Momentum flux of stratospheric gravity waves generated by Typhoon Ewiniar(2006)

The momentum flux of stratospheric gravity waves generated by Typhoon Ewiniar (2006) is examined using a Weather Research and Forecasting (WRF) model. In the stratosphere, zonal momentum flux with a positive sign by eastward-propagating waves is significant during the northward moving of the typhoon, while both zonal and meridional momentum fluxes with positive signs are significant during the typhoon decaying stage in which the typhoon moves northeastward. The magnitude of the momentum flux is greater during the mature stage of the typhoon than the decaying stage, and the phase speeds of the dominant momentum flux are less than 30 m s^?1 with a peak at 10–16 m s^?1. Positive momentum flux decreases with height overall in the stratosphere for both zonal and meridional components. The resultant gravity-wave drag forcing plays a role to decelerate the easterly background wind in the stratosphere. This drag forcing is relatively large above z = 40 km and below z = 20 km, and lower stratospheric wave drag is expected to affect the typhoon dynamics by modifying the background wind shear and inducing the secondary circulation in the troposphere.     

Vertical mixing of passive scalars owing to breaking gravity waves

In this paper, some aspects of dispersion of air pollutants as emitted from aircraft in the lower stratosphere have been investigated. As this part of the atmosphere is always stably stratified, mixing as a result of small-scale turbulence is very slow. Instead, effective vertical mixing can be provided by breaking gravity waves. We have examined the mixing properties of those events by means of a numerical model, which simulates the wave development as well as the dispersion of passive trace substances. From these simulations, an effective diffusion coefficient for the entire event of a breaking gravity wave of about 0.7 m² s⁻¹ was calculated.     

Characteristics and sources of inertia-gravity waves revealed in the KEOP-2007 radiosonde data

Characteristics and sources of inertia-gravity waves are investigated using high-resolution radiosonde data observed at ten stations in Korea during 15 June to 15 July 2007. The wave analyses are performed in the lower stratospheric region (Z = 17–30 km). The average intrinsic frequency, vertical wavelength, and horizontal wavelength for the observed waves are 2.77f (where f is the Coriolis parameter), 2.58 km, and 620.11 km, respectively. The average eastward and westward momentum fluxes are 0.005 m² s^?2 and ?0.003 m² s^?2, respectively, and the average northward and southward momentum fluxes are 0.007 m² s^?2 and ?0.002 m² s^?2, respectively. To understand the propagation and the sources of the observed gravity waves, a three-dimensional ray-tracing model is used. The observed gravity waves are classified into two groups based on the existence of convection when and where the rays reach altitudes of 6–13 km. Sources are mostly located in the northeast and southeast of the observation stations below Z = 5 km for the convection-related cases (CONV), while those for the other cases (NCONV) are located in the northeast and southeast of the observation stations above Z = 20 km. The average intrinsic frequency and vertical wavelength of the CONV cases are somewhat larger than those of the NCONV cases. The average potential, kinetic, and total wave energies of the CONV cases are less than those of the NCONV cases.     

Diagnosis of the forcing of inertial-gravity waves in a severe convection system

The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.     

On the mean and tidal currents in Hudson strait

Abstract

The vertical structures of the mean and tidal flows in Hudson Strait are described from moored current‐meter data collected during an 8‐week period in August to October of 1982. The residual flow in the strongly stratified waters off Quebec is directed along the Strait to the southeast, is highly baroclinic and is concentrated near shore (within an offshore length scale of approximately an internal Rossby radius). Maximum mean speeds of 0.3 m s^?1 were observed near‐surface (30 m). In the weakly stratified waters on the northern side of the Strait along Baffin Island the mean flow is northwestward. The maximum speeds are 0.1 m s^?1 near‐surface (30 m) and the current amplitudes decrease to 0.05 m s^?1 at 100 m. The mean southeastward transport is estimated to be 0.93 ±0.23 × 10⁶ m³ s^?1 with a northwestward transport of 0.82 ± 0.24 × 10⁶ m³ s^?1. Over most of the Strait the across‐channel residual currents are directed towards the Quebec shore with velocities ranging from 0.02 to 0.1 ms^?1. Current variability is dominated by the tides, the M₂ being the major tidal constituent. In the vicinity of the mooring the M₂ tide is primarily barotropic, progressive in nature, and has along‐channel current amplitudes varying across the Strait from 0.20 to 0.45 m s^?1. Observed differences in tidal sea‐level elevations across the Strait can be accounted for by the cross‐channel variations characteristic of Kelvin waves.     

