scholarly journals Effects of Asymmetric Latent Heating on Typhoon Movement Crossing Taiwan: The Case of Morakot (2009) with Extreme Rainfall

2012 ◽  
Vol 69 (11) ◽  
pp. 3172-3196 ◽  
Author(s):  
Chung-Chieh Wang ◽  
Hung-Chi Kuo ◽  
Yu-Han Chen ◽  
Hsiao-Ling Huang ◽  
Chao-Hsuan Chung ◽  
...  
Keyword(s):  
Extreme Rainfall ◽  
Slow Motion ◽  
Cloud Microphysics ◽  
Precipitation Pattern ◽  
Mesoscale Convection ◽  
Typhoon Morakot ◽  
Translation Speed ◽  
Steering Flow ◽  
Monsoon Flow ◽  
Moving Speed

Abstract Typhoon Morakot struck Taiwan during 6–9 August 2009, and it produced the highest rainfall (approaching 3000 mm) and caused the worst damage in the past 50 yr. Typhoon–monsoon flow interactions with mesoscale convection, the water vapor supply by the monsoon flow, and the slow moving speed of the storm are the main reasons for the record-breaking precipitation. Analysis of the typhoon track reveals that the steering flow, although indeed slow, still exceeded the typhoon moving speed by approximately 5 km h−1 (1 km h−1 = 0.28 m s−1) during the postlandfall period on 8 August, when the rainfall was the heaviest. The Cloud-Resolving Storm Simulator (CReSS) is used to study the dynamics of the slow storm motion toward the north-northwest upon leaving Taiwan. The control simulations with 3-km grid size compare favorably with the observations, including the track, slow speed, asymmetric precipitation pattern, mesoscale convection, and rainfall distribution over Taiwan. Sensitivity tests with reduced moisture content reveal that not only did the model rainfall decrease but also the typhoon translation speed increased. Specifically, the simulations consistently show a discernible impact on storm motion by as much as 50%, as the storms with full moisture move slower (~5 km h−1), while those with limited moisture (≤25%) move faster (~10 km h−1). Thus, in addition to a weak steering flow, the prolonged asymmetric precipitation in Typhoon Morakot also contributed to its very slow motion upon leaving Taiwan, and both lengthened the heavy-rainfall period and increased the total rainfall amount. The implications of a realistic representation of cloud microphysics from the standpoint of tropical cyclone track forecasts are also briefly discussed.

scholarly journals A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima

2015 ◽  
Vol 15 (6) ◽  
pp. 8479-8523
Author(s):  
C.-C. Wang ◽  
H.-C. Kuo ◽  
R. H. Johnson ◽  
C.-Y. Lee ◽  
S.-Y. Huang ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Extreme Rainfall ◽  
Vertical Wind ◽  
Cold Pool ◽  
Rear Side ◽  
Gradient Force ◽  
Typhoon Morakot ◽  
Low Level ◽  
Pressure Perturbations

Abstract. This paper investigates the formation and evolution of deep convection inside the east–west oriented rainbands associated with a low-level jet (LLJ) in Typhoon Morakot (2009). With typhoon center to the northwest of Taiwan, the westerly LLJ was resulted from the interaction of typhoon circulation with the southwest monsoon flow, which supplied the water vapor for the extreme rainfall (of ~1000 mm) over southwestern Taiwan. The Cloud-Resolving Storm Simulator with 1 km grid spacing was used to simulate the event, and it successfully reproduced the slow-moving rainbands, the embedded cells, and the dynamics of merger and back-building (BB) on 8 August as observed. Our model results suggest that the intense convection interacted strongly with the westerly LLJ that provided reversed vertical wind shear below and above the jet core. Inside mature cells, significant dynamical pressure perturbations (pd') are induced with positive (negative) pd' at the western (eastern) flank of the updraft near the surface and a reversed pattern aloft (>2 km). This configuration produced an upward directed pressure gradient force (PGF) to the rear side and favors new development to the west, which further leads to cell merger as the mature cells slowdown in eastward propagation. The strong updrafts also acted to elevate the jet and enhance the local vertical wind shear at the rear flank. Additional analysis reveals that the upward PGF there is resulted mainly by the shearing effect but also by the extension of upward acceleration at low levels. In the horizontal, the upstream-directed PGF induced by the rear-side positive pd' near the surface is much smaller, but can provide additional convergence for BB development upstream. Finally, the cold-pool mechanism for BB appears to be not important in the Morakot case, as the conditions for strong evaporation in downdrafts do not exist.

scholarly journals Landslide Susceptibility Based on Extreme Rainfall-Induced Landslide Inventories and the Following Landslide Evolution

