scholarly journals Environmental interactions during the extreme rain event associated with ex-tropical cyclone Oswald (2013)

2019 ◽  
Vol 69 (1) ◽  
pp. 216
Author(s):  
Marie-Dominique Leroux ◽  
Mai C. Nguyen-Hankinson ◽  
Noel E. Davidson ◽  
Jeffrey Callaghan ◽  
Kevin Tory ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Extreme Rainfall ◽  
Heavy Rain ◽  
Rain Event ◽  
North East ◽  
Structure Changes ◽  
Environmental Interactions ◽  
Outward Transport ◽  
Extreme Rain ◽  
Upper Level

Tropical cyclone (TC) Oswald made landfall over north-east Australia as a minimal or Category 1 TC on the Australian scale on 21 January 2013. As it moved southward, it intensified over land and produced extreme rainfall for nearly 7 days. Tornadoes were reported and confirmed. Tragically, seven people died and insurance estimates were ~$1 billion. It is demonstrated that the event was associated with an interaction between the ex-Oswald circulation and an amplifying Rossby wave, which propagated north-eastward from high latitudes. Diagnoses showed that as the wave amplified and broke, a potential vorticity (PV) anomaly (PVA) extended to mid-levels, moved equatorward, merged with or axisymmetrised the ex-Oswald circulation through mid-levels. Backward trajectories from locations regularly scattered within the mid-level circulation illustrated that the storm transitioned from an isolated vortex into a circulation which was strongly influenced by its environment for at least 5 days. During this interaction, PV was advected from the environment towards the storm through mid-levels. The heavy rain coincided with the commencement and maintenance of this PV injection. The PV injection is quantified and shown to be consistent with PV advection by the mean radial flow. In addition, eddy angular momentum convergence in the mid- to upper levels coincided with an intensification of the circulation through this region. This was first related to outward transport of anticyclonic momentum by the asymmetric outflow at upper levels, followed by inward transport of cyclonic momentum by the asymmetric inflow. It is shown that the environmental interaction had an impact on vortex structure changes, rainfall and tornado development. We propose that the environmental processes influenced the ascent within the storm (1) via differential vorticity advection and baroclinic forcing, as the mid- to upper level PVA approached the circulation and (2) by low- to mid-level warm air advection.

scholarly journals Potential Vorticity Perspective of Vortex Structure Changes of Tropical Cyclone Bilis (2006) during a Heavy Rain Event following Landfall

2017 ◽  
Vol 145 (5) ◽  
pp. 1875-1895 ◽  
Author(s):  
Difei Deng ◽  
Noel E. Davidson ◽  
Liang Hu ◽  
Kevin J. Tory ◽  
Mai C. N. Hankinson ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
Potential Vorticity ◽  
Lower Troposphere ◽  
Heavy Rain ◽  
Economic Loss ◽  
Rapid Decline ◽  
Rain Event ◽  
Structure Changes ◽  
Strong Gradient ◽  
Favorable Conditions

Abstract Tropical Cyclone (TC) Bilis made landfall on the China coast at 0500 UTC 14 July 2006. Following the landfall, sudden and unforecast torrential rain commenced some 400 km southwest of the weakening circulation center at around 1200 UTC 14 July 2006. At least 843 people were killed and the direct economic loss was estimated at up to $5 billion (U.S. dollars) in this event. Prior to the rain event, as the environmental fields evolved, the vertical vorticity weakened and deformation increased around Bilis’s circulation. It is illustrated that a strong gradient wind imbalance (GWI) through midlevels became established over the northwestern quadrant of Bilis, from which a large quantity of air with high potential vorticity (PV) was redistributed from the inner circulation to the outer radii. Both backward and forward Lagrangian trajectories show this redistribution as an outward bulge of midlevel PV toward the rainfall areas. The transport of midlevel PV from inner to outer radii provides a dynamical reason for the rapid decline in rainfall around Bilis’s center. It is also associated with large differential horizontal PV advection below 400 hPa over the rainfall area. Diagnostic analysis further demonstrates that the redistribution of high PV to over the rainfall areas is associated with a raising of the local isentropic surfaces and the formation of a cold dome in the mid- to lower troposphere. This is not only a direct lifting mechanism but also establishes favorable conditions for warm advection and ascent on the raised isentropic surfaces. These adiabatic ascent mechanisms are considered to have released conditional instability, resulting in broadscale convection and heavy rainfall.

