Search Results

You are looking at 1 - 10 of 20 items for :

  • Author or Editor: S. Wang x
  • Journal of the Atmospheric Sciences x
  • Refine by Access: All Content x
Clear All Modify Search
P. K. Wang and S. M. Denzer

Abstract

Simple mathematical expressions are presented for describing the shapes of some plane hexagonal snow crystals. These expressions provide convenient means for cloud physical calculations and can also serve as a method for quantitative classification of snow crystal shapes. A few examples am worked out to illustrate the use of these expressions. They can be further developed for describing more complicated shapes.

Full access
J. L. Lions, O. P. Manley, R. Temam, and S. Wang

Abstract

In a series of recent papers, some of the authors have addressed with mathematical rigor some aspects of the primitive equations governing the large-scale atmospheric motion. Among other results, they derived without evaluating it an expression for the dimension of the attractor for those equations.

It is known that the long-term behavior of the motion and states of the atmosphere can be described by the global attractor. Namely, starting with a given initial value, the solution will tend to the attractor as t goes to infinity. The dimension estimate of the global attractor is evaluated in this article, showing that this global attractor possesses a finite but large number of degrees of freedom. Using some arguments based on the known physical dissipation mechanisms, the bound on the dimension of the attractor in terms of the observable quantities governing the heating and energy dissipation accompanying the motion of the atmosphere is made immediately transparent. Consequently, to the extent that the resolution needed in numerical simulations of the long-term atmospheric motion is related to the dimension of the attractor, the result in this article suggests that the required resolution is quite sensitive to the magnitude of the effective (or eddy) viscosity, while it appears to be less sensitive to the details of the way that the atmosphere is heated.

Full access
Xuyang Ge, Tim Li, Yuqing Wang, and Melinda S. Peng

Abstract

The three-dimensional (3D) Rossby wave energy dispersion of a tropical cyclone (TC) is studied using a baroclinic primitive equation model. The model is initialized with a symmetric vortex on a beta plane in an environment at rest. The vortex intensifies while becoming asymmetric and moving northwestward because of the beta effect. A synoptic-scale wave train forms in its wake a few days later. The energy-dispersion-induced Rossby wave train has a noticeable baroclinic structure with alternating cyclonic–anticyclonic–cyclonic (anticyclonic–cyclonic–anticyclonic) circulations in the lower (upper) troposphere.

A key feature associated with the 3D wave train development is a downward propagation of the relative vorticity and kinetic energy. Because of the vertical differential inertial stability, the upper-level wave train develops faster than the lower-level counterpart. The upper anticyclonic circulation rapidly induces an intense asymmetric outflow jet in the southeast quadrant, and then further influences the lower-level Rossby wave train. On one hand, the outflow jet exerts an indirect effect on the lower-level wave train strength through changing TC intensity and structure. On the other hand, it triggers downward energy propagation that further enhances the lower-level Rossby wave train. A sudden removal of the diabatic heating may initially accelerate the energy dispersion through the increase of the radius of maximum wind and the reduction of the lower-level inflow. The latter may modulate the group velocity of the Rossby wave train through the Doppler shift effect. The 3D numerical results illustrate more complicated Rossby wave energy dispersion characteristics than 2D barotropic dynamics.

Full access
S. J. Martin, P. K. Wang, and H. R. Pruppacher

Abstract

Two theoretical models are presented which allow computing the efficiency with which aerosol particles of radius 0.001 ≤ r ≤ 10 μm are collected by simple ice crystal plates of radius 50 ≤ ac ≤ 640 μm, in air of various relative humidity, temperature and pressure. Particle capture due to Brownian diffusion, thermophoresis, diffusiophoresis and inertial impaction is considered. It is shown that, analogous to water drops, ice crystal plates exhibit a minimum collection efficiency within a specific size interval of aerosol particles. This minimum is strongly affected by the relative humidity of the ambient air. The collection efficiency of particles with r > 1 μm is controlled by the flow field around the ice crystal, while the collection efficiency of particles with r < 0.01 μm is controlled by convective Brownian diffusion. Trajectory analysis predicts that aerosol particles are preferentially captured by the ice crystal rim. Our theoretical results are found to agree satisfactorily with laboratory studies presently available.

Full access
P. K. Wang, S. N. Grover, and H. R. Pruppacher

Abstract

A theoretical model is described which determines the efficiency E with which aerosol particles of radius r are collected by water drops of radius a due to the combined action of Brownian diffusion, thermo- and diffusiophoresis and electric forces, in the absence of inertial impaction effects. The results of this model are combined with the results of our earlier model which determines the collection efficiency of drops for particles due to the combined action of inertial impaction, thermo- and diffusiophoresis and electric forces, in the absence of effects due to Brownian diffusion. Both models combined quantitatively determine the variation of E vs r for 0.001≤r≤10 μm, and 42≤a≤310 μm, for relative humidities up to and including 100%, and for electric charges on drops and aerosol particles ranging in magnitude up to that found under thunder-storm conditions. In particular, a combination of both models allows a quantitative description of the particle size range where the collection efficiency of drops is minimum.