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2609 ◽  
Author(s):  
Chunhung Wu
Keyword(s):  
Landslide Susceptibility ◽  
Extreme Rainfall ◽  
Susceptibility Map ◽  
Typhoon Morakot ◽  
Landslide Susceptibility Map ◽  
Related Factors ◽  
Extreme Rainfall Events ◽  
River Watershed ◽  
Correct Ratio ◽  
Landslide Evolution

Landslide susceptibility assessment is crucial for mitigating and preventing landslide disasters. Most landslide susceptibility studies have focused on creating landslide susceptibility models for specific rainfall or earthquake events, but landslide susceptibility in the years after specific events are also valuable for further discussion, especially after extreme rainfall events. This research provides a new method to draw an annual landslide susceptibility map in the 5 years after Typhoon Morakot (2009) in the Chishan River watershed in Taiwan. This research establishes four landslide susceptibility models by using four methods and 12 landslide-related factors and selects the model with the optimum performance. This research analyzes landslide evolution in the 5 years after Typhoon Morakot and estimates the average landslide area different ratio (LAD) in upstream, midstream, and downstream of the Chishan River watershed. We combine landslide susceptibility with the model with the highest performance and average annual LAD to draw an annual landslide susceptibility map, and its mean correct ratio ranges from 62.5% to 73.8%.

Characterizing precipitation in convective cloud regimes in the trades with the polarimetric C-band radar POLDIRAD

2020 ◽  
Author(s):  
Martin Hagen ◽  
Florian Ewald ◽  
Silke Groß ◽  
Qiang Li ◽  
Lothar Oswald ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
High Resolution ◽  
Temporal Evolution ◽  
Convective Cloud ◽  
Weather Radar ◽  
Cloud Microphysics ◽  
Radiation Budget ◽  
Precipitation Pattern ◽  
Aircraft Measurements ◽  
The Earth

<p>Low-level clouds in the trade regions play an important role in the Earth’s climate system since they have a considerable influence on the Earth’s radiation budget. However, the understanding of the coupling between cloud dynamics, cloud microphysics, and mesoscale organization is limited. This results in a large uncertainty in current climate predictions. Despite the importance, observations in these regions are limited. Geostationary satellites cannot provide high resolution three-dimensional details of clouds and precipitation. Polar orbiting satellites like the A-Train satellites Cloudsat and Calipso or the upcoming EarthCARE satellite do provide detailed profiles of cloud properties, but the temporal evolution cannot be observed. On the other hand, long range weather radar observations can provide both, high spatial and temporal observations, however not many weather radar do cover the trades.</p><p>During the Eurec4a campaign DLRs C-band polarimetric weather radar POLDIRAD was installed on the island of Barbados. The scope of the radar measurements is manifold:</p><p>- POLDIRAD will provide high resolution observations of the different mesoscale cloud patterns as observed from satellites: Flowers, Gravel, Fish, and Sugar. Will the mesoscale organization have an influence on observable microphysical properties?</p><p>- POLDIRAD will put the detailed measurements by aircraft (in situ and remote sensing) into a greater context. How are the aircraft measurements related to the spatial distribution of the precipitation pattern? How are the aircraft measurements related to the temporal evolution of the precipitation pattern?</p><p>- POLDIRAD will put the observed profiles of clouds and precipitation at the Barbados Cloud Observatory BCO at Deebles Point into a greater context. How are the profile measurements related to the spatial distribution of the precipitation pattern? How are the profile measurements related to the temporal evolution of the precipitation pattern?</p>

scholarly journals The Influence of Island Topography on Typhoon Track Deflection

2011 ◽  
Vol 139 (6) ◽  
pp. 1708-1727 ◽  
Author(s):  
Yi-Hsuan Huang ◽  
Chun-Chieh Wu ◽  
Yuqing Wang
Keyword(s):  
High Resolution ◽  
Inner Core ◽  
Realistic Model ◽  
Cloud Microphysics ◽  
The North ◽  
Steering Flow ◽  
Typhoon Track ◽  
Physics Model ◽  
Channeling Effect ◽  
Prediction And Simulation