Inertial oscillations near the coast of Nova Scotia during CASP

Abstract

Analysis of current, temperature and salinity records in the nearshore region of the Scotian Shelf during the Canadian Atlantic Storms Program (CASP), reveals that the inertial wave field is highly intermittent, with comparable amplitudes in the surface and deep layers. Clockwise current energy in the surface layer is concentrated at a frequency slightly below inertial, consistent with Doppler shifting by the strong mean current and/or straining by the mean flow shear, whereas the spectral peak in deep water is at the local inertial frequency. Clockwise coherence is high (γ² ≥ 0.8) horizontally over the scale of the array (60 km × 120 km) and in the vertical, with upward phase propagation rates of 0.15–0.50 × 10^?12 ms^?1, inversely proportional to the local value of the Brunt Väisälä frequency. Clockwise current energy decreases in the onshore direction and appears to be completely inhibited on the 60‐m isobath.

A case study of the response to the CASP IOP 14 storm indicates that the inertial waves may be generated by a strong wind shift propagating onshore at a speed of 10 ms^?1. On the eastern side of the array (Liscomb line), clockwise current oscillations propagate onshore in the surface layer at a rate (8.1 ± 0.9 m s^?1) comparable with the speed of the atmospheric front, while waves in the pycnocline move offshore at a lower (internal wave) speed (1.8 m s^?1). Furthermore the temperature and salinity fluctuations are in (out) of phase with longshore current in the deep (surface) layer. However, on the western side of the array (Halifax line), the inertial waves are more complex. A sharp steepening of phase lines at the coast indicates that the phase speed of clockwise current oscillations is considerably reduced and the evidence for offshore propagation of internal waves is less clear. The discrepancies between observations on the two lines suggest that the internal wave field is three‐dimensional.

Results of simple mixed‐layer models indicate that the inertial response near the surface is sensitive to the accurate definition of the local wind field, but not to certain model physics, such as the form of the decay term. The observations also show some qualitative similarities with models for two‐dimensional response to a moving front (e.g. Kundu, 1986), but the actual forcing terms are more complicated, based on IOP 14 wind measurements.     

Richardson number,vertical wind shear and storm occurrences at Kano,Nigeria

Radiosonde data for thirteen summer months have been used to relate Richardson under Ri and vertical wind shear to storm occurrences at Kano. It is shown that thunderstorms occur most frequently in association with low-level shears, ΔU_L, below the Africal Easterly Jet (surface to 700 mb) within −20⩽ΔU_L⩽−5 ms⁻¹ and for the 700-400 layer, ΔU_m, in the range 0<ΔU_m<10 m s⁻¹. The Richardson number with which storm occurrences are most common is bi-modal in both lower and middle troposphere: −2⩽Ri⩽0 and Ri⩽ −10 in the boundary layer (surface to 900 mb); 1⩽Ri⩽4 and Ri⩾15 in the inflow region (origin) of the downdraft air between 800 and 600 mb.Storms rarely occur (one in every seven cases) if boundary layer Ri>0 and virtually no storm should be expected if the boundary layer Ri>0 and for DDR (the regional origin of down draft air) Ri satisfying 4<Ri<15 simultaneously. The lower cut-off (Ri ⩾ 1) for the inflow air is close to the value (Ri⩾2) obtained by Moncrieff and Miller (1976) for propagating tropical storms.     

Air–Sea Interaction Features in the Baltic Sea and at a Pacific Trade-Wind Site: An Inter-comparison Study

