A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves

A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO

Wave Dynamics and Transport in the Stratosphere

The report discusses: (1) Gravity waves generated by tropical convection: A study in which a two-dimensional cloud-resolving model was used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation was completed. (2) Gravity wave ray tracing studies:It was developed a linear ray tracing model of gravity wave propagation to extend the nonlinear storm model results into the mesosphere and thermosphere. (3) tracer filamentation: Vertical soundings of stratospheric ozone often exhibit laminated tracer structures characterized by strong vertical tracer gradients. (4) Mesospheric gravity wave modeling studies: Although our emphasis in numerical simulation of gravity waves generated by convection has shifted from simulation of idealized two-dimensional squall lines to the most realistic (and complex) study of wave generation by three-dimensional storms. (5) Gravity wave climatology studies: Mr. Alexander applied a linear gravity wave propagation model together with observations of the background wind and stability fields to compute climatologies of gravity wave activity for comparison to observations. (6) Convective forcing of gravity waves: Theoretical study of gravity wave forcing by convective heat sources has completed. (7) Gravity waves observation from UARS: The objective of this work is to apply ray tracing, and other model technique, in order to determine to what extend the horizontal and vertical variation in satellite observed distribution of small-scale temperature variance can be attributed to gravity waves from particular sources. (8) The annual and interannual variations in temperature and mass flux near the tropical tropopause. and (9) Three dimensional cloud model

The role of viscosity in stratified rotating fluids

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1964.Vita.Includes bibliographical references (leaf 109).by James Reed Holton.Ph.D

Seasonal Variation of Mass Transport Across the Tropopause

The annual cycle of the net mass transport across the extratropical tropopause is examined. Contributions from both the global-scale meridional circulation and the mass variation of the lowermost stratosphere are included. For the northern hemisphere the mass of the lowermost stratosphere has a distinct annual cycle, whereas for the southern hemisphere, the corresponding variation is weak. The net mass transport across the tropopause in the northern hemisphere has a maximum in late spring and a distinct minimum in autumn. This variation and its magnitude compare well with older estimates based on representative Sr-90 mixing ratios. For the southern hemisphere the seasonal cycle of the net mass transport is weaker and follows roughly the annual variation of the net mass flux across a nearby isentropic surface

Assessing and Manipulating The Illusion of Control of Video Poker Players

The present investigation explored the presence of illusory control in recreation-al video poker players. Using a multi-monitor computer which allowed for two different types of games to be presented concurrently, one on each monitor, players were allowed to freely choose which game they wished to play. One option allowed for the player to select the cards they wished to hold and discard, while the other option was designed such that the computer automatically se-lected the most probabilistically optimal sequence of cards to hold and discard. In the first experiment, two groups of ten participants were exposed to one of two rules (accurate or inaccurate) regarding the chances of winning. No differ-ences in response allocations between the games were found. In the second experiment, thirteen participants were sequentially exposed to a non-rule base-line followed by an inaccurate and subsequently accurate rule. Twelve of the thirteen players preferred the self-selecting game, and following the introduction of an experimenter given rule that was designed to strengthen the illusion (i.e., that the self-selecting option was better), most players increased their preference for this option. However, following the introduction of an experimenter given rule that attempted to weaken the illusion, only about half the participants fol-lowed that rule and reduced playing the self-selecting option. Variability across participants was able to be explained by examining each player’s verbal talk which was emitted overtly throughout the duration of the experiment. Implica-tions for understanding the illusion of control and the verbal behavior of gam-blers are presented

El Niño and the delayed action oscillator

We study the dynamics of the El Niño phenomenon using the mathematical model of delayedaction oscillator (DAO). Topics such as the influence of the annual cycle, global warming, stochastic influences due to weather conditions and even off-equatorial heat-sinks can all be discussed using only modest analytical and numerical resources. Thus the DAO allows for a pedagogical introduction to the science of El Niño and La Niña while at the same time avoiding the need for large-scale computing resources normally associated with much more sophisticated coupled atmosphere-ocean general circulation models. It is an approach which is ideally suited for student projects both at high school and undergraduate level

A Method of Specifying the Gravity Wave Spectrum above Convection Based on Latent Heating Properties and Background Wind

