scholarly journals The characteristics and structure of extra-tropical cyclones in a warmer climate

2020 ◽  
Vol 1 (1) ◽  
pp. 1-25 ◽  
Author(s):  
Victoria A. Sinclair ◽  
Mika Rantanen ◽  
Päivi Haapanala ◽  
Jouni Räisänen ◽  
Heikki Järvinen
Keyword(s):  
Tropical Cyclones ◽  
Diabatic Heating ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Intermediate Step ◽  
Thermal Advection ◽  
Vorticity Advection ◽  
Omega Equation ◽  
Total Column

Abstract. Little is known about how the structure of extra-tropical cyclones will change in the future. In this study aqua-planet simulations are performed with a full-complexity atmospheric model. These experiments can be considered an intermediate step towards increasing knowledge of how, and why, extra-tropical cyclones respond to warming. A control simulation and a warm simulation in which the sea surface temperatures are increased uniformly by 4 K are run for 11 years. Extra-tropical cyclones are tracked, cyclone composites created, and the omega equation applied to assess causes of changes in vertical motion. Warming leads to a 3.3 % decrease in the number of extra-tropical cyclones, with no change to the median intensity or lifetime of extra-tropical cyclones but to a broadening of the intensity distribution resulting in both more stronger and more weaker storms. Composites of the strongest extra-tropical cyclones show that total column water vapour increases everywhere relative to the cyclone centre and that precipitation increases by up to 50 % with the 4 K warming. The spatial structure of the composite cyclone changes with warming: the 900–700 hPa layer averaged potential vorticity, 700 hPa ascent, and precipitation maximums associated with the warm front all move polewards and downstream, and the area of ascent expands in the downstream direction. Increases in ascent forced by diabatic heating and thermal advection are responsible for the displacement, whereas increases in ascent due to vorticity advection lead to the downstream expansion. Finally, maximum values of ascent due to vorticity advection and thermal advection weaken slightly with warming, whereas those attributed to diabatic heating increase. Thus, cyclones in warmer climates are more diabatically driven.

scholarly journals The characteristics and structure of extra-tropical cyclones in a warmer climate

2019 ◽  
Author(s):  
Victoria A. Sinclair ◽  
Mika Rantanen ◽  
Päivi Haapanala ◽  
Jouni Räisänen ◽  
Heikki Järvinen
Keyword(s):  
Tropical Cyclones ◽  
Diabatic Heating ◽  
Vertical Motion ◽  
Life Time ◽  
Atmospheric Model ◽  
Intermediate Step ◽  
Thermal Advection ◽  
Vorticity Advection ◽  
Omega Equation ◽  
Total Column

Abstract. Little is known about how the structure of extra-tropical cyclones will change in the future. In this study aquaplanet simulations are performed with a full complexity atmospheric model. These experiments can be considered as an intermediate step towards increasing knowledge of how, and why, extra-tropical cyclones respond to warming. A control simulation and a warm simulation in which the sea surface temperatures are increased uniformly by 4 K are run for 11 years. Extra-tropical cyclones are tracked, cyclone composites created, and the omega equation applied to assess causes of changes in vertical motion. Warming leads to a 3.3 % decrease in the number of extra-tropical cyclones, no change to the median intensity nor life time of extra-tropical cyclones, but to a broadening of the intensity distribution resulting in both more stronger and more weaker storms. Composites of the strongest extra-tropical cyclones show that total column water vapour increases everywhere relative to the cyclone centre and that precipitation increases by up to 50 % with the 4 K warming. The spatial structure of the composite cyclone changes with warming: the 900–700-hPa layer averaged potential vorticity, 700-hPa ascent and precipitation maximums associated with the warm front all move polewards and downstream and the area of ascent expands in the downstream direction. Increases in ascent forced by diabatic heating and thermal advection are responsible for the displacement whereas increases in ascent due to vorticity advection lead to the downstream expansion. Finally, maximum values of ascent due to vorticity advection and thermal advection weaken slightly with warming whereas those attributed to diabatic heating increase. Thus, cyclones in warmer climates are more diabatically driven.

scholarly journals Systematic Variation in Wintertime Precipitation in East Asia by MJO-Induced Extratropical Vertical Motion