A systematic comparison of wind profiles and momentum exchange at a trade wind site outside Oahu, Hawaii and corresponding data from the Baltic Sea is presented. The trade wind data are to a very high degree swell dominated, whereas the Baltic Sea data include a more varied assortment of wave conditions, ranging from a pure growing sea to swell. In the trade wind region swell waves travel predominantly in the wind direction, while in the Baltic, significant cross-wind swells are also present. Showing the drag coefficient as a function of the 10-m wind speed demonstrates striking differences for unstable conditions with swell for the wind-speed range 2 m s^?1 < U ₁₀ < 7 m s^?1, where the trade-wind site drag values are significantly larger than the corresponding Baltic Sea values. In striking contrast to this disagreement, other features studied are surprisingly similar between the two sites. Thus, exactly as found previously in Baltic Sea studies during unstable conditions and swell, the wind profile in light winds (3 m s^?1) shows a wind maximum at around 7–8 m above the water, with close to constant wind speed above. Also, for slightly higher wind speeds (4 m s^?1 < U ₁₀ < 7 m s^?1), the similarity between wind profiles is striking, with a strong wind-speed increase below a height of about 7–8 m followed by a layer of virtually constant wind speed above. A consequence of these wind-profile features is that Monin–Obukhov similarity is no longer valid. At the trade-wind site this was observed to be the case even for wind speeds as high as 10 m s^?1. The turbulence kinetic energy budget was evaluated for four cases of 8–16 30- min periods at the trade-wind site, giving results that agree very well with corresponding figures from the Baltic Sea.     

Is there a stratospheric radiative feedback in global warming simulations?

The radiative impacts of the stratosphere in global warming simulations are investigated using abrupt CO₂ quadrupling experiments of the Coupled Model Inter-comparison Project phase 5 (CMIP5), with a focus on stratospheric temperature and water vapor. It is found that the stratospheric temperature change has a robust bullhorn-like zonal-mean pattern due to a strengthening of the stratospheric overturning circulation. This temperature change modifies the zonal mean top-of-the-atmosphere energy balance, but the compensation of the regional effects leads to an insignificant global-mean radiative feedback (?0.02 ± 0.04 W m^?2 K^?1). The stratospheric water vapor concentration generally increases, which leads to a weak positive global-mean radiative feedback (0.02 ± 0.01 W m^?2 K^?1). The stratospheric moistening is related to mixing of elevated upper-tropospheric humidity, and, to a lesser extent, to change in tropical tropopause temperature. Our results indicate that the strength of the stratospheric water vapor feedback is noticeably larger in high-top models than in low-top ones. The results here indicate that although its radiative impact as a forcing adjustment is significant, the stratosphere makes a minor contribution to the overall climate feedback in CMIP5 models.     

Radar observations of precipitation production in thunderstorms

Abstract

Precipitation production is investigated for 9 intense thunderstorms that developed over the Lowveld in South Africa. A C‐band radar is used to observe the 3‐dimensional reflectivity pattern. Using an empirical relation between reflectivity factor and precipitation content and integrating over the storm volume provides an estimate of the total precipitation content aloft. Likewise, an area integration of the instantaneous rain rate at cloud base yields an estimate of the rate of total outflow. At their maturing stage, the storms had precipitation contents of 0.2 to 5.0 Tg and rainfall rates of about 0.3 to 2.0 Gg s^?1. The total accumulation of rain at the ground ranged from 1 to 10 Tg. The characteristic storm updraft, defined as the ratio of the area‐averaged rainfall rate to the volume‐averaged precipitation content, was about 5 ms^?1 for all storms. The time evolution of integral storm parameters is also presented and related to the overall storm development. The precipitation production values observed in the Lowveld storms compares well with previous estimates reported for large thunderstorms observed in Alberta and New England.     

夏季青藏高原地区水汽向平流层的等熵绝热和非绝热传输的气候学特征及其与落基山地区的对比

夏季亚洲季风区是对流层向平流层物质输送的主要通道,其对平流层水汽的变化有重要贡献。以往的研究表明亚洲季风区向平流层的水汽传输主要在青藏高原及周边地区。本文利用多年平均的逐日ERAi、MERRA再分析数据和微波临边观测仪（Microwave Limb Sounder,MLS）数据,首先对比分析夏季青藏高原周边上空水汽的分布特征,再利用再分析资料分析了对流层—平流层水汽传输的特征。结果表明:青藏高原周边特定的等熵面和对流层顶结构分布有利于水汽向平流层的绝热输送;在南亚高压的东北侧,从青藏高原到中太平洋地区,340~360 K层次存在最为显著的水汽向平流层的纬向等熵绝热输送通道,7~8月平均输送强度可达约7×103 kg s-1。此外,在伊朗高原及南亚高压的西部,350~360 K层次也存在一支水汽向平流层的经向等熵绝热输送通道,但强度相对较弱（约2.5×103 kg s-1）。在青藏高原南侧370~380 K层次存在强的水汽向平流层的非绝热输送,主要由深对流和大尺度上升运动引起,7~8月平均输送强度约0.4×103 kg s-1。落基山以东到大西洋西部,350~360 K层次存在水汽向平流层的纬向等熵绝热输送通道,但强度也弱得多（约2.5×103 kg s-1）。     

