scholarly journals Tropical Cyclones in Rotating Radiative–Convective Equilibrium with Coupled SST

2017 ◽  
Vol 74 (3) ◽  
pp. 879-892 ◽  
Author(s):  
Wenyu Zhou ◽  
Isaac M. Held ◽  
Stephen T. Garner
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
Tropical Cyclones ◽  
Atmospheric Model ◽  
Ocean Model ◽  
Sea Surface ◽  
Global Atmospheric Model ◽  
Small Depth ◽  
Ocean Layer ◽  
Slab Ocean

Abstract Tropical cyclones are studied under the idealized framework of rotating radiative–convective equilibrium, achieved in a large doubly periodic f plane by coupling the column physics of a global atmospheric model to rotating hydrostatic dynamics. Unlike previous studies that prescribe uniform sea surface temperature (SST) over the domain, SSTs are now predicted by coupling the atmosphere to a simple slab ocean model. With coupling, SSTs under the eyewall region of tropical cyclones (TCs) become cooler than the environment. However, the domain still fills up with multiple long-lived TCs in all cases examined, including at the limit of the very small depth of the slab. The cooling of SSTs under the eyewall increases as the depth of the slab ocean layer decreases but levels off at roughly 6.5 K as the depth approaches zero. At the eyewall, the storm interior is decoupled from the cooler surface and moist entropy is no longer well mixed along the angular momentum surface in the boundary layer. TC intensity is reduced from the potential intensity computed without the cooling, but the intensity reduction is smaller than that estimated by a potential intensity taking into account the cooling and assuming that moist entropy is well mixed along angular momentum surfaces within the atmospheric boundary layer.

scholarly journals Parameter Study of Tropical Cyclones in Rotating Radiative–Convective Equilibrium with Column Physics and Resolution of a 25-km GCM

2014 ◽  
Vol 71 (3) ◽  
pp. 1058-1069 ◽  
Author(s):  
Wenyu Zhou ◽  
Isaac M. Held ◽  
Stephen T. Garner
Keyword(s):  
Tropical Cyclones ◽  
Rotation Rate ◽  
Surface Wind ◽  
Domain Size ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Parameter Study ◽  
Surface Drag ◽  
Tropical Depression ◽  
Global Atmospheric Model

Abstract Rotating radiative–convective equilibrium is studied by extracting the column physics of a mesoscale-resolution global atmospheric model that simulates realistic hurricane frequency statistics and then coupling it to rotating hydrostatic dynamics in doubly periodic domains. The parameter study helps in understanding the tropical cyclones simulated in the global model and also provides a reference point for analogous studies with cloud-resolving models. The authors first examine the sensitivity of the equilibrium achieved in a large square domain (2 × 104 km on a side) to sea surface temperature, ambient rotation rate, and surface drag coefficient. In such a large domain, multiple tropical cyclones exist simultaneously. The size and intensity of these tropical cyclones are investigated. The variation of rotating radiative–convective equilibrium with domain size is also studied. As domain size increases, the equilibrium evolves through four regimes: a single tropical depression, an intermittent tropical cyclone with widely varying intensity, a single sustained storm, and finally multiple storms. As SST increases or ambient rotation rate f decreases, the sustained storm regime shifts toward larger domain size. The storm’s natural extent in large domains can be understood from this regime behavior. The radius of maximum surface wind, although only marginally resolved, increases with SST and increases with f for small f when the domain is large enough. These parameter dependencies can be modified or even reversed if the domain is smaller than the storm’s natural extent.

scholarly journals Characteristics of Size Change of Tropical Cyclones Traversing the Philippines

2018 ◽  
Vol 146 (9) ◽  
pp. 2891-2911 ◽  
Author(s):  
Shu-Jeng Lin ◽  
Kun-Hsuan Chou
Keyword(s):  
Angular Momentum ◽  
Relative Humidity ◽  
Tropical Cyclones ◽  
Momentum Flux ◽  
Vertical Wind Shear ◽  
The Philippines ◽  
Sea Surface ◽  
Japan Meteorological Agency ◽  
The South ◽  
Size Change

