Influence of lee waves and rotors on the near‐surface flow and pressure fields in the northern foreland of the Tatra Mountains

Abstract

This study presents the results of a field campaign aimed at observing near-surface flow and pressure fields downwind of the Tatra Mountains. The general objective was to study low-level turbulence associated with lee waves and rotors and to improve weather forecasts for aviation. The main instrumentation consisted of a network of nine weather stations arranged as a transect perpendicular to the Tatra Mountains. The stations recorded the wind speed and direction (at 10 m), atmospheric pressure, temperature and humidity (at 2 m) for ∼2 years. Gliding flights and cloud cover observations using two digital sky cameras also formed part of the campaign. The measurements were supported by data from atmospheric soundings in Poprad (Slovakia) and satellite images provided by the Moderate Resolution Imaging Spectroradiometer (MODIS). During a stable southerly flow, episodes of flow separation were observed, which are associated with lee-wave and rotor activity aloft. Based on data from the selected period, surface-pressure perturbations arranged as alternate positive and negative anomalies with extreme values of up to ∼0.7 hPa were detected. Positive (negative) anomalies are assumed to be a response of the surface-pressure field under the influence of descending (ascending) wave or rotor currents because of the downward (upward) component of the air movement in the atmosphere. The relationship between the decreasing magnitudes of the pressure perturbations with the distance from the Tatra Mountains was exposed. It was also possible to demonstrate the dependence of the position and intensity of pressure anomalies in relation to changes in wind conditions.

Downslope windstorm study in the Isthmus of Tehuantepec using WRF high-resolution simulations

“…Temperature errors are equal or below 1 K in both locations and domains, hence the surface thermal evolution is well captured. Lee waves can promote orographic cloud formation at different scales, depending on the amplitude of the wave and elevation (Armi and Mayr, 2011;Szmyd, 2016). Model results in d05 suggest that lenticular clouds form at the crests of the trapped lee waves depicted in Figure 7.…”

Influence of geographical factors on thermal stress in northern Carpathians

“…(Trepińska 2002 ; Migała 2005 ). It is an effect of air cooling during crossing mountain ridge which generate formation of clouds and dynamic changes in air pressure and air temperature in surrounded areas (Szmyd 2016 ). Important factors that affect the mountainous climate are geographical position and the orientation of the mountain ridges (Smith 2015 ).…”

Downslope windstorms in the Isthmus of Tehuantepec during Tehuantepecer events: a numerical study with WRF high-resolution simulations

“…There is evidence from observations and earlier numerical studies (Steenburgh et al, 1998) that the low-elevation topography of Chivela Pass can excite mountain waves and also that these are not only restricted to the pass itself but extend into the much higher mountain crests to the west and especially to the east, as the cold air pool is often thick enough to surpass them. This gravity wave activity can potentially result in downslope windstorms (DSWSs hereafter) producing severe turbulent phenomena such as rotors and hydraulic jumps (HJs hereafter) (Durran, 1986a;Sheridan and Vosper, 2006) on the Pacific side of the isthmus, to the lee of local orography, which would explain several accidents related to strong winds reported by the Oaxaca's Civil Protection Commission (Santiago, 2018;Hernández, 2018;Televisa, 2018;Rodríguez, 2018) every year during some Tehuano occurrences. The ability to understand and forecast these events is very relevant since the isthmus has been an important development site for wind farms since the 2000s (Coldwell et al, 2017).…”