Manuel Pulido

Recent developments in gravity-wave effects in climate models and the global distribution of gravity-wave momentum flux from observations and models

Quarterly Journal of The Royal Meteorological Society, 2010

Recent observational and theoretical studies of the global properties of small-scale atmospheric ... more Recent observational and theoretical studies of the global properties of small-scale atmospheric gravity waves have highlighted the global effects of these waves on the circulation from the surface to the middle atmosphere. The effects of gravity waves on the large-scale circulation have long been treated via parametrizations in both climate and weather-forecasting applications. In these parametrizations, key parameters describe the global distributions of gravity-wave momentum flux, wavelengths and frequencies. Until recently, global observations could not define the required parameters because the waves are small in scale and intermittent in occurrence. Recent satellite and other global datasets with improved resolution, along with innovative analysis methods, are now providing constraints for the parametrizations that can improve the treatment of these waves in climate-prediction models. Research using very-high-resolution global models has also recently demonstrated the capability to resolve gravity waves and their circulation effects, and when tested against observations these models show some very realistic properties. Here we review recent studies on gravity-wave effects in stratosphere-resolving climate models, recent observations and analysis methods that reveal global patterns in gravity-wave momentum fluxes and results of very-high-resolution model studies, and we outline some future research requirements to improve the treatment of these waves in climate simulations. Copyright © 2010 Royal Meteorological Society and Crown in the right of Canada

Download

On the Doppler effect in a transient gravity-wave spectrum

Quarterly Journal of The Royal Meteorological Society, 2005

The power-spectrum evolution of a transient gravity-wave disturbance propagating conservatively u... more The power-spectrum evolution of a transient gravity-wave disturbance propagating conservatively upwards in a shear flow is examined. It is proven that the wave action for a disturbance suffering Doppler shifting is invariant in the wave-number space. On the other hand, vertical wave-momentum flux, even when it is invariant for waves of fixed frequency, is not invariant in the wave-number space for a transient disturbance. The principle is used to derive a transformation law between a source spectrum and the resultant Doppler-shifted spectrum. The Doppler-shifted spectrum has a −3 power law in the spectral tail, the asymptotic behaviour of the tail is shown to be independent of the gravity-wave source. The result is obtained in two ways: from the gravity-wave energy equation and also by Fourier transforming the solution to the gravity-wave equations. The derived spectral transformation law should be a key point in spectral gravity-wave parametrizations.

Download

Power spectrum of a gravity wave propagating in a shearing background wind

Geophysical Research Letters, 2000

We re-analyze the effect on the spectral tail of a gravity wave propagating in a shearing backgro... more We re-analyze the effect on the spectral tail of a gravity wave propagating in a shearing background. The contribution to the spectrum of horizontal wind perturbations for low vertical wavenumbers comes from the Doppler shifting with a -1 slope and for high wavenumbers from the leakage effect with slopes ranging between -4 to -2. If leakage is not present, it becomes necessary to consider the termination of the wave in order to account for the spectral tail. We show that the decreasing of the wave amplitude when the overturning starts, leads to a spectral slope of -3, and an amplitude proportional to N 2 (the square of the Brünt Väisälä frequency).

Download

Spectral Tail of a Gravity Wave Train Propagating in a Shearing Background

Journal of The Atmospheric Sciences, 2000

Abstract The causes of the appearance of a tail in the power spectrum of a gravity wave train in ... more

Power spectrum of a gravity wave propagating in a shearing background wind

Geophysical Research Letters, 2000

We re-analyze the effect on the spectral tail of a gravity wave propagating in a shearing backgro... more We re-analyze the effect on the spectral tail of a gravity wave propagating in a shearing background. The contribution to the spectrum of horizontal wind perturbations for low vertical wavenumbers comes from the Doppler shifting with a -1 slope and for high wavenumbers from the leakage effect with slopes ranging between -4 to -2. If leakage is not present, it becomes necessary to consider the termination of the wave in order to account for the spectral tail. We show that the decreasing of the wave amplitude when the overturning starts, leads to a spectral slope of -3, and an amplitude proportional to N 2 (the square of the Brünt Väisälä frequency).

Download

Spectral Tail of a Gravity Wave Train Propagating in a Shearing Background

Journal of The Atmospheric Sciences, 2000

Abstract The causes of the appearance of a tail in the power spectrum of a gravity wave train in ... more

Gravity wave drag estimation from global analyses using variational data assimilation principles. I: Theory and implementation

Quarterly Journal of The Royal Meteorological Society, 2005

A novel technique to estimate gravity wave drag from global-scale analyses is presented. It is ba... more A novel technique to estimate gravity wave drag from global-scale analyses is presented. It is based on the principles of four-dimensional variational data assimilation, using a dynamical model of the middle atmosphere and its adjoint. The global analyses are treated as observations. A cost function that measures the mismatch between the model state and observations is defined. The control variables are the components of the threedimensional gravity wave drag field, so that minimization of the cost function gives the optimal gravity wave drag field. The minimization is performed using a conjugate gradient method, with the adjoint model used to calculate the gradient of the cost function.

Download

The Seasonal Cycle of Gravity Wave Drag in the Middle Atmosphere

Journal of Climate, 2008

Abstract Using a variational technique, middle atmosphere gravity wave drag (GWD) is estimated fr... more

Gravity-wave drag estimation from global analyses using variational data assimilation principles. II: Case study

Quarterly Journal of The Royal Meteorological Society, 2006

An estimate of the three-dimensional gravity-wave drag field derived from middle-atmosphere analy... more An estimate of the three-dimensional gravity-wave drag field derived from middle-atmosphere analyses is presented. It is obtained using a novel technique based on variational data assimilation principles described in Part I. The assimilation is performed for a one-week period starting on 1 July 2002 using Met Office middle-atmosphere analyses as the observations as well as the initial condition. The rotational component of the gravity-wave drag is robustly estimated by the technique. The zonal-mean drag estimates reach maximum amplitudes of 50 m s −1 day −1 at 0.4 hPa near the winter-hemisphere polar jet. In the middle stratosphere, drag estimates are much weaker with zonal-mean peak values of 5 m s −1 day −1 and show transient small-scale features not obviously correlated with the local background flow. Vertical variations in the sign and pattern of the estimated drag suggest filtering of the gravity-wave spectrum by the background flow.

Download

Uploads

Papers by Manuel Pulido

Log In