Abstract This study investigates the size changes of tropical cyclones (TCs) traversing the Philippines based on a 37-yr statistical analysis. TC size is defined by the radius of 30-kt (≈15.4 m s−1) wind speed (R30) from the best track data of the Japan Meteorological Agency. A total of 71 TCs passed the Philippines during 1979–2015. The numbers of size increase (SI; 36) and size decrease (SD; 34) cases are very similar; however, the last 15 years have seen more SI cases (17) than SD cases (11). SI and SD cases mostly occur along northerly and southerly paths, respectively, after TCs pass the Philippines. Before landfall, SI cases have small initial sizes and weak intensities, but SD cases have larger initial sizes and stronger intensities. After landfall, most SI cases are intensifying storms, and most SD cases are nonintensifying storms. Composite analyses of vertical wind shear, absolute angular momentum flux, relative humidity, and sea surface temperature between SI and SD cases are compared. All of these values are larger in SI cases than in SD cases. Furthermore, the interdecadal difference in the ratio of the numbers of SI to SD cases reveals an unusually high number of SI cases during 2001–15. The synoptic patterns between 1979–2000 and 2001–15 are analyzed. The high SI ratio in the latter period is related to strong southwesterly wind in the south of the South China Sea that raised relative humidity, warmed the sea surface, and increased import of angular momentum flux.

scholarly journals Characteristics of convective snow bands along the Swedish east coast

2017 ◽  
Vol 8 (1) ◽  
pp. 163-175 ◽  
Author(s):  
Julia Jeworrek ◽  
Lichuan Wu ◽  
Christian Dieterich ◽  
Anna Rutgersson
Keyword(s):  
Regional Climate Model ◽  
East Coast ◽  
Climate Model ◽  
Regional Climate ◽  
Open Water ◽  
Atmospheric Model ◽  
Ocean Model ◽  
Sea Surface ◽  
Precipitation Rate ◽  
Shallow Convection

Abstract. Convective snow bands develop in response to a cold air outbreak from the continent or the frozen sea over the open water surface of lakes or seas. The comparatively warm water body triggers shallow convection due to increased heat and moisture fluxes. Strong winds can align with this convection into wind-parallel cloud bands, which appear stationary as the wind direction remains consistent for the time period of the snow band event, delivering enduring snow precipitation at the approaching coast. The statistical analysis of a dataset from an 11-year high-resolution atmospheric regional climate model (RCA4) indicated 4 to 7 days a year of moderate to highly favourable conditions for the development of convective snow bands in the Baltic Sea region. The heaviest and most frequent lake effect snow was affecting the regions of Gävle and Västervik (along the Swedish east coast) as well as Gdansk (along the Polish coast). However, the hourly precipitation rate is often higher in Gävle than in the Västervik region. Two case studies comparing five different RCA4 model setups have shown that the Rossby Centre atmospheric regional climate model RCA4 provides a superior representation of the sea surface with more accurate sea surface temperature (SST) values when coupled to the ice–ocean model NEMO as opposed to the forcing by the ERA-40 reanalysis data. The refinement of the resolution of the atmospheric model component leads, especially in the horizontal direction, to significant improvement in the representation of the mesoscale circulation process as well as the local precipitation rate and area by the model.

Comparisons of atmosphere–ocean simulations of greenhouse gas-induced climate change for pre-industrial and hypothetical ‘no-anthropogenic’ radiative forcing, relative to present day

The Holocene ◽  
2011 ◽  
Vol 21 (5) ◽  
pp. 793-801 ◽  
Author(s):  
J.E. Kutzbach ◽  
S.J. Vavrus ◽  
W.F. Ruddiman ◽  
G. Philippon-Berthier
Keyword(s):  
Climate Change ◽  
Sea Ice ◽  
Greenhouse Gas ◽  
Ocean Circulation ◽  
Radiative Forcing ◽  
Deep Ocean ◽  
Lower Surface ◽  
Atmospheric Model ◽  
Ocean Model ◽  
Slab Ocean

