Long-period unstable gravity-waves and associated VHF radar echoes

Abstract. VHF atmospheric radar is used to measure the wind velocity and radar echo power related to long-period wind perturbations, including gravity waves, which are observed commonly in the lower stratosphere and tropopause region, and sometimes in the troposphere. These wind structures have been identified previously as either inertia-gravity waves, often associated with jet streams, or mountain waves. At heights of peak wind shear, imbalances are found between the echo powers of a symmetric pair of radar beams, which are expected to be equal. The largest of these power differences are found for conditions of simultaneous high wind shear and high aspect sensitivity. It is suggested that the effect might arise from tilted specular reflectors or anisotropic turbulent scatterers, a result of, for example, Kelvin-Helmholtz instabilities generated by the strong wind shears. This radar power-difference effect could offer information about the onset of saturation in long-period waves, and the formation of thin layers of turbulence.

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Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-3583-2010 ◽

2010 ◽

Vol 10 (8) ◽

pp. 3583-3599 ◽

Cited By ~ 24

Author(s):

S. Kirkwood ◽

M. Mihalikova ◽

T. N. Rao ◽

K. Satheesan

Keyword(s):

Wind Shear ◽

Weather Forecasting ◽

Mesoscale Model ◽

Vertical Mixing ◽

Static Stability ◽

Thin Layers ◽

Vertical Wind ◽

Vhf Radar ◽

Mountain Waves ◽

Vertical Winds

Abstract. We use measurements by the 52 MHz wind-profiling radar ESRAD, situated near Kiruna in Arctic Sweden, and simulations using the Advanced Research and Weather Forecasting model, WRF, to study vertical winds and turbulence in the troposphere in mountain-wave conditions on 23, 24 and 25 January 2003. We find that WRF can accurately match the vertical wind signatures at the radar site when the spatial resolution for the simulations is 1 km. The horizontal and vertical wavelengths of the dominating mountain-waves are ~10–20 km and the amplitudes in vertical wind 1–2 m/s. Turbulence below 5500 m height, is seen by ESRAD about 40% of the time. This is a much higher rate than WRF predictions for conditions of Richardson number (Ri) <1 but similar to WRF predictions of Ri<2. WRF predicts that air crossing the 100 km wide model domain centred on ESRAD has a ~10% chance of encountering convective instabilities (Ri<0) somewhere along the path. The cause of low Ri is a combination of wind-shear at synoptic upper-level fronts and perturbations in static stability due to the mountain-waves. Comparison with radiosondes suggests that WRF underestimates wind-shear and the occurrence of thin layers with very low static stability, so that vertical mixing by turbulence associated with mountain waves may be significantly more than suggested by the model.

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Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign

Annales Geophysicae ◽

10.5194/angeo-29-2259-2011 ◽

2011 ◽

Vol 29 (12) ◽

pp. 2259-2276 ◽

Cited By ~ 5

Author(s):

S. K. Dhaka ◽

R. Bhatnagar ◽

Y. Shibagaki ◽

H. Hashiguchi ◽

S. Fukao ◽

...

Keyword(s):

Gravity Waves ◽

Zonal Wind ◽

Wind Shear ◽

Radiosonde Data ◽

Strong Wind ◽

Mean Flow ◽

Vertical Wavelength ◽

Short Period ◽

Radiosonde Observation ◽

Wind Shears

Abstract. Analyses of hourly radiosonde data of temperature, wind, and relative humidity during four days (two with convection and two with no convection) as a part of an intensive observation period in CPEA-2 campaign over Koto Tabang (100.32° E, 0.20° S), Indonesia, are presented. Characteristics of gravity waves in terms of dominant wave frequencies at different heights and their vertical wavelengths are shown in the lower stratosphere during a convective and non-convective period. Gravity waves with periods ~10 h and ~4–5 h were found dominant near tropopause (a region of high stability) on all days of observation. Vertical propagation of gravity waves were seen modified near heights of the three identified strong wind shears (at ~16, 20, and 25 km heights) due to wave-mean flow interaction. Between 17 and 21 km heights, meridional wind fluctuations dominated over zonal wind, whereas from 22 to 30 km heights, wave fluctuations with periods ~3–5 h and ~8–10 h in zonal wind and temperature were highly associated, suggesting zonal orientation of wave propagation. Gravity waves from tropopause region to 30 km heights were analyzed. In general, vertical wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean) wind and temperature hourly profiles. Computed vertical wavelength spectra are similar, in most of the cases, to the source spectra (1–16 km height) except that of zonal wind spectra, which is broad during active convection. Interestingly, during and after convection, gravity waves with short vertical wavelength (~2 km) and short period (~2–3 h) emerged, which were confined in the close vicinity of tropopause, and were not identified on non-convective days, suggesting convection to be the source for them. Some wave features near strong wind shear (at 25 km height) were also observed with short vertical wavelengths in both convective and non-convective days, suggesting wind shear to be the sole cause of generation and seemingly not associated with deep convection below. A drop in the temperature up to ~4–5 K (after removal of diurnal component) was observed at ~16 km height near a strong wind shear (~45–55 m s−1 km−1) during active period of convection.

