Turbulence and Gravity Waves within an Upper-Level Front

Abstract High-resolution dropwindsonde and in-flight measurements collected by a research aircraft during the Severe Clear-Air Turbulence Colliding with Aircraft Traffic (SCATCAT) experiment and simulations from numerical models are analyzed for a clear-air turbulence event associated with an intense upper-level jet/frontal system. Spectral, wavelet, and structure function analyses performed with the 25-Hz in situ data are used to investigate the relationship between gravity waves and turbulence. Mesoscale dynamics are analyzed with the 20-km hydrostatic Rapid Update Cycle (RUC) model and a nested 1-km simulation with the nonhydrostatic Clark–Hall (CH) cloud-scale model. Turbulence occurred in association with a wide spectrum of upward propagating gravity waves above the jet core. Inertia–gravity waves were generated within a region of unbalanced frontogenesis in the vicinity of a complex tropopause fold. Turbulent kinetic energy fields forecast by the RUC and CH models displayed a strongly banded appearance associated with these mesoscale gravity waves (horizontal wavelengths of ∼120–216 km). Smaller-scale gravity wave packets (horizontal wavelengths of 1–20 km) within the mesoscale wave field perturbed the background wind shear and stability, promoting the development of bands of reduced Richardson number conducive to the generation of turbulence. The wavelet analysis revealed that brief episodes of high turbulent energy were closely associated with gravity wave occurrences. Structure function analysis provided evidence that turbulence was most strongly forced at a horizontal scale of 700 m. Fluctuations in ozone measured by the aircraft correlated highly with potential temperature fluctuations and the occurrence of turbulent patches at altitudes just above the jet core, but not at higher flight levels, even though the ozone fluctuations were much larger aloft. These results suggest the existence of remnant “fossil turbulence” from earlier events at higher levels, and that ozone cannot be used as a substitute for more direct measures of turbulence. The findings here do suggest that automated turbulence forecasting algorithms should include some reliable measure of gravity wave activity.

Download Full-text

IDENTIFIKASI GRAVITY WAVES MENGGUNAKAN HIGH PASS FILTER WATER VAPOR BAND SATELIT HIMAWARI DAN DATA MODEL NUMERIK

Jurnal Sains & Teknologi Modifikasi Cuaca ◽

10.29122/jstmc.v21i1.4143 ◽

2020 ◽

Vol 21 (1) ◽

pp. 37-41

Author(s):

I Kadek Nova Arta Kusuma ◽

Firman Setiabudi ◽

Eka Fibriantika ◽

Yunus Subagyo Swarinoto

Keyword(s):

Water Vapor ◽

Gravity Wave ◽

Gravity Waves ◽

Data Model ◽

Vertical Wind Shear ◽

Pass Filter ◽

High Pass Filter ◽

Air Turbulence ◽

Filter Water ◽

High Pass

Di Indonesia, pemanfaatan citra satelit dan model numerik menjadi acuan utama dalam kegiatan operasional cuaca penerbangan. Fenomena cuaca penerbangan yang masih sulit dideteksi adalah clear air turbulence (CAT). Salah satu penyebab terjadinya CAT adalah adanya gravity wave yang terbentuk di atmosfer. Pada paper ini akan ditunjukkan studi kasus fenomena gravity wave yang diidentifikasi menggunakan metode high pass filter pada water vapor band satelit Himawari dan dianalisis menggunakan model ECMWF 0.125 degree. Dari hasil penelitian diperoleh bahwa metode high pass filter dapat membantu mengenali fenomena gravity wave menjadi lebih mudah dalam bentuk paralel strips. Pada studi kasus ini, gravity wave terbentuk karena selisih angin yang besar pada lapisan 200 mb dan 250 mb sehingga membentuk vertical wind shear dan cloud billows yang terdeteksi pada Water Vapor Band dan memiliki pola tegak lurus terhadap angin.

Download Full-text

Seasonal and nightly variations of gravity-wave energy density in the middle atmosphere measured by the Purple Crow Lidar

Annales Geophysicae ◽

10.5194/angeo-25-2139-2007 ◽

2007 ◽

Vol 25 (10) ◽

pp. 2139-2145 ◽

Cited By ~ 7

Author(s):

R. J. Sica ◽

P. S. Argall

Keyword(s):

Energy Density ◽

Gravity Wave ◽

Gravity Waves ◽

Wave Energy ◽

Numerical Models ◽

Spatial Scales ◽

Density Fluctuations ◽

Kinetic Energy Density ◽

Large Power ◽

Wave Energy Density

Abstract. The Purple Crow Lidar (PCL) is a large power-aperture product monostatic Rayleigh-Raman-Sodium-resonance-fluorescence lidar, which has been in operation at the Delaware Observatory (42.9° N, 81.4° W, 237 m elevation) near the campus of The University of Western Ontario since 1992. Kinetic-energy density has been calculated from the Rayleigh-scatter system measurements of density fluctuations at temporal-spatial scales relevant for gravity waves, e.g. soundings at 288 m height resolution and 9 min temporal resolution in the upper stratosphere and mesosphere. The seasonal averages from 10 years of measurements show in all seasons some loss of gravity-wave energy in the upper stratosphere. During the equinox periods and summer the measurements are consistent with gravity waves growing in height with little saturation, in agreement with the classic picture of the variations in the height at which gravity waves break given by Lindzen (1981). The mean values compare favourably to previous measurements when computed as nightly averages, but the high temporal-spatial resolution measurements show considerable day-to-day variability. The variability over a night is often extremely large, with typical RMS fluctuations of 50 to 100% at all heights and seasons common. These measurements imply that using a daily or nightly-averaged gravity-wave energy density in numerical models may be highly unrealistic.