We compare climate simulations for Present-Day (PD), Pre-Industrial (PI) time, and a hypothetical (inferred) state termed No-Anthropogenic (NA) based upon the low greenhouse gas (GHG) levels of the late stages of previous interglacials that are comparable in time (orbital configuration) to the present interglacial. We use a fully coupled dynamical atmosphere–ocean model, the CCSM3. We find a consistent trend toward colder climate (lower surface temperature, more snow and sea-ice cover, lower ocean temperature, and modified ocean circulation) as the net change in GHG radiative forcing trends more negative from PD to PI to NA. The climatic response of these variables becomes larger relative to the changed GHG forcing for each step toward a colder climate state (PD to PI to NA). This amplification is significantly enhanced using the dynamical atmosphere–ocean model compared with our previous results with an atmosphere–slab ocean model, a result that conforms to earlier idealized GHG forcing experiments. However, in our case this amplification is not an idealized result, but instead helps frame important questions concerning aspects of Holocene climate change. This enhanced amplification effect leads to an increase in our estimate of the climate’s response to inferred early anthropogenic CO2 increases (NA to PI) relative to the response to industrial-era CO2 increases (PI to PD). Although observations of the climate for the hypothetical NA (inferred from observations of previous interglacials) and for PI have significant uncertainties, our new results using CCSM3 are in better agreement with these observations than our previous results from an atmospheric model coupled to a static slab ocean. The results support more strongly inferences by Ruddiman concerning indirect effects of ocean solubility/sea-ice/deep ocean ventilation feedbacks that may have contributed to a further increase in late-Holocene atmospheric CO2 beyond that caused by early anthropogenic emissions alone.

scholarly journals Intraseasonal Sea Surface Temperature Variability across the Indonesian Seas*

2015 ◽  
Vol 28 (22) ◽  
pp. 8710-8727 ◽  
Author(s):  
Asmi M. Napitu ◽  
Arnold L. Gordon ◽  
Kandaga Pujiana
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Intraseasonal Variability ◽  
Longwave Radiation ◽  
Active Phase ◽  
Ocean Model ◽  
Sea Surface ◽  
Indonesian Seas ◽  
Sst Variability ◽  
Slab Ocean

Abstract Sea surface temperature (SST) variability at intraseasonal time scales across the Indonesian Seas during January 1998–mid-2012 is examined. The intraseasonal variability is most energetic in the Banda and Timor Seas, with a standard deviation of 0.4°–0.5°C, representing 55%–60% of total nonseasonal SST variance. A slab ocean model demonstrates that intraseasonal air–sea heat flux variability, largely attributed to the Madden–Julian oscillation (MJO), accounts for 69%–78% intraseasonal SST variability in the Banda and Timor Seas. While the slab ocean model accurately reproduces the observed intraseasonal SST variations during the northern winter months, it underestimates the summer variability. The authors posit that this is a consequence of a more vigorous cooling effect induced by ocean processes during the summer. Two strong MJO cycles occurred in late 2007–early 2008, and their imprints were clearly evident in the SST of the Banda and Timor Seas. The passive phase of the MJO [enhanced outgoing longwave radiation (OLR) and weak zonal wind stress) projects on SST as a warming period, while the active phase (suppressed OLR and westerly wind bursts) projects on SST as a cooling phase. SST also displays significant intraseasonal variations in the Sulawesi Sea, but these differ in characteristics from those of the Banda and Timor Seas and are attributed to ocean eddies and atmospheric processes independent from the MJO.

scholarly journals A Highly Configurable Vortex Initialization Method for Tropical Cyclones

2013 ◽  
Vol 141 (10) ◽  
pp. 3556-3575 ◽  
Author(s):  
Eric D. Rappin ◽  
David S. Nolan ◽  
Sharanya J. Majumdar
Keyword(s):  
Boundary Layer ◽  
Angular Momentum ◽  
Steady State ◽  
Tropical Cyclones ◽  
Mesoscale Model ◽  
Layer Structure ◽  
Numerical Models ◽  
Secondary Circulation ◽  
Free Atmosphere ◽  
Vortex Initialization