华南地区春季平流层入侵对对流层低层臭氧影响的模拟研究

利用中尺度大气化学模式WRF/Chem对2013年3月6日华南地区一次平流层入侵事件及其对对流层低层臭氧的影响进行模拟研究。通过加入UBC（Upper Boundary Condition）上边界处理方案,弥补WRF/Chem模式未考虑平流层臭氧化学反应的不足。结合臭氧探空廓线资料、地面O₃、CO、NO_x、相对湿度、温度和风速等观测资料以及再分析资料对模拟结果进行定量评估,结果表明模式能较为真实地模拟本次平流层入侵过程。模拟分析进一步揭示:（1）副热带高空急流是本次平流层入侵的主要原因。当华南地区处在副热带急流入口区左侧下沉区域时,平流层入侵将富含臭氧的干燥空气输送到对流层中低层。（2）本次平流层入侵对对流层低层臭氧收支有重要影响,导致香港地区近地层臭氧体积混合比浓度明显上升,如塔门站夜间臭氧浓度升高21.3 ppb（1 ppb=1×10-9）。地面气象场和化学物种的分析进一步确认了平流层入侵的贡献。（3）采用动力学对流层顶高度时零维箱式模型和Wei公式计算得到的平流层入侵通量相当,分别为-1.42×10-3 kg m-2 s-1和-1.59×10-3 kg m-2 s-1,这一结果与前人研究相吻合,且与采用热力学对流层顶高度计算所得到的结果具有可比性。     

The Entrainment Rate for Buoyant Plumes in a Crossflow

We consider large-eddy simulations (LES) of buoyant plumes from a circular source with initial buoyancy flux F ₀ released into a stratified environment with constant buoyancy frequency N and a uniform crossflow with velocity U. We make a systematic comparison of the LES results with the mathematical theory of plumes in a crossflow. We pay particular attention to the limits [(U)\tilde] << 1{\tilde{U}\ll1} and [(U)\tilde] >> 1{\tilde{U}\gg 1}, where [(U)\tilde]=U/(F₀ N)^1/4{\tilde{U}=U/(F_0 N)^{1/4}}, for which analytical results are possible. For [(U)\tilde] >> 1{\tilde{U}\gg 1}, the LES results show good agreement with the well-known two-thirds law for the rise in height of the plume. Sufficiently far above the source, the centreline vertical velocity of the LES plumes is consistent with the analytical z ^−1/3 and z ^−1/2 scalings for respectively [(U)\tilde] << 1{\tilde{U}\ll 1} and [(U)\tilde] >> 1{\tilde{U}\gg 1}. In the general case, where the entrainment is assumed to be the sum of the contributions from the horizontal and vertical velocity components, we find that the discrepancy between the LES data and numerical solutions of the plume equations is largest for [(U)\tilde]=O(1){\tilde{U}=O(1)}. We propose a modified additive entrainment assumption in which the contributions from the horizontal and vertical velocity components are not equally weighted. We test this against observations of the plume generated by the Buncefield fire in the U.K. in December 2005 and find that the results compare favourably. We also show that the oscillations of the plume as it settles down to its final rise height may be attenuated by the radiation of gravity waves. For [(U)\tilde] << 1{\tilde{U}\ll 1} the oscillations decay rapidly due to the transport of energy away from the plume by gravity waves. For ${\tilde{U}>rsim 1}${\tilde{U}>rsim 1} the gravity waves travel in the same direction and at the same speed as the flow. In this case, the oscillations of the plume do not decay greatly by radiation of gravity waves.     

Significance of nitrogen dioxide absorption in estimating aerosol optical depth and size distributions

Abstract

Changes to the Beaufort Sea shoreline occur due to the impact of storms and rising relative sea level. During the open‐water season (June to October), storm winds predominantly from the north‐west generate waves and storm surges which are effective in eroding thawing ice‐rich cliffs and causing overwash of gravel beaches. Climate change is expected to be enhanced in Arctic regions relative to the global mean and include accelerated sea‐level rise, more frequent extreme storm winds, more frequent and extreme storm surge flooding, decreased sea‐ice extent, more frequent and higher waves, and increased temperatures. We investigate historical records of wind speeds and directions, water levels, sea‐ice extent and temperature to identify variability in past forcing and use the Canadian Global Coupled Model ensembles 1 and 2 (CGCM1 and CGCM2) climate modelling results to develop a scenario forcing future change of Beaufort Sea shorelines. This scenario and future return periods of peak storm wind speeds and water levels likely indicate increased forcing of coastal change during the next century resulting in increased rates of cliff erosion and beach migration, and more extreme flooding.     

