Outer Tropical Cyclone Rainbands Associated with Typhoon Matmo (2014)

2020 ◽  
Vol 148 (7) ◽  
pp. 2935-2952
Author(s):  
Cheng-Ku Yu ◽  
Lin-Wen Cheng ◽  
Chun-Chieh Wu ◽  
Chia-Lun Tsai
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Leading Edge ◽  
Heavy Rain ◽  
Squall Line ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Commercial Aircraft ◽  
Near Surface ◽  
Stormy Weather

Abstract On 23 July 2014, a commercial aircraft (GE222) crashed near the Ma-Gong Airport on Penghu Island off the southwestern coast of Taiwan as it struggled to land in the stormy weather that was caused by the outer tropical cyclone rainbands (OTCRs) of Typhoon Matmo. This study aims to document the detailed aspects of airflow and precipitation of OTCRs through high-resolution radar and surface observations and to identify how these observed structures contribute to aviation weather hazards. Analyses indicate that the weather at the airport was significantly influenced by the passage of three OTCRs (R1, R2, and R3), and these rainbands share common characteristics of squall-line-like airflow and precipitation structures. As GE222 descended to approach the runway and flew immediately behind and roughly parallel to the leading edge of R3, the aircraft encountered the heaviest precipitation of the rainband and the prominent crosswind that was a manifestation of the rear-to-front flow generated locally by the rainband. The heavy rain–induced poor visibility and the occurrence of strong crosswinds were primary weather hazards affecting this flight event. Momentum budget analyses suggest that the frontward pressure gradient force provided by the near-surface, convectively generated mesohigh played a major role in driving the low-level rear-to-front flow inside the band. The results from the present study imply that closely monitoring convective activities in the outer regions of tropical cyclones and their potential transformation into squall-line-like storms is crucial to complement the routine aviation alert of severe weather under the influence of tropical cyclones.

scholarly journals A numerical study of back-building process in a quasistationary rainband with extreme rainfall over northern Taiwan during 11–12 June 2012

2016 ◽  
Vol 16 (18) ◽  
pp. 12359-12382 ◽  
Author(s):  
Chung-Chieh Wang ◽  
Bing-Kui Chiou ◽  
George Tai-Jen Chen ◽  
Hung-Chi Kuo ◽  
Ching-Hwang Liu
Keyword(s):  
Numerical Study ◽  
Leading Edge ◽  
Extreme Rainfall ◽  
Cold Pool ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Northern Taiwan

Abstract. During 11–12 June 2012, quasistationary linear mesoscale convective systems (MCSs) developed near northern Taiwan and produced extreme rainfall up to 510 mm and severe flooding in Taipei. In the midst of background forcing of low-level convergence, the back-building (BB) process in these MCSs contributed to the extreme rainfall and thus is investigated using a cloud-resolving model in the case study here. Specifically, as the cold pool mechanism is not responsible for the triggering of new BB cells in this subtropical event during the meiyu season, we seek answers to the question why the location about 15–30 km upstream from the old cell is still often more favorable for new cell initiation than other places in the MCS. With a horizontal grid size of 1.5 km, the linear MCS and the BB process in this case are successfully reproduced, and the latter is found to be influenced more by the thermodynamic and less by dynamic effects based on a detailed analysis of convective-scale pressure perturbations. During initiation in a background with convective instability and near-surface convergence, new cells are associated with positive (negative) buoyancy below (above) due to latent heating (adiabatic cooling), which represents a gradual destabilization. At the beginning, the new development is close to the old convection, which provides stronger warming below and additional cooling at mid-levels from evaporation of condensates in the downdraft at the rear flank, thus yielding a more rapid destabilization. This enhanced upward decrease in buoyancy at low levels eventually creates an upward perturbation pressure gradient force to drive further development along with the positive buoyancy itself. After the new cell has gained sufficient strength, the old cell's rear-flank downdraft also acts to separate the new cell to about 20 km upstream. Therefore, the advantages of the location in the BB process can be explained even without the lifting at the leading edge of the cold outflow.

scholarly journals On the fine vertical structure of the low troposphere over the coastal margins of East Antarctica

