Role Of Tropical Cyclones Research Articles

Water Lifting and Outflow Gain of Kinetic Energy in Tropical Cyclones

Abstract While water lifting plays a recognized role in the global atmospheric power budget, estimates for this role in tropical cyclones vary from no effect to a major reduction in storm intensity. To better assess this impact, here we consider the work output of an infinitely narrow thermodynamic cycle with two streamlines connecting the top of the boundary layer in the vicinity of maximum wind (without assuming gradient-wind balance) to an arbitrary level in the inviscid free troposphere. The reduction of a storm’s maximum wind speed due to water lifting is found to decline with increasing efficiency of the cycle and is about 5% for maximum observed Carnot efficiencies. In the steady-state cycle, there is an extra heat input associated with the warming of precipitating water. The corresponding positive extra work is of an opposite sign and several times smaller than that due to water lifting. We also estimate the gain of kinetic energy in the outflow region. Contrary to previous assessments, this term is found to be large when the outflow radius is small (comparable to the radius of maximum wind). Using our framework, we show that Emanuel’s maximum potential intensity (E-PI) corresponds to a cycle where total work equals work performed at the top of the boundary layer (net work in the free troposphere is zero). This constrains a dependence between the outflow temperature and heat input at the point of maximum wind, but does not constrain the radial pressure gradient. We outline the implications of the established patterns for assessing real storms.

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.

Role of Tropical Cyclones in Determining ENSO Characteristics

Role of Tropical Cyclones in Determining ENSO Characteristics

Tropical Cyclone Flooding in the Carolinas

Abstract The climatology of tropical cyclone flooding in the Carolinas is analyzed through annual flood peak observations from 411 U.S. Geological Survey (USGS) stream gauging stations. Tropical cyclones (TCs) account for 28% of the top 10 annual flood peaks, 55% of record floods, and 91% of floods with peak magnitudes at least 5 times greater than the 10-yr floods, highlighting the prominent role of TCs for flood extremes in the Carolinas. Of all TC-related flood events, the top 10 storms account for nearly 1/3 of annual flood peaks and more than 2/3 of record floods, reflecting the dominant role of a small number of storms in determining the upper tail of flood peak distributions. Analyses of the 10 storms highlight both common elements and diversity in storm properties that are responsible for flood peaks. Extratropical transition and orographic enhancement are important elements of extreme TC flooding in the Carolinas. Analyses of the Great Flood of 1916 highlight the flood peak of 3115 m3 s−1 in French Broad River at Asheville, 2.6 times greater than the second-largest peak from a record of 124 years. We also examine the hydroclimatology, hydrometeorology, and hydrology of flooding from Hurricanes Matthew (2016) and Florence (2018). Results point to contrasting storm properties for the two events, including tracks as well as rainfall distribution and associated physical mechanisms. Climatological analyses of vertically integrated water vapor transport (IVT) highlight the critical role of anomalous moisture transport from the Atlantic Ocean in producing extreme rainfall and flooding over the Carolinas.

Transport of Water Vapor from Tropical Cyclones to the Upper Troposphere

This paper investigates the influence of tropical cyclones on water vapor concentrations in the upper atmosphere above these storms. We use independent data sets of tropical storm intensity, water vapor and lightning activity to investigate this relationship. Water vapor in the upper troposphere is a key greenhouse gas, with direct impacts on surface temperatures. Both the amount and altitude of water vapor impact the radiative balance and the greenhouse effect of the atmosphere. The water vapor enters the upper troposphere through deep convective storms, often associated with lightning activity. The intensity of the lightning activity represents the intensity of the convection in these storms, and hence the amount of water vapor transported aloft. In this paper, we investigate the role of tropical cyclones on the contribution of water vapor to the upper atmosphere moistening. Tropical cyclones are the largest most intense storms on Earth and can last for up to two weeks at a time. There is also evidence that the intensity of tropical cyclones is increasing, and will continue to increase, due to global warming. In this study we find that the maximum moistening of the upper atmosphere occurs at the 200 hPa level (~12 km altitude), with a lag of 1–2 days after the maximum sustained winds in the tropical cyclone. While the water vapor peaks after the maximum of the storm intensity, the lightning activity peaks before the maximum intensity of the storms, as shown previously. We show here that the absolute amount of water vapor in the upper troposphere above tropical storms increases linearly with the intensity of the storms. For every 10 hPa decrease in the minimum pressure of tropical storms, the specific humidity increases around 0.2 g/kg at the 200 hPa level.

