◽  
Gabriel A. Vecchi ◽  
Wenchang Yang
Keyword(s):  
Boundary Conditions ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Latent Heat Release ◽  
Synoptic Scale ◽  
Spatially Varying ◽  
The Impact ◽  
Realistic Boundary Conditions

AbstractThe impact of radiative interactions on tropical cyclones (TC) climatology is investigated using a global, TC-permitting general circulation model (GCM) with realistic boundary conditions. In this model, synoptic-scale radiative interactions are suppressed by overwriting the model-generated atmospheric radiative cooling rates with its monthly-varying climatological values. When radiative interactions are suppressed, the global TC frequency is significantly reduced, indicating that radiative interactions are a critical component of TC development even in the presence of spatially varying boundary conditions. The reduced TC activity is primarily due to a decrease in the frequency of pre-TC synoptic disturbances (“seeds”), whereas the likelihood that the seeds undergo cyclogenesis is less affected. When radiative interactions are suppressed, TC genesis shifts toward coastal regions, whereas TC lysis locations stay almost unchanged; together the distance between genesis and lysis is shortened, reducing TC duration. In a warmer climate, the magnitude of TC reduction from suppressing radiative interactions is diminished due to the larger contribution from latent heat release with increased sea surface temperatures. These results highlight the importance of radiative interactions in modulating the frequency and duration of TCs.

The Impact of Radiative Interactions on Tropical Cyclone Development in a General Circulation Model

2021 ◽  
Author(s):  
Bosong Zhang ◽  
Brian Soden ◽  
Gabriel Vecchi ◽  
Wenchang Yang
Keyword(s):  
Tropical Cyclone ◽  
Boundary Conditions ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Latent Heat Release ◽  
Synoptic Scale ◽  
Spatially Varying ◽  
The Impact

<p>The impact of radiative interactions on tropical cyclone (TC) climatology is investigated using a global, TC-permitting general circulation model (GCM) with realistic boundary conditions. In this model, synoptic-scale radiative interactions are suppressed by overwriting the model-generated atmospheric radiative cooling rates with its monthly-varying climatological values. When radiative interactions are suppressed, the global TC frequency is significantly reduced, indicating that radiative interactions are a critical component of TC development even in the presence of spatially varying boundary conditions. The reduced TC activity is primarily due to a decrease in the frequency of pre-TC synoptic disturbances (“seeds”), whereas the likelihood that the seeds undergo cyclogenesis is less affected. When radiative interactions are suppressed, TC genesis shifts toward coastal regions, whereas TC lysis locations stay almost unchanged; together the distance between genesis and lysis is shortened, reducing TC duration. In a warmer climate, the magnitude of TC reduction from suppressing radiative interactions is diminished due to the larger contribution from latent heat release with increased sea surface temperatures. These results highlight the importance of radiative interactions in modulating the frequency and duration of TCs.</p>

scholarly journals Simulating the mid-Pliocene climate with the MIROC general circulation model: experimental design and initial results

2011 ◽  
Vol 4 (4) ◽  
pp. 1035-1049 ◽  
Author(s):  
W.-L. Chan ◽  
A. Abe-Ouchi ◽  
R. Ohgaito
Keyword(s):  
Experimental Design ◽  
Boundary Conditions ◽  
General Circulation Model ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Sea Surface ◽  
Future Climate Change ◽  
Model Intercomparison ◽  
Initial Results

Abstract. Recently, PlioMIP (Pliocene Model Intercomparison Project) was established to assess the ability of various climate models to simulate the mid-Pliocene warm period (mPWP), 3.3–3.0 million years ago. We use MIROC4m, a fully coupled atmosphere-ocean general circulation model (AOGCM), and its atmospheric component alone to simulate the mPWP, utilizing up-to-date data sets designated in PlioMIP as boundary conditions and adhering to the protocols outlined. In this paper, a brief description of the model is given, followed by an explanation of the experimental design and implementation of the boundary conditions, such as topography and sea surface temperature. Initial results show increases of approximately 10°C in the zonal mean surface air temperature at high latitudes accompanied by a decrease in the equator-to-pole temperature gradient. Temperatures in the tropical regions increase more in the AOGCM. However, warming of the AOGCM sea surface in parts of the northern North Atlantic Ocean and Nordic Seas is less than that suggested by proxy data. An investigation of the model-data discrepancies and further model intercomparison studies can lead to a better understanding of the mid-Pliocene climate and of its role in assessing future climate change.

