H. Teitelbaum

Inertia gravity wave generation by the tropospheric midlatitude jet as given by the Fronts and Atlantic Storm‐Track Experiment radio soundings

[1]xa0Generation of inertia gravity waves by the midlatitude tropospheric jet is studied on the basis of the data obtained from the radio soundings over the North Atlantic during the Fronts and Atlantic Storm-Track Experiment campaign. A sample of 224 radio soundings is used to analyze the wave activity as a function of the distance to the jet. It is shown that radio soundings displaying the most intense gravity wave activity, both in the stratosphere and in the troposphere, are the ones closest to the jet axis. Thus the jet region is the dominant source of gravity waves in this region far from orography. Further examination allows for identification of two specific regions of the flow that are associated with intense gravity wave activity: the vicinity of the maximum of the jet velocity and the regions of strong curvature of the jet. The detailed case studies we provide suggest that geostrophic adjustment is the dynamical mechanism responsible for the generation of large-amplitude inertia gravity waves in the regions of the strong curvature of the wind. The generation of waves in the vicinity of the regions where the wind veers, in the deep troughs of the geopotential, appears to be systematic.

Observational Evidence of Internal Inertia-Gravity Waves in the Tropical Stratosphere

Abstract Twenty-nine highly accurate wind profiles up to 30 km obtained during four days of the GARP Atlantic Tropical Experiment (GATE) by tracking vertically ascending balloons with radar are presented and analyzed. The existence of short, vertical wavelength easterly waves propagating upward in the tropical stratosphere, as suggested by a quick look at the profiles, is demonstrated and the wave characteristics are determined. The period of the waves is determined from the power spectra of the u (eastward) and v (north-ward) components at different heights, computed by the lag correlation method and from the rotary spectra computed by the maximum entropy method (35 h). Clockwise rotation of wind vector with time at various levels indicates westward propagation of the phase relative to the medium. Cross spectra between different levels are computed and phase differences demonstrate the downward propagation of phase. From the chronological sequence of u and v profiles, the vertical profile of vertical pha...

Exploring polar stratospheric cloud and ozone minihole formation: The primary importance of synoptic‐scale flow perturbations

The formation of polar stratospheric clouds (PSCs) is sometimes attributed to cooling induced by mountain waves. Some examples of PSCs explained by this mechanism are found in the literature. Other studies show that the cooling producing PSCs is of synoptic scale. In this paper we use data from Polar Ozone Aerosol Measurement (POAM) II and from TIROS Operational Vertical Sounder (TOVS) showing coincident occurrences of PSCs and ozone miniholes over the sea and land. Using European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, we show that when both PSCs and localized ozone minima appear, they are associated primarily with anticyclonic potential vorticity anomalies near the tropopause. The flow anomaly penetrates upward and downward, inducing an upward displacement of isentropic surfaces above and a downward displacement below, the upward and downward penetration being consistent with the deformation scale. These flow anomalies result in synoptic-scale quasi-adiabatic uplift through the lower stratosphere. The adiabatic cooling of the air masses creates the conditions for PSC formation. Coincidentally, the ozone partial pressure decreases, and the localized ozone minimum appears. Our purpose in this paper is to show that the primary PSC formation mechanism in the Arctic is the same as for minihole formation: synoptic-scale dynamics. We show three multiday sequences of PSCs and localized ozone minima. We reveal the robustness of the PSC/dynamics link by showing multiyear, monthly statistics of POAM II PSC sighting fraction compared with PSC formation temperature and isentropic geopotential.

Mixing Layer Formation near the Tropopause Due to Gravity Wave-Critical Level Interactions in a Cloud-Resolving Model

Abstract A plausible mechanism for the formation of mixing layers in the lower stratosphere above regions of tropical convection is demonstrated numerically using high-resolution, two-dimensional (2D), anelastic, nonlinear, cloud-resolving simulations. One noteworthy point is that the mixing layer simulated in this study is free of anvil clouds and well above the cloud anvil top located in the upper troposphere. Hence, the present mechanism is complementary to the well-known process by which overshooting cloud turrets causes mixing within stratospheric anvil clouds. The paper is organized as a case study verifying the proposed mechanism using atmospheric soundings obtained during the Central Equatorial Pacific Experiment (CEPEX), when several such mixing layers, devoid of anvil clouds, had been observed. The basic dynamical ingredient of the present mechanism is (quasi stationary) gravity wave–critical level interactions, occurring in association with a reversal of stratospheric westerlies to easterlies b...

A very deep ozone minihole in the Northern Hemisphere stratosphere at mid-latitudes during the winter of 2000

Ozone miniholes appear on total ozone maps as localized ozone minima with horizontal extentsof a few hundreds of kilometres. They are characterized by a rapid and small-scale appearanceof a columnar ozone decrease with an equally rapid recovery after a few days. They are frequentlyobserved at Northern Hemisphere mid-latitudes in winter. Evolving too rapidly to be the resultof an ozone chemical destruction, miniholes should be the result of meteorological processes.According to some authors, miniholes should be due to the northeast motions of air patcheswith low total ozone content. However, several studies attribute the formation of ozone miniholesto the uplift of air masses, which decreases the ozone columnar content by simply decreasingthe pressure thickness of the ozone layer, without changing the mixing ratio. According tothese studies, the latter mechanism explains the main reduction of ozone that occurs betweenthe tropopause and the ozone maximum during an ozone minihole event. A region of extremelow ozone values passed over Europe from 27 to 30 November 2000. The total ozone valueswere measured with the Total Ozone Mapping Spectrometer (TOMS). A radio sounding, launched on 29 November 2000 from Payerne at the place and time of the deepening of theminihole, allows us to perform a detailed analysis of its formation mechanism. It is shown thatthe uplift of isentropic surfaces plays an important role in the columnar ozone decrease andexplains the lower part of the depleted ozone profile. However, the deepening of the miniholeis explained by another mechanism: namely, at this time the minihole air column intersects thepolar vortex at high altitudes and then encounters ozone-poor air masses.

