scholarly journals Impacts of Oceanic Preexisting Conditions on Predictions of Typhoon Hai-Tang in 2005

2010 ◽  
Vol 2010 ◽  
pp. 1-15 ◽  
Author(s):  
Akiyoshi Wada ◽  
Norihisa Usui
Keyword(s):  
Mixed Layer ◽  
Initial Conditions ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Central Pressure ◽  
Surface Cooling ◽  
Heat Potential ◽  
Spiral Rainbands ◽  
The Impact ◽  
Preexisting Conditions

We investigated the impact of variations in oceanic preexisting conditions on predictions of Typhoon Hai-Tang (2005) by using a coupled atmosphere-ocean model with 6-km horizontal resolution and providing the oceanic initial conditions on 12 July from 1997 to 2005 to the model. Variations in oceanic preexisting conditions caused variation in predicted central pressure of nearly 18 hPa at 72 h, whereas sea-surface cooling (SSC) induced by Hai-Tang caused a predicted central pressure difference of about 40 hPa. Warm-core oceanic eddies up to a few hundred kilometers across and a deep mixed layer climatologically distributed in the western North Pacific led to high mixed-layer heat potential, which increased latent heat flux, water vapor, and liquid water contents around Hai-Tang's center. These increases were closely associated with Hai-Tang's intensification. SSC negatively affected the eyewall, whereas variations in oceanic preexisting conditions remarkably affected spiral rainbands and the magnitude of SSC.

scholarly journals The Effect of Atmosphere–Ocean Coupling on the Structure and Intensity of Tropical Cyclone Bejisa in the Southwest Indian Ocean

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 688
Author(s):  
Soline Bielli ◽  
Christelle Barthe ◽  
Olivier Bousquet ◽  
Pierre Tulet ◽  
Joris Pianezze
Keyword(s):  
Tropical Cyclone ◽  
Mixed Layer ◽  
Heat Fluxes ◽  
Sea Surface ◽  
Ocean Mixed Layer ◽  
Surface Cooling ◽  
Southwest Indian Ocean ◽  
Left Hand ◽  
Sea Surface Cooling ◽  
The Impact

A set of numerical simulations is relied upon to evaluate the impact of air-sea interactions on the behaviour of tropical cyclone (TC) Bejisa (2014), using various configurations of the coupled ocean-atmosphere numerical system Meso-NH-NEMO. Uncoupled (SST constant) as well as 1D (use of a 1D ocean mixed layer) and 3D (full 3D ocean) coupled experiments are conducted to evaluate the impact of the oceanic response and dynamic processes, with emphasis on the simulated structure and intensity of TC Bejisa. Although the three experiments are shown to properly capture the track of the tropical cyclone, the intensity and the spatial distribution of the sea surface cooling show strong differences from one coupled experiment to another. In the 1D experiment, sea surface cooling (∼1 ∘C) is reduced by a factor 2 with respect to observations and appears restricted to the depth of the ocean mixed layer. Cooling is maximized along the right-hand side of the TC track, in apparent disagreement with satellite-derived sea surface temperature observations. In the 3D experiment, surface cooling of up to 2.5 ∘C is simulated along the left hand side of the TC track, which shows more consistency with observations both in terms of intensity and spatial structure. In-depth cooling is also shown to extend to a much deeper depth, with a secondary maximum of nearly 1.5 ∘C simulated near 250 m. With respect to the uncoupled experiment, heat fluxes are reduced from about 20% in both 1D and 3D coupling configurations. The tropical cyclone intensity in terms of occurrence of 10-m TC wind is globally reduced in both cases by about 10%. 3D-coupling tends to asymmetrize winds aloft with little impact on intensity but rather a modification of the secondary circulation, resulting in a slight change in structure.

scholarly journals Ensemble forecasting greatly expands the prediction horizon for ocean mesoscale variability

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Prasad G. Thoppil ◽  
Sergey Frolov ◽  
Clark D. Rowley ◽  
Carolyn A. Reynolds ◽  
Gregg A. Jacobs ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Mesoscale Dynamics ◽  
Predictive Skill ◽  
Freshwater Transport ◽  
Prediction Horizon ◽  
Initial Location ◽  
Ocean Models ◽  
High Uncertainty

AbstractMesoscale eddies dominate energetics of the ocean, modify mass, heat and freshwater transport and primary production in the upper ocean. However, the forecast skill horizon for ocean mesoscales in current operational models is shorter than 10 days: eddy-resolving ocean models, with horizontal resolution finer than 10 km in mid-latitudes, represent mesoscale dynamics, but mesoscale initial conditions are hard to constrain with available observations. Here we analyze a suite of ocean model simulations at high (1/25°) and lower (1/12.5°) resolution and compare with an ensemble of lower-resolution simulations. We show that the ensemble forecast significantly extends the predictability of the ocean mesoscales to between 20 and 40 days. We find that the lack of predictive skill in data assimilative deterministic ocean models is due to high uncertainty in the initial location and forecast of mesoscale features. Ensemble simulations account for this uncertainty and filter-out unconstrained scales. We suggest that advancements in ensemble analysis and forecasting should complement the current focus on high-resolution modeling of the ocean.

