Institute Of Atmospheric Physics Research Articles

Modelling the interannual variation of regional precipitation over China

The interannual change of regional precipitation over China during 1979–1988, simulated by the IAP 2-L AGCM (the atmospheric general circulation model) developed in the Institute of Atmospheric Physics and by using the observational monthly sea surface temperature (SST) and sea ice occupations, was analysed and compared with that of observation. Results show that the abilities of the model to simulate the interannual variabilities of precipitation are different from one region to another in China. Studies indicate that the regional precipitation interannual variation which is correlated to the strong sign of sea surface temperature anomalies (SSTA) could be simulated well by the model, strong SSTA is important for the seasonal and extra-seasonal climate predictions through climate models. The results also suggest that the horizontal resolution of the model should be more refined in order to give better representations of regional details.

A free surface general circulation model for the tropical Pacific Ocean

A free surface tropical ocean model is presented for explicit prediction of the actual topography of sea surface and other variables, for further intercomparative studies among differently formulated oceanic general circulation models (OGCMs), and data assimilation of the observed sea level. Based on an OGCM without the rigid‐lid approximation developed at the Institute of Atmospheric Physics (Beijing, China), the dynamic formulation and numerics of the model have some unique features such as explicit treatment of sea level elevation as a prognostic variable, calculation of the departures of thermodynamic variables in time integration by subtracting the standard stratification, introduction of the σ vertical coordinate, total available energy consideration, and a barotropic‐baroclinic mode‐splitting algorithm for computational efficiency. The model covers the tropical Pacific Ocean between 30°N and 30°S with horizontal grid spacing of 1° in latitude and 2° in longitude. There are 14 vertical layers with 8 layers in the top 200 m. Prior to further applications of the model, simulations of the annual mean and seasonal cycle of the tropical Pacific Ocean have been carried out to examine performance of this free surface OGCM forced by climatological atmospheric fluxes. It is shown that with the appropriate treatments of the governing equations and numerical methods, the free surface baroclinic OGCM can be computed at least as efficiently as a rigid‐lid model. By eliminating the rigid‐lid approximation, keeping explicitly the available surface energy and energy conversion related with divergence of vertically integrated flow, and by subtracting the standard stratification, the model would be more accurate, reasonable, and effective in representing the energy cycle in the real ocean. The misrepresentation of energy conversion caused by the rigid‐lid approximation is shown and estimated on the basis of the simulated data. The simulated results show that the model is able to reproduce not only the observed current system and thermal structure and their variations but also the actual sea level in the tropical Pacific, which shares many observed sea surface features. The preliminary comparison with other existing simulations shows some noticeable differences in the simulated circulation in spite of using the same wind stress, which need to be investigated further.

Introduction to Einstein's contribution to time-series analysis

HE HISTORY of ideas evolves endlessly, sometimes becoming more accurate with the passage of time, sometimes more distorted. This is so even for ideas originating as recently as 100 years ago. In spite of the documentation provided by published books and papers, personal letters, and recollections, historians are inevitably limited by the substantial loss of information with the passing of participants and by the unavoidable subjectivityof the historians’ own interpretations of the available information. The recent discovery of a long forgotten early paper by Albert Einstein on the topic of time-series analysis [I] provides an interesting example of the evolutionary process of tracing the history of ideas. This very brief paper, entitled ”Method for the determination of the statistical values of observations concerning quantities subject to irregular fluctuations,’’ was originally published in the Archives des Sciences Physiques et Naturelles in 1914 following an oral presentation at a meeting of the Swiss Physical Society earlier that year. An English translation of this paper is reproduced in this issue of the ASSP Magazine. The paper discusses the autocorrelation function and its relationship to the spectral content of a time-series, the crosscorrelation function as a measure of interdependence of two time-series, and two methods for measurementor computation of spectral content: the frequency-smoothed periodogram method and the Fourier-transformed autocorrelation method. Two experts in the field of time-series analysis, Professor A. M. Yaglom from the Instituteof Atmospheric Physics, Academy of Sciences of the USSR, and Professor P. R. Masani from the Department of Mathematics, University of Pittsburgh, have written extensive commentaries on this paper and its place in the history of time-series analysis [2], [3]. The differences in the backgrounds and points of view of this physicist and this mathematician have led to some interesting differences in their interpretations of Einstein‘s accomplishments in his paper.