2019 ◽  
Author(s):  
Étienne Vignon ◽  
Olivier Traullé ◽  
Alexis Berne
Keyword(s):  
Pressure Gradient ◽  
Vertical Structure ◽  
East Antarctica ◽  
Radiosonde Data ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Ice Shelves ◽  
Low Level ◽  
Humidity Profiles

Abstract. Eight years of high-resolution radiosonde data at nine Antarctic stations are analysed to provide the first large scale characterization of the fine scale vertical structure of the low troposphere up to 3 km of altitude over the coastal margins of East Antarctica. Radiosonde data show a large spatial variability of wind, temperature and humidity profiles, with different features between stations in katabatic regions (e.g., Dumont d'Urville and Mawson stations), stations over two ice shelves (Neumayer and Halley stations) and regions with complex orography (e.g., Mc Murdo). At Dumont d'Urville, Mawson and Davis stations, the yearly median wind speed profiles exhibit a clear low-level katabatic jet. During precipitation events, the low-level flow generally remains of continental origin and its speed is even reinforced due to the increase in the continent- ocean pressure gradient. Meanwhile, the relative humidity profiles show a dry low troposphere, suggesting the occurence of low-level sublimation of precipitation in katabatic regions but such a phenomenon does not appreciably occur over the ice-shelves near Halley and Neumayer. Although ERA-Interim and ERA5 reanalyses assimilate radiosoundings at most stations considered here, substantial – and sometimes large – low-level wind and humidity biases are revealed but ERA5 shows overall better performances. A free simulation with the regional model Polar WRF (at a 35-km resolution) over the entire continent shows too strong and too shallow near-surface jets in katabatic regions especially in winter. This may be a consequence of an understimated coastal cold air bump and associated sea-continent pressure gradient force due to the coarse 35 km resolution of the Polar WRF simulation. Beyond documenting the vertical structure of the low troposphere over coastal East-Antarctica, this study gives insights into the reliability and accuracy of two major reanalysis products in this region on the Earth and it raises the difficulty of modeling the low-level flow over the margins of the ice sheet with a state-of-the-art climate model.

scholarly journals Large Sensitivity of Near-Surface Vertical Vorticity Development to Heat Sink Location in Idealized Simulations of Supercell-Like Storms

2017 ◽  
Vol 74 (4) ◽  
pp. 1095-1104 ◽  
Author(s):  
Paul M. Markowski ◽  
Yvette P. Richardson
Keyword(s):  
Heat Sink ◽  
Vertical Axis ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Vertical Vorticity ◽  
Supercell Storm ◽  
History Of ◽  
Perturbation Pressure ◽  
Negative Buoyancy

Abstract In idealized numerical simulations of supercell-like “pseudostorms” generated by a heat source and sink in a vertically sheared environment, a tornado-like vortex develops if air possessing large circulation about a vertical axis at the lowest model levels can be converged. This is most likely to happen if the circulation-rich air possesses only weak negative buoyancy (the circulation-rich air has a history of descent, so typically possesses at least some negative buoyancy) and is subjected to an upward-directed vertical perturbation pressure gradient force. This paper further explores the sensitivity of the development of near-surface vertical vorticity to the horizontal position of the heat sink. Shifting the position of the heat sink by only 2–3 km can significantly influence vortex intensity by altering both the baroclinic generation of circulation and the buoyancy of circulation-rich air. Many of the changes in the pseudostorms that arise from shifting the position of the heat sink would be difficult to anticipate. The sensitivity of the pseudostorms to heat sink position probably at least partly explains the well-known sensitivity of near-surface vertical vorticity development to the microphysics parameterizations in more realistic supercell storm simulations, as well as some of the failures of actual supercells to produce tornadoes in seemingly favorable environments.