scholarly journals Ensemble forecasting with a stochastic convective parametrization based on equilibrium statistics

2011 ◽  
Vol 11 (11) ◽  
pp. 30457-30485 ◽  
Author(s):  
P. Groenemeijer ◽  
G. C. Craig
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Ensemble Forecasting ◽  
Total Variance ◽  
Ensemble Prediction ◽  
Ensemble Prediction System ◽  
The Impact

Abstract. The stochastic Plant-Craig scheme for deep convection was implemented in the COSMO mesoscale model and used for ensemble forecasting. Ensembles consisting of 100 48 h forecasts at 7 km horizontal resolution were generated for a 2000 × 2000 km domain covering central Europe. Forecasts were made for seven case studies and characterized by different large-scale meteorological environments. Each 100 member ensemble consisted of 10 groups of 10 members, with each group driven by boundary and initial conditions from a selected member from the global ECMWF Ensemble Prediction System. The precipitation variability within and among these groups of members was computed, and it was found that the relative contribution to the ensemble variance introduced by the stochastic convection scheme was substantial, amounting to as much as 76% of the total variance in the ensemble in one of the studied cases. The impact of the scheme was not confined to the grid scale, and typically contributed 25–50% of the total variance even after the precipitation fields had been smoothed to a resolution of 35 km. The variability of precipitation introduced by the scheme was approximately proportional to the total amount of convection that occurred, while the variability due to large-scale conditions changed from case to case, being highest in cases exhibiting strong mid-tropospheric flow and pronounced meso- to synoptic scale vorticity extrema. The stochastic scheme was thus found to be an important source of variability in precipitation cases of weak large-scale flow lacking strong vorticity extrema, but high convective activity.

The impact of a parameterisation of submesoscale mixed layer eddies on mixed layer depths in the NEMO ocean model

2020 ◽  
Author(s):  
Daley Calvert ◽  
George Nurser ◽  
Mike Bell ◽  
Baylor Fox-Kemper
Keyword(s):  
Mixed Layer ◽  
Global Climate ◽  
Mixed Layer Depth ◽  
Mixing Layer ◽  
Ocean Model ◽  
Alternative Form ◽  
Depth Scale ◽  
Hadley Centre ◽  
The Impact ◽  
Global Mean

<p><span><span><span>A parameterisation scheme for restratification of the mixed layer by submesoscale mixed layer eddies is implemented in the NEMO ocean model. Its impact on the mixed layer depth (MLD) is examined in 30-year integrations of "uncoupled" ocean-ice and "coupled" atmosphere-ocean-ice-land global climate configurations used by the Met Office Hadley Centre. The specification of the mixed-layer Rossby radius in the scheme is shown to affect its impact on the MLD in the 1/4 degree uncoupled configuration by up to a factor of 2 in subtropical and mid-latitudes. This factor has been limited in the extent to which small mixed-layer Rossby radii are utilised to guard against CFL-type instabilities in the scheme, but such a limit was not found to be necessary for this implementation. An alternative form of the scheme is described that approximates the mixed-layer Rossby radius as a function only of latitude. This form is shown to yield similar results to the original formulation for an appropriate choice of parameters. The global mean impact of the scheme on the MLD is found to be almost twice as large in the 1 degree and 2 degree uncoupled configurations as it is in the 1/4 degree configuration, although the parameterised vertical buoyancy fluxes have closer agreement. This is shown to be the result of the scheme overcompensating for the decay in strength of resolved mixed layer density fronts in this model with decreasing horizontal grid resolution. The MLD criterion defining the depth scale of the scheme is shown to affect its global mean impact on the MLD by nearly a factor of 3 in the 1/4 degree uncoupled and coupled configurations, depending on whether the criterion is chosen to capture the actively mixing layer or well-mixed layer. Climatological MLD biases are improved overall in both cases, substantively reducing deep winter biases whilst slightly increasing shallow summer biases.</span></span></span></p>

scholarly journals Experimental Tropical Cyclone Forecasts Using a Variable-Resolution Global Model

2015 ◽  
Vol 143 (10) ◽  
pp. 4012-4037 ◽  
Author(s):  
Colin M. Zarzycki ◽  
Christiane Jablonowski
Keyword(s):  
High Resolution ◽  
Tropical Cyclone ◽  
Initial Conditions ◽  
Weather Prediction ◽  
Horizontal Resolution ◽  
Hurricane Sandy ◽  
Track Forecast ◽  
Time Step ◽  
Variable Resolution ◽  
The Impact

