Increased hurricane intensities with CO2-induced warming as simulated using the GFDL hurricane prediction system

 The impact of CO₂-induced global warming on the intensities of strong hurricanes is investigated using the GFDL regional high-resolution hurricane prediction system. The large-scale initial conditions and boundary conditions for the regional model experiments, including SSTs, are derived from control and transient CO₂ increase experiments with the GFDL R30-resolution global coupled climate model. In a case study approach, 51 northwest Pacific storm cases derived from the global model under present-day climate conditions are simulated with the regional model, along with 51 storm cases for high CO₂ conditions. For each case, the regional model is integrated forward for five days without ocean coupling. The high CO₂ storms, with SSTs warmer by about 2.2 °C on average and higher environmental convective available potential energy (CAPE), are more intense than the control storms by about 3–7 m/s (5%–11%) for surface wind speed and 7 to 24 hPa for central surface pressure. The simulated intensity increases are statistically significant according to most of the statistical tests conducted and are robust to changes in storm initialization methods. Near-storm precipitation is 28% greater in the high CO₂ sample. In terms of storm tracks, the high CO₂ sample is quite similar to the control. The mean radius of hurricane force winds is 2 to 3% greater for the composite high CO₂ storm than for the control, and the high CO₂ storms penetrate slightly higher into the upper troposphere. More idealized experiments were also performed in which an initial storm disturbance was embedded in highly simplified flow fields using time mean temperature and moisture conditions from the global climate model. These idealized experiments support the case study results and suggest that, in terms of thermodynamic influences, the results for the NW Pacific basin are qualitatively applicable to other tropical storm basins. Received: 20 July 1998/Accepted: 24 December 1998     

Response of hurricane-type vortices to global warming as simulated by ARPEGE-Climat at high resolution

Atlantic hurricanes and their sensitivity to anthropogenic warming are investigated using very high (0.5°×0.5° over the Atlantic domain) resolution global simulations. The ARPEGE-Climat variable resolution grid demonstrates its usefulness in regional climate studies since resolution can be multiplied by a factor of 2.5 over the domain of interest compared to a uniform grid, for a similar computer cost. The question of hurricane characteristics dependence on anthropogenic warming is tackled trough the implementation of a tracking method. Changes in the total number, as well as locations, of hurricanes appear to depend more on sea surface temperature (SST) spatial patterns anomaly than Atlantic mean intensity, essentially through the change in large scale vertical wind shear. A uniform SST anomaly forcing produces increased and eastward shifted systems while a spatially contrasted anomaly leads to a decrease. Comparison between cyclogenesis density calculated from tracking or large scale combined variables (as a modified Gray parameter) brings some confidence in the use of the latter to investigate low resolution simulations. Mean hurricane dynamical characteristics are weakly changed by the warming but precipitation core and latent heat flux are enhanced in all scenarios.     

Atlantic Basin Hurricanes: Indices of Climatic Changes

Accurate records of basinwide Atlantic and U.S. landfalling hurricanes extend back to the mid 1940s and the turn of the century, respectively, as a result of aircraft reconnaissance and instrumented weather stations along the U.S. coasts. Such long-term records are not exceeded elsewhere in the tropics. The Atlantic hurricanes, U.S. landfalling hurricanes and U.S. normalized damage time series are examined for interannual trends and multidecadal variability. It is found that only weak linear trends can be ascribed to the hurricane activity and that multidecadal variability is more characteristic of the region. Various environmental factors including Caribbean sea level pressures and 200mb zonal winds, the stratospheric Quasi-Biennial Oscillation, the El Niño-Southern Oscillation, African West Sahel rainfall and Atlantic sea surface temperatures, are analyzed for interannual links to the Atlantic hurricane activity. All show significant, concurrent relationships to the frequency, intensity and duration of Atlantic hurricanes. Additionally, variations in the El Niño-Southern Oscillation are significantly linked to changes in U.S. tropical cyclone-caused damages. Finally, much of the multidecadal hurricane activity can be linked to the Atlantic Multidecadal Mode - an empirical orthogonal function pattern derived from a global sea surface temperature record. Such linkages may allow for prediction of Atlantic hurricane activity on a multidecadal basis. These results are placed into the context of climate change and natural hazards policy.     