Numerical Study on the Extremely Rapid Intensification of an Intense Tropical Cyclone: Typhoon Ida (1958)

2015 ◽  
Vol 72 (11) ◽  
pp. 4194-4217 ◽  
Author(s):  
Sachie Kanada ◽  
Akiyoshi Wada
Keyword(s):  
Tropical Cyclone ◽  
Inner Core ◽  
Numerical Study ◽  
Vertical Wind Shear ◽  
Leading Edge ◽  
Central Pressure ◽  
Rapid Intensification ◽  
Near Surface ◽  
Warm Core ◽  
Upper Level

Abstract Extremely rapid intensification (ERI) of Typhoon Ida (1958) was examined with a 2-km-mesh nonhydrostatic model initiated at three different times. Ida was an extremely intense tropical cyclone with a minimum central pressure of 877 hPa. The maximum central pressure drop in 24 h exceeded 90 hPa. ERI was successfully simulated in two of the three experiments. A factor crucial to simulating ERI was a combination of shallow-to-moderate convection and tall, upright convective bursts (CBs). Under a strong environmental vertical wind shear (>10 m s−1), shallow-to-moderate convection on the downshear side that occurred around the intense near-surface inflow moistened the inner-core area. Meanwhile, dry subsiding flows on the upshear side helped intensification of midlevel (8 km) inertial stability. First, a midlevel warm core appeared below 10 km in the shallow-to-moderate convection areas, being followed by the development of the upper-level warm core associated with tall convection. When tall, upright, rotating CBs formed from the leading edge of the intense near-surface inflow, ERI was triggered at the area in which the air became warm and humid. CBs penetrated into the upper troposphere, aligning the areas with high vertical vorticity at low to midlevels. The upper-level warm core developed rapidly in combination with the midlevel warm core. Under the preconditioned environment, the formation of the upright CBs inside the radius of maximum wind speeds led to an upright axis of the secondary circulation within high inertial stability, resulting in a very rapid central pressure deepening.

scholarly journals Origin of Strong Winds in an Explosive Mediterranean Extratropical Cyclone

2019 ◽  
Vol 147 (10) ◽  
pp. 3649-3671 ◽  
Author(s):  
Mihaela Brâncuş ◽  
David M. Schultz ◽  
Bogdan Antonescu ◽  
Christopher Dearden ◽  
Sabina Ştefan
Keyword(s):  
Boundary Layer ◽  
Conveyor Belt ◽  
Heat Fluxes ◽  
The Black Sea ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Strong Wind ◽  
Near Surface ◽  
Cyclone Center ◽  
Strong Winds

Abstract During 2–3 December 2012, the Black Sea and east coast of Romania were affected by a rapidly deepening Mediterranean cyclone. The cyclone developed a bent-back front along which short-lived (2–4 h) strong winds up to 38 m s−1 were recorded equatorward of the cyclone center. A mesoscale model simulation was used to analyze the evolution of the wind field, to investigate the physical processes that were responsible for the strong winds and their acceleration, and to investigate the relative importance of the stability of the boundary layer to those strong winds. The origin of the air in the wind maximum equatorward of the cyclone center was twofold. The first was associated with a sting jet, a descending airstream from the midlevels of the cloud head and the lower part of the cyclonic branch of the warm conveyor belt. The sting jet started to descend west of the cyclone center, ending at the frontolytic tip of the bent-back front. The second was a low-level airstream associated with the cold conveyor belt that originated northeast of the cyclone center and traveled below 900 hPa along the cold side of the bent-back front, ending behind the cold front. Both airstreams were accelerated by the along-flow pressure gradient force, with the largest accelerations acting on the sting-jet air before entering into the near-surface strong-wind area. The sensible heat fluxes destabilized the boundary layer to near-neutral conditions south of the cyclone center, facilitating downward mixing and allowing the descending air to reach the surface. Mesoscale instabilities appeared to be unimportant in the sting-jet formation.

Nocturnal Destabilization Associated with the Summertime Great Plains Low-Level Jet

2020 ◽  
Vol 148 (11) ◽  
pp. 4641-4656
Author(s):  
Thomas R. Parish ◽  
Richard D. Clark ◽  
Todd D. Sikora
Keyword(s):  
Great Plains ◽  
The United States ◽  
Temperature Gradients ◽  
Gradient Force ◽  
Wind Component ◽  
Pressure Gradient Force ◽  
Near Surface ◽  
Low Level ◽  
Temperature Advection ◽  
Low Level Jet