scholarly journals Impact of high-resolution sea surface temperature representation on the forecast of small Mediterranean catchments' hydrological responses to heavy precipitation

2020 ◽  
Vol 24 (1) ◽  
pp. 269-291 ◽  
Author(s):  
Alfonso Senatore ◽  
Luca Furnari ◽  
Giuseppe Mendicino
Keyword(s):  
High Resolution ◽  
Boundary Conditions ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Sources Of Uncertainty ◽  
Operational Forecasting ◽  
Forecasting System

Abstract. Operational meteo-hydrological forecasting chains are affected by many sources of uncertainty. In coastal areas characterized by complex topography, with several medium-to-small size catchments, quantitative precipitation forecast becomes even more challenging due to the interaction of intense air–sea exchanges with coastal orography. For such areas, which are quite common in the Mediterranean Basin, improved representation of sea surface temperature (SST) space–time patterns can be particularly important. The paper focuses on the relative impact of different resolutions of SST representation on regional operational forecasting chains (up to river discharge estimates) over coastal Mediterranean catchments, with respect to two other fundamental options while setting up the system, i.e. the choice of the forcing general circulation model (GCM) and the possible use of a three-dimensional variational assimilation (3D-Var) scheme. Two different kinds of severe hydro-meteorological events that affected the Calabria region (southern Italy) in 2015 are analysed using the WRF-Hydro atmosphere–hydrology modelling system in its uncoupled version. Both of the events are modelled using the 0.25∘ resolution global forecasting system (GFS) and the 16 km resolution integrated forecasting system (IFS) initial and lateral atmospheric boundary conditions, which are from the European Centre for Medium-Range Weather Forecasts (ECMWF), applying the WRF mesoscale model for the dynamical downscaling. For the IFS-driven forecasts, the effects of the 3D-Var scheme are also analysed. Finally, native initial and lower boundary SST data are replaced with data from the Medspiration project by Institut Français de Recherche pour L'Exploitation de la Mer (IFREMER)/Centre European Remote Sensing d'Archivage et de Traitement (CERSAT), which have a 24 h time resolution and a 2.2 km spatial resolution. Precipitation estimates are compared with both ground-based and radar data, as well as discharge estimates with stream gauging stations' data. Overall, the experiments highlight that the added value of high-resolution SST representation can be hidden by other more relevant sources of uncertainty, especially the choice of the general circulation model providing the boundary conditions. Nevertheless, in most cases, high-resolution SST fields show a non-negligible impact on the simulation of the atmospheric boundary layer processes, modifying flow dynamics and/or the amount of precipitated water; thus, this emphasizes the fact that uncertainty in SST representation should be duly taken into account in operational forecasting in coastal areas.

Orographic Influences on Subtropical Stratocumulus

2006 ◽  
Vol 63 (10) ◽  
pp. 2585-2601 ◽  
Author(s):  
I. Richter ◽  
C. R. Mechoso
Keyword(s):  
General Circulation ◽  
Atmospheric General Circulation Model ◽  
Circulation Model ◽  
South American ◽  
Instability Mechanism ◽  
Peruvian Coast ◽  
Westerly Winds ◽  
Stratocumulus Clouds ◽  
The Impact

