scholarly journals SIMULASI NUMERIK MEKANISME TURBULENSI DEKAT AWAN KONVEKTIF

2021 ◽  
Vol 22 (1) ◽  
pp. 25-33
Author(s):  
Ni Putu Tiana Verayanti ◽  
I Kadek Nova Arta Kusuma
Keyword(s):  
Kinetic Energy ◽  
Satellite Imagery ◽  
Wind Shear ◽  
Richardson Number ◽  
Vertical Wind Shear ◽  
Commercial Aircraft ◽  
Convective Clouds ◽  
Air Turbulence ◽  
North Sumatra ◽  
Cumulonimbus Cloud

Intisari Turbulensi yang dialami oleh pesawat komersial rute Jakarta-Medan telah dilaporkan mengalami Clear Air Turbulence (CAT) di atas Sumatera Utara pada tanggal 24 Oktober 2017. Namun berdasarkan data citra satelit Himawari dari Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) Indonesia menyebutkan bahwa di sekitar lokasi turbulensi terdapat awan kumulonimbus. Penelitian ini memanfaatkan model WRF-ARW dengan resolusi spasial dan temporal tinggi untuk mengetahui secara detail proses yang terjadi pada awan konvektif penyebab Near Cloud Turbulence (NCT). Turbulensi tersebut disebabkan oleh bilangan Richardson rendah yang terbentuk di wilayah udara jernih (clear air) yang berjarak 300-700 m di atas puncak awan dan diperkuat dengan adanya Turbulensi Energi Kinetik (TKE) mencapai 4,4 m2 / s2 dan geser angin vertikal (VWS) oleh arus keluar awan konvektif.  Abstract Turbulence encountered by commercial aircraft Jakarta-Medan routes has been reported that experienced Clear Air Turbulence (CAT) over North Sumatra on October 24th, 2017. However, based on Himawari satellite imagery data produced by Agency for Meteorology, Climatology, and Geophysics (BMKG), Indonesia stated that there was a cumulonimbus cloud around the turbulence location. This study utilizes WRF-ARW models with a high spatial and temporal resolution to find out in detail the processes that occur in convective clouds causing Near Cloud Turbulence (NCT). The turbulence was caused by a low Richardson number formed in the clear-air area, which has a distance of 300 - 700 m above the cloud top and reinforced by the existence of Turbulence Kinetic Energy (TKE) reaching 4,4 m2/s2 and vertical wind shear (VWS) by deep convection’s outflow.

scholarly journals Turbulence Adjustment and Scaling in an Offshore Convective Internal Boundary Layer: A CASPER Case Study

2020 ◽  
Vol 77 (5) ◽  
pp. 1661-1681
Author(s):  
Qingfang Jiang ◽  
Qing Wang ◽  
Shouping Wang ◽  
Saša Gaberšek
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Kinetic Energy ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Internal Boundary Layer ◽  
Turbulence Kinetic Energy ◽  
Internal Boundary ◽  
Field Observations ◽  
The Mean

Abstract The characteristics of a convective internal boundary layer (CIBL) documented offshore during the East Coast phase of the Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER-EAST) field campaign has been examined using field observations, a coupled mesoscale model (i.e., Navy’s COAMPS) simulation, and a couple of surface-layer-resolving large-eddy simulations (LESs). The Lagrangian modeling approach has been adopted with the LES domain being advected from a cool and rough land surface to a warmer and smoother sea surface by the mean offshore winds in the CIBL. The surface fluxes from the LES control run are in reasonable agreement with field observations, and the general CIBL characteristics are consistent with previous studies. According to the LESs, in the nearshore adjustment zone (i.e., fetch < 8 km), the low-level winds and surface friction velocity increase rapidly, and the mean wind profile and vertical velocity skewness in the surface layer deviate substantially from the Monin–Obukhov similarity theory (MOST) scaling. Farther offshore, the nondimensional vertical wind shear and scalar gradients and higher-order moments are consistent with the MOST scaling. An elevated turbulent layer is present immediately below the CIBL top, associated with the vertical wind shear across the CIBL top inversion. Episodic shear instability events occur with a time scale between 10 and 30 min, leading to the formation of elevated maxima in turbulence kinetic energy and momentum fluxes. During these events, the turbulence kinetic energy production exceeds the dissipation, suggesting that the CIBL remains in nonequilibrium.