Ensemble-Based Analysis of the May 2010 Extreme Rainfall in Tennessee and Kentucky

2014 ◽  
Vol 142 (1) ◽  
pp. 222-239 ◽  
Author(s):  
Samantha L. Lynch ◽  
Russ S. Schumacher
Keyword(s):  
Mississippi River ◽  
Flash Flood ◽  
Extreme Rainfall ◽  
Heavy Rain ◽  
Heavy Precipitation ◽  
Extreme Rainfall Event ◽  
Ensemble Forecasts ◽  
Surface Cyclone ◽  
Upper Level ◽  
Surrounding Areas

Abstract From 1 to 3 May 2010, persistent heavy rainfall occurred in the Ohio and Mississippi River valleys due to two successive quasi-stationary mesoscale convective systems (MCSs), with locations in central Tennessee accumulating more than 483 mm of rain, and the city of Nashville experiencing a historic flash flood. This study uses operational global ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) to diagnose atmospheric processes and assess forecast uncertainty in this event. Several ensemble analysis methods are used to examine the processes that led to the development and maintenance of this precipitation system. Differences between ensemble members that correctly predicted heavy precipitation and those that did not were determined, in order to pinpoint the processes that were favorable or detrimental to the system's development. Statistical analysis was used to determine how synoptic-scale flows were correlated to 5-day area-averaged precipitation. The precipitation throughout Nashville and the surrounding areas occurred ahead of an upper-level trough located over the central United States. The distribution of precipitation was found to be closely related to the strength of this trough and an associated surface cyclone. In particular, when the upper-level trough was elongated, the surface cyclone remained weaker with a narrower low-level jet from the south. This caused the plume of moisture from the Caribbean Sea to be concentrated over Tennessee and Kentucky, where, in conjunction with focused ascent, heavy rain fell. Relatively small differences in the wind and pressure fields led to important differences in the precipitation forecasts and highlighted some of the uncertainties associated with predicting this extreme rainfall event.

Influence of a Predecessor Rain Event on the Track of Tropical Cyclone Isaac (2012)

2015 ◽  
Vol 143 (9) ◽  
pp. 3354-3376 ◽  
Author(s):  
Thomas J. Galarneau
Keyword(s):  
Tropical Cyclone ◽  
Gulf Of Mexico ◽  
Precipitable Water ◽  
Track Forecast ◽  
Rain Event ◽  
Straits Of Florida ◽  
Eastern Gulf Of Mexico ◽  
Upper Level ◽  
Environmental Prediction ◽  
Tropical Moisture

Abstract Analysis of a predecessor rain event (PRE) over the Straits of Florida ahead of Tropical Cyclone (TC) Isaac on 25 August 2012 is presented. This PRE is unique compared to previously documented PREs in midlatitudes because it occurred over the oceanic subtropics and impacted the track of an approaching TC. The Isaac PRE developed in conjunction with a tropical moisture plume with precipitable water values over 60 mm that intersected a region of mid- and upper-level frontogenesis and warm air advection on the southeast flank of an upper-level trough. The PRE occurred in an environment with more abundant tropical moisture and weaker synoptic-scale forcing for ascent compared to the environments in which midlatitude PREs developed. The Isaac PRE contributed to the fracture of the upper-level trough through negative potential vorticity advection by convectively driven divergent outflow. Fracture of the upper-level trough and midlevel cyclonic vorticity amplification associated with the PRE acted to steer Isaac south of Florida into the Gulf of Mexico. Forecasts from the National Centers for Environmental Prediction–Global Forecast System (NCEP–GFS) initialized at 0000 UTC 21–24 August 2012 failed to predict the PRE and as a result recurved TC Isaac over Florida and the eastern Gulf of Mexico rather than continued Isaac on a northwest course toward southeast Louisiana. Vorticity inversion and detailed diagnosis of the NCEP–GFS TC track forecast initialized at 0000 UTC 22 August is also presented to assess the relationship between the PRE and TC Isaac’s track.