Abstract Tropical cyclone (TC) forecasts at 14-km horizontal resolution (0.125°) are completed using variable-resolution (V-R) grids within the Community Atmosphere Model (CAM). Forecasts are integrated twice daily from 1 August to 31 October for both 2012 and 2013, with a high-resolution nest centered over the North Atlantic and eastern Pacific Ocean basins. Using the CAM version 5 (CAM5) physical parameterization package, regional refinement is shown to significantly increase TC track forecast skill relative to unrefined grids (55 km, 0.5°). For typical TC forecast integration periods (approximately 1 week), V-R forecasts are able to nearly identically reproduce the flow field of a globally uniform high-resolution forecast. Simulated intensity is generally too strong for forecasts beyond 72 h. This intensity bias is robust regardless of whether the forecast is forced with observed or climatological sea surface temperatures and is not significantly mitigated in a suite of sensitivity simulations aimed at investigating the impact of model time step and CAM’s deep convection parameterization. Replacing components of the default physics with Cloud Layers Unified by Binormals (CLUBB) produces a statistically significant improvement in forecast intensity at longer lead times, although significant structural differences in forecasted TCs exist. CAM forecasts the recurvature of Hurricane Sandy into the northeastern United States 60 h earlier than the Global Forecast System (GFS) model using identical initial conditions, demonstrating the sensitivity of TC forecasts to model configuration. Computational costs associated with V-R simulations are dramatically decreased relative to globally uniform high-resolution simulations, demonstrating that variable-resolution techniques are a promising tool for future numerical weather prediction applications.

scholarly journals Reconstructing Upper-Ocean Vertical Velocity Field from Sea Surface Height in the Presence of Unbalanced Motion

2020 ◽  
Vol 50 (1) ◽  
pp. 55-79 ◽  
Author(s):  
Bo Qiu ◽  
Shuiming Chen ◽  
Patrice Klein ◽  
Hector Torres ◽  
Jinbo Wang ◽  
...  
Keyword(s):  
Spatial Correlation ◽  
Mixed Layer ◽  
Vertical Velocity ◽  
Measurement Errors ◽  
Kuroshio Extension ◽  
Sea Surface Height ◽  
Horizontal Resolution ◽  
Sea Surface ◽  
Upper Ocean ◽  
The Impact

AbstractReconstructability of upper-ocean vertical velocity w and vorticity ζ fields from high-resolution sea surface height (SSH) data is explored using the global 1/48° horizontal-resolution MITgcm output in the context of the forthcoming Surface Water and Ocean Topography (SWOT) mission. By decomposing w with an omega equation of the primitive equation system and by taking into account the measurement design of the SWOT mission, this study seeks to reconstruct the subinertial, balanced w and ζ signals. By adopting the effective surface quasigeostrophic (eSQG) framework and applying to the Kuroshio Extension region of the North Pacific, we find that the target and reconstructed fields have a spatial correlation of ~0.7 below the mixed layer for w and 0.7–0.9 throughout the 1000-m upper ocean for ζ in the error-free scenario. By taking the SWOT sampling and measurement errors into account, the spatial correlation is found to decrease to 0.4–0.6 below the mixed layer for w and 0.6–0.7 for ζ, respectively. For both w and ζ reconstruction, the degradation due to the SWOT errors is more significant in the surface layer and for smaller-scale signals. The impact of errors lessens with the increasing depth and lengthening horizontal scales.

Testing robustness of co-existing climate states

2021 ◽  
Author(s):  
Charline Ragon ◽  
Valerio Lembo ◽  
Valerio Lucarini ◽  
Christian Vérard ◽  
Jérôme Kasparian ◽  
...  
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Water Mass ◽  
Hydrological Cycle ◽  
Initial Conditions ◽  
Frictional Heating ◽  
Horizontal Resolution ◽  
Climate Dynamics ◽  
Mechanical Work ◽  
The Impact

