scholarly journals Large-scale control on the frequency of tropical cyclones and seeds: a consistent relationship across a hierarchy of global atmospheric models

2020 ◽  
Vol 55 (11-12) ◽  
pp. 3177-3196
Author(s):  
Tsung-Lin Hsieh ◽  
Gabriel A. Vecchi ◽  
Wenchang Yang ◽  
Isaac M. Held ◽  
Stephen T. Garner
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Sea Surface ◽  
Spatial Gradient ◽  
Atmospheric Models ◽  
Probability Of Transition ◽  
The Difference ◽  
Convergence Zones ◽  
Diagnostic Framework ◽  
Scale Control

Abstract A diagnostic framework is developed to explain the response of tropical cyclones (TCs) to climate in high-resolution global atmospheric models having different complexity of boundary conditions. The framework uses vortex dynamics to identify the large-scale control on the evolution of TC precursors—first non-rotating convective clusters and then weakly rotating seeds. In experiments with perturbed sea surface temperature (SST) and $$\hbox {CO}_2$$ CO 2 concentration from the historical values, the response of TCs follows the response of seeds. The distribution of seeds is explained by the distribution of the non-rotating convective clusters multiplied by a probability that they transition to seeds. The distribution of convective clusters is constrained by the large-scale vertical velocity and is verified in aquaplanet experiments with shifting Inter tropical Convergence Zones. The probability of transition to seeds is constrained by the large-scale vorticity via an analytical function, representing the relative importance between vortex stretching and vorticity advection, and is verified in aquaplanet experiments with uniform SST. The consistency between seed and TC responses breaks down substantially when the realistic SST is perturbed such that the spatial gradient is significantly enhanced or reduced. In such cases, the difference between the responses is explained by a change in the ventilation index, which influences the fraction of seeds that develop into TCs. The proposed TC-climate relationship serves as a framework to explain the diversity of TC projection across models and forcing scenarios.

scholarly journals Weak Tropical Cyclones Dominate the Poleward Migration of the Annual Mean Location of Lifetime Maximum Intensity of Northwest Pacific Tropical Cyclones since 1980

2017 ◽  
Vol 30 (17) ◽  
pp. 6873-6882 ◽  
Author(s):  
Ruifen Zhan ◽  
Yuqing Wang
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Surface Wind ◽  
Surface Wind Speed ◽  
Maximum Intensity ◽  
Sea Surface ◽  
Northwest Pacific ◽  
The Past ◽  
Increasing Trend ◽  
Sst Warming

The poleward migration of the annual mean location of tropical cyclone (TC) lifetime maximum intensity (LMI) has been identified in the major TC basins of the globe over the past 30 years, which is particularly robust over the western North Pacific (WNP). This study has revealed that this poleward migration consists mainly of weak TCs (with maximum sustained surface wind speed less than 33 m s−1) over the WNP. Results show that the location of LMI of weak TCs has migrated about 1° latitude poleward per decade since 1980, while such a trend is considerably smaller for intense TCs. This is found to be linked to a significant decreasing trend of TC genesis in the southern WNP and a significant increasing trend in the northwestern WNP over the past 30 years. It is shown that the greater sea surface temperature (SST) warming at higher latitudes associated with global warming and its associated changes in the large-scale circulation favor more TCs to form in the northern WNP and fewer but stronger TCs to form in the southern WNP.

scholarly journals An oceanic pathway for Madden–Julian Oscillation influence on Maritime Continent Tropical Cyclones

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Karthik Balaguru ◽  
L. Ruby Leung ◽  
Samson M. Hagos ◽  
Sujith Krishnakumar
Keyword(s):  
Numerical Model ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Sea Surface ◽  
Madden Julian Oscillation ◽  
Surface Cooling ◽  
Maritime Continent ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Sea Surface Cooling

AbstractWhile the Madden–Julian Oscillation (MJO) has been shown to affect tropical cyclones (TCs) worldwide through its modulation of large-scale circulation in the atmosphere, little or no role for the ocean has been identified to date in this influence of MJO on TCs. Using observations and numerical model simulations, we demonstrate that MJO events substantially impact TCs over the Maritime Continent (MC) region through an oceanic pathway. While propagating across the MC region, MJO events cause significant sea surface cooling with an area-averaged value of about 0.35 ± 0.12 °C. Hence, TCs over the MC region immediately following the passage of MJO events encounter considerably cooler sea surface temperatures. Consequently, the enthalpy fluxes under the storms are reduced and the intensification rates decrease by more than 50% on average. These results highlight an important role played by the ocean in facilitating MJO-induced sub-seasonal variability in TC activity over the MC region.