Abstract High-resolution simulations for Typhoon Krosa (2007) and a set of idealized experiments are conducted using a full-physics model to investigate the eminent deflection of typhoon track prior to its landfall over mountainous island topography. The terrain height of Taiwan plays the most important role in Typhoon Krosa’s looping motion at its landfall, while the surface properties, details in the topographic shape of Taiwan, and the cloud microphysics are shown to be secondary to the track deflection. A simulation with 3-km resolution and realistic model settings reproduces the observed Krosa’s track, while that with 9-km resolution fails, suggesting that high resolution to better resolve the typhoon–terrain interactions is important for the prediction and simulation of typhoon track deflection prior to landfall. Results from idealized experiments with model configurations mimicking those of Supertyphoon Krosa show that vortices approaching the northern and central topography are significantly deflected to the south before making sharp turns to the north, forming a kinked track pattern prior to and during landfall. This storm movement is consistent with the observed looping cases in Taiwan. Both real-case and idealized simulations show strong channel winds enhanced between the storm and the terrain when deflection occurs. Backward trajectory analyses support the concept of the channeling effect, which has been previously found to be crucial to the looping motion of Typhoon Haitang (2005) as well. However, the inner-core asymmetric ventilation flow does not match the movement of a deflected typhoon perfectly, partly because the steering flow is not well defined and could not completely capture the terrain-induced deflection in the simulation and in nature.

scholarly journals A numerical study of convection in rainbands of Typhoon Morakot (2009) with extreme rainfall: roles of pressure perturbations with low-level wind maxima

2015 ◽  
Vol 15 (19) ◽  
pp. 11097-11115 ◽  
Author(s):  
C.-C. Wang ◽  
H.-C. Kuo ◽  
R. H. Johnson ◽  
C.-Y. Lee ◽  
S.-Y. Huang ◽  
...  
Keyword(s):  
Wind Shear ◽  
Vertical Wind Shear ◽  
Extreme Rainfall ◽  
Vertical Wind ◽  
Cold Pool ◽  
Rear Side ◽  
Gradient Force ◽  
Typhoon Morakot ◽  
Low Level ◽  
Pressure Perturbations

Abstract. This paper investigates the formation and evolution of deep convection inside the east–west oriented rainbands associated with a low-level jet (LLJ) in Typhoon Morakot (2009). With the typhoon center to the northwest of Taiwan, the westerly LLJ occurred as a result from the interaction of typhoon circulation with the southwest monsoon flow, which supplied the water vapor for the extreme rainfall (of ~ 1000 mm) over southwestern Taiwan. The Cloud-Resolving Storm Simulator with 1 km grid spacing was used to simulate the event, and it successfully reproduced the slow-moving rainbands, the embedded cells, and the dynamics of merger and back-building (BB) on 8 August as observed. Our model results suggest that the intense convection interacted strongly with the westerly LLJ that provided reversed vertical wind shear below and above the jet core. Inside mature cells, significant dynamical pressure perturbations (p'd) are induced with positive (negative) p'd at the western (eastern) flank of the updraft near the surface and a reversed pattern aloft (> 2 km). This configuration produced an upward-directed pressure gradient force (PGF) to the rear side and favors new development to the west, which further leads to cell merging as the mature cells slowdown in eastward propagation. The strong updrafts also acted to elevate the jet and enhance the local vertical wind shear at the rear flank. Additional analysis reveals that the upward PGF there is resulted mainly by the shearing effect but also by the extension of upward acceleration at low levels. In the horizontal, the upstream-directed PGF induced by the rear-side positive p'd near the surface is much smaller, but can provide additional convergence for BB development upstream. Finally, the cold-pool mechanism for BB appears to be not important in the Morakot case, as the conditions for strong evaporation in downdrafts do not exist.

scholarly journals Improving the extreme rainfall forecast of Typhoon Morakot (2009) by assimilating radar data from Taiwan Island and mainland China

2017 ◽  
Vol 31 (4) ◽  
pp. 747-766 ◽  
Author(s):  
Xuwei Bao ◽  
Dan Wu ◽  
Xiaotu Lei ◽  
Leiming Ma ◽  
Dongliang Wang ◽  
...  
Keyword(s):  
Mainland China ◽  
Extreme Rainfall ◽  
Radar Data ◽  
Typhoon Morakot ◽  
Rainfall Forecast ◽  
Taiwan Island

Drawing the landslide susceptibility maps based on long term evolution of extreme rainfall-induced landslide

2020 ◽  
Author(s):  
Chunhung Wu
Keyword(s):  
Landslide Susceptibility ◽  
Extreme Rainfall ◽  
Landslide Inventory ◽  
Landslide Area ◽  
Typhoon Morakot ◽  
Extreme Rainfall Events ◽  
Susceptibility Maps ◽  
Susceptibility Model ◽  
Landslide Ratio ◽  
Landslide Susceptibility Maps