Abstract The impact of South American orography on subtropical stratocumulus clouds off the Peruvian coast is investigated in the context of an atmospheric general circulation model. It is found that stratocumulus incidence is significantly reduced when South American orography is removed. Key to this behavior is a decrease in lower tropospheric stability (LTS) that allows for more frequent stratocumulus destruction through the model’s cloud-top entrainment instability mechanism. The role of orography in enhancing Peruvian stratocumulus is as follows. Within the PBL, orography deflects the midlatitude westerly winds equatorward in association with cold air advection and blocking of the low-level flow from the continent. Above the PBL, the steep and high South American orography deflects a significant portion of the midlatitude westerlies equatorward. This flow sinks along the equatorward sloping isentropes, thus promoting subsidence. Both processes increase LTS over the stratocumulus region. In further AGCM experiments, the sensitivity of Peruvian stratocumulus to the use of unsmoothed orographic boundary conditions is assessed. The results show no significant differences to the control simulation, which uses smoothed orography. This suggests that, in the context of GCMs, a representation of South American orography more detailed than is generally used has little potential for improving the performance of coupled ocean–atmosphere models in the eastern tropical Pacific.

scholarly journals Simulating the mid-Pliocene climate with the MIROC general circulation model: experimental design and initial results

2011 ◽  
Vol 4 (3) ◽  
pp. 2011-2046 ◽  
Author(s):  
W.-L. Chan ◽  
A. Abe-Ouchi ◽  
R. Ohgaito
Keyword(s):  
Experimental Design ◽  
Boundary Conditions ◽  
General Circulation Model ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Sea Surface ◽  
Future Climate Change ◽  
Model Intercomparison ◽  
Initial Results

Abstract. Recently, PlioMIP (Pliocene Model Intercomparison Project) was established to assess the ability of various climate models to simulate the mid-Pliocene warm period (MPWP), 3.29–2.97 million years ago. We use MIROC4m, a fully coupled atmosphere-ocean general circulation model (AOGCM), and its atmospheric component alone to simulate the MPWP, utilizing up-to-date data sets designated in PlioMIP as boundary conditions and adhering to the protocols outlined. In this paper, a brief description of the model is given, followed by an explanation of the experimental design and implementation of the boundary conditions, such as topography and sea surface temperature. Initial results show increases of approximately 10 °C in the zonal mean surface air temperature at high latitudes accompanied by a decrease in the equator-to-pole temperature gradient. Temperature in the tropical regions increase more in the AOGCM. However, warming of the AOGCM sea surface in parts of the northern North Atlantic Ocean and Nordic Seas is less than that suggested by proxy data. An investigation of the model-data discrepancies and further model intercomparison studies can lead to a better understanding of the mid-Pliocene climate and of its role in assessing future climate change.

scholarly journals Role of Diurnal Cycle in the Maritime Continent Barrier Effect on MJO Propagation in an AGCM

2021 ◽  
Vol 78 (5) ◽  
pp. 1545-1565
Author(s):  
R. S. Ajayamohan ◽  
Boualem Khouider ◽  
V. Praveen ◽  
Andrew J. Majda
Keyword(s):  
Diurnal Cycle ◽  
General Circulation ◽  
Dominant Role ◽  
Circulation Model ◽  
Striking Difference ◽  
Barrier Effect ◽  
Maritime Continent ◽  
Stochastic Case ◽  
The Impact

AbstractThe barrier effect of the Maritime Continent (MC) in stalling or modifying the propagation characteristics of the MJO is widely accepted. The strong diurnal cycle of convection over the MC is believed to play a dominant role in this regard. This hypothesis is studied here, with the help of a coarse-resolution atmospheric general circulation model (AGCM). The dry dynamical core of the AGCM is coupled to the multicloud parameterization piggybacked with a dynamical bulk boundary layer model. A set of sensitivity experiments is carried out by systematically varying the strength of the MC diurnal flux to assess the impact of the diurnal convective variability on the MJO propagation. The effects of deterministic and stochastic diurnal forcings on MJO characteristics are compared. It is found that the precipitation and zonal wind variance, on the intraseasonal time scales, over the western Pacific region decreases with the increase in diurnal forcing, indicating the blocking of MC precipitation. An increase in precipitation variance over the MC associated with the weakening of precipitation variance over the west Pacific is evident in all experiments. The striking difference between deterministic and stochastic diurnal forcing experiments is that the strength needed for the deterministic case to achieve the same degree of blocking is almost double that of stochastic case. The stochastic diurnal flux over the MC seems to be more detrimental in blocking the MJO propagation. This hints at the notion that the models with inadequate representation of organized convection tend to suffer from the MC-barrier effect.