The Role of Tropical Cyclones on the Total Precipitation in Cuba during the Hurricane Season from 1980 to 2016

This study quantifies the amount of rainfall supplied by tropical cyclones (TCs) to Cuba. It uses the long–term global gridded Multi–Source Weighted–Ensemble Precipitation (MSWEP) v2 data set, with a resolution of 0.1° in latitude and longitude, and a temporal resolution of 3 h during the hurricane seasons from 1980–2016. During this study period, 146 TCs were identified within a 500–km radius of Cuba. The contribution of TCs to the total precipitation over Cuba during the cyclonic season was ~11%. The maximum contribution occurs in October and November, representing 18% and 28% of the total precipitation, respectively. The interannual precipitation contribution shows a positive correlation (~0.74) with the number of TCs, but without a significant trend for the period. A climatological spatial analysis of the rainfall associated with TCs revealed great heterogeneity, although the major contribution was observed along the southern coast of the eastern and central provinces of Cuba, and in the western province of Pinar del Río. No significant difference was observed between the number of TCs that affected Cuba and their rainfall contribution under the positive and negative phases of the El Niño Southern Oscillation. However, the negative phase of the NAO led to an increase in the genesis of TCs that later affected Cuba, which led to a greater contribution to precipitation compared to that obtained from TCs during the positive phase of this oscillation. Our results also confirm that anomalous warmth of the tropical Atlantic Ocean, revealed through the Atlantic Meridional Mode, and enlargement of the Atlantic Warm Pool, enhances the genesis in the North Atlantic Basin of the TCs that affect Cuba, which was associated with an increase of the rainfall contribution to the total precipitation compared to that calculated for TCs formed during the opposite phases.

Flood impact on Mainland Southeast Asia between 1985 and 2018—The role of tropical cyclones

AbstractFloods are disastrous natural hazards accused of human live losses. As a flood‐prone area, Mainland Southeast Asia (MSEA) has often been hit by floods, resulting in the highest fatality in the world. Despite the destructive flood impacts, how has flood occurrence changed over the past decades, and to what extent did floods affect the MSEA are not yet clear. Using the Dartmouth Flood Observatory large flood data archive, we aim to assess the trend of flood occurrence in the MSEA in 1985–2018, and quantify the associated impacts on humans. Particularly, the contribution of tropical cyclone (TC) landfall induced floods (TCFloods) is quantified, because of the frequent TC landfalls. Results show that (a) occurrence and maximum magnitude of floods by all causes (ALLFloods) significantly increased (p < .01), but not for TCFloods; (b) On average, TCFloods accounted for 24.6% occurrence of ALLFloods; (c) TCFloods caused higher mortality and displacement rate than ALLFloods did. As low flood protection standards in Cambodia and Myanmar is considered a reason for high flood‐induced mortalities, building higher flood protection standards should be taken as a priority for mitigating potential flood impacts. With quantifying flood occurrence and impacts, this study offers scientific understandings for better flood risk management.

Role of tropical cyclones over the western North Pacific in the East Asian summer monsoon system

Precipitation observations collected at weather stations in eastern China, the NCEP/NCAR reanalysis data, the tropical cyclone (TC) Best Track Dataset, and a sensitivity numerical experiment were used in the present study to investigate the role in the East Asian summer monsoon (EASM) system played by frequent TC activities over the western North Pacific (WNP). Results indicated that, in active TC years, the EASM is stronger and the southerly winds in the lower troposphere advance farther north and reach higher latitudes. Meanwhile, the monsoon rain belt remains in the lower and middle reaches of the Yangtze River valley for a relatively short period, leading to less precipitation there. Both the western Pacific subtropical high and the South Asian high weaken with the northward shift of the ridgelines for both high-pressure systems as well as the East Asian subtropical upper-level jet. Therefore, the impacts of frequent TC activities over the WNP on each individual component of the EASM are in phase with those of the stronger EASM itself, amplifying features of the already strengthened EASM.