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Turbulence associated with mountain waves over Northern Scandinavia – a case study using the ESRAD VHF radar and the WRF mesoscale model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-20775-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 20775-20817 ◽

Cited By ~ 1

Author(s):

S. Kirkwood ◽

M. Mihalikova ◽

T. N. Rao ◽

K. Satheesan

Keyword(s):

Wind Shear ◽

Weather Forecasting ◽

Mesoscale Model ◽

Vertical Mixing ◽

Static Stability ◽

Thin Layers ◽

Vertical Wind ◽

Vhf Radar ◽

Mountain Waves ◽

Vertical Winds

Abstract. We use measurements by the 52 MHz wind-profiling radar ESRAD, situated near Kiruna in Arctic Sweden, and simulations using the Advanced Research and Weather Forecasting model, WRF, to study vertical winds and turbulence in the troposphere in mountain-wave conditions on 23 , 24 and 25 January 2003. We find that WRF can accurately match the vertical wind signatures at the radar site when the spatial resolution for the simulations is 1 km. The horizontal and vertical wavelengths of the dominating mountain-waves are ∼10–20 km and the amplitudes in vertical wind 1–2 m/s. Turbulence below 5500 m height, is seen by ESRAD about 40% of the time. This is a much higher rate than WRF predictions for conditions of Richardson number (Ri) >1 but similar to WRF predictions of Ri>2. WRF predicts that air crossing the 100 km wide model domain centred on ESRAD has a ∼10% chance of encountering convective instabilities (Ri>0.) somewhere along the path. The cause of low Ri is a combination of wind-shear at synoptic upper-level fronts and perturbations in static stability due to the mountain-waves. Comparison with radiosondes suggests that WRF underestimates wind-shear and the occurrence of thin layers with very low static stability, so that vertical mixing by turbulence associated with mountain waves may be significantly more than suggested by the model.

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Night-to-night changes in the characteristics of gravity waves at stratospheric and lower-mesospheric heights

Annales Geophysicae ◽

10.1007/s00585-998-0229-0 ◽

1998 ◽

Vol 16 (2) ◽

pp. 229-237 ◽

Cited By ~ 6

Author(s):

A. J. McDonald ◽

L. Thomas ◽

D. P. Wareing

Keyword(s):

Gravity Waves ◽

Wave Activity ◽

Mountain Waves ◽

Long Period ◽

Convective Instabilities ◽

Radar Systems ◽

Mst Radar ◽

Vertical Propagation ◽

Rayleigh Lidar ◽

Lidar Observations

Abstract. Observations made with the co-located Rayleigh lidar and MST radar systems at Aberystwyth (52.4°N, 4.1°W) in Wales and radiosondes from Valentia (51.9°N, 10.2°W) in Eire are used to investigate the changes in the vertical propagation of gravity waves during periods of 4 days in June 1995 and February 1993. In each month, the lidar observations show that the wave activity in the upper stratosphere and lower mesosphere changes between two pairs of days. The radar and radiosonde measurements indicate that mountain waves make no contribution to the changes in intensity. Instead, the changes seem to arise largely from the presence or absence of long-period waves with vertical wavelengths near 8 and 10 km in June and February, respectively. The influence of such waves on the vertical wavenumber spectra is examined and related to the evidence for convective instabilities provided by the temperature profiles.Key words. Rayleigh lidar · MST radar systems · Radiosondes · Gravity waves

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Dynamical Effects of Aerosol Perturbations on Simulated Idealized Squall Lines

Monthly Weather Review ◽

10.1175/mwr-d-13-00156.1 ◽

2014 ◽

Vol 142 (3) ◽

pp. 991-1009 ◽

Cited By ~ 42

Author(s):

Zachary J. Lebo ◽

Hugh Morrison

Keyword(s):

Mass Flux ◽

Wind Shear ◽

Cold Pool ◽

Strong Wind ◽

Low Level ◽

Aerosol Loading ◽

Squall Lines ◽

Wide Range ◽

Wind Shears ◽

Convective Mass Flux

Abstract The dynamical effects of increased aerosol loading on the strength and structure of numerically simulated squall lines are explored. Results are explained in the context of Rotunno–Klemp–Weisman (RKW) theory. Changes in aerosol loading lead to changes in raindrop size and number that ultimately affect the strength of the cold pool via changes in evaporation. Thus, the balance between cold pool and low-level wind shear–induced vorticities can be changed by an aerosol perturbation. Simulations covering a wide range of low-level wind shears are performed to study the sensitivity to aerosols in different environments and provide more general conclusions. Simulations with relatively weak low-level environmental wind shear (0.0024 s−1) have a relatively strong cold pool circulation compared to the environmental shear. An increase in aerosol loading leads to a weakening of the cold pool and, hence, a more optimal balance between the cold pool– and environmental shear–induced circulations according to RKW theory. Consequently, there is an increase in the convective mass flux of nearly 20% in polluted conditions relative to pristine. This strengthening coincides with more upright convective updrafts and a significant increase (nearly 20%) in cumulative precipitation. An increase in aerosol loading in a strong wind shear environment (0.0064 s−1) leads to less optimal storms and a suppression of the convective mass flux and precipitation. This occurs because the cold pool circulation is weak relative to the environmental shear when the shear is strong, and further weakening of the cold pool with high aerosol loading leads to an even less optimal storm structure (i.e., convective updrafts begin to tilt downshear).