The Impact of High-Resolution Sea Surface Temperatures on the Simulated Nocturnal Florida Marine Boundary Layer

2008 ◽  
Vol 136 (4) ◽  
pp. 1349-1372 ◽  
Author(s):  
Katherine M. LaCasse ◽  
Michael E. Splitt ◽  
Steven M. Lazarus ◽  
William M. Lapenta
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Large Scale ◽  
Flow Direction ◽  
Thermal Structure ◽  
Sea Surface ◽  
Scale Model ◽  
Florida Current ◽  
Convergence Zones ◽  
The Impact

Abstract High- and low-resolution sea surface temperature (SST) analysis products are used to initialize the Weather Research and Forecasting (WRF) Model for May 2004 for short-term forecasts over Florida and surrounding waters. Initial and boundary conditions for the simulations were provided by a combination of observations, large-scale model output, and analysis products. The impact of using a 1-km Moderate Resolution Imaging Spectroradiometer (MODIS) SST composite on subsequent evolution of the marine atmospheric boundary layer (MABL) is assessed through simulation comparisons and limited validation. Model results are presented for individual simulations, as well as for aggregates of easterly- and westerly-dominated low-level flows. The simulation comparisons show that the use of MODIS SST composites results in enhanced convergence zones, earlier and more intense horizontal convective rolls, and an increase in precipitation as well as a change in precipitation location. Validation of 10-m winds with buoys shows a slight improvement in wind speed. The most significant results of this study are that 1) vertical wind stress divergence and pressure gradient accelerations across the Florida Current region vary in importance as a function of flow direction and stability and 2) the warmer Florida Current in the MODIS product transports heat vertically and downwind of this heat source, modifying the thermal structure and the MABL wind field primarily through pressure gradient adjustments.

scholarly journals Variability of the Indian Monsoon in the ECHAM3 Model: Sensitivity to Sea Surface Temperature, Soil Moisture, and the Stratospheric Quasi-Biennial Oscillation

1998 ◽  
Vol 11 (8) ◽  
pp. 1837-1858 ◽  
Author(s):  
K. Arpe ◽  
L. Dümenil ◽  
M. A. Giorgetta
Keyword(s):  
Soil Moisture ◽  
Arabian Sea ◽  
Large Scale ◽  
Monsoon Season ◽  
Sea Surface ◽  
Northern Indian Ocean ◽  
Quasi Biennial Oscillation ◽  
The Difference ◽  
Biennial Oscillation

Abstract The variability of the monsoon is investigated using a set of 90-day forecasts [MONEG (Tropical Ocean Global Atmosphere Monsoon Numerical Experimentation Group) experiments] and a set of AMIP-type (Atmospheric Model Intercomparison Project) long-term simulations of the atmospheric circulation with the ECHAM3 model. The large-scale aspects of the summer monsoon circulation as represented by differences of dynamical quantities between the two extreme years 1987 and 1988 were reproduced well by the model in both kinds of experiments forced with observed sea surface temperature (SST). At the regional scale the difference of precipitation over India during summer 1987 and 1988 was well reproduced by the model in the 90-day forecasts using interannually varying SSTs; however, similarly good results were achieved in forecasts using climatological SSTs. The long-term simulations forced with interannually varying SST at the lower boundary of the atmosphere over a period of 14 years, on the other hand, only partly reproduce the observed differences of precipitation over India between 1987 and 1988. For the ensemble mean of five simulations averaged from June to September and for the whole of India an increase from 1987 to 1988 is simulated by the model as observed but with smaller values. The difference in observed precipitation between 1987 and 1988 is of opposite sign for May to that for September. The simulations and observations agree in the manifestation of this sense of opposing variability within a monsoon season for these two years and also for other years. The simulations and observations differ most during July. The paper concentrates on the question why the interannual variability in the long-term simulations on one hand and the 90-day forecasts and in the observations of precipitation on the other hand differ so strongly during the peak of the monsoon in July. Large-scale dynamics over India are mainly forced by the anomalies of Pacific SST. For the variability of precipitation over India other forcings than the Pacific SST are important as well. Due to enhanced evaporation, warmer SSTs over the northern Indian Ocean lead to increased precipitation over India. Changes in the SST there within the range of uncertainty (0.5 K) can lead to clear impacts. As a further boundary forcing, the impact of soil moisture is investigated. The use of realistic soil moisture differences between 1987 and 1988 in the MONEG forecasts resulted in improved skill of precipitation forecasts over India. Also the two individual AMIP simulations with realistic precipitation differences over India had more realistic soil moisture differences over east Asia in the beginning of the monsoon season between the two years than those experiments that failed to produce the correct precipitation differences. The years 1987 and 1988 were quite different with respect to the phase of the stratospheric quasi-biennial oscillation (QBO). As atmospheric circulation models cannot yet reproduce stratospheric QBOs realistically, their impact was tested by nudging observed QBOs into AMIP simulations for July 1987 and 1988. Seven out of eight experiments showed an impact toward a more realistic simulation of precipitation over India; however, during the west phase of the QBO (1987) impacts are very small. None of these forcings gave a dominant effect. If this finding is confirmed by further experimentation, improvements of practical long-range forecasts may be very difficult as two of these quantities are hardly known with the required accuracy (northern Indian Ocean SSTs and the Eurasian soil moisture) and because models are not yet able to simulate the stratospheric QBO realistically. This study confirms that El Niño has two direct effects: it reduces the precipitation over India and reduces the surface winds over the Arabian Sea. Due to the latter, the SST of the Arabian Sea can increase as there is less mixing and upwelling in the ocean. Here it is suggested that because of this increased SST there would be more precipitation over India, thus counteracting the expected decrease from the direct El Niño effect. Sensitivity experiments were carried out with the ECHAM3 model to substantiate this hypothesis. The results may be model-dependent and model deficiencies might influence sensitivities from boundary forcings adversely. Therefore observational data have been investigated as far as possible to seek independent confirmation of the findings obtained through the model simulations.