The Role of Tropical Cyclones in Precipitation Over the Tropical and Subtropical North America

Tropical cyclones (TCs) are essential elements of the hydrological cycle in tropical and subtropical regions. In the present study, the contribution of TCs to seasonal precipitation around the tropical and subtropical North America is examined. When TC activity over the tropical eastern Pacific (TEP) or the Intra Americas Seas (IAS) is below (above-normal), regional precipitation may be below (above-normal). However, it is not only the number of TCs what may change seasonal precipitation, but the trajectory of the systems. TCs induce intense precipitation over continental regions if they are close enough to shorelines, for instance, if the TC center is located, on average, less than 500 km-distant from the coast. However, if TCs are more remote than this threshold distance, the chances of rain over continental regions decrease, particularly in arid and semi-arid regions. In addition, a distant TC may induce subsidence or produce moisture divergence that inhibits, at least for a few days, convective activity farther away than the threshold distance. An analysis of interannual variability in the TCs that produce precipitation over the tropical and subtropical North America shows that some regions in northern Mexico, which mostly depend on this effect to undergo wet years, may experience seasonal negative anomalies in precipitation if TCs trajectories are remote. Therefore, TCs (activity and trajectories) are important modulators of climate variability on various time scales, either by producing intense rainfall or by inhibiting convection at distant regions from their trajectory. The impact of such variations on water availability in northern Mexico may be relevant, since water availability in dams recovers under the effects of TC rainfall. Seasonal precipitation forecasts or climate change scenarios for these regions should take into account the effect of TCs, if regional adaptation strategies are implemented.

入境宁波的热带气旋活动特征的气候统计及其年代际变化

本文利用中国气象局热带气旋(TC)资料中心最佳路径数据集，对入境宁波的TC进行统计，从1949到2014年共有71个TC入境宁波，通过合成分析和显著性检验发现：TC源地强东风引导气流的存在和西风带的南北位置是影响TC路径的重要原因。在1990s中后期以来的全球变暖减缓阶段，入境宁波的TC频数在9~10月份显著增多。1990s中后期之后，整个太平洋海表面温度(SST)呈现出太平洋年代际涛动(PDO)的负位相和赤道太平洋的类拉尼娜型海温分布，Walker环流增强，调制了西太副高的加强和西伸，使得西北太平洋TC移动路径偏西，登陆我国海岸线中段的TC频数增多，造成了在9~10月份入境宁波的TC频数增多。就TC生成而言，1990s年代中期之后西北太平洋TC源地西部垂直风切变的减弱和相对湿度的增加可能造成了TC生成的增加，而较东位置则与之相反。 Based on the Best Track Dataset from China Meteorological Administration during 1949-2014, there were 71 tropical cyclones (TCs) during the period landfall in Ningbo. According to composited analysis and t-test, the area which TC genesis with strong east-wind and the location of westerlies play an important role in TC moving. During the autumn season (September and October) of global warming hiatus epoch after the mid-to-end of 1990s, the TC number of moving to Ningbo was increased significantly. The reason may be associated with the Pacific decadal oscillation became into its negative phase. Since the sea surface temperature showing a La Nina-like pattern, which enhanced Walker Circulation and further modulated western Pacific subtropical high (WPSH), the WPSH extended westward and intensified, causing TC moving favorite to western region and favorite landing at Chinese mainland. The genesis of TC over the western North Pacific also appears interdecadal shift indicated by genesis potential index of TC. The decreasing of vertical wind shear and increasing of relative humidity play a dominant role in TC genesis increasing.

Role of Tropical Cyclones along the Monsoon Trough in the 2011 Thai Flood and Interannual Variability

Abstract The atmospheric circulation patterns that were responsible for the heavy flooding that occurred in Thailand in 2011 are examined. This paper also investigates the interannual variation in precipitation over Indochina over a 33-yr period from 1979–2011, focusing on the role of westward-propagating tropical cyclones (TCs) over the Asian monsoon region. Cyclonic anomalies and more westward-propagating TCs than expected from the climatology of the area were observed in 2011 along the monsoon trough from the northern Indian subcontinent, the Bay of Bengal, Indochina, and the western North Pacific, which contributed significantly to the 2011 Thai flood. The strength of monsoon westerlies was normal, which implies that the monsoon westerly was not responsible for the seasonal heavy rainfall in 2011. Similar results were also obtained from the 33-yr statistical analysis. The 5-month total precipitation over Indochina covaried interannually with that along the monsoon trough. In addition, above-normal precipitation over Indochina was observed when enhanced cyclonic circulation with more westward-propagating TCs along the monsoon trough was observed. Notably, the above-normal precipitation was not due to the enhanced monsoon westerly over Indochina. Therefore, the 2011 Thai flood was caused by the typical atmospheric circulation pattern for an above-normal precipitation year. It is noteworthy that the effect of sea surface temperature (SST) forcing over the western North Pacific and the Niño-3.4 region on total precipitation during the summer rainy season over Indochina was unclear over the 33-yr period.