<p>This research is concerned with the prediction accuracy and applicability of statistical landslide susceptibility model to the areas with dense landslide distribution caused by extreme rainfall events and how to draw the annual landslide susceptibility maps after the extreme rainfall events. The landslide induced by 2009 Typhoon Morakot, i.e. an extreme rainfall event, in the Chishan river watershed is dense distributed. We compare the annual landslide inventories in the following 5 years after 2009 Typhoon Morakot and finds the similarity of landslide distribution.</p><p>The landslide distributions from 2008 to 2014 are concentrated in the midstream and upstream watersheds. The landslide counts and area in 2009 are 3.4 times and 7.4 times larger than those in 2008 due to 2009 Typhoon Morakot. The landslide counts and area in 2014 are only 69.8% and 53.4 % of those in 2009. The landslide area from 2010 to 2014 shows that the landslide area in the following years after 2009 Typhoon Morakot gradually decreases if without any heavy rainfall event with more accumulated rainfall than that during 2009 Typhoon Morakot.</p><p>The landslide ratio in the upstream watershed in 2008 is 1.37%, and that from 2009 to 2014 are over 3.51%. The landslide ratio in the upstream watershed in 2014 is 1.17 times larger than that in 2009. On average, the landslide inventory from 2010 to 2014 in the upstream watershed is composed of 60.1 % old landslide originated from 2009 Typhoon Morakot and 39.9 % new landslide.</p><p>The landslide ratio in the midstream watershed reaches peak (9.19%) in 2009 and decreases gradually to 2.56 % in 2014. The landslide ratio in 2014 in the midstream watershed is only 27.9% of that in 2009, and that means around 72.1 % of landslide area in 2009 in the midstream watershed has recovered. On average, the landslide inventory from 2010 to 2014 in the midstream watershed is composed of 76.1 % old landslide originated from 2009 Typhoon Morakot and 23.9 % new landslide.</p><p>The research uses the landslide area in 2009 and 2014 in the same subareas to calculate the expanding or contracting ratio of landslide area. The contracting ratio of riverbank and non-riverbank landslide area in the midstream watershed are 0.760 and 0.788, while that in the downstream watershed are 0.732 and 0.789. The expanding ratio of riverbank and non-riverbank landslide area in the upstream watershed are 1.04 and 1.02.</p><p>The annual landslide susceptibility in each subarea in the Chishan river watershed in a specific year from 2010 to 2014 is the production of landslide susceptibility in 2009 and the contraction or expanding ratio to the Nth power, and the N number is how many years between 2009 and the specific year. We adopt the above-mentioned equation and the landslide susceptibility model based on the landslide inventory after 2009 Typhoon Morakot to draw the annual landslide susceptibility maps in 2010 to 2014. The mean correct ratio value of landslide susceptibility model in 2009 is 70.9%, and that from 2010 to 2014 are 62.5% to 73.8%.</p>

scholarly journals A Numerical Study of the Track Deflection of Supertyphoon Haitang (2005) Prior to Its Landfall in Taiwan

2008 ◽  
Vol 136 (2) ◽  
pp. 598-615 ◽  
Author(s):  
Guo-Ji Jian ◽  
Chun-Chieh Wu
Keyword(s):  
Control Experiment ◽  
Inner Core ◽  
Numerical Study ◽  
Sensitivity Study ◽  
Weather Research And Forecasting ◽  
Translation Speed ◽  
Fine Mesh ◽  
Steering Flow ◽  
Moving Storm ◽  
Channeling Effect

Abstract A series of numerical simulations are conducted using the advanced research version of the Weather Research and Forecasting model with a 4-km fine mesh to examine the physical processes responsible for the significant track deflection and looping motion before the landfall of Supertyphoon Haitang (2005) in Taiwan, which poses a unique scientific and forecasting issue. In the control experiment, a low-level northerly jet induced by the channeling effect forms in the western quadrant of the approaching storm, where the inner-core circulation is constrained by the presence of Taiwan’s terrain. Because of the channeling effect, the strongest winds of the storm are shifted to the western portion of the eyewall. The northerly advection flow (averaged asymmetric winds within 100-km radius) results in a sharp southward turn of the westward-moving storm. The time series of the advection flow shows that the advection wind vectors rotate cyclonically in time and well match the motion of the simulated vortex during the looping process. A sensitivity study of lowering the Taiwan terrain elevations to 70% or 40% of those in the control experiment reduces the southward track deflection and loop amplitude. The experiment with the reduced elevation to 10% of the control experiment does not show a looping track and thus demonstrates the key role of the terrain-induced channeling effect. Experiments applying different values of the structure parameter α illustrate that increasing the strength, size, and translation speed of the initial storm results in a smaller interaction with Taiwan’s terrain and a smaller average steering flow caused by the asymmetric circulation, which leads to a proportionally smaller southward track deflection without making a loop.

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