2008 ◽  
Vol 21 (4) ◽  
pp. 788-801 ◽  
Author(s):  
Jee-Hoon Jeong ◽  
Baek-Min Kim ◽  
Chang-Hoi Ho ◽  
Yeon-Hee Noh
Keyword(s):  
East Asia ◽  
Large Scale ◽  
Diabatic Heating ◽  
Daily Precipitation ◽  
Lower Troposphere ◽  
Vertical Motion ◽  
Mean Value ◽  
Asian Countries ◽  
The Indian Ocean ◽  
Omega Equation

Abstract The variations in the wintertime precipitation over East Asia and the related large-scale circulation associated with the Madden–Julian oscillation (MJO) are examined. By analyzing the observed daily precipitation for the period 1974–2000, it is found that the MJO significantly modulates the distribution of precipitation over four East Asian countries; the precipitation rate difference between wet and dry periods over East Asia, when the centers of MJO convective activities are located over the Indian Ocean and western Pacific, respectively, reaches 3–4 mm day−1, which corresponds to the climatological winter-mean value. Composite analysis with respect to the MJO suggests that the MJO–precipitation relation is mostly explained by the strong vertical motion anomalies near an entrance region of the East Asia upper-tropospheric jet and moisture supply in the lower troposphere. To elucidate different dynamic origins of the vertical motion generated by the MJO, diagnostic analysis of a generalized omega equation is adopted. It is revealed that about half of the vertical motion anomalies in East Asia are induced by the quasigeostrophic forcings by the MJO, while diabatic heating forcings explain a very small fraction, less than 10% of total anomalies.

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 OZO v.1.0: software for solving a generalised omega equation and the Zwack–Okossi height tendency equation using WRF model output

2017 ◽  
Vol 10 (2) ◽  
pp. 827-841 ◽  
Author(s):  
Mika Rantanen ◽  
Jouni Räisänen ◽  
Juha Lento ◽  
Oleg Stepanyuk ◽  
Olle Räty ◽  
...  
Keyword(s):  
Diabatic Heating ◽  
Physical Mechanism ◽  
Wrf Model ◽  
Vertical Motion ◽  
Weather Research And Forecasting ◽  
Cartesian Geometry ◽  
Diabatic Processes ◽  
Research And Education ◽  
The Individual ◽  
Omega Equation

Abstract. A software package (OZO, Omega–Zwack–Okossi) was developed to diagnose the processes that affect vertical motions and geopotential height tendencies in weather systems simulated by the Weather Research and Forecasting (WRF) model. First, this software solves a generalised omega equation to calculate the vertical motions associated with different physical forcings: vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term between vorticity and temperature tendencies. After this, the corresponding height tendencies are calculated with the Zwack–Okossi tendency equation. The resulting height tendency components thus contain both the direct effect from the forcing itself and the indirect effects (related to the vertical motion induced by the same forcing) of each physical mechanism. This approach has an advantage compared with previous studies with the Zwack–Okossi equation, in which vertical motions were used as an independent forcing but were typically found to compensate the effects of other forcings.The software is currently tailored to use input from WRF simulations with Cartesian geometry. As an illustration, results for an idealised 10-day baroclinic wave simulation are presented. An excellent agreement is found between OZO and the direct WRF output for both the vertical motion and the height tendency fields. The individual vertical motion and height tendency components demonstrate the importance of both adiabatic and diabatic processes for the simulated cyclone. OZO is an open-source tool for both research and education, and the distribution of the software will be supported by the authors.

scholarly journals OZO v.1.0: Software for solving a generalized omega equation and the Zwack-Okossi height tendency equation using WRF model output

2016 ◽  
Author(s):  
Mika Rantanen ◽  
Jouni Räisänen ◽  
Juha Lento ◽  
Oleg Stepanyuk ◽  
Olle Räty ◽  
...  
Keyword(s):  
Diabatic Heating ◽  
Physical Mechanism ◽  
Wrf Model ◽  
Vertical Motion ◽  
Weather Research And Forecasting ◽  
Cartesian Geometry ◽  
Diabatic Processes ◽  
Research And Education ◽  
The Individual ◽  
Omega Equation