The spectrum of convectively generated gravity waves is currently not resolved in general circulation models and must be parameterized. Due to the lack of understanding of the connection between convection properties and gravity waves, such parameterizations assume a source spectrum of gravity waves that is not linked to the forcing region. This paper introduces a method of specifying the gravity wave spectrum above convection based on the latent heating properties and background wind in the convective region that can be implemented in general circulation models. This method is based on linear calculations of momentum flux generated by a multifrequency thermal forcing and incorporates the effects of tropospheric mean wind in the convective environment. In the analysis, gravity waves that are generated by both the steady and the oscillatory component of the heating are included. It is shown that an accurate spectrum of convectively generated gravity waves can be deduced from the knowledge of approximate horizontal and vertical scales of the latent heating region, the heating rate, and tropospheric wind profile. 1

Simulation of the Pinatubo aerosol cloud in general circulation model

A high resolution stratospheric version of the NCAR Community Climate Model (CCM2) with an annual cycle was used to simulate the global transport and dispersion of the Pinatuboa aerosol cloud. A passive tracer was injected into the model stratosphere over the Philippines Islands on model day June15, and the transport was simulated for 180 days using an accurate semi-Lagrangian advection scheme. The simulated volcanic aerosol cloud initially drifted westward and expanded in longitude and latitude. The bulk of the aerosol cloud dispersed zonally to form a continuous belt in longitude and remained confined to the tropics (30°N- 25°S) centered near the 20 mb level for the entire 180 day model run, although a small amount was transported episodically into the upper troposphere in association with convective disturbances. Aerosol transported to the troposphere was dispersed within a few weeks into the Northern Hemisphere extratropics. In the Southern Hemisphere the aerosol was mixed into the region equatorward of the core of the polar night jet during the first 50 days, but penetration into Southern Polar latitudes was delayed until the final warming in November. These results, which are generally consistent with observed behavior of the El Chichon aerosol, will be compared with observations of the Pinatubo cloud in the course of the next several months

A comparison of observed (HALOE) and modeled (CCM2) methane and stratospheric water vapor

Recent measurements (21 September - 15 October 1992) of methane and water vapor by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) are compared with model results for the same season from a troposphere-middle atmosphere version of the National Center for Atmospheric Research (NCAR )Community Climate Model (CCM2). Several important features of the two constituent fields are well reproduced by the CCM2, despite the use of simplified methane photochemistry in the CCM2 and some notable differences between the model's zonal mean circulation and climatology. Observed features simulated by the model include the following: 1) subsidence over a deep layer in the Southern Hemisphere polar vortex; 2) widespread dehydration in the polar vortex; 3) existence of a region of low water vapor mixing ratios extending from the Antarctic into the Northern Hemisphere tropics, which suggests that Antarctic dehydration contributes to midlatitude and tropical dryness in the stratosphere

Characteristics of stratosphere-troposphere exchange in a general circulation model

Air and trace gases are exchanged between the stratosphere and the troposphere on a variety of scales; but general circulation models (GCMs) are unable to represent the smaller scales. It would be useful to see how a GCM represents stratosphere-troposphere exchange (STE), both to identify possible model deficiencies which would affect other studies and to see how important the smaller-scale physics might be in the atmosphere itself. Our understanding of observed STE depends largely on inferences from tracer distributions. In this study we examine mass exchange, water vapor exchange, and the behavior of idealized tracers and parcels to diagnose STE in the National Center for Atmospheric Research GCM, the Community Climate Model (CCM2). The CCM2 correctly represents the seasonality of mass exchange across 100 hPa, but values are uniformly too strong. Water vapor, however, indicates that tropical STE is not well represented in the CCM2; even though mean tropopause temperatures are colder than observed, the lower stratosphere is too moist. Most net mass flux occurs at water vapor mixing ratios of about 4-5 parts per million by volume (ppmv), about 1 ppmv too moist. Vertical resolution has little impact on the nature of tropical STE. In midlatitudes, CCM2 more successfully represents STE, which occurs in developing baroclinic waves and stationary anticyclones. Exchange from troposphere to stratosphere does occur but only influences the lowest few kilometers of the extratropical stratosphere, even for tracers with large vertical gradient