Caribbean hurricanes: changes of intensity and track prediction

The meteorological conditions of hurricanes passing near Puerto Rico (18N, 68W) are analyzed using composite daily reanalysis and satellite data. When an intense hurricane is present, the regional circulation is dominated by upper easterly flow over the Caribbean and central Atlantic and a surge of low-level westerly anomalies across the tropics. Warm SST anomalies extend along the coast of Venezuela, doubling the convective energy available to Caribbean hurricanes. Intensifying hurricanes tend to propagate westward with an atmospheric ridge over the Gulf Stream, in an environment with aerosol optical depth <0.6. Hurricanes form and strengthen in the east-shear phase of the Madden Julian Oscillation. Sinking motions and dry air appear in an anti-cyclonic gyre behind intensifying hurricanes. Numerical model 48-h forecasts of Caribbean hurricane tracks are analyzed over the period 2000–2010. A “slow right” bias is found east of Puerto Rico in comparison with observed.     

Projected future changes in tropical cyclone-related wave climate in the North Atlantic

Tropical cyclones are a major hazard for numerous countries surrounding the tropical-to-subtropical North Atlantic sub-basin including the Caribbean Sea and Gulf of Mexico. Their intense winds, which can exceed 300 km h⁻¹, can cause serious damage, particularly along coastlines where the combined action of waves, currents and low atmospheric pressure leads to storm surge and coastal flooding. This work presents future projections of North Atlantic tropical cyclone-related wave climate. A new configuration of the ARPEGE-Climat global atmospheric model on a stretched grid reaching ~ 14 km resolution to the north-east of the eastern Caribbean is able to reproduce the distribution of tropical cyclone winds, including Category 5 hurricanes. Historical (1984–2013, 5 members) and future (2051–2080, 5 members) simulations with the IPCC RCP8.5 scenario are used to drive the MFWAM (Météo-France Wave Action Model) spectral wave model over the Atlantic basin during the hurricane season. An intermediate 50-km resolution grid is used to propagate mid-latitude swells into a higher 10-km resolution grid over the tropical cyclone main development region. Wave model performance is evaluated over the historical period with the ERA5 reanalysis and satellite altimetry data. Future projections exhibit a modest but widespread reduction in seasonal mean wave heights in response to weakening subtropical anticyclone, yet marked increases in tropical cyclone-related wind sea and extreme wave heights within a large region extending from the African coasts to the North American continent.

     

The Potential Effects of Elevated Co2 and Climate Change on Tropical Forest Soils and Biogeochemical Cycling

Tropical forests are responsible for a large proportion of the global terrestrial C flux annually for natural ecosystems. Increased atmospheric CO₂ and changes in climate are likely to affect the distribution of C pools in the tropics and the rate of cycling through vegetation and soils. In this paper, I review the literature on the pools and fluxes of carbon in tropical forests, and the relationship of these to nutrient cycling and climate. Tropical moist and humid forests have the highest rates of annual net primary productivity and the greatest carbon flux from soil respiration globally. Tropical dry forests have lower rates of carbon circulation, but may have greater soil organic carbon storage, especially at depths below 1 meter. Data from tropical elevation gradients were used to examine the sensitivity of biogeochemical cycling to incremental changes in temperature and rainfall. These data show significant positive correlations of litterfall N concentrations with temperature and decomposition rates. Increased atmospheric CO₂ and changes in climate are expected to alter carbon and nutrient allocation patterns and storage in tropical forest. Modeling and experimental studies suggest that even a small increase in temperature and CO₂ concentrations results in more rapid decomposition rates, and a large initial CO₂ efflux from moist tropical soils. Soil P limitation or reductions in C:N and C:P ratios of litterfall could eventually limit the size of this flux. Increased frequency of fires in dry forest and hurricanes in moist and humid forests are expected to reduce the ecosystem carbon storage capacity over longer time periods.     