Nonlinear dissipative critical level interaction in a stratified shear flow: Instabilities and gravity waves

Abstract A two-dimensional numerical model is used to investigate the nonlinear dissipative interaction between a disturbance and an unbounded stratified shear flow. The disturbances considered are Kelvin-Helmholtz instabilities and forced gravity waves. The nonlinear stabilization (destabilization) of Kelvin-Helmholtz instabilities at Prandtl number, Pr 1), found by Brown et al. (1981) is recovered. The model confirms that it is mostly due to a stabilization (destabilization) of the mean flow by the wave. The nonlinear evolution of instabilities existing when thermal dissipation is large and when the Richardson number is everywhere larger than 0.25 is also investigated. It is shown that such a mode stops growing when the nonlinear distortion of the mean flow becomes significant. For forced gravity waves, and when the initial minimum Richardson number, J = 0.25, it is found that mean flow stabilization (destabilization) also occurs at the critical level for Pr 1). More generally, the v...

Analysis of Gravity Waves during the POLINAT Experiment and Some Consequences for Stratosphere–Troposphere Exchange

Abstract Measurements of horizontal wind speed and direction obtained during the Pollution from Aircraft Emissions in the North Atlantic Flight Corridor experiment are used to identify some waves propagating near the tropopause level. The variation observed simultaneously in the ozone and water vapor distribution allows the signature and different characteristics of the waves to be identified. With the help of the analysis of European Centre for Medium-Range Weather Forecasts the conditions for generation of different kinds of waves are reviewed. It is shown that some of the characteristics of the observed waves are a consequence of nonlinear wave–wave interaction. The irregularity of the tropopause height in the region suggests that the propagating waves can be a mechanism for cross-tropopause mixing.

Nonlinear modulation of O3 and CO induced by mountain waves in the upper troposphere and lower stratosphere during terrain‐induced rotor experiment

[1]xa0We analyze and explain distributions of trace gases (O3, CO) and potential temperature observed in aircraft measurements in the upper troposphere and lower stratosphere during the terrain-induced rotor experiment. These distributions show fluctuations induced by mountain waves, with phases and amplitudes that are modulated and correlations that reverse sign along legs of the aircraft at constant altitudes. It is demonstrated that the observed correlations and distributions of gas traces can be explained by reversible processes induced by interactions between mountain waves with different wavelengths evolving on top of a mean vertical profile of ozone that is perturbed by synoptic scale motion. A wave with a large wavelength displaces the air column, causing horizontal variations in the vertical mean gradients. The short waves evolving in these modulated gradients induce wave signatures in O3 and CO, with amplitudes and phase relationships that depend on the vertical gradients encountered along the path of the aircraft. The proposed explanation is confirmed by reconstructed tracer variations deduced under this dynamical process. This is further supported by nonlinear analytical calculations that use background mean profiles from the observations, where the tracer variations induced by mutual wave-wave interaction are investigated.

Deep Convection East of the Andes Cordillera: A Test Case Analysis of Airmass Origin

Warm and moist air masses, required to generate deep convection east of the Andes Cordillera, are generally the result of humidity transport by the so-called low-level jet (LLJ). In this paper, it is shown from detailed test cases that the eastern part of the continent and the adjacent Atlantic Ocean may constitute another source of moist, warm air, which could be of potential importance even in the presence of a southerly LLJ. The position of the anticyclones crossing South America from the Pacific Ocean to the Atlantic Ocean appears to be a key factor affecting the origin of moisture over the continent. In particular, the LLJ may weaken and even change its direction when the eastern side of the South Pacific anticyclone crosses the mountains; this wind reversal is generally associated with deep convection suppression. Thus, as a South Pacific anticyclone crosses the continent more to the east and its western side reaches the east coast of South America, deep convection can reappear east of the Andes, over the Mendoza region, although the LLJ is frequently suppressed. This is associated with a transport of warm and moist air from Uruguay, southeast Brazil, or even directly from the Atlantic Ocean.

Vertical Displacements Induced by Quasi-Stationary Waves in the Southern Hemisphere Stratosphere during Spring

Abstract Vertical displacements induced by the quasi-stationary wave with wavenumber 1 (QSW1) in the Southern Hemisphere stratosphere during spring are studied. The displacement exhibits two amplitude maxima located in the upper and lower stratosphere with a phase change of 180° between the two regions. Ozone mixing ratio and temperature wave signatures are explained by the wave-induced displacement in the presence of mean vertical gradients. The QSW1 induces radiative diabatic forcing in the upper stratosphere that results in a cross-isentropic ozone transport. Correlation between vertical displacement at different levels and total ozone indicates that total ozone is directly connected to the displacement in the lower stratosphere. The displacement extends to the tropopause and results in a correlation between total ozone and the tropopause height, but with smaller values. Relative deviation between reconstructed potential vorticity (PV) by using a high-resolution model and PV from observations indicates...