Search Results

You are looking at 1 - 10 of 10 items for :

  • Author or Editor: Jan Paegle x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: Content accessible to me x
Clear All Modify Search
Jan Paegle

Abstract

The transient adjustment of the baroclinic structure of a warm core disturbance forced by heating is studied as an initial value problem. It is found that the divergent flow in convective regions adjusts on a time scale of a few hours, and the surrounding divergence field outward to about 2000 km adjusts on a time scale of about 1 day. This rapid adjustment is due to the outward radiation of gravity inertia waves. The adjustment is sufficiently rapid that diurnally periodic forcings produce divergence fields that are almost in phase, and in practically instantaneous equilibrium with the forcings.

In the case of latent heating associated with local precipitation rates in excess of a few centimeters per day, the strongly anticyclonic upper tropospheric pressure field may render the balance equation non-elliptic. When they occur in the tropics, isolated events of this magnitude can produce cross-isobaric flows on the order of 1 m s−1 outward to beyond 2000 km. A plausible influence of these tropical flows upon midlatitudes is hypothesized, following the argument in a climatological study by Blackmon et al. (1977). The present results suggest that the mechanism in question can act on time scales as short as one or two days after the inception of a strong tropical disturbance.

Full access
Julia Paegle and Jan Paegle

Abstract

The effect of friction in strongly divergent steady flows is studied. It is found that friction weakens flow divergence out of strong high-pressure centers, contrary to the more commonly studied case for weaker high-pressure centers in rotating flows, for which friction produces divergence. The stability of the solution is discussed for the general case on a linear basis. Nonlinear analytic solutions are presented for the case of no deformation in the flow. The conclusions are quantified in a drag, deformation and Laplacian of geopotential parameter space.

Full access
Julia Nogues Paegle and Jan Paegle

Abstract

Frequency spectra of heights and geostrophic vorticities are computed for several points over the western continental United States and eastern Pacific. These spectra exhibit horizontal variations which appear to be, at least partly, attributable to the underlying topography. This conclusion is supported by a highly simplified, barotropic, mountain-flow model.

Full access
Julia Nogues Paegle and Jan Paegle

Abstract

Time-dependent flow solutions for steady supergradient pressure patterns are presented for a variety of initial flow configurations. These solutions discriminate initial conditions and pressure patterns that produce stable and unstable flow evolutions. It is shown that steady-state divergent flows are realizable for commonly observed pressure patterns of the upper troposphere. In these cases, the steady state is approached on relatively short time scales. Solutions agree roughly with observed features of atmospheric flows and constitute a plausible explanation for strong upper level outflows.

Full access
Jan Paegle, Julia N. Paegle, and Hong Yan

Abstract

Among the various energy transfer mechanisms that might be relevant for teleconnections between tropical and higher latitudes, Rossby wave propagation is certainly one of the most important. In view of this, it is of interest to understand how the propagation of Rossby waves might be affected by ambient flows which locally may be unable to sustain oscillations due to vorticity gradients. This concept is re-examined based on the observation that there are large areas over the Pacific where the upper tropospheric absolute vorticity and its horizontal gradient are small. These key areas for teleconnections might be suspected to be unfavorable to the local propagation of Rossby waves. Results of integrations of the barotropic vorticity equation on the sphere are presented to show the role that regions with small absolute vorticity gradient play in this problem. Implications regarding the maintenance of blocks and the influence of divergent effects are also addressed.

Full access
Jan Paegle and J. E. Geisler

Abstract

The low-level circulation in summer over the western Indian Ocean is characterized by southeast trades that are channeled near the African coast into a concentrated southerly flow across the equator and thence north-eastward into the southwest monsoon over the Arabian Sea. It is widely accepted that deflection by the East African highlands is responsible for this flow configuration. Existing theoretical models to a greater or lesser extent, build in this deflection by imposing a western boundary extending all the way to the top of the fluid or by prescribing longitudinally dependent sources and sinks for driving the flow.

The purpose of this study is to determine what flow configuration occurs when these constraints are removed. For this we use zonally symmetric forcing to drive a planetary boundary layer model formulated in a terrain-following coordinate system that permits fluid to flow over as well as along, a topographic barrier. The results support the conclusion that East African topography alone can channel incident flow into a pattern with most of the observed features. An analysis of the diurnal oscillation in the model suggests a mechanism for the diurnal variation of low-level wind observed in northeastern Somalia.

Full access
Jan Paegle and Wayman E. Baker

Abstract

Time averages of the latitudinal distribution of kinetic energy and terms of the kinetic energy equation are presented as depicted by the Goddard Laboratory for Atmospheric Science (GLAS) analyses of the First GARP Global Experiment (FGGE) during the First Special Observing Period (SOP-1). Monthly averages display peaks in the stationary wave energy at 30°N and in the tropics. Global decompositions of the streamfunction and velocity potential in spherical harmonics are truncated at the fourth degree. The kinetic energy distribution of the associated wind field displays peaks in the tropics and northern mid-latitudes in January, but only a tropical peak in February.

