Carlos Yagüe

STUDY OF COHERENT STRUCTURES AND ESTIMATION OF THE PRESSURE TRANSPORT TERMS FOR THE NOCTURNAL STABLE BOUNDARY LAYER

During the CASES-99 field experiment, three quartz-based microbarographs were installed on the 58-m main tower at the Central Site. These devices measuredabsolute pressure with temperature compensated output at a resolution better than 0.2 Pa and a sampling frequency of 2 s-1 during the whole campaign. This sampling rate is not adequate to compute turbulent pressure fluxes with the classic averaging method, but the wavelet transform allows flux estimations at a wide range of scales. The resolution of the devices is suitable to study pressure perturbations such as internal gravity waves. The night period of the Intensive Operational Period number 6 (IOP6), where wave-like structures were present, is chosen to illustrate the method. A complete wavelet analysis of pressure recordsand data from sonic anemometers located at the same heights in the tower is performed. Wavelet methods make it possible to identify the relevant scales in the flowand to study the vertical structure of pressure perturbations, including coherent structures and small-scale motions.A study of a simplified turbulence kinetic energy budget equation is made and the contribution of the pressure terms is discussed.

Analysis of Gravity Waves Generated at the Top of a Drainage Flow

Abstract Drainage or katabatic flows are common mesoscale circulations established as a result of differential radiative cooling of near-surface air masses in sloping terrain. The initial irruption of these flows, with sudden shifts in wind speed and direction, may result in vertical displacements of air parcels from their equilibrium position, which prove to be a common source of internal gravity waves. This paper illustrates this mechanism and describes the main features of the oscillations following the study of observational data gathered throughout one night during the Stable Atmospheric Boundary Layer Experiment in Spain 2006 (SABLES2006) field campaign. Pressure differences, measured by microbarometers set at different levels of a tower, help to interpret the evolution of other atmospheric variables, provide a detailed picture of the irruption of a drainage current, and reveal the formation of gravity waves at its top. The main parameters of the waves are derived from wavelet cross correlation of p...

Review of wave‐turbulence interactions in the stable atmospheric boundary layer

Flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. Understanding turbulence intermittency and wave-turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. The stable atmospheric boundary layer (SABL) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. Intermittent turbulence intensification in the SABL impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. This failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave-turbulence interaction is a potential mechanism for turbulence intermittency. A workshop on wave-turbulence interactions in the SABL addressed the current understanding and challenges of wave-turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. There have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave-turbulence interactions. This review focuses on the nocturnal SABL; however, the discussions here on intermittent turbulence and wave-turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general.

Eddy transfer processes in the atmospheric boundary layer

Abstract In this work the influence of stratification (evaluated through the gradient Richardson number) on the eddy transfer of momentum and heat (Km and Kh) has been studied. A wide range of Richardson numbers (Ri) has been covered with data recorded in summer at Valladolid (Spain) from a 100 m high tower situated on a flat and homogeneous terrain. The results show how the eddy transfers are inhibited for high stabilities (Ri > 0.1), and the importance of the wind shear at night. Different mixing mechanisms have been studied (convection and shear). The ratio of eddy transfer coefficients shows no constant value and a sharp dependence on Richardson number. Finally the effect of surface thermal inversions on the turbulent transfer is analysed.

Vertical structure of the stable boundary layer detected by RASS-SODAR and in-situ measurements in SABLES 2006 field campaign

Data from the SABLES 2006 field campaign are used in order to analyse some of the main processes present along the nocturnal periods: surface-based inversions, low level jets, katabatic winds, wave-like motions, pressure perturbations, etc. These processes have an important influence on the vertical structure (both thermal and dynamical) of the atmospheric boundary layer, and can be better described with the synergetic combination of RASS-SODAR data and in-situ measurements (such as sonic anemometer data and high-resolution pressure series from microbarometers). It is shown how the different air masses and their evolution are easily identified when pressure and RASS-SODAR wind and temperature data are presented together. Likewise, periodic pressure fluctuations observed in the surface array of microbarometers reveal the existence of gravity wave motions whose propagation is better understood after locating the wave ducting layers with the help of RASS-SODAR average wind ant temperature profiles.

The Vertical Structure of Second-Order Turbulence Moments in the Stable Boundary Layer from SABLES98 Observations

Observations of the stable boundary layer (SBL) obtained during the SABLES98 experiment are analyzed in order to investigate the vertical variations of the momentum flux

Seasonal dependence of WRF model biases and sensitivity to PBL schemes over Europe

\tau >0

A numerical study of the Urban Heat Island over Madrid during the DESIREX (2008) campaign with WRF and an evaluation of simple mitigation strategies

τ>0, the heat flux