Download Full-text

Observations and Numerical Simulations of Inertia–Gravity Waves and Shearing Instabilities in the Vicinity of a Jet Stream

Journal of the Atmospheric Sciences ◽

10.1175/jas3305.1 ◽

2004 ◽

Vol 61 (22) ◽

pp. 2692-2706 ◽

Cited By ~ 59

Author(s):

Todd P. Lane ◽

James D. Doyle ◽

Riwal Plougonven ◽

Melvyn A. Shapiro ◽

Robert D. Sharman

Keyword(s):

Numerical Simulations ◽

Gravity Waves ◽

Jet Stream ◽

Sheared Flow ◽

Mesoscale Structure ◽

Air Turbulence ◽

Research Aircraft ◽

Wave Development ◽

Upper Level ◽

Inertia Gravity Waves

Abstract The characteristics and dynamics of inertia–gravity waves generated in the vicinity of an intense jet stream/ upper-level frontal system on 18 February 2001 are investigated using observations from the NOAA Gulfstream-IV research aircraft and numerical simulations. Aircraft dropsonde observations and numerical simulations elucidate the detailed mesoscale structure of this system, including its associated inertia–gravity waves and clear-air turbulence. Results from a multiply nested numerical model show inertia–gravity wave development above the developing jet/front system. These inertia–gravity waves propagate through the highly sheared flow above the jet stream, perturb the background wind shear and stability, and create bands of reduced and increased Richardson numbers. These bands of reduced Richardson numbers are regions of likely Kelvin–Helmholtz instability and a possible source of the clear-air turbulence that was observed.

Download Full-text

Interaction of Upper-Tropospheric Turbulence and Gravity Waves as Obtained from Spectral and Structure Function Analyses

Journal of the Atmospheric Sciences ◽

10.1175/2007jas2660.1 ◽

2008 ◽

Vol 65 (8) ◽

pp. 2676-2690 ◽

Cited By ~ 12

Author(s):

Chungu Lu ◽

Steven E. Koch

Keyword(s):

Structure Function ◽

Gravity Waves ◽

Function Analysis ◽

Power Spectra ◽

Physical Space ◽

Energy Cascade ◽

Small Scale ◽

Order Structure ◽

Scale Interactions ◽

Inverse Energy Cascade

Abstract Spectral and structure function analyses of horizontal velocity fields observed in the upper troposphere and lower stratosphere during the Severe Clear Air Turbulence Collides with Air Traffic (SCATCAT) field program, conducted over the Pacific, were carried out in an effort to identify the scale interactions of turbulence and small-scale gravity waves. Because of the intermittent nature of turbulence, these analyses were conducted by clearly separating out the cases when turbulence did or did not occur in the data. In the presence of turbulence, transitional power spectra from k−2 to k−5/3 were found to be associated with gravity waves and turbulence, respectively. The second-order structure function analysis was able to translate these spectral slopes into r and r 2/3 scaling, consistent with the Monin and Yaglom conversion law, in physical space, which presented clearer pictures of scale interactions between turbulence and gravity waves. The third-order structure function analysis indicated the existence of a narrow region of inverse energy cascade from the scales of turbulence up to the gravity waves scales. This inverse energy cascade region was linked to the occurrence of Kelvin–Helmholtz instability and other wave-amplifying mechanisms, which were conjectured to lead to the breaking of small-scale gravity waves and the ensuing generation of turbulence. The multifractal analyses revealed further scale breaks between gravity waves and turbulence. The roughness and intermittent properties were also calculated for turbulence and gravity waves, respectively. Based on these properties, turbulence and gravity waves in a bifractal parameter space were mapped. In this way, their physical and statistical attributes were clearly manifested and understood.

