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

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.

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

Weather and Climate Dynamics ◽

10.5194/wcd-1-1-2020 ◽

2020 ◽

Vol 1 (1) ◽

pp. 1-25 ◽

Cited By ~ 3

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.

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

Journal of Climate ◽

10.1175/2007jcli1801.1 ◽

2008 ◽

Vol 21 (4) ◽

pp. 788-801 ◽

Cited By ~ 83

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.

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

Geoscientific Model Development ◽

10.5194/gmd-10-827-2017 ◽

2017 ◽

Vol 10 (2) ◽

pp. 827-841 ◽

Cited By ~ 6

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.

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

10.5194/gmd-2016-219 ◽

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.

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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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0039.1 ◽

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.

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Climatological Increased Precipitation from July to August in the Western North Pacific Region Simulated by CMIP6 Models

Atmosphere ◽

10.3390/atmos12060664 ◽

2021 ◽

Vol 12 (6) ◽

pp. 664

Author(s):

Xiao Dong ◽

Renping Lin

Keyword(s):

North Pacific ◽

Western North Pacific ◽

Vertical Motion ◽

Atmospheric Model ◽

Coupled Models ◽

Model Simulations ◽

Observational Analysis ◽

Budget Analysis ◽

Circulation Change ◽

Precipitation Increase

In this study, the climatological precipitation increase from July to August over the western North Pacific (WNP) region was investigated through observations and simulations in the Coupled Model Intercomparison Project Phase 6 (CMIP6), atmospheric model simulations and historical experiments. Firstly, observational analysis showed that the precipitation increase is associated with a decrease in the local sea surface temperature (SST), indicating that the precipitation increase is not driven by the change in SST. In addition, the pattern of precipitation increase is similar to the vertical motion change at 500-hPa, suggesting that the precipitation increase is related to the circulation change. Moisture budget analysis further confirmed this relation. In addition to the observational analysis, the outputs from 26 CMIP6 models were further evaluated. Compared with atmospheric model simulations, air–sea coupled models largely improve the simulation of the climatological precipitation increase from July to August. Furthermore, model simulations confirmed that the bias in the precipitation increase is intimately associated with the circulation change bias. Thus, two factors are responsible for the bias of the precipitation increase from July to August in climate models: air–sea coupling processes and the performance in vertical motion change.

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Why does rapid contraction of the radius of maximum wind precede rapid intensification in tropical cyclones?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-21-0129.1 ◽

2021 ◽

Author(s):

Yuanlong Li ◽

Yuqing Wang ◽

Yanluan Lin ◽

Xin Wang

Keyword(s):

Tropical Cyclones ◽

Radial Distribution ◽

Diabatic Heating ◽

Rate Of Change ◽

Rapid Intensification ◽

Absolute Vorticity ◽

Radial Gradient ◽

Maximum Wind ◽

Tangential Wind ◽

Vorticity Flux

AbstractThe radius of maximum wind (RMW) has been found to contract rapidly well preceding rapid intensification in tropical cyclones (TCs) in recent literature but the understanding of the involved dynamics is incomplete. In this study, this phenomenon is revisited based on ensemble axisymmetric numerical simulations. Consistent with previous studies, because the absolute angular momentum (AAM) is not conserved following the RMW, the phenomenon can not be understood based on the AAM-based dynamics. Both budgets of tangential wind and the rate of change in the RMW are shown to provide dynamical insights into the simulated relationship between the rapid intensification and rapid RMW contraction. During the rapid RMW contraction stage, due to the weak TC intensity and large RMW, the moderate negative radial gradient of radial vorticity flux and small curvature of the radial distribution of tangential wind near the RMW favor rapid RMW contraction but weak diabatic heating far inside the RMW leads to weak low-level inflow and small radial absolute vorticity flux near the RMW and thus a relatively small intensification rate. As RMW contraction continues and TC intensity increases, diabatic heating inside the RMW and radial inflow near the RMW increase, leading to a substantial increase in radial absolute vorticity flux near the RMW and thus the rapid TC intensification. However, the RMW contraction rate decreases rapidly due to the rapid increase in the curvature of the radial distribution of tangential wind near the RMW as the TC intensifies rapidly and RMW decreases.