Moisture transport from the Atlantic to the Pacific basin and its response to North Atlantic cooling and global warming

Atmospheric moisture transport from the Atlantic to the Pacific basin plays an important role in regulating North Atlantic salinity and thus the strength of the thermohaline circulation. Potential changes in the strength of this moisture transport are investigated for two different climate-change scenarios: North Atlantic cooling representative of Heinrich events, and increased greenhouse gas (GHG) forcing. The effect of North Atlantic cooling is studied using a coupled regional model with comparatively high resolution that successfully simulates Central American gap winds and other important aspects of the region. Cooler North Atlantic sea surface temperature (SST) in this model leads to a regional decrease of atmospheric moisture but also to an increase in wind speed across Central America via an anomalous pressure gradient. The latter effect dominates, resulting in a 0.13 Sv (1 Sv = 10⁶ m³ s^?1) increase in overall moisture transport to the Pacific basin. In fresh water forcing simulations with four different general circulation models, the wind speed effect is also present but not strong enough to completely offset the effect of moisture decrease except in one model. The influence of GHG forcing is studied using simulations from the Intergovernmental Panel on Climate Change archive. In these simulations atmospheric moisture increases globally, resulting in an increase of moisture transport by 0.25 Sv from the Atlantic to Pacific. Thus, in both scenarios, moisture transport changes act to stabilize the thermohaline circulation. The notion that the Andes effectively block moisture transport from the Atlantic to the Pacific basin is not supported by the simulations and atmospheric reanalyses examined here. This indicates that such a blocking effect does not exist or else that higher resolution is needed to adequately represent the steep orography of the Andes.     

平流层大气动力学及其与对流层大气相互作用的研究:进展与问题

本文综述了近年来关于平流层大气动力学及其与对流层大气相互作用动力过程的研究进展,特别是回顾了近年来关于平流层大气环流和行星波动力学、热带平流层大气波动及其与基本气流相互作用、平流层大气环流变异对对流层环流和气候变异的影响及其动力过程、平流层大气数值模拟以及在全球变暖背景下平流层大气的长期演变趋势预估等的研究进展。最近的研究揭示了大气准定常行星波传播波导的振荡现象、重力波在热带平流层准两年振荡和全球物质输送中的作用、平流层长期的变冷趋势变化、平流层在对流层天气和气候变化中的作用等现象,表明了平流层大气动力学研究的重要性。平流层大气动力学的深入研究,以及对数值模式中平流层模拟性能的提高,最终都会推动整个大气科学和气候变化研究的进一步发展。     

The impact of weak synoptic forcing on the valley-wind circulation in the Alpine Inn Valley

This paper investigates the impact of weak synoptic-scale forcing on the thermally induced valley-wind circulation in the Alpine Inn Valley and one of its largest tributaries, the Wipp Valley. To this end, high-resolution numerical simulations with realistic topography but idealized large-scale atmospheric conditions are performed. The large-scale flow has a speed increasing linearly from 5 m s^?1 at sea level to 12.5 m s^?1 at tropopause level, but its direction is varied between each experiment. For reference, an experiment without large-scale winds is conducted as well. The results indicate that the sensitivity to ambient flow forcing differs substantially between the Inn Valley and the Wipp Valley. The valley-wind circulation of the Inn Valley is found to be fairly robust against weak ambient forcing, changing by a much smaller amount than the along-valley component of the imposed large-scale flow. The valley wind tends to be intensified (weakened) when the ambient flow is aligned with (opposite to) the local valley orientation. However, the flow response is complicated by larger-scale interactions of the ambient flow with the Alpine massif. Most notably, northerly and northwesterly flow is deflected around the Alps, leading to the formation of a low-level jet along the northern edge of the Alps which in turn affects the valley-wind circulation in the lower Inn Valley. For the Wipp Valley, which is oriented approximately normal to the Alpine crest line and constitutes a deep gap in the Alpine crest, two distinctly different flow regimes are found depending on whether the large-scale flow has a significant southerly component or not. In the absence of a southerly flow component, the valley-wind circulation is similarly robust against ambient forcing as in the Inn Valley, with a fairly weak response of the local wind speeds. However, southerly ambient flow tends to force continuous downvalley (southerly) wind in the Wipp Valley. The flow dynamics can then be described as a pressure-driven gap flow during the day and as a mixture between katabatic flow and gap flow during the night. The responsible pressure forcing arises from the larger-scale interaction of the ambient flow with the Alpine massif, with southerly flow causing lifting on the southern side of the Alps and subsidence in the north.     