Assessing the influence of large-scale environmental conditions on rainfall structure of Atlantic tropical cyclones: An observational study

2020 ◽  
pp. 1-40
Author(s):  
Kim Dasol ◽  
Chang-Hoi Ho ◽  
Hiroyuki Murakami ◽  
Doo-Sun R. Park
Keyword(s):  
High Pressure ◽  
Wind Speed ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Tropical Cyclones ◽  
North Atlantic ◽  
Environmental Conditions ◽  
Large Scale ◽  
Environmental Flows ◽  
Sea Surface

AbstractUnderstanding the mechanisms related to the variations in the rainfall structure of tropical cyclones (TCs) is crucial in improving forecasting systems of TC rainfall and its impact. Using satellite precipitation and reanalysis data, we examined the influence of along-track large-scale environmental conditions on inner-core rainfall strength (RS) and total rainfall area (RA) for Atlantic TCs during the TC season (July to November) from 1998 to 2019. Factor analysis revealed three major factors associated with variations in RS and RA: large-scale low- and high-pressure systems (F1), environmental flows, sea surface temperature, and humidity (F2), and maximum wind speed of TCs (F3). Results from our study indicate that RS increases with an increase in the inherent primary circulation of TCs (i.e., F3), but is less affected by large-scale environmental conditions (i.e., F1 and F2), whereas RA is primarily influenced by large-scale low- and high-pressure systems (i.e., F1) over the entire North Atlantic and partially influenced by environmental flows, sea surface temperature, humidity, and maximum wind speed (i.e., F2 and F3). A multi-variable regression model based on the three factors accounted for the variations of RS and RA across the entire basin. In addition, regional distributions of mean RS and RA from the model significantly resembled those from observations. Therefore, our study suggests that large-scale environmental conditions over the North Atlantic are important predictors for TC rainfall forecasts, particularly regarding RA.

scholarly journals Analysis of Near-Cloud Changes in Atmospheric Aerosols Using Satellite Observations and Global Model Simulations

2021 ◽  
Vol 13 (6) ◽  
pp. 1151
Author(s):  
Tamás Várnai ◽  
Alexander Marshak
Keyword(s):  
Atmospheric Aerosols ◽  
Large Scale ◽  
Climate Models ◽  
Orthogonal Polarization ◽  
Atmospheric Models ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
The Difference ◽  
Modern Era

This paper examines cloud-related variations of atmospheric aerosols that occur in partly cloudy regions containing low-altitude clouds. The goal is to better understand aerosol behaviors and to help better represent the radiative effects of aerosols on climate. For this, the paper presents a statistical analysis of a multi-month global dataset that combines data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) satellite instruments with data from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) global reanalysis. Among other findings, the results reveal that near-cloud enhancements in lidar backscatter (closely related to aerosol optical depth) are larger (1) over land than ocean by 35%, (2) near optically thicker clouds by substantial amounts, (3) for sea salt than for other aerosol types, with the difference from dust reaching 50%. Finally, the study found that mean lidar backscatter is higher near clouds not because of large-scale variations in meteorological conditions, but because of local processes associated with individual clouds. The results help improve our understanding of aerosol-cloud-radiation interactions and our ability to represent them in climate models and other atmospheric models.

