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RODERICK S. QUIROZ and MELVYN E. GELMAN

Abstract

The direct use of measured radiances for determining the thickness of stratospheric layers is investigated. We hypothesize that the equivalent blackbody temperature, weighted according to the transmittance weighting functions for the stratospheric channels of the satellite infrared spectrometers and the selective chopper radiometer, gives a good approximation of the geometric mean temperature of some layer within the transmittance (τv) domain 0<τv <1. A priori, it is shown that under certain conditions this is not a good assumption. However, it is of interest to determine for what atmospheric layers acceptably small error in the mean temperature, and therefore in the thickness, would be incurred. Layers based at 100-10 mb, with upper boundaries at 10-0.5 mb, are investigated using a carefully selected family of stratospheric temperature profiles and computed radiances. On the basis of physical reasoning, a high correlation of thickness with radiance is anticipated for deep layers, such as the 100- to 2-mb layer (from about 15 to 43 km), that emit a substantial part of the infrared energy reaching a satellite radiometer in a particular channel. Empirical regression curves relating thickness and radiance are developed and are compared with “blackbody” curves obtained by substituting the blackbody temperature in the hydrostatic equation. Maximum thickness-radiance correlation is found, for each infrared channel, for the layer having the best agreement of empirical and blackbody curves. For these layers, the data from a single radiation channel accounts for a reduction of variance by up to 97 percent. The utility of thickness data based on actual radiances is demonstrated through independent testing and with a sample 2-mb map constructed by adding thicknesses based on measured radiances to the observed 100-mb height field.

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KEITH W. JOHNSON and MELVYN E. GELMAN

Abstract

Daily 50- and 10-mb. height and temperature values for 3 yr. (1964–1966) are interpolated for specific locations from objectively analyzed charts. Time sections are constructed using these values, and the relationship of the time sections to the sequence of synoptic charts is discussed. Values from weekly 5-, and 2, and 0.4-mb. synoptic analyses (1964–65) are used in making vertical comparisons with the 50- and 10-mb. values.

Monthly means and standard deviations of daily values from these monthly means are calculated and are compared with similar parameters derived directly from data. Comparisons of these statistical parameters are made for three geographical sections: 1) a north-south section near 80°W., 2) an east-west section across North America in middle latitudes, and 3) an east-west section across the Western Hemisphere at high latitudes. Vertical differences in variability and standard deviation are discussed.

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Marvin A. Geller, Mao-Fou Wu, and Melvyn E. Gelman

Abstract

Monthly mean Northern Hemisphere general circulation statistics are presented for the four-year average December, January and February months of the winters 1978–79 through 1981–82. These calculations start with daily maps for eighteen pressure levels between 1000 and 0.4 mb of Northern Hemisphere temperature at 1200 GMT that are supplied by NOAA/NMC. Geopotential height and geostrophic wind are constructed using the hydrostatic and geostrophic relationships, respectively. Fields presented in this paper are zonally averaged temperature, mean zonal wind, and amplitude and phase of planetary waves with zonal wave-numbers 1-3. Diagnostic quantities, such as the northward fluxes of heat and eastward momentum by standing and transient eddies along with their wavenumber decomposition and Eliassen-Palm flux propagation vectors and divergences by the standing and transient eddies along with their wavenumber decomposition, are also given. The observations indicate that polar temperatures in the lower stratosphere are warmer in February than in December or January. Upper stratospheric mean zonal winds are also strongest in December and weakest in February, as is consistent with the thermal wind relationship. Stationary planetary waves are observed to have the largest amplitudes in January. Stationary eddy heat and momentum fluxes and the Eliassen-Palm fluxes from the standing eddies are largest in January. This is consistent with the large amplitude wavenumber 1 in January. The results of this paper are compared with those of several other works.

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KEITH W. JOHNSON, ALVIN J. MILLER, and MELVYN E. GELMAN

Abstract

Two indices are proposed that characterize and quantify the circulation and temperature fields at stratospheric constant-pressure levels. The circulation index is calculated at 60° N. latitude as a normalized difference of the squared amplitudes of wave numbers 2 and 1 of the height field. The temperature index is the mean temperature gradient hetween the North Pole and 60° N.

Comparisons of values of these parameters during several stratospheric warming episodes are utilized to show the difference between small-scale and large-scale warming events. Comparisons of values at different levels lead to the possibility of studying tropospheric-stratospheric interactions during periods of stratospheric warming.

