ALPEX The GARP Mountain Subprogram

Kuettner, Joachim P.; O'Neill, Thomas H. R.

doi:10.1175/1520-0477-62.6.793

Cited by 19 publications

(12 citation statements)

References 4 publications

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“…Solid and dashed black lines: PSDs of vertical velocities measured during SUCCESS (Toon et al, 1998) and MACPEX (Rollins et al, 2014), respectively. Blue dashed and dashed-dotted lines: data from the ALPEX campaign for active and quiet days, respectively (Kuettner, 1981).…”

Section: Temperature Fluctuationsmentioning

confidence: 99%

“…This can be assessed by comparing the PSD of the model to PSDs measured during field campaigns in the upper troposphere. For comparison to our model data we use the vertical velocity data from SUCCESS (Toon et al, 1998) and MACPEX (Rollins et al, 2014) and furthermore from the ALPEX campaign carried out over the Alps (Kuettner, 1981). In a dry atmosphere the PSD of vertical velocities is directly linked to the occurring cooling rates by the dry adiabatic lapse rate; however, it is not directly related to the temperature PSD.…”

Section: Vertical Velocity Fluctuationsmentioning

confidence: 99%

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Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

et al. 2015

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Abstract. Simulations of cirrus are subject to uncertainties in model physics and meteorological input data. Here we model cirrus clouds along air mass trajectories, whose extinction has been measured with an elastic backscatter lidar at Jungfraujoch research station in the Swiss Alps, with a microphysical stacked box model. The sensitivities of these simulations to input data uncertainties (trajectory resolution, unresolved vertical velocities, ice nuclei number density and upstream specific humidity) are investigated.Variations in the temporal resolution of the wind field data (COSMO-Model at 2.2 km resolution) between 20 s and 1 h have only a marginal impact on the trajectory path, while the representation of the vertical velocity variability and therefore the cooling rate distribution are significantly affected. A temporal resolution better than 5 min must be chosen in order to resolve cooling rates required to explain the measured extinction. A further increase in the temporal resolution improves the simulation results slightly. The close match between the modelled and observed extinction profile for high-resolution trajectories suggests that the cooling rate spectra calculated by the COSMO-2 model suffice on the selected day. The modelled cooling rate spectra are, however, characterized by significantly lower vertical velocity amplitudes than those found previously in some aircraft campaigns (SUCCESS, MACPEX). A climatological analysis of the vertical velocity amplitude in the Alpine region based on COSMO-2 analyses and balloon sounding data suggests large day-to-day variability in small-scale temperature fluctuations. This demonstrates the necessity to apply numerical weather prediction models with high spatial and temporal resolutions in cirrus modelling, whereas using climatological means for the amplitude of the unresolved air motions does generally not suffice.The box model simulations further suggest that uncertainties in the upstream specific humidity ( ± 10 % of the model prediction) and in the ice nuclei number density (0-100 L −1 ) are more important for the modelled cirrus cloud than the unresolved temperature fluctuations if temporally highly resolved trajectories are used. For the presented case the simulations are incompatible with ice nuclei number densities larger than 20 L −1 and insensitive to variations below this value.

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Section: Temperature Fluctuationsmentioning

confidence: 99%

Section: Vertical Velocity Fluctuationsmentioning

confidence: 99%

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

et al. 2015

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“…Early mesoscale research focused on the katabatic model of bora [4], which was later shown to be deficient in explaining stronger bora events. A major breakthrough in bora mesoscale research started with the ALPEX (Alpine Experiment) project in 1981 [5] and the subsequent findings by Smith [2], which showed that bora is essentially a dynamically generated wind, best explained by the hydraulic and wave breaking theory [6,7]. In recent years, bora's mesoscale characteristics have been extensively studied during the Mesoscale Alpine Programme (MAP) project [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Micro-Scale Properties of Different Bora Types

et al. 2018

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Abstract:In this paper we use 20 Hz wind measurements on three levels (2, 5, and 10 m) to investigate the differences in micro-scale properties of different bora types, i.e., deep and shallow bora with further subdivision to cyclonic and anticyclonic bora cases. Using Fourier spectral analysis, we investigate a suitable turbulence averaging scale and bora gust pulsations. The obtained data set is further used to test the Monin-Obukhov similarity theory, the surface layer stratification, the behavior of the terms in the prognostic turbulence kinetic energy equation, and the wind profiles. One of our main goals is to identify possible micro-scale differences between shallow and deep bora types because of the possible different mountain wave dynamics in those flows. We found that a turbulence averaging scale of 30 min is suitable for this location and is in agreement with previous bora studies. The wind speed power spectral densities of all selected bora episodes showed pulsations with periods of 2-8 min. This suggests that mountain wave breaking was present in all cases, regardless of flow depth and synoptic type. The stability parameter analysis confirmed the near-neutral thermal stratification of bora; a consequence of intensive mechanical mixing. No significant differences related to bora type were observed in other micro-scale parameters.

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“…While its macroscale properties have been relatively well resolved and understood, the mesoscale characteristics of bora were initially investigated only with simple, katabatic flow models (Yoshino 1976;Jurčec 1981). However, after The Alpine Experiment (ALPEX) field campaign (Kuettner and O'Neill 1981), the importance of hydraulic theory in successfully explaining bora's downslope character, at least for the north-eastern Adriatic Coast, has been repeteadly highlighted (Smith 1987;Klemp and Durran 1987;Mahrt and Gamage 1987;Bajić 1991). During the Mesoscale Alpine Programm (MAP) project (Bougeault et al 2001), bora's mesoscale characteristics have been extensively studied (Bencetić Klaić et al 2003;Grubišić 2004;Gohm and Mayr 2005).…”

Section: Introductionmentioning

confidence: 99%

On Turbulent Fluxes During Strong Winter Bora Wind Events

Babić

Večenaj

Kozmar

et al. 2015

Boundary-Layer Meteorol

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Well known for its severity, the bora downslope windstorms have been extensively studied over the last several decades. This study focuses on the turbulence characteristics of bora at a topographically complex site near the eastern coast of the Adriatic Sea. For this purpose, a 3-month eddy-covariance dataset obtained at three levels (10, 22, 40 m) on a 60-m flux tower is used. After determining a suitable averaging time scale of 15 min using the fast Fourier transform and the ogive method, vertical fluxes of momentum and heat were calculated for 17 bora episodes. Up to a wind speed of 12 m s −1 , typical vertical profiles of momentum and heat were observed. However, for wind speeds >12 m s −1 , several interesting observations arose. First, the nighttime heat flux at the 10-m level was often found to be positive rather negative. Second, vertical profiles of the momentum flux were larger at the 22-m level than at 10-and 40-m levels, mostly during nearly neutral to weakly stable thermal stratification. Third, these momentum flux profiles showed a large dependence on wind direction, with virtually no vertical transport of momentum for the largest observed wind speeds. For the first time, bora coherent structures have been analyzed using the so-called variable-interval time averaging (VITA) method. The method detected coherent structures in all three wind-speed components, with structure topologies similar to those observed over forest canopies. The momentum flux increase at the 22-m level, relative to the 10-and 40-m levels, is further supported by the VITA findings.

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ALPEX The GARP Mountain Subprogram

Cited by 19 publications

References 4 publications

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

Sensitivities of Lagrangian modelling of mid-latitude cirrus clouds to trajectory data quality

Micro-Scale Properties of Different Bora Types

On Turbulent Fluxes During Strong Winter Bora Wind Events

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