Full access
Zhuo Wang, Weiwei Li, Melinda S. Peng, Xianan Jiang, Ron McTaggart-Cowan, and Christopher A. Davis

Abstract

Practical predictability of tropical cyclogenesis over the North Atlantic is evaluated in different synoptic flow regimes using the NCEP Global Ensemble Forecast System (GEFS) reforecasts with forecast lead time up to two weeks. Synoptic flow regimes are represented by tropical cyclogenesis pathways defined in a previous study based on the low-level baroclinicity and upper-level forcing of the genesis environmental state, including nonbaroclinic, low-level baroclinic, trough-induced, weak tropical transition (TT), and strong TT pathways. It is found that the strong TT and weak TT pathways have lower predictability than the other pathways, linked to the lower predictability of vertical wind shear and midlevel humidity in the genesis vicinity of a developing TT storm. Further analysis suggests that stronger extratropical influences contribute to lower genesis predictability. It is also shown that the regional and seasonal variations of the genesis predictive skill in the GEFS can be largely explained by the relative frequency of occurrence of each pathway and the predictability differences among pathways. Predictability of tropical cyclogenesis is further discussed using the concept of the genesis potential index.

Full access
P. Jing, D. M. Cunnold, H. J. Wang, and E-S. Yang

Abstract

This paper investigates isentropic ozone exchange between the extratropical lower stratosphere and the subtropical upper troposphere in the Northern Hemisphere. The quantification method is based on the potential vorticity (PV) mapping of Stratospheric Aerosol and Gas Experiment (SAGE)-II ozone measurements and contour advection calculations using the NASA Goddard Space Center Data Assimilation Office (DAO) analysis for the year 1990. The magnitude of the annual isentropic stratosphere-to-troposphere ozone flux is calculated to be approximately twice the flux that is directed from the troposphere into the stratosphere. The net effect is that ∼46 × 109 kg yr−1 of ozone are transferred quasi horizontally from the extratropical lower stratosphere into the subtropical upper troposphere between the isentropic surfaces of 330 and 370 K. The estimated monthly ozone fluxes show that the isentropic cross-tropopause ozone transport is stronger in summer/fall than in winter/ spring, and this seasonality is more obvious at the upper three levels (i.e., 345, 355, and 365 K) than at 335 K. The distributions of the estimated monthly ozone fluxes indicate that the isentropic stratosphere-to-troposphere ozone exchange is associated with wave breaking and occurs preferentially over the eastern Atlantic Ocean and northwest Africa in winter and over the Atlantic and Pacific Oceans in summer.

Full access
C. Walcek, P. K. Wang, J. H. Topalian, S. K. Mitra, and H. R. Pruppacher

Abstract

An experimental method involving the UCLA Rain Shaft is described. This method allows determining the rate at which SO2 is scavenged from air by freely falling water drops. In the present experiment water drops of radii near 300 μm were allowed to pass through a chamber filled with SO2 whose partial pressure was determined by an infrared spectrometer. By varying the length of the gas compartment, the drops could be exposed to SO2 for different intervals of time. An electrochemical method verified by three quantitative chemical methods was used to determine the total amount of sulfur taken up by the drops falling through the gas compartment. The present experimental results were compared with the results from our theoretical model (Baboolal et at., 1981), which was evaluated for the present experimental conditions. Satisfactory agreement between experiment and theory was found.

Full access
Gan Zhang, Zhuo Wang, Timothy J. Dunkerton, Melinda S. Peng, and Gudrun Magnusdottir

Abstract

With warm sea surface temperature (SST) anomalies in the tropical Atlantic and cold SST anomalies in the east Pacific, the unusually quiet hurricane season in 2013 was a surprise to the hurricane community. The authors’ analyses suggest that the substantially suppressed Atlantic tropical cyclone (TC) activity in August 2013 can be attributed to frequent breaking of midlatitude Rossby waves, which led to the equatorward intrusion of cold and dry extratropical air. The resultant mid- to upper-tropospheric dryness and strong vertical wind shear hindered TC development. Using the empirical orthogonal function analysis, the active Rossby wave breaking in August 2013 was found to be associated with a recurrent mode of the midlatitude jet stream over the North Atlantic, which represents the variability of the intensity and zonal extent of the jet. This mode is significantly correlated with Atlantic hurricane frequency. The correlation coefficient is comparable to the correlation of Atlantic hurricane frequency with the main development region (MDR) relative SST and higher than that with the Niño-3.4 index. This study highlights the extratropical impacts on Atlantic TC activity, which may have important implications for the seasonal predictability of Atlantic TCs.

Full access
S. Garimella, D. A. Rothenberg, M. J. Wolf, C. Wang, and D. J. Cziczo

Abstract

Field and laboratory measurements using continuous flow diffusion chambers (CFDCs) have been used to construct parameterizations of the number of ice nucleating particles (INPs) in mixed-phase and completely glaciated clouds in weather and climate models. Because of flow nonidealities, CFDC measurements are subject to systematic low biases. Here, the authors investigate the effects of this undercounting bias on simulated cloud forcing in a global climate model. The authors assess the influence of measurement variability by constructing a stochastic parameterization framework to endogenize measurement uncertainty. The authors find that simulated anthropogenic longwave ice-bearing cloud forcing in a global climate model can vary up to 0.8 W m−2 and can change sign from positive to negative within the experimentally constrained bias range. Considering the variability in the undercounting bias, in a range consistent with recent experiments, leads to a larger negative cloud forcing than that when the variability is ignored and only a constant bias is assumed.

Full access