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Tropical Cyclogenesis Associated with Kelvin Waves and the Madden–Julian Oscillation

Monthly Weather Review ◽

10.1175/mwr-d-10-05060.1 ◽

2011 ◽

Vol 139 (9) ◽

pp. 2723-2734 ◽

Cited By ~ 40

Author(s):

Carl J. Schreck ◽

John Molinari

Keyword(s):

Tropical Cyclone ◽

Tropical Cyclones ◽

North Pacific ◽

Western North Pacific ◽

Diabatic Heating ◽

Kelvin Waves ◽

Tropical Cyclogenesis ◽

Madden Julian Oscillation ◽

Convective Envelope

The Madden–Julian oscillation (MJO) influences tropical cyclone formation around the globe. Convectively coupled Kelvin waves are often embedded within the MJO, but their role in tropical cyclogenesis remains uncertain. This case study identifies the influences of the MJO and a series of Kelvin waves on the formation of two tropical cyclones. Typhoons Rammasun and Chataan developed in the western North Pacific on 28 June 2002. Two weeks earlier, conditions had been unfavorable for tropical cyclogenesis because of uniform trade easterlies and a lack of organized convection. The easterlies gave way to equatorial westerlies as the convective envelope of the Madden–Julian oscillation moved into the region. A series of three Kelvin waves modulated the development of the westerlies. Cyclonic potential vorticity (PV) developed in a strip between the growing equatorial westerlies and the persistent trade easterlies farther poleward. Rammasun and Chataan emerged from the apparent breakdown of this strip. The cyclonic PV developed in association with diabatic heating from both the MJO and the Kelvin waves. The tropical cyclones also developed during the largest superposition of equatorial westerlies from the MJO and the Kelvin waves. This chain of events suggests that the MJO and the Kelvin waves each played a role in the development of Rammasun and Chataan.

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Sensitivity of Idealized Moist Baroclinic Waves to Environmental Temperature and Moisture Content

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-17-0188.1 ◽

2018 ◽

Vol 75 (1) ◽

pp. 337-360 ◽

Cited By ~ 9

Author(s):

D. J. Kirshbaum ◽

T. M. Merlis ◽

J. R. Gyakum ◽

R. McTaggart-Cowan

Keyword(s):

Kinetic Energy ◽

Moisture Content ◽

Potential Energy ◽

Diabatic Heating ◽

Environmental Temperature ◽

Mechanical Energy ◽

Negative Relationship ◽

Vertical Motion ◽

Periodic Wave ◽

Cloud Band

Idealized simulations are used to examine the sensitivity of moist baroclinic wave growth to environmental temperature and moisture content. With relative humidity held fixed, the surface temperature at 45°N, denoted T0, is varied from 275 to 290 K. As T0 increases, the atmospheric moisture content, moist instability, and moist available potential energy also increase. For the chosen initial configuration, moist waves develop larger eddy kinetic energy K e than corresponding dry waves, but enhanced diabatic heating at larger T0 does not further increase K e. This finding is linked to a warm-frontal cyclonic potential vorticity (PV) anomaly that strengthens and shifts downstream at larger T0 owing to increased diabatic heating along the frontal cloud band. This eastward shift feeds back negatively on the parent cyclone by increasing the downstream export of mechanical energy aloft and degrading the phasing between dry baroclinic vertical motion and buoyancy within the warm sector. The latter suppresses the conversion from eddy potential energy to K e [ C( P e, K e)], offsetting a direct enhancement of C( P e, K e) by diabatic heating. Compared to their dry counterparts, isolated moist waves (initiated by a single finite-amplitude PV anomaly) display a similar sensitivity to T0, while periodic wave trains (initiated by multiple such anomalies) exhibit a stronger negative relationship. The latter stems from anticyclonic diabatic PV anomalies aloft that originate along the warm front and recirculate through the system to interact with the upper-level trough. This interaction leads to a horizontal forward wave tilt that enhances the conversion of wave K e into zonal-mean kinetic energy.

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