Orographic Influences on an Oahu Flood

2011 ◽  
Vol 139 (7) ◽  
pp. 2198-2217 ◽  
Author(s):  
Michael J. Murphy ◽  
Steven Businger
Keyword(s):  
Flash Flood ◽  
Wrf Model ◽  
Extreme Rainfall ◽  
Heavy Rain ◽  
Weather Research And Forecasting ◽  
Mountain Range ◽  
Rain Event ◽  
Freezing Level ◽  
High Concentrations ◽  
Convective Cells

Abstract On 2 April 2006, Oahu’s Ko‘olau Mountain Range endured more than 6 h of heavy rain with accompanying flash flooding along its northeast-facing slopes. The storm responsible for the event left a pattern of precipitation characteristic of orographic anchoring of convection with extreme rainfall gradients along the slopes and maxima along the crest of the mountain range. In fact, this was the third flash-flood event to impact the Ko‘olau Mountains in just over 1 month, with each event occurring under conditions of moist southeasterly flow at low levels and moderate conditional instability. Under these conditions persistent convection and localized heavy rainfall often occur over the Ko‘olau Mountain Range. Mesoscale analyses of the thunderstorm complex responsible for the 2 April 2006 heavy rain event and the results of a high-resolution numerical simulation employing the Weather Research and Forecasting (WRF) model are described in this study. Key features of the convection that contributed to the longevity of the event include repeat formation of convective cells along the eastern side of the central Ko‘olaus, minimal horizontal cloud motion, and strong updrafts that sloped toward the northwest in the lower levels. The westerly shear of the low-level flow determined the pattern of accumulated precipitation by aligning the slope of the convective updrafts nearly parallel to the southeast-to-northwest-orientated Ko‘olau Mountain Range. The microphysical structure of the convection was complex, with the vertical advection of hydrometeors originating below the freezing level facilitating high concentrations of ice particles and an environment conducive to charge separation and lightning.

Equatorial Waves Triggering Extreme Rainfall and Floods in Southwest Sulawesi, Indonesia

2021 ◽  
Vol 149 (5) ◽  
pp. 1381-1401
Author(s):  
Beata Latos ◽  
Thierry Lefort ◽  
Maria K. Flatau ◽  
Piotr J. Flatau ◽  
Donaldi S. Permana ◽  
...  
Keyword(s):  
Mesoscale Convective System ◽  
Extreme Rainfall ◽  
Convective System ◽  
Rain Event ◽  
Equatorial Waves ◽  
Kelvin Wave ◽  
Atmospheric Variability ◽  
Low Level ◽  
Mesoscale Convective ◽  
Extreme Rain

AbstractOn the basis of detailed analysis of a case study and long-term climatology, it is shown that equatorial waves and their interactions serve as precursors for extreme rain and flood events in the central Maritime Continent region of southwest Sulawesi, Indonesia. Meteorological conditions on 22 January 2019 leading to heavy rainfall and devastating flooding in this area are studied. It is shown that a convectively coupled Kelvin wave (CCKW) and a convectively coupled equatorial Rossby wave (CCERW) embedded within the larger-scale envelope of the Madden–Julian oscillation (MJO) enhanced convective phase, contributed to the onset of a mesoscale convective system that developed over the Java Sea. Low-level convergence from the CCKW forced mesoscale convective organization and orographic ascent of moist air over the slopes of southwest Sulawesi. Climatological analysis shows that 92% of December–February floods and 76% of extreme rain events in this region were immediately preceded by positive low-level westerly wind anomalies. It is estimated that both CCKWs and CCERWs propagating over Sulawesi double the chance of floods and extreme rain event development, while the probability of such hazardous events occurring during their combined activity is 8 times greater than on a random day. While the MJO is a key component shaping tropical atmospheric variability, it is shown that its usefulness as a single factor for extreme weather-driven hazard prediction is limited.

scholarly journals Recent Advances in Our Understanding of Tropical Cyclone Intensity Change Processes from Airborne Observations

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 650
Author(s):  
Robert F. Rogers
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Vertical Shear ◽  
Intensity Change ◽  
Change Processes ◽  
Cyclone Intensity ◽  
Secondary Eyewall Formation ◽  
Warm Core ◽  
Major Hurricane ◽  
Upper Level

Recent (past ~15 years) advances in our understanding of tropical cyclone (TC) intensity change processes using aircraft data are summarized here. The focus covers a variety of spatiotemporal scales, regions of the TC inner core, and stages of the TC lifecycle, from preformation to major hurricane status. Topics covered include (1) characterizing TC structure and its relationship to intensity change; (2) TC intensification in vertical shear; (3) planetary boundary layer (PBL) processes and air–sea interaction; (4) upper-level warm core structure and evolution; (5) genesis and development of weak TCs; and (6) secondary eyewall formation/eyewall replacement cycles (SEF/ERC). Gaps in our airborne observational capabilities are discussed, as are new observing technologies to address these gaps and future directions for airborne TC intensity change research.