Abstract. A software package (OZO, Omega-Zwack-Okossi) was developed to diagnose the processes that affect vertical motions and geopotential height tendencies in weather systems simulated by the Weather Research and Forecasting (WRF) model. First, this software solves a generalized omega equation to calculate the vertical motions associated with different physical forcings: vorticity advection, thermal advection, friction, diabatic heating, and an imbalance term between vorticity and temperature tendencies. After this, the corresponding height tendencies are calculated with the Zwack-Okossi tendency equation. The resulting height tendency components thus contain both the direct effect from the forcing itself and the indirect effects (related to the vertical motion induced by the same forcing) of each physical mechanism. This approach has an advantage compared with previous studies with the Zwack-Okossi equation, in which vertical motions were used as an independent forcing but were typically found to compensate the effects of other forcings. The software is tailored to use input from WRF simulations with Cartesian geometry. As an illustration, results for an idealized 10-day baroclinic wave simulation are presented. An excellent agreement is found between OZO and the direct WRF output for both the vertical motion (correlation 0.97 in the midtroposphere) and the height tendency fields (correlation 0.95–0.98 in the whole troposphere). The individual vertical motion and height tendency components demonstrate the importance of both adiabatic and diabatic processes for the simulated cyclone. OZO is an open source tool for both research and education, and the distribution of the software will be supported by the authors.

scholarly journals Application of the Compressible, Nonhydrostatic, Balanced Omega Equation in Estimating Diabatic Forcing for Parameterization of Inertia–Gravity Waves: Case Study of Moist Baroclinic Waves Using WRF

2019 ◽  
Vol 77 (1) ◽  
pp. 113-129
Author(s):  
Mahnoosh Haghighatnasab ◽  
Mohammad Mirzaei ◽  
Ali R. Mohebalhojeh ◽  
Christoph Zülicke ◽  
Riwal Plougonven
Keyword(s):  
Gravity Waves ◽  
General Circulation ◽  
Diabatic Heating ◽  
Wrf Model ◽  
Vertical Motion ◽  
General Circulation Models ◽  
Baroclinic Waves ◽  
Diabatic Forcing ◽  
Omega Equation ◽  
Inertia Gravity Waves

Abstract The parameterization of inertia–gravity waves (IGWs) is of considerable importance in general circulation models. Among the challenging issues faced in studies concerned with parameterization of IGWs is the estimation of diabatic forcing in a way independent of the physics parameterization schemes, in particular, convection. The requirement is to estimate the diabatic heating associated with balanced motion. This can be done by comparing estimates of balanced vertical motion with and without diabatic effects. The omega equation provides the natural method of estimating balanced vertical motion without diabatic effects, and several methods for including diabatic effects are compared. To this end, the assumption of spatial-scale separation between IGWs and balanced flows is combined with a suitable form of the balanced omega equation. To test the methods constructed for estimating diabatic heating, an idealized numerical simulation of the moist baroclinic waves is performed using the Weather Research and Forecasting (WRF) Model in a channel on the f plane. In overall agreement with the diabatic heating of the WRF Model, in the omega-equation-based estimates, the maxima of heating appear in the warm sector of the baroclinic wave and in the exit region of the upper-level jet. The omega-equation-based method with spatial smoothing for estimating balanced vertical motion is thus presented as the proper way to evaluate diabatic forcing for parameterization of IGWs.

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 The Response of Tropical Cyclone Statistics to an Increase in CO2 with Fixed Sea Surface Temperatures

2011 ◽  
Vol 24 (20) ◽  
pp. 5353-5364 ◽  
Author(s):  
Isaac M. Held ◽  
Ming Zhao
Keyword(s):  
Tropical Cyclone ◽  
Vertical Motion ◽  
Atmospheric Model ◽  
Sea Surface ◽  
Intensity Increase ◽  
Average Intensity ◽  
Sea Surface Temperatures ◽  
Global Atmospheric Model ◽  
Relative Contribution ◽  
Surface Temperatures

