Global Tropical Cyclone Activity Research Articles

Applicability Evaluation of the Global Synthetic Tropical Cyclone Hazard Dataset in Coastal China

A tropical cyclone dataset is an important data source for tropical cyclone disaster research, and the evaluation of its applicability is a necessary prerequisite. The Global Synthetic Tropical Cyclone Hazard (GSTCH) dataset is a dataset of global tropical cyclone activity for 10,000 years from 2018, and has become accepted as a major data source for the study of global tropical cyclone hazards. On the basis of the authoritative Tropical Cyclone Best Track (TCBT) dataset proposed by the China Meteorological Administration, this study evaluated the applicability of the GSTCH dataset in relation to two regions: the Northwest Pacific and China’s coastal provinces. For the Northwest Pacific, the results show no significant differences in the means and standard deviations of landfall wind speed, landfall pressure, and annual occurrence number between the two datasets at the 95% confidence level. They also show the cumulative distributions of central minimum pressure and central maximum wind speed along the track passed the Kolmogorov–Smirnov (K-S) test at the 95% confidence level, thereby verifying that the GSTCH dataset is consistent with the TCBT dataset at sea-area scale. For China’s coastal provinces, the results show that the means or standard deviations of tropical cyclone characteristics between the two datasets were not significantly different in provinces other than Guangdong and Hainan, and further analysis revealed that the cumulative distributions of the tropical cyclone characteristics in Guangdong and Hainan provinces passed the K-S test at the 95% confidence level, thereby verifying that the GSTCH dataset is consistent with the TCBT dataset at province scale. The applicability evaluation revealed that no significant differences exist between most of the tropical cyclone characteristics in the TCBT and GSTCH datasets, and that the GSTCH dataset is an available and reliable data source for tropical cyclone hazard studies in China’s coastal areas.

Role of Tropical Cyclones in Determining ENSO Characteristics

AbstractEl Niño‐Southern Oscillation (ENSO) can effectively modulate global tropical cyclone (TC) activity, but the role TCs may play in determining ENSO characteristics remains unclear. Here we investigate the impact of TC winds on ENSO using a suite of Earth system model experiments where we insert TC winds, extracted from a TC‐permitting high‐resolution simulation, into a low‐resolution model configuration with nearly no intrinsic TCs. The presence of TC winds in the model increases ENSO power and shifts ENSO frequency closer to what we observe. TCs lead to an increase of strong to extreme El Niño events seen in observations and not simulated in the low‐resolution model without intrinsic TCs, mainly through enhanced zonal advection feedback and thermocline feedback. Our results indicate that TCs play a fundamental role in producing the ENSO characteristics we experience today in the climate system and point to a two‐way climatological interaction between TCs and ENSO.

Tropical Oceanic Influences on Observed Global Tropical Cyclone Frequency

AbstractThe global tropical cyclone (TC) number has historically been relatively constant from year‐to‐year, however, the reason remains unknown. Furthermore, climate projections are inconclusive regarding future global TC frequency changes. Here, we investigated years in which observed global TC activity deviated from the mean and potential links to ocean drivers from 1980 to 2021. We found that the annual global number of named storm days and accumulated cyclone energy (ACE) were significantly linked with El Niño–Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM). La Niña and positive AMM are associated with the bottom percentiles of both TC metrics, and vice versa for El Niño and negative AMM. The ENSO Longitude Index explains variability in annual global named storm days and ACE as well as the Niño 3.4 index. This research reveals that reliable future projections of ENSO are necessary, but not sufficient, to understand future changes in global TC frequency.

Tropical Cyclone Seeds, Transition Probabilities, and Genesis

Abstract It has been proposed that tropical cyclogenesis rates can be expressed as the product of the frequency of “seeds” and a transition probability that depends on the large-scale environment. Here it is demonstrated that the partitioning between seed frequency and transition probability depends on the seed definition and that the existence of such a partition does not resolve the long-standing issue of whether tropical cyclone frequency is controlled more by environmental conditions or by the statistics of background weather. It is here argued that tropical cyclone climatology is mostly controlled by regional environment and that the response of global tropical cyclone activity to globally uniform radiative forcing may be more controlled by the regionality of the response than by the mean response.

Substantial global influence of anthropogenic aerosols on tropical cyclones over the past 40 years.