SST-induced climate change in tropical North Africa: The intermediary role of lower tropospheric oscillations

Summary  The growth rates of amplifying mid-tropospheric perturbations in tropical North Africa is known to reduce with increased vertical shear in the troposphere. This phenomenon leads to a reduction in the frequency of generation of squall lines – the main rain-producing mechanism in tropical North Africa – because squalls are initiated by amplifying modes of African Easterly Waves (AEW). Ultimately, therefore, tropical North Africa experiences a shortfall, with respect to long-term averages, in annual rainfall. Weakening of AEW intensity is shown to be linked with the warming up to the sea-surface temperatures (SST) of the South Atlantic, Pacific and Indian Oceans. These findings are consistent with the observed reduction in the incidence of intense hurricanes along the entire westem Atlantic in Sahelian dry years. It is shown that the frequency of occurrence of Atlantic tropical storms and hurricanes is unaffected by the dryness or otherwise in the Sahel, but the paths of the storms are determined by the zonal exit point, from the African continental land mass to the Atlantic, of West African disturbance lines. These results have applications, and implications, in the level of preparedness for the economic impacts of Atlantic storms and hurricanes. Received June 8, 1996 Revised June 8, 2000     

Recent intense hurricane response to global climate change

An Anthropogenic Climate Change Index (ACCI) is developed and used to investigate the potential global warming contribution to current tropical cyclone activity. The ACCI is defined as the difference between the means of ensembles of climate simulations with and without anthropogenic gases and aerosols. This index indicates that the bulk of the current anthropogenic warming has occurred in the past four decades, which enables improved confidence in assessing hurricane changes as it removes many of the data issues from previous eras. We find no anthropogenic signal in annual global tropical cyclone or hurricane frequencies. But a strong signal is found in proportions of both weaker and stronger hurricanes: the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25–30 % per °C of global warming after accounting for analysis and observing system changes. This has been balanced by a similar decrease in Category 1 and 2 hurricane proportions, leading to development of a distinctly bimodal intensity distribution, with the secondary maximum at Category 4 hurricanes. This global signal is reproduced in all ocean basins. The observed increase in Category 4–5 hurricanes may not continue at the same rate with future global warming. The analysis suggests that following an initial climate increase in intense hurricane proportions a saturation level will be reached beyond which any further global warming will have little effect.     

Hurricane Wind Power Spectra, Cospectra, and Integral Length Scales

Atmospheric turbulence is an important factor in the modelling of wind forces on structures and the losses they produce in extreme wind events. However, while turbulence in non-hurricane winds has been thoroughly researched, turbulence in tropical cyclones and hurricanes that affect the Gulf and Atlantic coasts has only recently been the object of systematic study. In this paper, Florida Coastal Monitoring Program surface wind measurements over the sea surface and open flat terrain are used to estimate tropical cyclone and hurricane wind spectra and cospectra as well as integral length scales. From the analyses of wind speeds obtained from five towers in four hurricanes it can be concluded with high confidence that the turbulent energy at lower frequencies is considerably higher in hurricane than in non-hurricane winds. Estimates of turbulence spectra, cospectra, and integral turbulence scales presented can be used for the development in experimental facilities of hurricane wind flows and the forces they induce on structures.     

Assessing links between upper atmospheric vorticity patterns and directional changes in hurricane tracks

Links between hurricane track changes and upper atmospheric potential vorticity (PV) anomaly patterns were identified qualitatively and analytically between 1990 and 2005 in the Western Atlantic. Strong track changes of hurricanes, particularly the constellations that triggered northward acceleration of the storm systems, were associated with upper-air PV patterns characterized by strongly positive anomalies to the northeast in combination with weak PV to the north of the system center. Constellations that triggered eventual eastward acceleration were associated with strongly positive PV anomalies to the northwest in combination with weak PV to the northeast of the system center. These results may assist hurricane forecasters and modelers in identifying possible signatures of future tropical cyclone tracks.     