Download Full-text

Influences of Moist Convection on a Cold-Season Outbreak of Clear-Air Turbulence (CAT)

Monthly Weather Review ◽

10.1175/mwr-d-11-00353.1 ◽

2012 ◽

Vol 140 (8) ◽

pp. 2477-2496 ◽

Cited By ~ 38

Author(s):

Stanley B. Trier ◽

Robert D. Sharman ◽

Todd P. Lane

Keyword(s):

Gravity Waves ◽

Cold Season ◽

Vertical Shear ◽

Moist Convection ◽

Flow Perturbation ◽

Air Turbulence ◽

Central United States ◽

Upper Level ◽

Vertically Propagating ◽

Upper Level Jet

Abstract The 9–10 March 2006 aviation turbulence outbreak over the central United States is examined using observations and numerical simulations. Though the turbulence occurs within a deep synoptic cyclone with widespread precipitation, comparison of reports from commercial aircraft with radar and satellite data reveals the majority of the turbulence to be in clear air. This clear-air turbulence (CAT) is located above a strong upper-level jet, where vertical shear ranged between 20 and 30 m s−1 km−1. Comparison of a moist simulation with a dry simulation reveals that simulated vertical shear and subgrid turbulence kinetic energy is significantly enhanced by the anticyclonic upper-level flow perturbation associated with the organized convection in regions of observed CAT. A higher-resolution simulation is used to examine turbulence mechanisms in two primary clusters of reported moderate and severe turbulence. In the northern cluster where vertical shear is strongest, the simulated turbulence arises from Kelvin–Helmholtz (KH) instability. The turbulence farther south occurs several kilometers above shallow, but vigorous, moist convection. There, the simulated turbulence is influenced by vertically propagating gravity waves initiated when the convection impinges on a lowered tropopause. In some locations these gravity waves amplify and break leading directly to turbulence, while in others they aid turbulence development by helping excite KH instability within the layers of strongest vertical shear above them. Although both clusters of turbulence occur either above or laterally displaced from cloud, a shared characteristic is their owed existence to moist convection within the wintertime cyclone, which distinguishes them from traditional CAT.

Download Full-text

Gravity Wave Diagnostics and Characteristics in Mesoscale Fields

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-15-0079.1 ◽

2015 ◽

Vol 72 (11) ◽

pp. 4372-4392 ◽

Cited By ~ 23

Author(s):

Christopher G. Kruse ◽

Ronald B. Smith

Keyword(s):

Gravity Wave ◽

Energy Flux ◽

Gravity Waves ◽

Numerical Models ◽

Mountain Wave ◽

Atmospheric Flows ◽

Vertical Propagation ◽

The Relationship ◽

Zonal Momentum ◽

Selection Of

Abstract As numerical models of complex atmospheric flows increase their quality and resolution, it becomes valuable to isolate and quantify the embedded resolved gravity waves. The authors propose a spatial filtering method combined with a selection of quadratic diagnostic quantities such as heat, momentum, and energy fluxes to do this. These covariant quantities were found to be insensitive to filter cutoff length scales between 300 and 700 km, suggesting the existence of a “cospectral gap.” The gravity waves identified with the proposed method display known properties from idealized studies, including vertical propagation, upwind propagation, the relationship between momentum and energy flux, and agreement with fluxes derived from an alternative method involving simulations with and without terrain. The proposed method is applied to 2- and 6-km-resolution realistic WRF simulations of orographic and nonorographic gravity waves over and around New Zealand within complex frontal cyclones. Deep mountain wave, shallow mountain wave, jet-generated gravity wave, and convection-generated gravity wave events were chosen for analysis. The four wave events shared the characteristics of positive vertical energy flux, negative zonal momentum flux, and upwind horizontal energy flux. Two of the gravity wave events were dissipated nonlinearly.

Download Full-text

Performance Evaluation of Sub-Grid Orographic Parameterization in the WRF Model over Complex Terrain in Central Asia

Atmosphere ◽

10.3390/atmos11111164 ◽

2020 ◽

Vol 11 (11) ◽

pp. 1164

Author(s):

Huoqing Li ◽

Junjian Liu ◽

Hailiang Zhang ◽

Chenxiang Ju ◽

Junjie Shi ◽

...

Keyword(s):

Wind Speed ◽

Central Asia ◽

Gravity Wave ◽

Gravity Waves ◽

Surface Wind ◽

Wrf Model ◽

Wave Drag ◽

Near Surface ◽

Upper Level ◽

Orographic Drag

The terrain of Central Asia is complex and rugged over mountains. Consequently, wind speed is overestimated over mountains and plains when using the Weather Research Forecast (WRF) model in winter. To solve this problem, three different simulations (named as control simulation (CRTL), gravity waves (GWD), and flow-blocking drag (FBD), respectively) were designed to investigate the impact of sub-grid orography (gravity waves and flow-blocking drag) on wind forecasts. The results illustrated that near-surface wind-speed overestimations were alleviated when sub-grid orographic drag was used in GWD, though the upper-level wind fields at 500 hPa were excessively reduced compared to CRTL. Thus, we propose eliminating the gravity wave breaking at the upper level to improve upper-level wind underestimations and surface wind speeds at the same time. The sub-grid orographic drag stress of the vertical profile over mountains was reduced when only the flow-blocking drag was retained in FBD. This alleviated underestimations of the upper-level wind speed and near-surface wind, which both have the same positive effects as the gravity wave and flow-blocking total. The mean bias and root mean squared error reduced by 32.76% and 9.39%, respectively, compared to CRTL. Moreover, the temperature and specific humidity in the lower troposphere were indirectly improved. The results of the study demonstrate that it is better to remove sub-grid orographic gravity wave drag when using the gravity wave drag scheme of the WRF model.

Download Full-text