Over the past 40 years, anthropogenic aerosols have been substantially decreasing over Europe and the United States owing to pollution control measures, whereas they have increased in South and East Asia because of the economic and industrial growth in these regions. However, it is not yet clear how the changes in anthropogenic aerosols have altered global tropical cyclone (TC) activity. In this study, we reveal that the decreases in aerosols over Europe and the United States have contributed to significant decreases in TCs over the Southern Hemisphere as well as increases in TCs over the North Atlantic, whereas the increases in aerosols in South and East Asia have exerted substantial decreases in TCs over the western North Pacific. These results suggest that how society controls future emissions of anthropogenic aerosols will exert a substantial impact on the world’s TC activity.

Trends in Global Tropical Cyclone Activity: 1990–2021

AbstractThis study investigates global tropical cyclone (TC) activity trends from 1990 to 2021, a period marked by largely consistent observational platforms. Several global TC metrics have decreased during this period, with significant decreases in hurricane numbers and Accumulated Cyclone Energy (ACE). Most of this decrease has been driven by significant downward trends in the western North Pacific. Globally, short‐lived named storms, 24‐hr intensification events of ≥50 kt day−1, and TC‐related damage have increased significantly. The increase in short‐lived named storms is likely due to technological improvements, while rapidly intensifying TC increases may be fueled by higher potential intensity. Damage increases are largely due to increased coastal assets. The significant decrease in hurricane numbers and global ACE are likely due to the trend toward a more La Niña‐like base state from 1990 to 2021, favoring North Atlantic TC activity and suppressing North and South Pacific TC activity.

Recent migration of tropical cyclones toward coasts.

Poleward migrations of tropical cyclones have been observed globally, but their impact on coastal areas remains unclear. We investigated the change in global tropical cyclone activity in coastal regions over the period 1982-2018. We found that the distance of tropical cyclone maximum intensity to land has decreased by about 30 kilometers per decade, and that the annual frequency of global tropical cyclones increases with proximity to land by about two additional cyclones per decade. Trend analysis reveals a robust migration of tropical cyclone activity toward coasts, concurrent with poleward migration of cyclone locations as well as a statistically significant westward shift. This zonal shift of tropical cyclone tracks may be mainly driven by global zonal changes in environmental steering flow.

Influence of a spectral cumulus parametrization on simulating global tropical cyclone activity in an AGCM

AbstractThe influence of a new spectral cumulus parametrization (the spectral scheme) on simulating global tropical cyclone (TC) activity in an Atmospheric General Circulation Model (AGCM) is investigated. Experiments are performed using AFES (AGCM for the Earth Simulator) and two different convection schemes – the original convection scheme of the AGCM (the Emanuel scheme) and the spectral scheme. The result shows that the both schemes can capture qualitative features of global TC activity in terms of climatology, variability, and intensity. However, the spectral scheme simulates TC genesis and track density better than the original convection scheme by improving the cold bias in the upper troposphere. The spectral scheme also provides better results for TC response to interannual variability (i.e., El Niño Southern Oscillation, ENSO) by suppressing excessive convection response to ENSO. The spectral scheme is capable of simulating the variability of TC genesis related to the Madden–Julian Oscillation (MJO) much better than the original convection scheme. Consequently, the spectral scheme can outperform the original convection scheme in simulating global TC activity from various perspectives, and thus the scheme is expected to be useful for TC prediction and future projections.

Response of Global Tropical Cyclone Activity to Increasing CO2: Results from Downscaling CMIP6 Models

AbstractGlobal models comprising the sixth-generation Coupled Climate Model Intercomparison Project (CMIP6) are downscaled using a very high-resolution but simplified coupled atmosphere–ocean tropical cyclone model, as a means of estimating the response of global tropical cyclone activity to increasing greenhouse gases. As with a previous downscaling of CMIP5 models, the results show an increase in both the frequency and severity of tropical cyclones, robust across the models downscaled, in response to increasing greenhouse gases. The increase is strongly weighted to the Northern Hemisphere, and especially noteworthy is a large increase in the higher latitudes of the North Atlantic. Changes are insignificant in the South Pacific across metrics. Although the largest increases in track density are far from land, substantial increases in global landfalling power dissipation are indicated. The incidence of rapid intensification increases rapidly with warming, as predicted by existing theory. Measures of robustness across downscaled climate models are presented, and comparisons to tropical cyclones explicitly simulated in climate models are discussed.