scholarly journals The Different Impact of Positive-Neutral and Negative-Neutral ENSO Regimes on Australian Tropical Cyclones

2013 ◽  
Vol 26 (20) ◽  
pp. 8008-8016 ◽  
Author(s):  
Savin S. Chand ◽  
Kevin J. Tory ◽  
John L. McBride ◽  
Matthew C. Wheeler ◽  
Richard A. Dare ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Vertical Motion ◽  
Relative Vorticity ◽  
La Niña ◽  
Sea Level Pressure ◽  
Australian Region ◽  
La Nina ◽  
Significant Difference ◽  
The Difference

Abstract The number of tropical cyclones (TCs) in the Australian region exhibits a large variation between different ENSO regimes. While the difference in TC numbers and spatial distribution of genesis locations between the canonical El Niño and La Niña regimes is well known, the authors demonstrate that a statistically significant difference in TC numbers also exists between the recently identified negative-neutral and positive-neutral regimes. Compared to the negative-neutral and La Niña regimes, significantly fewer TCs form in the Australian region during the positive-neutral regime, particularly in the eastern subregion. This difference is attributed to concomitant changes in various large-scale environmental conditions such as sea level pressure, relative vorticity, vertical motion, and sea surface temperature.

Assessing future hurricane risk in the Caribbean based on large-scale predictor fields

2020 ◽  
Author(s):  
Peter Pfleiderer ◽  
Carl-Friedrich Schleußner
Keyword(s):  
Tropical Cyclones ◽  
Large Scale ◽  
Risk Model ◽  
Sea Surface ◽  
Classification Model ◽  
Climate Projections ◽  
Global Circulation ◽  
Global Circulation Models ◽  
The Caribbean ◽  
Hurricane Risk

<p>Hurricanes are the most damaging natural disasters in the Caribbean and global warming is expected to increase their impacts. It is well understood that tropical cyclones (TC) will intensify as sea surface temperatures warm and that the amount of precipitation brought by these TCs is going to increase with the water holding capacity of the atmosphere. However, for an assessment of future hurricane risk in the Caribbean it also important to better understand whether and how the overall frequency of tropical cyclones might change.</p><p>Projecting future tropical cyclone activity remains challenging because of the weak representation of tropical cyclones in most global circulation models. Here we want to overcome this shortcoming by estimating hurricane risk indirectly based on favorable climatic conditions in the region. These large-scale predictor fields are easier to model and therefore allow for an improved assessment of future hurricane risk.</p><p>We define hurricane risk as the accumulated energy that TCs produce in proximity of Caribbean islands. Using novel statistical methods, we identify regions of sea surface temperature, wind speeds and sea level pressure with predictive power for the next weeks hurricane activity. Based on these predictors we construct a classification model to estimate the probability of having TCs in proximity of islands and their strength for the following week. The expected value of seasonal hurricane risk based on these weekly probabilities shows high skill in reproducing the observational record.</p><p>Applying the same hurricane risk model to climate projections from global circulation models allows us to estimate future hurricane risk without relying on the ability of climate models to adequately represent tropical.</p>

Relationship between total plasma homocysteine and the risk of aneurysms – a meta-analysis

VASA ◽  
2020 ◽  
pp. 1-6
Author(s):  
Hanji Zhang ◽  
Dexin Yin ◽  
Yue Zhao ◽  
Yezhou Li ◽  
Dejiang Yao ◽  
...  
Keyword(s):  
Large Scale ◽  
Meta Analysis ◽  
Single Species ◽  
Total Plasma ◽  
Control Groups ◽  
Randomized Controlled ◽  
Randomized Controlled Studies ◽  
The Difference ◽  
The Relationship ◽  
Healthy Participants

Summary: Our meta-analysis focused on the relationship between homocysteine (Hcy) level and the incidence of aneurysms and looked at the relationship between smoking, hypertension and aneurysms. A systematic literature search of Pubmed, Web of Science, and Embase databases (up to March 31, 2020) resulted in the identification of 19 studies, including 2,629 aneurysm patients and 6,497 healthy participants. Combined analysis of the included studies showed that number of smoking, hypertension and hyperhomocysteinemia (HHcy) in aneurysm patients was higher than that in the control groups, and the total plasma Hcy level in aneurysm patients was also higher. These findings suggest that smoking, hypertension and HHcy may be risk factors for the development and progression of aneurysms. Although the heterogeneity of meta-analysis was significant, it was found that the heterogeneity might come from the difference between race and disease species through subgroup analysis. Large-scale randomized controlled studies of single species and single disease species are needed in the future to supplement the accuracy of the results.

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