Temperature depression in the lowland tropics in glacial times

Equatorial air temperatures at low elevations in the New World tropics are shown by pollen and other data to have been significantly lowered in long intervals of the last glaciation. These new data show that long recognized evidence for cooling at high elevations in the tropics were symptomatic of general tropical cooling and that they did not require appeal to altered lapse rates or other special mechanisms to be made to conform with conclusions that equatorial sea surface temperatures (SSTs) were scarcely changed in glacial times. The new data should be read in conjunction with recent findings that Caribbean (SSTs) were lowered in the order of 5 ° C, contrary to previous interpretations. Thus these accumulating data show that low latitudes as well as high were cooled in glaciations. In part the earlier failure to find evidence of low elevation cooling in the lowland tropics resulted from the data being masked by strong signals for aridity given by old lake levels in parts of Africa and elsewhere. Global circulation models used to predict future effects of greenhouse warming must also be able to simulate the significant cooling of the large tropical land masses at glacial times with reduced greenhouse gas concentrations. Plants and animals of the Amazon forest and similar ecosystems are able to survive in wide ranges of temperatures, CO₂ concentrations, and disturbance, though associations change constantly.     

On the change of the tropical cyclone structure during its passage over islands

The impact is studied of small land areas on the configuration and structure of the tropical cyclone as well as on the variations of different characteristics of hurricanes (wind field, kinetic energy, and vorticity) during their passage over islands. The results of computations based on the regional numerical atmospheric ETA model for the hurricanes of the Caribbean Sea and typhoons of the Northwestern Pacific revealed that the disturbance of the symmetric circulation in the vortex accompanied by significant kinetic energy losses takes place when crossing the archipelagos or separate islands. It is demonstrated that the vortex intensity depends not on the energy loss due to the underlying surface roughness only but on the heat flux from it as well. The kinetic energy generation in the hurricane sharply decreases as a result of the decrease in the pressure gradient over the land that is caused, in turn, by the tropical cyclone moving away from the oceanic heat source. At the recurring appearance of the cyclone over the warm ocean waters, its deepening and intensification recommence.     

Possible climatic impacts of tropical deforestation

Large-scale conversion of tropical forests into pastures or annual crops will likely lead to changes in the local microclimate of those regions. Larger diurnal fluctuations of surface temperature and humidity deficit, increased surface runoff during rainy periods and decreased runoff during the dry season, and decreased soil moistrue are to be expected.It is likely that evapotranspiration will be reduced because of less available radiative energy at the canopy level since grass presents a higher albedo than forests, also because of the reduced availability of soil moisture at the rooting zone primarily during the dry season. Recent results from general circulation model (GCM) simulations of Amazonian deforestation seem to suggest that the equilibrium climate for a grassy vegetation in Amazonia would be one in which regional precipitation would be significantly reduced.Global climate changes probably will occur if there is a marked change in rainfall patterns in tropical forest regions as a result of deforestation. Besides that, biomass burning of tropical forests is likely adding CO₂ into the atmosphere, thus contributing to the enhanced greenhouse warming.     

Millennial timescale carbon cycle and climate change in an efficient Earth system model

A new Earth system model, GENIE-1, is presented which comprises a 3-D frictional geostrophic ocean, phosphate-restoring marine biogeochemistry, dynamic and thermodynamic sea-ice, land surface physics and carbon cycling, and a seasonal 2-D energy-moisture balance atmosphere. Three sets of model climate parameters are used to explore the robustness of the results and for traceability to earlier work. The model versions have climate sensitivity of 2.8–3.3°C and predict atmospheric CO₂ close to present observations. Six idealized total fossil fuel CO₂ emissions scenarios are used to explore a range of 1,100–15,000 GtC total emissions and the effect of rate of emissions. Atmospheric CO₂ approaches equilibrium in year 3000 at 420–5,660 ppmv, giving 1.5–12.5°C global warming. The ocean is a robust carbon sink of up to 6.5 GtC year⁻¹. Under ‘business as usual’, the land becomes a carbon source around year 2100 which peaks at up to 2.5 GtC year⁻¹. Soil carbon is lost globally, boreal vegetation generally increases, whilst under extreme forcing, dieback of some tropical and sub-tropical vegetation occurs. Average ocean surface pH drops by up to 1.15 units. A Greenland ice sheet melt threshold of 2.6°C local warming is only briefly exceeded if total emissions are limited to 1,100 GtC, whilst 15,000 GtC emissions cause complete Greenland melt by year 3000, contributing 7 m to sea level rise. Total sea-level rise, including thermal expansion, is 0.4–10 m in year 3000 and ongoing. The Atlantic meridional overturning circulation shuts down in two out of three model versions, but only under extreme emissions including exotic fossil fuel resources.     

