Search Results
You are looking at 1 - 4 of 4 items for :
- Author or Editor: Wen Chen x
- Bulletin of the American Meteorological Society x
- Refine by Access: All Content x
Abstract
Recent decades have witnessed growing frequency and severity of catastrophic droughts in many regions of the world. Despite lots of studies having been dedicated to extreme drought investigation, the fundamental question that has long been ignored is, What is extreme drought? The answer is much more complex than it first appears, because a critical issue in the study of drought is the multiscalar nature. To address the challenge, this study establishes the theoretical basis of the super drought concept, which refers to the simultaneous occurrence of extreme droughts at multiple time scales. The physical significance of super drought represents compound dry extremes in all parts of water resources or equivalently a grand loss in total water storage, which is identified as the essential determinant distinguishing high-impact droughts from those causing mild damage. To have a quantitative representation, a novel monitoring index called comprehensive multiscalar index (CMI) is developed based on the vine copula framework. It turns out that CMI is a plausible measure to determine the overall rarity of multiscalar drought and recognize super drought. Furthermore, the worldwide skill of CMI and super drought identification are testified against Gravity Recovery and Climate Experiment (GRACE) total water storage. Compared to traditional indices that lack comprehensive treatment of drought, CMI performs better in capturing the variation of overall water availability and enables the accurate detection of real water scarcity, with gross improvements in correlation and root-mean-square error scores exceeding the 10−3 significance level. To facilitate end users and policy-makers, near-real-time monitoring and a historical data repository are available through the public website superdrought.com.
Abstract
Recent decades have witnessed growing frequency and severity of catastrophic droughts in many regions of the world. Despite lots of studies having been dedicated to extreme drought investigation, the fundamental question that has long been ignored is, What is extreme drought? The answer is much more complex than it first appears, because a critical issue in the study of drought is the multiscalar nature. To address the challenge, this study establishes the theoretical basis of the super drought concept, which refers to the simultaneous occurrence of extreme droughts at multiple time scales. The physical significance of super drought represents compound dry extremes in all parts of water resources or equivalently a grand loss in total water storage, which is identified as the essential determinant distinguishing high-impact droughts from those causing mild damage. To have a quantitative representation, a novel monitoring index called comprehensive multiscalar index (CMI) is developed based on the vine copula framework. It turns out that CMI is a plausible measure to determine the overall rarity of multiscalar drought and recognize super drought. Furthermore, the worldwide skill of CMI and super drought identification are testified against Gravity Recovery and Climate Experiment (GRACE) total water storage. Compared to traditional indices that lack comprehensive treatment of drought, CMI performs better in capturing the variation of overall water availability and enables the accurate detection of real water scarcity, with gross improvements in correlation and root-mean-square error scores exceeding the 10−3 significance level. To facilitate end users and policy-makers, near-real-time monitoring and a historical data repository are available through the public website superdrought.com.
Abstract
On 4 October 2015, a miniature supercell embedded in an outer rainband of Typhoon Mujigae produced a major tornado in Guangdong province of China, leading to 4 deaths and up to 80 injuries. This study documents the structure and evolution of the tornadic miniature supercell using coastal Doppler radars, a sounding, videos, and a damage survey. This tornado is rated at least EF3 on the enhanced Fujita scale. It is by far the strongest typhoon rainband tornado yet documented in China, and possessed double funnels near its peak intensity.
Radar analysis indicates that this tornadic miniature supercell exhibited characteristics similar to those found in United States landfalling hurricanes, including a hook echo, low-level inf low notches, an echo top below 10 km, a small and shallow mesocyclone, and a long lifespan (3 h). The environmental conditions—which consisted of moderate convective available potential energy (CAPE), a low lifting condensation level, a small surface dewpoint depression, a large veering low-level vertical wind shear, and a large cell-relative helicity—are favorable for producing miniature supercells. The mesocyclone, with its maximum intensity at 2 km above ground level (AGL), formed an hour before tornadogenesis. A tornado vortex signature (TVS) was identified between 1 and 3 km AGL, when the parent mesocyclone reached its peak radar-indicated intensity of 30 m s−1. The TVS was located between the updraft and forward-flank downdraft, near the center of the mesocyclone. Dual-Doppler wind analysis reveals that tilting of the low-level vorticity into the vertical direction and subsequent stretching by a strong updraft were the main contributors to the mesocyclone intensification.