AbstractThe Great Plains low-level jet (LLJ) has long been associated with summertime nocturnal convection over the central Great Plains of the United States. Destabilization effects of the LLJ are examined using composite fields assembled from the North American Mesoscale Forecast System for June and July 2008–12. Of critical importance are the large isobaric temperature gradients that become established throughout the lowest 3 km of the atmosphere in response to the seasonal heating of the sloping Great Plains. Such temperature gradients provide thermal wind forcing throughout the lower atmosphere, resulting in the establishment of a background horizontal pressure gradient force at the level of the LLJ. The attendant background geostrophic wind is an essential ingredient for the development of a pronounced summertime LLJ. Inertial turning of the ageostrophic wind associated with LLJ provides a westerly wind component directed normal to the terrain-induced orientation of the isotherms. Hence, significant nocturnal low-level warm-air advection occurs, which promotes differential temperature advection within a vertical column of atmosphere between the level just above the LLJ and 500 hPa. Such differential temperature advection destabilizes the nighttime troposphere above the radiatively cooled near-surface layer on a recurring basis during warm weather months over much of the Great Plains and adjacent states to the east. This destabilization process reduces the convective inhibition of air parcels near the level of the LLJ and may be of significance in the development of elevated nocturnal convection. The 5 July 2015 case from the Plains Elevated Convection at Night field program is used to demonstrate this destabilization process.

scholarly journals Strong Down-Valley Low-Level Jets over the Atacama Desert: Observational Characterization

2013 ◽  
Vol 52 (12) ◽  
pp. 2735-2752 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
Mark J. Falvey ◽  
Marcelo Araya ◽  
Martin Jacques-Coper
Keyword(s):  
Surface Wind ◽  
Atacama Desert ◽  
Surface Friction ◽  
Gradient Force ◽  
Turbulence Structure ◽  
Pressure Gradient Force ◽  
Surface Cooling ◽  
Environmental Implications ◽  
Near Surface ◽  
Drainage Flows

AbstractThe near-surface wind and temperature regime at three points in the Atacama Desert of northern Chile is described using two years of multilevel measurements from 80-m towers located in an altitude range between 2100 and 2700 m MSL. The data reveal the frequent development of strong nocturnal drainage flows at all sites. Down-valley, nose-shaped wind speed profiles are observed, with maximum values occurring at heights between 20 and 60 m AGL. The flow intensity shows considerable interdaily variability and a seasonal modulation of maximum speeds, which in the cold season can attain hourly average values of more than 20 m s−1. Turbulent mixing appears to be important over the full tower layer, affecting the curvature of the nighttime temperature profile and possibly explaining the observed increase of surface temperatures in the down-valley direction. Nocturnal valley winds and temperatures are weakly controlled by upper-air conditions observed at the nearest aerological station. Estimates of terms in the momentum budget for the development and quasi-stationary phases of the down-valley flows suggest that the pressure gradient force due to the near-surface cooling along the sloping valley axes plays an important role in these drainage flows. A scale for the jet nose height of equilibrium turbulent down-slope jets is proposed that is based on surface friction velocity and surface inversion intensity. At one of the sites, this scale explains about 70% of the case-to-case observed variance of jet nose heights. Further modeling and observations are needed, however, to define better the dynamics, extent, and turbulence structure of this flow system, which has significant wind-energy, climatic, and environmental implications.

scholarly journals Multiple Regimes of Wind, Stratification, and Turbulence in the Stable Boundary Layer

2015 ◽  
Vol 72 (8) ◽  
pp. 3178-3198 ◽  
Author(s):  
Adam H. Monahan ◽  
Tim Rees ◽  
Yanping He ◽  
Norman McFarlane
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Cloud Cover ◽  
Large Scale ◽  
Potential Temperature ◽  
Surface Wind ◽  
Geostrophic Wind ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Near Surface

Abstract A long time series of temporally high-resolution wind and potential temperature data from the 213-m tower at Cabauw in the Netherlands demonstrates the existence of two distinct regimes of the stably stratified nocturnal boundary layer at this location. Hidden Markov model (HMM) analysis is used to objectively characterize these regimes and classify individual observed states. The first regime is characterized by strongly stable stratification, large wind speed differences between 10 and 200 m, and relatively weak turbulence. The second is associated with near-neutral stratification, weaker wind speed differences between 10 and 200 m, and relatively strong turbulence. In this second regime, the state of the boundary layer is similar to that during the day. The occupation statistics of these regimes are shown to covary with the large-scale pressure gradient force and cloud cover such that the first regime predominates under clear skies with weak geostrophic wind speed and the second regime predominates under conditions of extensive cloud cover or large geostrophic wind speed. These regimes are not distinguished by standard measures of stability, such as the Obukhov length or the bulk Richardson number. Evidence is presented that the mechanism generating these distinct regimes is associated with a previously documented feedback resulting from the existence of an upper limit on the maximum downward heat flux that can be sustained for a given near-surface wind speed.