Modulation of bay of bengal tropical cyclone activity by the madden-julian oscillation

The influence of the Madden-Julian oscillation (MJO) on global tropical cyclone (TC) activity has been well documented in many earlier studies. However, no prior studies have focused specifically on the MJO's impacts on TCs in the Bay of Bengal (BoB). Therefore, the present study examines the impact of the MJO on BoB TC activity during the two peak TC periods i.e. April–June (AMJ) and October–December (OND) from 1974 to 2015. The MJO considerably modulates various measures of TC activity in the BoB, including the number of TCs, the number of TC days, accumulated cyclone energy, the power dissipation index, TC genesis location and TC tracks. TC activity is significantly enhanced (suppressed) over the BoB when the convectively active MJO phase is positioned over the eastern Indian Ocean and the Maritime Continent (the Western Hemisphere and Africa). Alterations in the TC genesis locations and their tracks are more pronounced in OND than in AMJ. These changes in TC characteristics are mainly attributed to MJO-driven modulations in large-scale environmental conditions such as deep convection, mid-tropospheric relative humidity, sea surface temperature, sea level pressure, lower- and upper-level winds and vertical wind shear. A comprehensive knowledge of the MJO-TC relationship may be beneficial for short-term predictions of TC activity in the BoB.

Little evidence of reduced global tropical cyclone activity following recent volcanic eruptions

The impact of volcanic aerosols on recent global tropical cyclone (TC) activity is examined in observations, reanalysis, and models (the Coupled Model Intercomparison Project phase 5 - CMIP5 multi-model, and one single model large ensemble). In observations, we find a reduction of TC activity only in the North Atlantic following the last three strong volcanic eruptions; that signal, however, cannot be clearly attributed to volcanoes, as all three eruptions were simultaneous with El Niño events. In reanalyses, we find no robust impact of volcanic eruptions on potential intensity (PI) and genesis indices. In models, we find a reduction in PI after volcanic eruptions in the historical simulations, but this effect is significantly reduced when differences between the model environment and observations are accounted for. Morever, the CMIP5 multi-model historical ensemble shows no effect of volcanic eruptions on a TC genesis index. Finally, there is no robust and consistent reduction in recent TC activity following recent volcanic eruptions in a large set of synthetic TCs downscaled from these simulations. Taken together, these results show that in recent eruptions volcanic aerosols did not reduce global TC activity.

Impact of air–sea coupling on the simulated global tropical cyclone activity in the high-resolution Community Earth System Model (CESM)

Atmosphere–ocean coupling is critical for tropical cyclones (TC) formation and development. TCs derive their energy from the upper ocean, and the associated TC-ocean interactions can in turn modulate storm evolution. This study assesses the impact of ocean coupling on directly-simulated global TC activity in the high-resolution “TC-permitting” Community Earth System Model (CESM). Model-simulated global TC activity is evaluated in a 30-year fully-coupled CESM simulation (CPL), in which the 0.25° atmosphere component is coupled to the nominal 1° dynamic ocean (with ~ 0.27° horizontal grid spacing in the tropics). An atmosphere-only simulation (ATM) is branched from CPL, with sea surface temperature (SST) specified from CPL, which we use to isolate the effect of ocean coupling on TC activity. We find that the two-way ocean coupling can affect global TC frequency, geographical distribution, storm intensity, and interannual variability. ATM on average simulates 27% more major TC events than CPL globally, and the TC power dissipation is higher than CPL poleward of 12° latitude in both hemispheres. The lack of negative SST feedbacks in ATM allows TCs to have a longer intensification period and reach the maximum intensity at a higher latitude. In CPL, TC interannual variability is heavily influenced by El Nino/La Nina events. This relationship can be captured in ATM under strong events but is less predictable during weak and neutral years. Results help to better understand the connections and feedbacks linking air–sea coupling, tropical variability, and the directly simulated TC activity within the high-resolution Earth System Models.

Plausible modulation of solar wind energy flux input on global tropical cyclone activity

Studies on Sun-climate connection have been carried out for several decades, and almost all of them focused on the effects of solar total irradiation energy. As the second major terrestrial energy source from outer space, the solar wind energy flux exhibits more significant long-term variations. However, its link to the global climate change is rarely concerned and remains a mystery. As a fundamental and important aspect of the Earth's weather and climate system, tropical cyclone activity has been causing more and more attentions. Here we investigate the possible modulation of the total energy flux input from the solar wind into the Earth's magnetosphere on the global tropical cyclone activity during 1963–2012. From a global perspective, the accumulated cyclone energy increases gradually since 1963 and starts to decrease after 1994. Compare to the previously frequently used parameters, e.g., the sunspot number, the total solar irradiation, the solar F10.7 irradiation, the tropical sea surface temperature, and the south oscillation index, the total solar wind energy flux input exhibits a better correlation with the global tropical cyclone activity. Furthermore, the tropical cyclones seem to be stronger with more intense geomagnetic activities. A plausible modulation mechanism is thus proposed to link the terrestrial weather phenomenon to the seemingly-unrelated solar wind energy input.