scholarly journals Tropical cyclone contribution to extreme rainfall over southwest Pacific Island nations

2021 ◽  
Author(s):  
Anil Deo ◽  
Savin S. Chand ◽  
Hamish Ramsay ◽  
Neil J. Holbrook ◽  
Simon McGree ◽  
...  
Keyword(s):  
Tropical Cyclone ◽  
El Niño ◽  
El Nino ◽  
Extreme Rainfall ◽  
Pacific Island ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Southwest Pacific ◽  
Inactive Phase ◽  
Pacific Island Nations

AbstractSouthwest Pacific nations are among some of the worst impacted and most vulnerable globally in terms of tropical cyclone (TC)-induced flooding and accompanying risks. This study objectively quantifies the fractional contribution of TCs to extreme rainfall (hereafter, TC contributions) in the context of climate variability and change. We show that TC contributions to extreme rainfall are substantially enhanced during active phases of the Madden–Julian Oscillation and by El Niño conditions (particularly over the eastern southwest Pacific region); this enhancement is primarily attributed to increased TC activity during these event periods. There are also indications of increasing intensities of TC-induced extreme rainfall events over the past few decades. A key part of this work involves development of sophisticated Bayesian regression models for individual island nations in order to better understand the synergistic relationships between TC-induced extreme rainfall and combinations of various climatic drivers that modulate the relationship. Such models are found to be very useful for not only assessing probabilities of TC- and non-TC induced extreme rainfall events but also evaluating probabilities of extreme rainfall for cases with different underlying climatic conditions. For example, TC-induced extreme rainfall probability over Samoa can vary from ~ 95 to ~ 75% during a La Niña period, if it coincides with an active or inactive phase of the MJO, and can be reduced to ~ 30% during a combination of El Niño period and inactive phase of the MJO. Several other such cases have been assessed for different island nations, providing information that have potentially important implications for planning and preparing for TC risks in vulnerable Pacific Island nations.

scholarly journals Dynamical and Physical Processes Leading to Tropical Cyclone Intensification under Upper-Level Trough Forcing

2013 ◽  
Vol 70 (8) ◽  
pp. 2547-2565 ◽  
Author(s):  
Marie-Dominique Leroux ◽  
Matthieu Plu ◽  
David Barbary ◽  
Frank Roux ◽  
Philippe Arbogast
Keyword(s):  
Angular Momentum ◽  
Tropical Cyclone ◽  
Potential Vorticity ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Thick Layer ◽  
Limited Area ◽  
Southwest Indian Ocean ◽  
Upper Level

Abstract The rapid intensification of Tropical Cyclone (TC) Dora (2007, southwest Indian Ocean) under upper-level trough forcing is investigated. TC–trough interaction is simulated using a limited-area operational numerical weather prediction model. The interaction between the storm and the trough involves a coupled evolution of vertical wind shear and binary vortex interaction in the horizontal and vertical dimensions. The three-dimensional potential vorticity structure associated with the trough undergoes strong deformation as it approaches the storm. Potential vorticity (PV) is advected toward the tropical cyclone core over a thick layer from 200 to 500 hPa while the TC upper-level flow turns cyclonic from the continuous import of angular momentum. It is found that vortex intensification first occurs inside the eyewall and results from PV superposition in the thick aforementioned layer. The main pathway to further storm intensification is associated with secondary eyewall formation triggered by external forcing. Eddy angular momentum convergence and eddy PV fluxes are responsible for spinning up an outer eyewall over the entire troposphere, while spindown is observed within the primary eyewall. The 8-km-resolution model is able to reproduce the main features of the eyewall replacement cycle observed for TC Dora. The outer eyewall intensifies further through mean vertical advection under dynamically forced upward motion. The processes are illustrated and quantified using various diagnostics.

A localised heavy rain event in Hong Kong

Weather ◽  
1998 ◽  
Vol 53 (8) ◽  
pp. 259-262
Author(s):  
C. C. Fu ◽  
C. C. Chan
Keyword(s):  
Hong Kong ◽  
Heavy Rain ◽  
Rain Event ◽  
Heavy Rain Event
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