Effects of Non-orographic Gravity Wave Drag on Seasonal and Medium-range Predictions in a Global Forecast Model

This study implements the parameterizations of convective and frontal gravity wave drag (GWD) with wide phase speed spectra into a global forecast model with a model top near 0.3 hPa. The new convective GWD scheme replaces the existing one that considers only a stationary convective GW, and the frontal GWD scheme is newly introduced. When the new GWD schemes are used, the Rayleigh friction, applied above 2 hPa to mimic the effects of missing GWD, is removed. The convective (frontal) GWs are generated mainly in the Intertropical Convergence Zone and winter extratropical storm track regions (extratropics where strong baroclinicity exists). The convective and frontal GWD derived from the new schemes are significant near the model top, with maxima of ~2-4 and ~26-58 m s^?1 day^?1, respectively. The differences in convective GWD between the stationary and non-stationary schemes appear mainly in the tropics and summer hemisphere, where stationary GWs cannot propagate upward. The new schemes improve the seasonal representation of stratospheric wind, through changes in both the GWD and the resolved wave forcing, which is modulated by the changed large-scale wind due to the GWD. The downward influence, in response to the changed GWD, is also positive in the tropospheric fields, such as subtropical jet and planetary-scale disturbances. For the medium-range forecasts, improved skill scores on wind speed are achieved globally with the new schemes. The improvements mostly appear only in the stratosphere during the early forecast period (~3 days) but expand to the troposphere as forecast time increases.     

经圈环流在大气对SSTA强迫响应中的作用

本文建立了一个包括经向Hadley环流作用的简单半谱模式并从1982年欧洲中心的客观分析资料中得到全球纬向平均场。经一系列数值实验发现，当SSTA处于赤道地区时，由它强迫产生的波动可以同时向南北半球传播。但若考虑经向Hadley环流（υ）的作用，波传播的空间位相和振幅就有比较明显的变化，并更接近于实际大气环流异常情况。当非绝热加热源位于偏离赤道的南北半球时，实验结果表明，如果不考虑Hadley环流，南北半球的非绝热加热很难在另一半球产生强的大气响应；考虑了Hadley环流后，则非绝热加热产生的波动可向另一半球传播。数值实验结果还表明，夏季当非绝热加热源的位置改变时，大气对其改变的响应不明显，而冬季大气对非绝热加热源的纬向位置的响应却非常敏感。     

Fine-resolution regional climate model simulations of the impact of climate change on tropical cyclones near Australia

Fine-resolution regional climate simulations of tropical cyclones (TCs) are performed over the eastern Australian region. The horizontal resolution (30 km) is fine enough that a good climatological simulation of observed tropical cyclone formation is obtained using the observed tropical cyclone lower wind speed threshold (17 m s^–1). This simulation is performed without the insertion of artificial vortices (bogussing). The simulated occurrence of cyclones, measured in numbers of days of cyclone activity, is slightly greater than observed. While the model-simulated distribution of central pressures resembles that observed, simulated wind speeds are generally rather lower, due to weaker than observed pressure gradients close to the centres of the simulated storms. Simulations of the effect of climate change are performed. Under enhanced greenhouse conditions, simulated numbers of TCs do not change very much compared with those simulated for the current climate, nor do regions of occurrence. There is a 56% increase in the number of simulated storms with maximum winds greater than 30 m s^–1 (alternatively, a 26% increase in the number of storms with central pressures less than 970 hPa). In addition, there is an increase in the number of intense storms simulated south of 30°S. This increase in simulated maximum storm intensity is consistent with previous studies of the impact of climate change on tropical cyclone wind speeds.