Future Changes in Tropical Cyclone Activity in High‐Resolution Large‐Ensemble Simulations

AbstractProjected future changes in global tropical cyclone (TC) activity are assessed using 5,000 year scale ensemble simulations for both current and 4 K surface warming climates with a 60 km global atmospheric model. The global number of TCs decreases by 33% in the future projection. Although geographical TC occurrences decrease generally, they increase in the central and eastern parts of the extra tropical North Pacific. Meanwhile, very intense (category 4 and 5) TC occurrences increase over a broader area including the south of Japan and south of Madagascar. The global number of category 4 and 5 TCs significantly decreases, contrary to the increase seen in several previous studies. Lifetime maximum surface wind speeds and precipitation rate are amplified globally. Regional TC activity changes have large uncertainty corresponding to sea surface temperature warming patterns. TC‐resolving large‐ensemble simulations provide useful information, especially for policy making related to future climate change.

The Sensitivity of Tropical Cyclone Activity to Off-Equatorial Thermal Forcing in Aquaplanet Simulations

Abstract The sensitivity of global tropical cyclone (TC) activity to changes in a zonally symmetric sea surface temperature (SST) distribution and the associated large-scale atmospheric circulation are investigated. High-resolution (~50-km horizontal grid spacing) atmospheric general circulation model simulations with maximum SST away from the equator are presented. Simulations with both fixed-SST and slab ocean lower boundary conditions are compared. The simulated TCs that form on the poleward flank of the intertropical convergence zone (ITCZ) are tracked and changes in the frequency and intensity of those storms are analyzed between the different experiments. The total accumulated cyclone energy (ACE) increases as the location of the maximum SST shifts farther away from the equator. The location of the ITCZ also shifts in conjunction with changes to the SST profile, and this plays an important role in mediating the frequency and intensity of the TCs that form within this modeling framework.

Variations in global tropical cyclone activity and the Madden‐Julian Oscillation since the midtwentieth century

AbstractThe Madden‐Julian oscillation (MJO) has been documented in previous studies to significantly impact tropical cyclone activity in all ocean basins. Most of these studies have utilized the Wheeler‐Hendon index. This index is only available since 1974, the period over which remotely sensed outgoing longwave radiation data has been available. Our study utilizes a long reconstructed MJO index, based on surface pressures, which extends back to 1905. We document consistent modulation of tropical cyclone activity by the MJO in all basins over this time period. These modulations are shown to be remarkably stable over the entire analysis period. We also examine the combined impacts of El Niño‐Southern Oscillation and the MJO on tropical cyclone activity in each basin over multidecadal time scales.

Assessment on historical cyclone tracks in the Bay of Bengal, east coast of India

The Bay of Bengal (BoB) basin in the North Indian Ocean reports the highest number of tropical cyclones, and the frequency is much higher almost five times compared with the Arabian Sea (AS). Semi-enclosed nature of this basin in conjunction with its funnel shape steers the cyclone pathway striking the land. Historical reports signify that most deadly cyclones with highest catastrophe and death tolls occurred in this basin. The four maritime states located in the east coast of India are highly vulnerable to tropical cyclones. Hence, there is a need to understand the risk factors attributed from extreme winds, storm surge, and associated coastal inundation. Historical data signify higher frequency of post-monsoon cyclones compared with pre-monsoon cyclones in the BoB. This study aims to develop a synthetic track or the most probable cyclone track for each state located along the east coast of India. The synthetic track is a general guidance for numerical models, with utility to evaluate and assess the risk factors along coastal belts. This study also deals with aspects on frequency and cyclogenesis locations in the BoB based on analysis from historical data. Results for decadal scale variability signify that in the present decade, the eastern BoB is quite conducive for cyclogenesis. In this region, oceanic thermal field exhibits a warming trend, and found to extend up to water depth of 600 m. In addition, this study also evaluates the energy metrics such as Power Dissipation Index (PDI), and Accumulated Cyclone Energy (ACE) for tropical cyclones that occurred during past four decades in the BoB. The results signify that PDI for tropical cyclones in the present decade is six times higher when compared with the past. The study has practical applications for mapping coastal vulnerability in a changing climate. Tropical cyclones are associated with devastation resulting in enormous loss of life and property during its landfall. In a broad perspective, lack of disaster management pre- paredness would contribute to high vulnerability. The gen- esis of a cyclone usually referred as 'cyclogenesis' is the development stage or strengthening of a cyclonic circula- tion in the atmosphere during the initial stage of its forma- tion. Tropical cyclones form over warm ocean surface, and favourable conditions are sea-surface temperature (SST) greater than 26 ∘ C; low magnitude of vertical wind shear; larger low-level vorticity; and higher mid-troposphere rel- ative humidity. In global oceans, the western part of the North Pacific reported the maximum number of tropical cyclones (average of 26 per year) followed by eastern North Pacific (average of 17 per year). The South Indian Ocean and North Atlantic has an average of 10 per year, while regions in the North Indian Ocean (NIO) have an average of five cyclones per year (Niyas et al., 2009). Notably, the NIO alone accounts for about 7% of global tropical cyclone activity, with a frequency about five