scholarly journals Rapid dynamical evolution of ITCZ events over the east Pacific

2021 ◽  
pp. 1-48
Author(s):  
Marie C. McGraw ◽  
James G. Larson
Keyword(s):  
Coriolis Force ◽  
Dynamical Evolution ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Surface Dynamics ◽  
Near Surface ◽  
East Pacific ◽  
Dynamical Features ◽  
East Pacific Ocean ◽  
Meridional Advection

Abstract The latitudinal location of the east Pacific Ocean intertropical convergence zone (ITCZ) changes on time scales of days to weeks during boreal spring. This study focuses on tropical near-surface dynamics in the days leading up to the two most frequent types of ITCZ events, nITCZ (Northern Hemisphere) and dITCZ (double). There is a rapid, daily evolution of dynamical features on top of a slower, weekly evolution that occurs leading up to and after nITCZ and dITCZ events. Zonally-elongated bands of anomalous cross-equatorial flow and off-equatorial convergence rapidly intensify and peak one day before or the day of these ITCZ events, followed one or two days later by a peak in near-equatorial zonal wind anomalies. In addition, there is a wide region north of the southeast Pacific subtropical high where anomalous northwesterlies strengthen prior to nITCZ events and southeasterlies strengthen before dITCZ events. Anomalous zonal and meridional near-surface momentum budgets reveal that the terms associated with Ekman balance are of first-order importance preceding nITCZ events, but that the meridional momentum advective terms are just as important before dITCZ events. Variations in cross-equatorial flow are promoted by the meridional pressure gradient force (PGF) prior to nITCZ events and the meridional advection of meridional momentum in addition to the meridional PGF before dITCZ events. Meanwhile, variations in near-equatorial easterlies are driven by the zonal PGF and the Coriolis force preceding nITCZ events and the zonal PGF, the Coriolis force, and the meridional advection of zonal momentum before dITCZ events.

scholarly journals Important Factors for Tornadogenesis as Revealed by High-Resolution Ensemble Forecasts of the Tsukuba Supercell Tornado of 6 May 2012 in Japan

2018 ◽  
Vol 146 (4) ◽  
pp. 1109-1132 ◽  
Author(s):  
Sho Yokota ◽  
Hiroshi Niino ◽  
Hiromu Seko ◽  
Masaru Kunii ◽  
Hiroshi Yamauchi
Keyword(s):  
Ground Level ◽  
Gradient Force ◽  
Pressure Gradient Force ◽  
Atmospheric Conditions ◽  
Ensemble Forecasts ◽  
Near Surface ◽  
Large Water ◽  
Perturbation Pressure ◽  
The Relationship ◽  
The City

To identify important factors for supercell tornadogenesis, 33-member ensemble forecasts of the supercell tornado that struck the city of Tsukuba, Japan, on 6 May 2012 were conducted using a mesoscale numerical model with a 50-m horizontal grid. Based on the ensemble forecasts, the sources of the rotation of simulated tornadoes and the relationship between tornadogenesis and mesoscale environmental processes near the tornado were analyzed. Circulation analyses of near-surface, tornadolike vortices simulated in several ensemble members showed that the rotation of the tornadoes could be frictionally generated near the surface. However, the mechanisms responsible for generating circulation were only weakly related to the strength of the tornadoes. To identify the mesoscale processes required for tornadogenesis, mesoscale atmospheric conditions and their correlations with the strength of tornadoes were examined. The results showed that two near-tornado mesoscale factors were important for tornadogenesis: strong low-level mesocyclones (LMCs) at about 1 km above ground level and humid air near the surface. Strong LMCs and large water vapor near the surface strengthened the nonlinear dynamic vertical perturbation pressure gradient force and buoyancy, respectively. These upward forces made contributions essential for tornadogenesis via tilting and stretching of vorticity near the surface.

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