scholarly journals The Role of Air-Sea Coupling on November-April Intraseasonal Rainfall Variability Over the South Pacific

2021 ◽  
Author(s):  
Sunil Kumar Pariyar ◽  
Noel Keenlyside ◽  
Wan-Ling Tseng ◽  
Huang Hsiung Hsu ◽  
Ben-jei Tsuang
Keyword(s):  
General Circulation ◽  
Rainfall Variability ◽  
Phase Relationship ◽  
Coupled Model ◽  
Circulation Model ◽  
South Pacific ◽  
Ocean Model ◽  
The South ◽  
The Impact

Abstract We investigate the impact of resolving air-sea interaction on the simulation of the intraseasonal rainfall variability over the South Pacific using the ECHAM5 atmospheric general circulation model coupled with the Snow-Ice-Thermocline (SIT) ocean model. We compare the fully coupled simulation with two uncoupled ECHAM5 simulations, one forced with sea surface temperature (SST) climatology and one forced with daily SST from the coupled model. The intraseasonal rainfall variability over the South Pacific is reduced by 17% in the uncoupled model forced with SST climatology and increased by 8% in the uncoupled simulation forced with daily SST, suggesting the role of air-sea coupling and SST variability. The coupled model best simulates the key characteristics of two intraseasonal rainfall modes over the South Pacific with reasonable propagation and correct periodicity. The spatial structure of the two rainfall modes in all three simulations is very similar, suggesting these modes are primarily generated by the dynamics of the atmosphere. The southeastward propagation of rainfall anomalies associated with two leading rainfall modes in the South Pacific depends upon the eastward propagating MJO signals over the Indian Ocean and western Pacific. Air-sea interaction seems crucial for such propagation as both eastward and southeastward propagations are substantially reduced in the uncoupled model forced with SST climatology. The simulation of both eastward and southeastward propagations improved considerably in the uncoupled model forced with daily SST; however, the periodicity differs from the coupled model. Such discrepancy in the periodicity is attributed to the changes in the SST-rainfall relationship with weaker correlations and the nearly in-phase relationship.

scholarly journals Impact of Atmospheric and Model Physics Perturbations On a High-Resolution Ensemble Data Assimilation System of the Red Sea

2020 ◽  
Author(s):  
siva reddy sanikommu ◽  
Habib Toye ◽  
Peng Zhan ◽  
Sabique Langodan ◽  
George Krokos ◽  
...  
Keyword(s):  
High Resolution ◽  
Data Assimilation ◽  
Red Sea ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Massachusetts Institute Of Technology ◽  
Basin Scale ◽  
Subsurface Layers ◽  
The Impact

<p>The Ensemble Adjustment Kalman Filter of the Data Assimilation Research Testbed is implemented to assimilate observations of satellite sea surface temperature, altimeter sea surface height and in-situocean temperature and salinity profiles into an eddy-resolving 4km-Massachusetts Institute of Technology general circulation model (MITgcm) of the Red Sea. We investigate the impact of three different assimilation strategies (1) <em>Iexp</em>– inflates filter error covariance by 10%, (2) <em>IAexp</em>– adds ensemble of atmospheric forcing to Iexp, and (3) <em>IAPexp</em>– adds perturbed model physics toIAexp. The assimilation experiments are run for one year, starting from the same initial ensemble on 1<sup>st</sup>January, 2011 and the data are assimilated every three days.</p><p>Results demonstrate that the <em>Iexp</em> mainly improved the model outputs with respect to assimilation-free MITgcm run in the first few months, before showing signs of dynamical imbalances in the ocean estimates, particularly in the data-sparse subsurface layers. The <em>IAexp</em> yielded substantial improvements throughout the assimilation period with almost no signs of imbalances, including the subsurface layers. It further well preserved the model mesoscales features resulting in an improved forecasts for eddies, both in terms of intensity and location. Perturbing model physics in <em>IAPexp</em> slightly improved the forecast statistics. It further increased smoothness in the ocean forecasts and improved the placement of basin-scale eddies, but caused loss of some high-resolution features. Increasing hydrographic coverage helps recovering the losses and yields more improvements in <em>IAPexp</em> compared to <em>IAexp</em>. Switching off inflation in <em>IAexp</em> and <em>IAPexp</em> leads to further improvements, especially in the subsurface layers.</p>