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Marvin A. Geller, Mao-Fou Wu, and Melvyn E. Gelman

Abstract

Individual monthly mean general circulation statistics for the Northern Hemisphere winters of 1978–79, 1979–80, 1980–81, and 1981–82 are examined for the altitude region from the earth's surface to 55 km. Substantial interannual variability is found in the mean zonal geostrophic wind; planetary waves with zonal wavenumber one and two; the heat and momentum fluxes; and the divergence of the Eliassen–Palm flux. These results are compared with previous studies by other workers. This variability in the monthly means is examined further by looking at both time-latitude sections at constant pressure levels and time-height sections at constant latitudes. The implications of this interannual variability for verifying models and interpreting observations are discussed.

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MELVYN E. GELMAN, ALVIN J. MILLER, and HAROLD M. WOOLF

Abstract

This paper describes a statistical regression technique for specifying the vertical temperature profile above 10 mb from satellite radiances simulated for the Satellite Infrared Spectrometer B (SIRS B) instrument when the temperature profile up to 10 mb is known. Sensitivity of the radiance information to temperature at the high atmospheric levels is attained by subtracting, from the total radiance, that part of the radiance emanating from the known temperature profile below 10 mb. The remainder is that portion of the radiance representative of the temperature profile above 10 mb. Statistics are derived using a sample of 50 carefully selected temperature profiles representative of worldwide atmospheric conditions above 30 km during all times of the year. Regression equations are developed relating temperature at 10 pressure levels between 10 and 0.5 mb to a set of predictors [temperature at 50, 30, and 10 mb and radiance information derived from SIRS B channels 7 (679.8 cm−1) and 8 (668.7 cm−1)]. For an independent data set, root-mean-square errors in specification ranged from 2.1°C at 9 mb to 8.8°C at 0.5 mb, with the shapes of all profiles very well distinguished. Regression-specified temperatures above 10 mb are then used as first guess in simulated retrievals of complete atmospheric temperature profiles. These regression results are shown to significantly increase the accuracy of temperature retrievals at tropospheric as well as stratospheric levels over those retrievals derived using a climatological first guess.

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Larry M. McMillin, Melvyn E. Gelman, A. Sanyal, and Mojgan Sylva

Abstract

This paper presents the results of a feasibility study to evaluate a method for the use of satellite measurements as a transfer standard to determine temperature biases between radiosonde types. The method was evaluated on a sample of satellite observations that were paired with nighttime radiosonde observations. Only nighttime cases were used in this study in order to avoid the additional complication of heating of the radiosonde by solar radiation; however, the method should be equally valid in daylight. Radiances were calculated from radiosonde temperature profiles and compared to radiances for the same location as measured from the satellite. With the use of radiosonde–satellite pairs for two different radiosonde types, the satellite radiances were used to remove radiance differences due to atmospheric temperature differences from the radiosonde radiances. This step allowed radiosondes at different locations to be compared. Biases between the U.S. civilian instrument and the Väisälä instrument were derived and compared with published values; the results of the new method were found to be consistent with results obtained from direct comparisons of radiosonde instruments when measurements were made under similar atmospheric conditions. However, the direct measurements were made in a limited range of atmospheric conditions, whereas the satellite measurements were made under a wide range of atmospheric conditions. Results based on the indirect satellite comparisons showed substantial variation in the biases obtained under different atmospheric conditions. This variation is consistent with differences in temperature errors that are the result of differences in the radiation balance between the instrument and its surroundings. The results demonstrated the ability of the method to provide estimates of radiosonde biases. They also show that radiosondes are subject to substantial errors owing to longwave radiation and other sources. These errors are not only large (0−2 K), but also highly variable.

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Frederick G. Finger, Melvyn E. Gelman, Francis J. Schmidlin, Robert Leviton, and Bruce W. Kennedy

Abstract

Under the auspices of the Commission for Instruments and Methods of Observation of the World Meteorological Organization, meteorological rocketsonde intercomparisons took place at Wallops Island in March 1972 and at the Guiana Space Center, French Guiana, in September 1973. France, Japan and the United States participated in the Wallops tests, and France, the United Kingdom, the Union of Soviet Socialist Republics and the United States participated in the Guiana tests. Measurements were made during the day as well as at night.

Comparisons ire presented of temperature and wind data obtained by the different rocketsonde systems over the. altitude region from 25 to 80 km. Results indicate generally good compatibility among temperatures obtained below approximately 50 km. Above that level, biases increasing with height are evident. Temperature adjustments are derived, which, when applied to operational rocketsonde data, would in the mean achieve compatibility for synoptic analyses and other uses. Comparisons among wind observations indicate generally good agreement below approximately 60 km. However, some significant problem areas are pointed out and discussed.