A High-Speed Time-Resolved Spectroscopic Study of the Lightning Return Stroke: Part I. A Qualitative Analysis

Abstract The first time-resolved spectra of return strokes between the cloud and ground have been obtained. During the summers of 1965 and 1966 twenty-two spectra were obtained at the Institute of Atmospheric Physics, Tuscon, Ariz. The spectra were recorded with two high-speed streaking cameras converted to slitless spectrographs. The conversion was accomplished by mounting Bausch and Lomb replica transmission gratings in front of the cameras' objective lenses. The gratings are blazed for 5500 A and have 600 lines mm−1. Inverse dispersions from 70'140 A mm−1 were used. Most of the data were obtained with a Beckman and Whitley high-speed camera. A 200-mm objective lens was used to focus the return stroke on a 0.5-mm horizontal slit. Thus, a 10-m section of the lightning channel was isolated for a discharge occurring at a distance of 4 km. Data have been obtained with a time resolution of 2-5 μsec. All spectra have been recorded on film calibrated for intensity and wavelength with a xenon source of known re...

Growth in Four Species of Sonoran Desert Trees

Trees of moist, warm tropical areas where contrasting seasons are lacking pass from one season to the next with little synchronization of phenologies among species. This is in direct contrast with trees of temperate regions where conditions during one or more seasons drastically curtail growth phenomiiena. Many detailed studies of tree growth in temperate regioiis (see bibliography by Kozlowski 1956) have slhown (lefinite periods of growth quiescenice that can be correlated with insufficient soil moisture, unfavorable temperatures, variations in duration of darkness, or some combination of these factors. Studies of tree growth in arid subtropical regions (Phillips 1927, MacDougal 1920, 1936, 1938, Fahn 1955, 1958) are few in nuumber, and relatively little is kno,wn of the periodicity of stemradius change where drouth periods are often sharply defined and( where winter temperatures are mild. This paper presents the results of a study of stemi-ra(litus chatnges and season of leaf, flower, anid fruit dlevelopmeint in four species of small leguminous trees, eaclh of whiclh has a widlespread distribution in the arid subtropical portion of North America referred to as the Sonoran Desert (sensu Shreve 1951). The four species studied were Olneva tesota A. Gray (ironwood), Prosopis juliflora (Swartz) DC var. velittina (Woot.) Sarg. (velvet mesquite), Cercidin ni viicrophyliumtut (Torr. ) Rose & Johnston (foothill palo-verde), and C. floriduiwPi Beluth. (blue palo-verde). Trees, mostly legumes, occur throtughout much of the Sonorani Desert anid mlay be founid under regimes of predominanitlv winter or summer precipitation or with precipitation divided betweenl winiter and sumiimer. Temperature conditions vary as well. In the north, winter minima frequently fall below 320 F (00 C), while a gradual amelioration of wiinter temperatures toward the south produces large areas of the deserts that are often frost-free for several consecutive years. Tree growth was studied in the northeasterln portioln of the Sonoraii Desert in the viciniity of TuLcson, Arizona, where the average total annual precipitationi is al)out 11 inches (280 mm) and is abotut eqtually divided between winter and summer. W\Vinter miiinimial temperatures frequently fall below freezing here. The trees selected for study vary 1 Presenit address: U.S. Geological Survey, Institute of Atmospheric Physics, Uiniversity of Arizolna, Tucson, Ariz. considerably in their growth habits and include an evergreen species (0. tesota) and species with foliage appearing only during periods of favorable combinations of moisture and temperature (C. floridum, C. microphyllum, and P. juliflora var. velutina). The stems of two of the species (C. floridum and C. microphyllum) have smooth, greeni bark apparently allowing for a high level of photosyntlhetic activity even in the absence of leaves. The topographic preference of these trees varies throughout their ranges but within the study area two of the species (P. juliflora. var. velutina and C. floridum) are found typically along the margins of intermittent stream courses whereas the other two occur on the adjacent uplands. This study was aided by funds from National Science Foundation Grant G-3218. I should like to express my appreciation to Mr. S. Clark Martin of the U.S. Forest Service, who made available the precipitationi data. I am indebted to Dr. R. Daubenmire, Dr. H. C. Fritts, and Dr. Henry Tucker for reviewing the manuscript.

CUMULUS CLOUD PRECIPITATION AS REVEALED BY RADAR-ARIZONA 1955

An AN/TPS-10 radar, located at the Institute of Atmospheric Physics, University of Arizona, has been used to make extensive measurements of radar returns from cumulus clouds in the vicinity of Tucson. Data from ten days in the summer of 1955 have been analyzed with a view toward establishing the level of first formation of precipitation, day-to-day variation, average dimensions of first echo, average duration, and fraction reaching ground. Strong day-to-day variations and mountain effects are revealed. Although echoes form much more frequently over mountains than over nearby valleys, these echoes individually are less likely to produce rain at the ground.

Establishment of an Institute of Atmospheric Physics at the University of Arizona at Tucson

Establishment of an Institute of Atmospheric Physics at the University of Arizona at Tucson