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Inertia gravity waves in the upper troposphere during the MaCWAVE winter campaign – Part I: Observations with collocated radars

Annales Geophysicae ◽

10.5194/angeo-24-2851-2006 ◽

2006 ◽

Vol 24 (11) ◽

pp. 2851-2862 ◽

Cited By ~ 7

Author(s):

P. Hoffmann ◽

A. Serafimovich ◽

D. Peters ◽

P. Dalin ◽

R. Goldberg ◽

...

Keyword(s):

Gravity Waves ◽

Opposite Direction ◽

Background Wind ◽

Energy Propagation ◽

Mountain Ridge ◽

Vhf Radar ◽

Mountain Waves ◽

Upper Troposphere ◽

The Mean ◽

Inertia Gravity Waves

Abstract. During the {MaCWAVE} campaign, combined rocket, radiosonde and ground-based measurements have been performed at the Norwegian Andøya Rocket Range (ARR) near Andenes and the Swedish Rocket Range (ESRANGE) near Kiruna in January 2003 to study gravity waves in the vicinity of the Scandinavian mountain ridge. The investigations presented here are mainly based on the evaluation of continuous radar measurements with the ALWIN VHF radar in the upper troposphere/ lower stratosphere at Andenes (69.3° N, 16.0° E) and the ESRAD VHF radar near Kiruna (67.9° N, 21.9° E). Both radars are separated by about 260 km. Based on wavelet transformations of both data sets, the strongest activity of inertia gravity waves in the upper troposphere has been detected during the first period from 24–26 January 2003 with dominant vertical wavelengths of about 4–5 km as well as with dominant observed periods of about 13–14 h for the altitude range between 5 and 8 km under the additional influence of mountain waves. The results show the appearance of dominating inertia gravity waves with characteristic horizontal wavelengths of ~200 km moving in the opposite direction than the mean background wind. The results show the appearance of dominating inertia gravity waves with intrinsic periods in the order of ~5 h and with horizontal wavelengths of 200 km, moving in the opposite direction than the mean background wind. From the derived downward energy propagation it is supposed, that these waves are likely generated by a jet streak in the upper troposphere. The parameters of the jet-induced gravity waves have been estimated at both sites separately. The identified gravity waves are coherent at both locations and show higher amplitudes on the east-side of the Scandinavian mountain ridge, as expected by the influence of mountains.

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Rolls of the internal gravity waves in the Earth's atmosphere

Annales Geophysicae ◽

10.5194/angeo-32-181-2014 ◽

2014 ◽

Vol 32 (2) ◽

pp. 181-186 ◽

Cited By ~ 7

Author(s):

O. Onishchenko ◽

O. Pokhotelov ◽

W. Horton ◽

A. Smolyakov ◽

T. Kaladze ◽

...

Keyword(s):

Nonlinear Dynamics ◽

Gravity Waves ◽

Closed System ◽

Wind Shear ◽

Internal Gravity Waves ◽

Temperature Gradients ◽

System Of Equations ◽

Vertical Temperature ◽

Earth’S Atmosphere ◽

Earth's Atmosphere

Abstract. The effect of the wind shear on the roll structures of nonlinear internal gravity waves (IGWs) in the Earth's atmosphere with the finite vertical temperature gradients is investigated. A closed system of equations is derived for the nonlinear dynamics of the IGWs in the presence of temperature gradients and sheared wind. The solution in the form of rolls has been obtained. The new condition for the existence of such structures was found by taking into account the roll spatial scale, the horizontal speed and wind shear parameters. We have shown that the roll structures can exist in a dynamically unstable atmosphere.

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Wind shear over the Nice Côte d'Azur airport: case studies

Natural Hazards and Earth System Science ◽

10.5194/nhess-13-2223-2013 ◽

2013 ◽

Vol 13 (9) ◽

pp. 2223-2238 ◽

Cited By ~ 6

Author(s):

A. Boilley ◽

J.-F. Mahfouf

Keyword(s):

Numerical Simulation ◽

Numerical Model ◽

Numerical Simulations ◽

Wind Shear ◽

Horizontal Wind ◽

Wind Profiler ◽

Measurement Campaign ◽

Wind Lidar ◽

Real Time Applications ◽

Wind Shears

Abstract. The Nice Côte d'Azur international airport is subject to horizontal low-level wind shears. Detecting and predicting these hazards is a major concern for aircraft security. A measurement campaign took place over the Nice airport in 2009 including 4 anemometers, 1 wind lidar and 1 wind profiler. Two wind shear events were observed during this measurement campaign. Numerical simulations were carried out with Meso-NH in a configuration compatible with near-real time applications to determine the ability of the numerical model to predict these events and to study the meteorological situations generating an horizontal wind shear. A comparison between numerical simulation and the observation dataset is conducted in this paper.

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