Abstract A highly configurable vortex initialization methodology has been constructed in order to permit manipulation of the initial vortex structure in numerical models of tropical cyclones. By using distinct specifications of the flow in the boundary layer and free atmosphere, an array of parameters is available to modify the structure. A nonlinear similarity model that solves the steady-state, height-dependent equations for a neutrally stratified, axisymmetric vortex is solved for the boundary layer flow. Above the boundary layer, a steady-state, moist-neutral, hydrostatic and gradient wind balanced model is used to generate the angular momentum distribution in the free atmosphere. In addition, an unbalanced mass-conserving secondary circulation is generated through the assumption of conservation of mass and angular momentum above the boundary layer. Numerical simulations are conducted using a full-physics mesoscale model to explore the sensitivity of the vortex evolution to different prescriptions of the initial vortex. Dynamical adjustment is found to be dominant in the early evolution of the simulations, thereby masking any sensitivity to initial changes in the secondary circulation and boundary layer structure. The adjustment time can be significantly reduced by arbitrarily enhancing the moisture in the eyewall region.

Optimizing COSMO_REA6 reanalysis radiation flux for a high resolution coastal ocean model

2020 ◽  
Author(s):  
Martin Vodopivec ◽  
Matjaž Ličer
Keyword(s):  
High Resolution ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Atmospheric Model ◽  
Short Wave ◽  
Ocean Model ◽  
Sea Surface ◽  
Atmospheric Models ◽  
Fine Grid ◽  
Wave Flux

<p>When modelling coastal areas in high spatial resolution, it is also essential to obtain atmospheric forcing with suitably fine grid. The complex coastline and coastal orography exert strong influence on atmospheric fields, wind in particular, and the east Adriatic coast with numerous islands and coastal mountain ridges is a fine example. We decided to use a high resolution COSMO atmospheric reanalysis for our long term ROMS_AGRIF hindcasts, but in our initial experiments we found out that the atmospheric model significantly underestimates the short wave flux over the Mediterranean Sea, probably due to overestimation of high clouds formation and erroneous sea surface temperature used as a boundary condition. We explore different atmospheric models and different combinations of fluxes - direct, diffuse and clear sky solar radiation and combinations of fluxes from different atmospheric models (eg. ERA5). We compare them with solar irradiance observations at a coastal meteorological station and run year-long simulations to compare model sea surface temperature (SST) with satellite observations obtained from Coprenicus Marine Environment Monitoring Service.</p>

scholarly journals Enhanced intensity of global tropical cyclones during the mid-Pliocene warm period

2016 ◽  
Vol 113 (46) ◽  
pp. 12963-12967 ◽  
Author(s):  
Qing Yan ◽  
Ting Wei ◽  
Robert L. Korty ◽  
James P. Kossin ◽  
Zhongshi Zhang ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Power Dissipation ◽  
Atmospheric Model ◽  
Historical Record ◽  
Warm Period ◽  
Global Atmospheric Model ◽  
Peak Intensity ◽  
The Pacific ◽  
Present World

Given the threats that tropical cyclones (TC) pose to people and infrastructure, there is significant interest in how the climatology of these storms may change with climate. The global historical record has been extensively examined, but it is short and plagued with recurring questions about its homogeneity, limiting its effectiveness at assessing how TCs vary with climate. Past warm intervals provide an opportunity to quantify TC behavior in a warmer-than-present world. Here, we use a TC-resolving (∼25 km) global atmospheric model to investigate TC activity during the mid-Pliocene warm period (3.264−3.025 Ma) that shares similarities with projections of future climate. Two experiments, one driven by the reconstructed sea surface temperatures (SSTs) and the other by the SSTs from an ensemble of mid-Pliocene simulations, consistently predict enhanced global-average peak TC intensity during the mid-Pliocene coupled with longer duration, increased power dissipation, and a poleward migration of the location of peak intensity. The simulations are similar to global TC changes observed during recent global warming, as well as those of many future projections, providing a window into the potential TC activity that may be expected in a warmer world. Changes to power dissipation and TC frequency, especially in the Pacific, are sensitive to the different SST patterns, which could affect the viability of the role of TCs as a factor for maintaining a reduced zonal SST gradient during the Pliocene, as recently hypothesized.

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