Abstract The effects on tropical cyclone statistics of doubling CO2, with fixed sea surface temperatures (SSTs), are compared to the effects of a 2-K increase in SST, with fixed CO2, using a 50-km resolution global atmospheric model. Confirming earlier results of Yoshimura and Sugi, a significant fraction of the reduction in globally averaged tropical storm frequency seen in simulations in which both SST and CO2 are increased can be thought of as the effect of the CO2 increase with fixed SSTs. Globally, the model produces a decrease in tropical cyclone frequency of about 10% due to doubling of CO2 and an additional 10% for a 2-K increase in SST, resulting in roughly a 20% reduction when both effects are present. The relative contribution of the CO2 effect to the total reduction is larger in the Northern than in the Southern Hemisphere. The average intensity of storms increases in the model with increasing SST, but intensity remains roughly unchanged, or decreases slightly, with the increase in CO2 alone. As a result, when considering the frequency of more intense cyclones, the intensity increase tends to compensate for the reduced total cyclone numbers for the SST increase in isolation, but not for the CO2 increase in isolation. Changes in genesis in these experiments roughly follow changes in mean vertical motion, reflecting changes in convective mass fluxes. Discussion of one possible perspective on how changes in the convective mass flux might alter genesis rates is provided.

scholarly journals Sea Surface Salinity Response to Tropical Cyclones Based on Satellite Observations

2021 ◽  
Vol 13 (3) ◽  
pp. 420
Author(s):  
Jingru Sun ◽  
Gabriel Vecchi ◽  
Brian Soden
Keyword(s):  
Tropical Cyclones ◽  
Sea Surface ◽  
Sea Surface Salinity ◽  
Surface Salinity ◽  
Translation Speed ◽  
Salinity Stratification ◽  
Left Hand ◽  
In Situ Data ◽  
Salinity Response ◽  
The Right

Multi-year records of satellite remote sensing of sea surface salinity (SSS) provide an opportunity to investigate the climatological characteristics of the SSS response to tropical cyclones (TCs). In this study, the influence of TC winds, rainfall and preexisting ocean stratification on SSS evolution is examined with multiple satellite-based and in-situ data. Global storm-centered composites indicate that TCs act to initially freshen the ocean surface (due to precipitation), and subsequently salinify the surface, largely through vertical ocean processes (mixing and upwelling), although regional hydrography can lead to local departure from this behavior. On average, on the day a TC passes, a strong SSS decrease is observed. The fresh anomaly is subsequently replaced by a net surface salinification, which persists for weeks. This salinification is larger on the right (left)-hand side of the storm motion in the Northern (Southern) Hemisphere, consistent with the location of stronger turbulent mixing. The influence of TC intensity and translation speed on the ocean response is also examined. Despite having greater precipitation, stronger TCs tend to produce longer-lasting, stronger and deeper salinification especially on the right-hand side of the storm motion. Faster moving TCs are found to have slightly weaker freshening with larger area coverage during the passage, but comparable salinification after the passage. The ocean haline response in four basins with different climatological salinity stratification reveals a significant impact of vertical stratification on the salinity response during and after the passage of TCs.

Comments on “Impacts of CO2-Induced Warming on Simulated Hurricane Intensity and Precipitation: Sensitivity to the Choice of Climate Model and Convective Scheme”

2005 ◽  
Vol 18 (23) ◽  
pp. 5179-5182 ◽  
Author(s):  
Patrick J. Michaels ◽  
Paul C. Knappenberger ◽  
Christopher Landsea
Keyword(s):  
Carbon Dioxide ◽  
Growth Rate ◽  
Tropical Cyclones ◽  
Real World ◽  
Climate Model ◽  
Mesoscale Model ◽  
Strong Relationship ◽  
Sea Surface ◽  
Hurricane Intensity ◽  
Convective Scheme

Abstract In a simulation of enhanced tropical cyclones in a warmer world, Knutson and Tuleya make several assumptions that are not borne out in the real world. They include an unrealistically large carbon dioxide growth rate, an overly strong relationship between sea surface temperature and hurricane intensity, and the use of a mesoscale model that has shown little to no useful skill in predicting current-day hurricane intensity. After accounting for these inaccuracies, a detectable increase in Atlantic hurricane intensity in response to growing atmospheric greenhouse gas levels during this century becomes unlikely.

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