The Guiana series of observations also provided valuable information on the diurnal temperature change at stratospheric and mesospheric levels. An evaluation of this aspect is presented, and results are compared with those predicted by tidal theory.

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FREDERICK G. FINGER, KEITH W. JOHNSON, MELVYN E. GELMAN, and RAYMOND M. McINTURFF

Abstract

The usefulness of Nimbus 4 satellite infrared spectrometer (SIRS)-derived temperature and height data for constant-pressure analyses at stratospheric levels is investigated by comparing SIRS data with rawinsonde observations and objective analyses of those data. Results from the various methods of comparison are difficult to interpret since systematic and random errors of observations at stratospheric altitudes do not permit the observed data to be used as an unquestioned standard. In addition, conclusions must be qualified by the fact that the SIRS information derived to date has depended in part on analyses of rawinsonde data.

The following conclusions were reached from the various comparison studies: (1) SIRS data are useful for constant-pressure analyses at stratospheric levels, (2) mean differences between analyzed rawinsonde temperatures and SIRS derivations are generally less than 3°C, (3) differences are greater during stratospheric warmings, but SIRS data generally indicate the proper trend of the temperature changes, thus adding information about the temperature of the real atmosphere to an analysis, and (4) stratospheric SIRS data after Nov. 5, 1971, can be used with more confidence than those derived before that date.

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Gerald D. Bell, Michael S. Halpert, Chester F. Ropelewski, Vernon E. Kousky, Arthur V. Douglas, Russell C. Schnell, and Melvyn E. Gelman

The global climate during 1998 was affected by opposite extremes of the ENSO cycle, with one of the strongest Pacific warm episodes (El Niño) in the historical record continuing during January–early May and Pacific cold episode (La Niña) conditions occurring from JulyñDecember. In both periods, regional temperature, rainfall, and atmospheric circulation patterns across the Pacific Ocean and the Americas were generally consistent with those observed during past warm and cold episodes.

Some of the most dramatic impacts from both episodes were observed in the Tropics, where anomalous convection was evident across the entire tropical Pacific and in most major monsoon regions of the world. Over the Americas, many of the El Niño– (La Niña–) related rainfall anomalies in the subtropical and extratropical latitudes were linked to an extension (retraction) of the jet streams and their attendant circulation features typically located over the subtropical latitudes of both the North Pacific and South Pacific.

The regions most affected by excessive El Niño–related rainfall included 1) the eastern half of the tropical Pacific, including western Ecuador and northwestern Peru, which experienced significant flooding and mudslides; 2) southeastern South America, where substantial flooding was also observed; and 3) California and much of the central and southern United States during January–March, and the central United States during April–June.

El Niño–related rainfall deficits during 1998 included 1) Indonesia and portions of northern Australia; 2) the Amazon Basin, in association with a substantially weaker-than-normal South American monsoon circulation; 3) Mexico, which experienced extreme drought throughout the El Niño episode; and 4) the Gulf Coast states of the United States, which experienced extreme drought during April–June 1998. The El Niño also contributed to extreme warmth across North America during January–May.

The primary La Niña–related precipitation anomalies included 1) increased rainfall across Indonesia, and a nearly complete disappearance of rainfall across the east-central equatorial Pacific; 2) above-normal rains across northwestern, eastern, and northern Australia; 3) increased monsoon rains across central America and Mexico during October–December; and 4) dryness across equatorial eastern Africa.

The active 1998 North Atlantic hurricane season featured 14 named storms (9 of which became hurricanes) and the strongest October hurricane (Mitch) in the historical record. In Honduras and Nicaragua extreme flooding and mudslides associated with Hurricane Mitch claimed more than 11 000 lives. During the peak of activity in August–September, the vertical wind shear across the western Atlantic, along with both the structure and location of the African easterly jet, were typical of other active seasons.

Other regional aspects of the short-term climate included 1) record rainfall and massive flooding in the Yangtze River Basin of central China during June–July; 2) a drier and shorter-than-normal 1997/98 rainy season in southern Africa; 3) above-normal rains across the northern section of the African Sahel during June–September 1998; and 4) a continuation of record warmth across Canada during June–November.

Global annual mean surface temperatures during 1998 for land and marine areas were 0.56°C above the 1961–90 base period means. This record warmth surpasses the previous highest anomaly of +0.43°C set in 1997. Record warmth was also observed in the global Tropics and Northern Hemisphere extratropics during the year, and is partly linked to the strong El Nino conditions during January–early May.

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