Coupled Data Assimilation and Ensemble Initialization with Application to Multiyear ENSO Prediction

2019 ◽  
Vol 32 (4) ◽  
pp. 997-1024 ◽  
Author(s):  
Terence J. O’Kane ◽  
Paul A. Sandery ◽  
Didier P. Monselesan ◽  
Pavel Sakov ◽  
Matthew A. Chamberlain ◽  
...  
Keyword(s):  
Data Assimilation ◽  
General Circulation ◽  
Circulation Model ◽  
Sea Surface ◽  
Optimal Interpolation ◽  
Tropical Ocean ◽  
Enso Prediction ◽  
Bred Vectors ◽  
Coupled Data Assimilation ◽  
The Impact

We develop and compare variants of coupled data assimilation (DA) systems based on ensemble optimal interpolation (EnOI) and ensemble transform Kalman filter (ETKF) methods. The assimilation system is first tested on a small paradigm model of the coupled tropical–extratropical climate system, then implemented for a coupled general circulation model (GCM). Strongly coupled DA was employed specifically to assess the impact of assimilating ocean observations [sea surface temperature (SST), sea surface height (SSH), and sea surface salinity (SSS), Argo, XBT, CTD, moorings] on the atmospheric state analysis update via the cross-domain error covariances from the coupled-model background ensemble. We examine the relationship between ensemble spread, analysis increments, and forecast skill in multiyear ENSO prediction experiments with a particular focus on the atmospheric response to tropical ocean perturbations. Initial forecast perturbations generated from bred vectors (BVs) project onto disturbances at and below the thermocline with similar structures to ETKF perturbations. BV error growth leads ENSO SST phasing by 6 months whereupon the dominant mechanism communicating tropical ocean variability to the extratropical atmosphere is via tropical convection modulating the Hadley circulation. We find that bred vectors specific to tropical Pacific thermocline variability were the most effective choices for ensemble initialization and ENSO forecasting.

scholarly journals Impact of Improved Mellor–Yamada Turbulence Model on Tropical Cyclone-Induced Vertical Mixing in the Oceanic Boundary Layer

2020 ◽  
Vol 8 (7) ◽  
pp. 497
Author(s):  
Taekyun Kim ◽  
Jae-Hong Moon
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Turbulence Model ◽  
Mixed Layer ◽  
General Circulation ◽  
Vertical Mixing ◽  
Circulation Model ◽  
Sea Surface ◽  
Oceanic Boundary Layer ◽  
The Impact

It has been identified that there are several limitations in the Mellor–Yamada (MY) turbulence model applied to the atmospheric mixed layer, and Nakanishi and Niino proposed an improved MY model using a database for large-eddy simulations. The improved MY model (Mellor–Yamada–Nakanishi–Niino model; MYNN model) is popular in atmospheric applications; however, it is rarely used in oceanic applications. In this study, the MY model and the MYNN model are compared to identify the efficiency of the MYNN model incorporated into an ocean general circulation model. To investigate the impact of the improved MY model on the vertical mixing in the oceanic boundary layer, the response of the East/Japan Sea to Typhoon Maemi in 2003 was simulated. After the typhoon event, the sea surface temperature obtained from the MYNN model showed better agreement with the satellite measurements than those obtained from the MY model. The MY model produced an extremely shallow mixed layer, and consequently, the surface temperatures were excessively warm. Furthermore, the near-inertial component of the velocity simulated using the MY model was larger than that simulated using the MYNN model at the surface layer. However, in the MYNN model, the near-inertial waves became larger than those simulated by the MY model at all depths except the surface layer. Comparatively, the MYNN model showed enhanced vertical propagation of the near-inertial activity from the mixed layer into the deep ocean, which results in a temperature decrease at the sea surface and a deepening of the mixed layer.

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