Clear-Air Turbulence Near the Jet-Stream Maxima *

1955 ◽  
Vol 36 (2) ◽  
pp. 53-60 ◽  
Author(s):  
Leroy H. Clem
Keyword(s):  
Wind Speed ◽  
Physical Model ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Vertical Wind ◽  
Stability Conditions ◽  
Jet Stream ◽  
Air Turbulence ◽  
Helical Vortices ◽  
High Level

The development of turbo-jet aircraft has made high-level clear air turbulence a major problem for aviation interests. This paper emphasizes the association of the majority of this turbulence with the pronounced vertical wind shear in and near the maximum wind speed centers that move along the jet stream. A physical model is proposed as a possible explanation of clear air turbulence, the associated cirrus bands and wind streaks in the jet maxima. This model is supported by an analogy drawn with similar low-level phenomena studied by Woodcock and others. The model can explain distribution of these features in the horizontal by means of helical vortices which are dependent upon proper vertical wind shear and stability conditions. The observed multiple layers in the vertical are also explained by this model. It is believed that the reason why most of the clear-air turbulence is found near the jet-stream maxima is simply because the necessary shear and stability conditions associated with this turbulence are most frequently fulfilled in that region.

scholarly journals A Physical Basis for the Probabilistic Prediction of the Accumulated Tropical Cyclone Kinetic Energy in the Western North Pacific

2013 ◽  
Vol 26 (20) ◽  
pp. 7981-7991 ◽  
Author(s):  
Hye-Mi Kim ◽  
Myong-In Lee ◽  
Peter J. Webster ◽  
Dongmin Kim ◽  
Jin Ho Yoo
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
El Niño ◽  
North Pacific ◽  
Wind Shear ◽  
Western North Pacific ◽  
El Nino ◽  
Vertical Wind Shear ◽  
Tropical Storm ◽  
Probabilistic Prediction

Abstract The relationship between El Niño–Southern Oscillation (ENSO) and tropical storm (TS) activity over the western North Pacific Ocean is examined for the period from 1981 to 2010. In El Niño years, TS genesis locations are generally shifted to the southeast relative to normal years and the passages of TSs tend to recurve to the northeast. TSs of greater duration and more intensity during an El Niño summer induce an increase of the accumulated tropical cyclone kinetic energy (ACE). Based on the strong relationship between the TS properties and ENSO, a probabilistic prediction for seasonal ACE is investigated using a hybrid dynamical–statistical model. A statistical relationship is developed between the observed ACE and large-scale variables taken from the ECMWF seasonal forecast system 4 hindcasts. The ACE correlates positively with the SST anomaly over the central to eastern Pacific and negatively with the vertical wind shear near the date line. The vertical wind shear anomalies over the central and western Pacific are selected as predictors based on sensitivity tests of ACE predictive skill. The hybrid model performs quite well in forecasting seasonal ACE with a correlation coefficient between the observed and predicted ACE at 0.80 over the 30-yr period. A relative operating characteristic analysis also indicates that the ensembles have significant probabilistic skill for both the above-normal and below-normal categories. By comparing the ACE prediction over the period from 2003 to 2011, the hybrid model appears more skillful than the forecast from the Tropical Storm Risk consortium.

Recent Advances in the Understanding of Near-Cloud Turbulence

2012 ◽  
Vol 93 (4) ◽  
pp. 499-515 ◽  
Author(s):  
Todd P. Lane ◽  
Robert D. Sharman ◽  
Stanley B. Trier ◽  
Robert G. Fovell ◽  
John K. Williams
Keyword(s):  
Hazard Identification ◽  
Commercial Aircraft ◽  
Convective Clouds ◽  
Air Turbulence ◽  
Reporting Systems ◽  
Deep Convective Clouds ◽  
Airline Passengers ◽  
Research Questions ◽  
Upper Level ◽  
The Cost

Anyone who has flown in a commercial aircraft is familiar with turbulence. Unexpected encounters with turbulence pose a safety risk to airline passengers and crew, can occasionally damage aircraft, and indirectly increase the cost of air travel. Deep convective clouds are one of the most important sources of turbulence. Cloud-induced turbulence can occur both within clouds and in the surrounding clear air. Turbulence associated with but outside of clouds is of particular concern because it is more difficult to discern using standard hazard identification technologies (e.g., satellite and radar) and thus is often the source of unexpected turbulence encounters. Although operational guidelines for avoiding near-cloud turbulence exist, they are in many ways inadequate because they were developed before the governing dynamical processes were understood. Recently, there have been significant advances in the understanding of the dynamics of near-cloud turbulence. Using examples, this article demonstrates how these advances have stemmed from improved turbulence observing and reporting systems, the establishment of archives of turbulence encounters, detailed case studies, and high-resolution numerical simulations. Some of the important phenomena that have recently been identified as contributing to near-cloud turbulence include atmospheric wave breaking, unstable upper-level thunderstorm outflows, shearing instabilities, and cirrus cloud bands. The consequences of these phenomena for developing new en route turbulence avoidance guidelines and forecasting methods are discussed, along with outstanding research questions.

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