The role of tropical cyclones in stimulating cyanobacterial (Microcystis spp.) blooms in hypertrophic Lake Taihu, China

Weather-related disturbances, such as wind-generated waves, major rainfall events and large temperature shifts associated with frontal passages, are important drivers of ecological processes in shallow lakes. The influence of Pacific tropical cyclones on cyanobacterial blooms in China's third largest lake, Taihu, was studied during the passage of two typhoons using a continuous monitoring as part of an on-lake high-frequency recording platform, coupled to satellite-based remote sensing data. Short-term (on the order of hours) nutrient pulsing resulting from the passage of typhoons played a key role in bloom initiation and maintenance. Decreasing wind speeds and increasing air and water temperatures in the aftermath of cyclones were accompanied by elevated phytoplankton biomass concentrations. The synergistic effects of nutrient pulsing, elevated water temperatures and increased water column stratification after the passage of the cyclones stimulated blooms of the toxic cyanobacteria Microcystis spp. There were short-term successions of blooms following typhoons, and as blooms “crashed” they provided nutrient inocula for future blooms. Trends determined from historical in situ data indicated higher frequencies and intensities of blooms in “cyclone years”. Typhoons are an important driver of biogeochemical and water quality perturbations at the ecosystem-level in this hypertrophic lake. These events play a key role in our ability to forecast blooms over both short (days) and longer-term (weeks) periods.

The impact of wind on trees in Australian tropical savannas: lessons from Cyclone Monica

Abstract The role of tropical cyclones in structuring tropical rainforests has long been recognized in the Americas and northern Australia. However, their role in the dynamics of Australian savannas has received little attention compared with the effects of fire and drought. In April 2006, Tropical Cyclone Monica caused trees to be snapped or uprooted across a swath about 50 km wide and 130 km inland in northern Australia. The proportion of trees damaged was assessed using on‐ground surveys and interpretation of aerial photographs along the cyclone path and along several perpendicular transects. From these data, a relationship between the damage to trees and estimated maximum gust speed was developed. From knowledge of gust recurrence, curves were then derived describing the changes with distance inland in the average recurrence interval for tree windthrow events. These relationships were consistent with the historical record of tree damage in the northwest of the Northern Territory. It was concluded that windthrow has profound, but hitherto unrecognized implications for ecological processes such as tree dynamics and fluxes of carbon and water in Australian tropical savannas.

The Role of Tropical Cyclones in the Formation of Tropical Upper-Tropospheric Troughs

Tropical upper-tropospheric troughs (TUTTs), also known as midoceanic troughs, are elongated troughs that appear in summer monthly averaged maps of the upper-tropospheric flow over the oceans. The transient part of these climatological features is composed of TUTT cells and their origin is the subject of this study. TUTT cells often occur to the east of tropical cyclones. A nonlinear shallow water model on the sphere was used in a simplified study of the interactions between tropical cyclones and the circumpolar vortex. Based on the results of these simulations and keeping in mind their limitations, it is proposed that dispersion of short Rossby wave energy is a possible mechanism to explain the formation of TUTT cells to the east of tropical cyclones. The model simulations suggest that two types of TUTT cells may form to the east of tropical cyclones. When embedded in cyclonic or weak anticyclonic shear, the trough to the east of the tropical cyclone may broaden, resulting in the formation of an intense TUTT cell that has a strong signature in the wind and mass fields. In the presence of stronger anticyclonic shear, the trough to the east of the tropical cyclone may become a thin and elongated TUTT cell that has a comparatively negligible signature in the mass and flow fields. Moreover, the model simulations indicate that the mode of evolution of TUTT cells that form to the east of a tropical cyclone is strongly dependent on the intensity and relative location of midlatitude waves. Wave–mean flow interaction calculations indicated that tropical cyclones produced a westerly acceleration of the mean zonal flow in the latitudinal band through which they move and an easterly acceleration elsewhere. These calculations also indicated that broadening TUTT cells may cause an easterly acceleration of the zonal mean flow.