The Eliassen-Palm relationship for latitudinal momentum and geopotential wave transport appears to have some support in these analyses, particularly in the mid-latitudes. In the deep tropics, latitudinal convergence of the fully resolved stationary wave momentum transport accompanies latitudinal convergence of stationary wave geopotential flux in westerly flow, in contradiction to this relationship.

Such results make it difficult to interpret time averages in terms of idealized wave propagation and linear theories. However, there is an interesting correspondence between observed weekly averages of the global-scale kinetic energy and the zonally averaged wind.

Full access
Jan Paegle and Wayman E. Baker

Abstract

The vertical and temporal Structure of the global scale flow in the Goddard Laboratory for Atmospheric Sciences analyses of data from the First GARP Global Experiment are presented. The fields are represented in terms of spherical harmonic expansions of the streamfunction, velocity potential and geopotential. The global scale patterns are obtained from triangular truncations of such series, neglecting terms past the fourth degree.

Some modes display prominent high frequency oscillations in the velocity potential and geopotential height that may be related to diurnal cycles of cumulus convection. Such oscillations are not apparent in the streamfunction. Low-order harmonics with nodes only along latitude circles are nearly equivalent barotropic. However, those harmonics that have no nodes between the poles reverse phase with height.

The following conclusions are drawn regarding the global scale patterns: 1) Since the divergent component of the meridional flow is not much smaller than the rotational part, the global scale pattern resembles forced modes of linear tidal theory more closely than it resembles free modes. 2) Because the vertical structure reverses, longitudinal heating gradients are probably important to the forcing. 3) The high frequency oscillations of the velocity potential and height field imply high frequency components in the forcing due to heating. 4) Monthly and weekly averages display suggestive teleconnection patterns.

Full access
Kingtse C. Mo, Julia Nogues-Paegle, and Jan Paegle

Abstract

The physical mechanisms responsible for the onset and maintenance of the 1993 summer floods were examined using the localized Eliassen-Palm flux diagnostics and solutions of a single-level primitive equation model linearized about a meridionally varying basic state. The unusually long persistent summer pattern is linked with the marked transient eddy activity in late May and June. The feedback of eddies in the time mean flow caused a strengthening and eastward extension of the Pacific jet and a strengthening of the jet over North America. Results from the model suggest that the summer pattern may be interpreted as that of a lee trough forced by the Rocky Mountains in the presence of a strong westerly mean flow maintained by the eddies upstream.

Composites from cases similar to that of the 1993 summer exhibit strong low-level southerly flow cast of the Rockies and suggest that the low-level jet may be an important mechanism to sustain the anomalous rainfall.

It is concluded that the effect of the eddies in maintaining a strong upper-level zonal flow, the role of the Rockies in sustaining a lee trough, and an associated low-level jet that brings in tropical moisture are essential ingredients in developing and maintaining floodlike conditions over the central United States.

Full access
Wilford G. Zdunkowski, Ronald M. Welch, and Jan Paegle

Abstract

A dynamic-numerical model is utilized to study the impact of air pollution on the temperature and wind distributions of the planetary boundary layer. The mathematical model uses a rather complete radiative treatment which comprises the entire solar and infrared spectrum ranging from 0.29 to 100 µm. In the solar spectral range, the absorption by water vapor, nitrogen dioxide and industrial haze is fully accounted for in addition to multiple scattering by air molecules and haze particles. In the spectral region of the strong absorption hands of the infrared emission spectrum, the effect of aerosol is very small and is disregarded. The emissivity method is applied here, allowing full treatment of the overlapping effects of water vapor and carbon dioxide. In the window region, however, the effect of aerosol and water vapor absorption and emission is taken into account in addition to multiple scattering by aerosol particles. The radiative treatment accounts for the influence of relative humidity on the particle distribution function and on the complex index of refraction of the aerosol. The spherical harmonic method is used to handle the scattering problem.

The dynamical part of the analysis consists of the numerical solution of a coupled system of partial differential equations comprising the equation of horizontal mean motion, the thermodynamic equations of the air and the soil, and the transport equations of moisture and pollution. Various models of the exchange coefficient are used to study the impact of model assumptions on the computed distributions of temperature, pollutant material and wind. It is found that the choice of the exchange model is not critical but has some effect on the model computations. The present calculations show that the maximum impact of air pollution on the evolution of temperature and wind profiles is highly significant, thus verifying the previous conclusions of Zdunkowski and McQuage (1972).

Full access