Simulation of the Global ENSO–Tropical Cyclone Teleconnection by a High-Resolution Coupled General Circulation Model

Abstract This study assesses the influence of the El Niño–Southern Oscillation (ENSO) on global tropical cyclone activity using a 150-yr-long integration with a high-resolution coupled atmosphere–ocean general circulation model [High-Resolution Global Environmental Model (HiGEM); with N144 resolution: ~90 km in the atmosphere and ~40 km in the ocean]. Tropical cyclone activity is compared to an atmosphere-only simulation using the atmospheric component of HiGEM (HiGAM). Observations of tropical cyclones in the International Best Track Archive for Climate Stewardship (IBTrACS) and tropical cyclones identified in the Interim ECMWF Re-Analysis (ERA-Interim) are used to validate the models. Composite anomalies of tropical cyclone activity in El Niño and La Niña years are used. HiGEM is able to capture the shift in tropical cyclone locations to ENSO in the Pacific and Indian Oceans. However, HiGEM does not capture the expected ENSO–tropical cyclone teleconnection in the North Atlantic. HiGAM shows more skill in simulating the global ENSO–tropical cyclone teleconnection; however, variability in the Pacific is overpronounced. HiGAM is able to capture the ENSO–tropical cyclone teleconnection in the North Atlantic more accurately than HiGEM. An investigation into the large-scale environmental conditions, known to influence tropical cyclone activity, is used to further understand the response of tropical cyclone activity to ENSO in the North Atlantic and western North Pacific. The vertical wind shear response over the Caribbean is not captured in HiGEM compared to HiGAM and ERA-Interim. Biases in the mean ascent at 500 hPa in HiGEM remain in HiGAM over the western North Pacific; however, a more realistic low-level vorticity in HiGAM results in a more accurate ENSO–tropical cyclone teleconnection.

Global tropical cyclone activity to decrease with climate change

Given its strong dependence on sea surface temperatures and atmospheric conditions, tropical cyclone activity is expected to be strongly affected by climate change. With observational records suggesting that tropical North Atlantic hurricane activity has increased in recent decades, some scientists have suggested that global tropical cyclone activity will increase as the planet warms. Using an ensemble atmosphere general circulation model, however, Sugi and Yoshimura found that global tropical cyclone activity has undergone a long‐term decline from 1872 to the present—a trend they found should continue throughout the coming century. They found that the rate of global tropical cyclone activity decreased by 12.4 hurricanes per century—8.7 fewer hurricanes per century in the Northern Hemisphere and 3.7 fewer in the Southern Hemisphere.

Investigating Global Tropical Cyclone Activity with a Hierarchy of AGCMs: The Role of Model Resolution

Abstract The ability to run general circulation models (GCMs) at ever-higher horizontal resolutions has meant that tropical cyclone simulations are increasingly credible. A hierarchy of atmosphere-only GCMs, based on the Hadley Centre Global Environmental Model version 1 (HadGEM1) with horizontal resolution increasing from approximately 270 to 60 km at 50°N, is used to systematically investigate the impact of spatial resolution on the simulation of global tropical cyclone activity, independent of model formulation. Tropical cyclones are extracted from ensemble simulations and reanalyses of comparable resolutions using a feature-tracking algorithm. Resolution is critical for simulating storm intensity and convergence to observed storm intensities is not achieved with the model hierarchy. Resolution is less critical for simulating the annual number of tropical cyclones and their geographical distribution, which are well captured at resolutions of 135 km or higher, particularly for Northern Hemisphere basins. Simulating the interannual variability of storm occurrence requires resolutions of 100 km or higher; however, the level of skill is basin dependent. Higher resolution GCMs are increasingly able to capture the interannual variability of the large-scale environmental conditions that contribute to tropical cyclogenesis. Different environmental factors contribute to the interannual variability of tropical cyclones in the different basins: in the North Atlantic basin the vertical wind shear, potential intensity, and low-level absolute vorticity are dominant, whereas in the North Pacific basins midlevel relative humidity and low-level absolute vorticity are dominant. Model resolution is crucial for a realistic simulation of tropical cyclone behavior, and high-resolution GCMs are found to be valuable tools for investigating the global location and frequency of tropical cyclones.