Climate sensitivity due to increased CO2: experiments with a coupled atmosphere and ocean general circulation model

A version of the National Center for Atmospheric Research community climate model — a global, spectral (R15) general circulation model — is coupled to a coarse-grid (5° latitude-] longitude, four-layer) ocean general circulation model to study the response of the climate system to increases of atmospheric carbon dioxide (CO₂). Three simulations are run: one with an instantaneous doubling of atmospheric CO₂ (from 330 to 660 ppm), another with the CO₂ concentration starting at 330 ppm and increasing linearly at a rate of 1% per year, and a third with CO₂ held constant at 330 pm. Results at the end of 30 years of simulation indicate a globally averaged surface air temperature increase of 1.6° C for the instantaneous doubling case and 0.7°C for the transient forcing case. Inherent characteristics of the coarse-grid ocean model flow sea-surface temperatures (SSTs) in the tropics and higher-than-observed SSTs and reduced sea-ice extent at higher latitudes] produce lower sensitivity in this model after 30 years than in earlier simulations with the same atmosphere coupled to a 50-m, slab-ocean mixed layer. Within the limitations of the simulated meridional overturning, the thermohaline circulation weakens in the coupled model with doubled CO₂ as the high-latitude ocean-surface layer warms and freshens and westerly wind stress is decreased. In the transient forcing case with slowly increasing CO₂ (30% increase after 30 years), the zonal mean warming of the ocean is most evident in the surface layer near 30°–50° S. Geographical plots of surface air temperature change in the transient case show patterns of regional climate anomalies that differ from those in the instantaneous CO₂ doubling case, particularly in the North Atlantic and northern European regions. This suggests that differences in CO₂ forcing in the climate system are important in CO₂ response in regard to time-dependent climate anomaly regimes. This confirms earlier studies with simple climate models that instantaneous CO₂ doubling simulations may not be analogous in all respects to simulations with slowly increasing CO₂.A portion of this study is supported by the US Department of Energy as part of its Carbon Dioxide Research Program     

利用卫星微波观测亮温与云辐射模拟亮温的台风定位分析北大核心

极轨气象卫星S-NPP、MetOp-A和FY-3B上搭载的微波湿度计观测资料可以反映出台风周围水汽和云雨结构。本文使用权重函数峰值在800 hPa附近的微波湿度计通道观测资料和ERA5再分析资料全天空模拟亮温,以飓风Sandy和Isaac为例,对用方位谱台风中心位置定位方法得到的观测和模拟中心位置进行了比较。利用下午星S-NPP搭载的先进技术微波探测仪(Advanced Technology Microwave Sounder,ATMS)和上午星MetOp-A搭载的微波湿度计(Microwave Humidity Sounder,MHS)观测亮温得到的飓风Sandy(Isaac)中心位置与最佳路径平均相差35.8 km(32.9 km),但用ERA5全天空模拟亮温得到的飓风Sandy(Isaac)中心位置与最佳路径平均相差73.3 km(82.1 km)。若按照热带风暴和台风等级来划分,ATMS和MHS观测和模拟亮温得到的台风中心位置与最佳路径的平均距离对热带风暴分别是36.5 km和105.9 km,对台风分别是25.8 km和56.4 km。若用FY-3B搭载的微波湿度计(以MWHS表示)替换ATMS,所得结果类似。ERA5作为全球大气再分析资料的典型代表,用方位谱台风中心位置定位方法得到的台风中心位置误差较大的原因是ERA5再分析资料全天空模拟亮温在台风中的分布结构与观测亮温相差较大,而模拟亮温与冰水路径分布结构极为相似。研究对台风数值预报中的全天空模拟亮温资料同化具有一定的参考意义。     