<p><span>The climate can be regarded as a stationary non-equilibrium statistical system (Gallavotti 2006): a continuous and spatially inhomogeneous input of solar energy enters at the top-of-atmosphere and compensates the action of non-conservative forces, mainly occurring at small scales, to give rise to a statistically steady state (or attractor) for the whole climate. </span></p><p><span>Depending on the initial conditions and the range of forcing, all other parameters being the same, some climate models have the property to settle down on different attractors. </span><span>Multi-stability reflects how energy, water mass and entropy can be re-distributed in multiple ways among the climate components, such as the atmosphere, the ocean or the ice, through a different balance between nonlinear mechanisms. </span></p><p><span>Starting from a configuration where competing climate attractors occur under the same forcing, we have explored their robustness performing two kinds of numerical experiment. </span><span>First, we have investigated the impact of frictional heating on the overall energy balance and we have shown that such contribution, generally neglected in the atmospheric component of climate models, has crucial </span><span>consequences on conservation properties: it improves the energy imbalance at top-of-atmosphere, typically non negligible in coarse simulations (Wild et al. 2020), strengthens the hydrological cycle, </span><span>mitigates the mechanical work associated to atmospheric circulation intensity </span><span>and reduces the heat transport peaks in the ocean. </span><span>Second, we have compared two bulk formulas for the cloud albedo, one where it is constant everywhere and the other where it increases with latitude, as implemented in the new version of the atmospheric module SPEEDY in order to improve comparisons with observational data (Kucharski 2013). We have che</span><span>cked that this new parameterization does not affect energy and water-mass imbalances, while reduces global temperature and water-mass transport on the attractor, giving rise to a larger conversion of heat into mechanical work in the atmosphere.</span></p><p><span>In order to perform such studies, we have run the climate model MITgcm on coupled aquaplanets at 2.8 horizontal resolution until steady states are reached (Brunetti el al. 2019) and we have applied the Thermodynamic Diagnostic Tool (<em>TheDiaTo</em>, Lembo et al. 2019). </span></p><p> </p><p><span>References: </span></p><p><span>Brunetti, Kasparian, Vérard, Climate Dynamics 53, 6293 (2019)</span></p><p><span>Gallavotti, </span>Math. Phys. 3, 530<span> (2006)</span></p><p>Kucharski<span> et al.</span>, Bulletin of the American Meteorological Society 94, 25<span> (2013)</span></p><p>Lembo, Lunkeit, Lucarini, Geoscientific Model Development 12, 3805<span> (2019)</span></p><p><span>Wild, </span>Climate Dynamics 55, 553<span> (2020)</span></p>

Numerical study on ocean response to storm in Arctic Ocean

2020 ◽  
Author(s):  
Hailun He ◽  
Long Lin
Keyword(s):  
Arctic Ocean ◽  
Mixed Layer ◽  
Initial Conditions ◽  
Numerical Study ◽  
Surface Current ◽  
Ocean Model ◽  
Storm Events ◽  
Ocean Response ◽  
Freshwater Fluxes ◽  
Storm Condition

<p>A one-column ocean model was used to study the ocean response to storm in Arctic Ocean. We design a number of idealized experiments by different surface forcing and initial condition. The results show the phenomena of mixed-layer extension during the storm events. The intensification of surface current reflects the momentum flux injected from wind and ice movement. Furthermore, by changing the surface heat and freshwater fluxes, the dependences of mixed-layer variation on surface forcing are discussed. Finally, the numerical tests on different initial conditions show how the pre-storm condition affects the ocean response to storm. The results therefore reveal the dependence of mixed-layer extension on the initial stratification.</p>

scholarly journals Land–Atmosphere Interactions during a Northwestern Argentina Low Event

2010 ◽  
Vol 138 (7) ◽  
pp. 2481-2498 ◽  
Author(s):  
Celeste Saulo ◽  
Lorena Ferreira ◽  
Julia Nogués-Paegle ◽  
Marcelo Seluchi ◽  
Juan Ruiz
Keyword(s):  
Soil Moisture ◽  
South America ◽  
Land Surface ◽  
Initial Conditions ◽  
Convective Available Potential Energy ◽  
Moisture Flux ◽  
Horizontal Resolution ◽  
Northwestern Argentina ◽  
Low Level ◽  
The Impact

Abstract The impact of changes in soil moisture in subtropical Argentina in rainfall distribution and low-level circulation is studied with a state-of-the-art regional model in a downscaling mode, with different scenarios of soil moisture for a 10-day period. The selected case (starting 29 January 2003) was characterized by a northwestern Argentina low event associated with well-defined low-level northerly flow that extended east of the Andes over subtropical latitudes. Four tests were conducted at 40-km horizontal resolution with 31 sigma levels, decreasing and increasing the soil moisture initial condition by 50% over the entire domain, and imposing a 50% reduction over northwest Argentina and 50% increase over southeast South America. A control run with NCEP/Global Data Assimilation System (GDAS) initial conditions was used to assess the impact of the different soil moisture configurations. It was found that land surface interactions are stronger when soil moisture is decreased, with a coherent reduction of precipitation over southern South America. Enhanced northerly winds result from an increase in the zonal gradient of pressure at low levels. In contrast, when soil moisture is increased, smaller circulation changes are found, although there appears to be a local feedback effect between the land and precipitation. The combined effects of changes in the circulation and in local stratification induced by soil wetness modifications, through variations in evaporation and Convective Available Potential Energy (CAPE), are in agreement with what has been found by other studies, resulting in coherent modifications of precipitation when variations of CAPE and moisture flux convergence mutually reinforce.

Sign in / Sign up

Export Citation Format

Share Document