Abstract
On 4 October 2015, a miniature supercell embedded in an outer rainband of Typhoon Mujigae produced a major tornado in Guangdong province of China, leading to 4 deaths and up to 80 injuries. This study documents the structure and evolution of the tornadic miniature supercell using coastal Doppler radars, a sounding, videos, and a damage survey. This tornado is rated at least EF3 on the enhanced Fujita scale. It is by far the strongest typhoon rainband tornado yet documented in China, and possessed double funnels near its peak intensity.
Radar analysis indicates that this tornadic miniature supercell exhibited characteristics similar to those found in United States landfalling hurricanes, including a hook echo, low-level inf low notches, an echo top below 10 km, a small and shallow mesocyclone, and a long lifespan (3 h). The environmental conditions—which consisted of moderate convective available potential energy (CAPE), a low lifting condensation level, a small surface dewpoint depression, a large veering low-level vertical wind shear, and a large cell-relative helicity—are favorable for producing miniature supercells. The mesocyclone, with its maximum intensity at 2 km above ground level (AGL), formed an hour before tornadogenesis. A tornado vortex signature (TVS) was identified between 1 and 3 km AGL, when the parent mesocyclone reached its peak radar-indicated intensity of 30 m s−1. The TVS was located between the updraft and forward-flank downdraft, near the center of the mesocyclone. Dual-Doppler wind analysis reveals that tilting of the low-level vorticity into the vertical direction and subsequent stretching by a strong updraft were the main contributors to the mesocyclone intensification.
The Hurricane Rainband and Intensity Change Experiment (RAINEX) used three P3 aircraft aided by high-resolution numerical modeling and satellite communications to investigate the 2005 Hurricanes Katrina, Ophelia, and Rita. The aim was to increase the understanding of tropical cyclone intensity change by interactions between a tropical cyclone's inner core and rainbands. All three aircraft had dual-Doppler radars, with the Electra Doppler Radar (ELDORA) on board the Naval Research Laboratory's P3 aircraft, providing particularly detailed Doppler radar data. Numerical model forecasts helped plan the aircraft missions, and innovative communications and data transfer in real time allowed the flights to be coordinated from a ground-based operations center. The P3 aircraft released approximately 600 dropsondes in locations targeted for optimal coordination with the Doppler radar data, as guided by the operations center. The storms were observed in all stages of development, from tropical depression to category 5 hurricane. The data from RAINEX are readily available through an online Field Catalog and RAINEX Data Archive. The RAINEX dataset is illustrated in this article by a preliminary analysis of Hurricane Rita, which was documented by multiaircraft flights on five days 1) while a tropical storm, 2) while rapidly intensifying to a category 5 hurricane, 3) during an eye-wall replacement, 4) when the hurricane became asymmetric upon encountering environmental shear, and 5) just prior to landfall.
The Hurricane Rainband and Intensity Change Experiment (RAINEX) used three P3 aircraft aided by high-resolution numerical modeling and satellite communications to investigate the 2005 Hurricanes Katrina, Ophelia, and Rita. The aim was to increase the understanding of tropical cyclone intensity change by interactions between a tropical cyclone's inner core and rainbands. All three aircraft had dual-Doppler radars, with the Electra Doppler Radar (ELDORA) on board the Naval Research Laboratory's P3 aircraft, providing particularly detailed Doppler radar data. Numerical model forecasts helped plan the aircraft missions, and innovative communications and data transfer in real time allowed the flights to be coordinated from a ground-based operations center. The P3 aircraft released approximately 600 dropsondes in locations targeted for optimal coordination with the Doppler radar data, as guided by the operations center. The storms were observed in all stages of development, from tropical depression to category 5 hurricane. The data from RAINEX are readily available through an online Field Catalog and RAINEX Data Archive. The RAINEX dataset is illustrated in this article by a preliminary analysis of Hurricane Rita, which was documented by multiaircraft flights on five days 1) while a tropical storm, 2) while rapidly intensifying to a category 5 hurricane, 3) during an eye-wall replacement, 4) when the hurricane became asymmetric upon encountering environmental shear, and 5) just prior to landfall.