2005年极端天气和气候事件及其他相关事件的概要回顾

极端气候在2005年创下了多项记录:2005年北半球的平均温度达到有历史记录以来的最高值;印度孟买,7月27日的暴雨使降雨量在24 h内达到了944 mm,创下历史最高;10月飓风“文斯”袭击西班牙海岸,成为第一个登陆欧洲大陆的飓风。此外,达到最高强度等级的飓风“卡特里娜”、“丽塔”和“威尔玛”给美国、墨西哥等美洲国家造成重创;我国东南沿海和台湾等地多次遭强台风袭击,华南、东北和渭河流域经历特大洪涝灾害;葡萄牙、西班牙等欧洲国家遭遇了自20世纪40年代后期以来最严重的旱灾。这些都表明2005年是极端天气和气候发生频繁及气象灾害很严重的一年。     

Tropical land savannization: impact of global warming

This study investigates the impact of global warming on the savannization of the tropical land region and also examines the relative roles of the impact of the increase of greenhouse gas concentration and future changes in land cover on the tropical climate. For this purpose, a mechanistic–statistical–dynamical climate model with a bidirectional interaction between vegetation and climate is used. The results showed that climate change due to deforestation is more than that due to greenhouse gases in the tropical region. The warming due to deforestation corresponds to around 60% of the warming in the tropical region when the increase of CO₂ concentration is included together. However, the global warming due to deforestation is negligible. On the other hand, with the increase of CO₂ concentration projected for 2100, there is a lower decrease of evapotranspiration, precipitation and net surface radiation in the tropical region compared with the case with only deforestation. Differently from the case with only deforestation, the effect of the changes in the net surface radiation overcomes that due to the evapotranspiration, so that the warming in the tropical land region is increased. The impact of the increase of CO₂ concentration on a deforestation scenario is to increase the reduction of the areas covered by tropical forest (and a corresponding increase in the areas covered by savanna) which may reach 7.5% in future compared with the present climate. Compared with the case with only deforestation, drying may increase by 66.7%. This corroborates with the hypothesis that the process of savannization of the tropical forest can be accelerated in future due to global warming.     

Tropical Forests Under the Climates of the Last 30,000 Years

Vegetational history can help us to predict future environments by providing data for testing AGCMs, for indicating the vegetational response to rapid warming and changing CO₂ concentrations, and for mathematical modelling of vegetation. Most of the data are palynological, and there are well over 100 pollen diagrams from tropical regions. Maps are presented showing summarized pollen diagrams from the lowlands of South-East Asia and the West Pacific, Tropical Latin America and Tropical Africa. In all these regions there is some evidence suggesting that at the LGM lowland forests were somewhat restricted in area and included montane elements. This is consistent with cooler and drier climate at the LGM. From the montane and lowland areas of these three regions, the pollen evidence is summarized in altitudinal diagrams. These suggest considerable depression of altitudinal zones at the LGM, suggesting temperatures c. 5–10°C cooler than now. These results conflict with earlier oxygen isotope data from marine foraminifera, but do not conflict with more recent oxygen isotope measurements from tropical corals. It is also suggested that altitudinal movements may be partly controlled by CO₂ concentration and ultraviolet light.     

北大西洋飓风频次与西半球的南极涛动的联系

To examine the zonal asymmetry of the Antarctic oscillation （AAO）, different portions of the AAO from June to October （JJASO） in the interannual variability of the Atlantic tropical hurricanes number （ATHN） are documented in this research. It follows that the AAO in the Western Hemisphere （AAOWH） is positively correlated with the ATHN, at 0.36 during the period of 1871-1998 and 0.42 during the period of 1949-98. After removing the linear regressions on the Southern Oscillation Index （SOI） in all time series, the above correlation coefficients are 0.25 and 0.30, respectively. The underlying mechanisms are studied through analyses of the atmospheric general circulation variability associated with the AAOWH. It turns out that the positive （negative） phase of JJASO AAOWH corresponds with several factors： decreased （increased） vertical zonal wind shear magnitude, low-level anomalous convergence （divergence）, high-level anomalous divergence （convergence）, and warmed （cooled） sea surface temperature in the tropical Atlantic. Therefore, the positive （negative） phase of JJASO AAOWH is favorable （unfavorable） to the tropical hurricane genesis.