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Roderick S. Quiroz

Abstract

In preference to the use of persistent height anomalies for determining the presence of blocking, new criteria were developed which take the observed flow conditions into account. These criteria were applied daily at 500 mb, using filtered Northern Hemisphere height maps retaining zonal waves 0–5, beginning in July 1981. Blocking statistics for the 3-yr period through June 1984 are in remarkably close agreement with the results from longer-period published data sets involving the use of a split-jet flow as a principal criterion. Thus this data set, albeit short, is deemed appropriate for investigating the long-wave properties of blocks.

During July 1981–June 1984, 47 blocks were observed; the long-wave composition of blocks lasting at least 10 days (24 cases) is examined in detail. Contrary to Austin's (1980) hypothesis that blocking should arise from the constructive interference of stationary long waves with enhanced amplitude but normal phase, it is found that traveling waves (predominantly retrogressive) played a significant role in 20 of the 24 cases. The long waves making up these blocks, in the zonal wavenumber domain 1–4, moreover had a phase behavior consistent with the wavenumber dependence in the Rossby wave dispersion equation.

A dramatic increase in Northern Hemisphere blocking activity within the sample, from 1982–83 to 1983–84, is shown to be due mainly to increases in the Pacific–North American (PNA) and North Soviet Union (NSU) sectors. A time–longitude diagram depicts the shifting of blocking activity from the main region of blocking, the Atlantic–west European area, to the PNA and NSU sectors. These regional shifts were substantially associated with the longitudinal phase pattern of travelling waves 1 in high latitudes.

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Roderick S. Quiroz

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No abstract available.

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Roderick S. Quiroz

Abstract

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Roderick S. Quiroz

Abstract

Relationships among the high-latitude stratospheric zonal wind, the tropospheric zonal wind in the region of the subtropical jet and over the equator, the Southern Oscillation, and the stratospheric tropical quasi-biennial oscillation (QBO) were examined from monthly anomaly data for 13 years (1968–80). Patterns of correlation wore found which are broadly consistent with the theory on vertical and latitudinal Rossby wave propagation, with high correlations diminishing rapidly in association with easterly basic flow. Lag correlations as high as 0.8–0.9 were found for leads of ∼1–7 months, based on three-month average anomalies for successive months. The simplified lead path is from Southern Oscillation to equatorial winds to subtropical winds to stratospheric high-latitude winds. Relationships involving the QBO appear weak compared to those involving the extratropical flows, the tropospheric equatorial flow of the east Pacific, and the Southern Oscillation. Even so, the structure of correlation found between the stratospheric high-latitude winds (or height gradients) and the QBO is consistent with “compositing” results of Holton and Tan (1980, 1982); moreover, the correlations found between the stratospheric high-latitude flow and the Southern Oscillation are consistent with compositing results of van Loon et al. (1982). Spectra for the variables examined all show a quasi-biennial signal, but coherences involving the QBO at periods 20–30 months were found to be weak to moderate, whereas coherences involving other pairs of variables were moderate to strong.

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Roderick S. Quiroz

Abstract

The period of the stratospheric quasi-biennial oscillation (QBO) in zonal wind is studied with the aid of rocket observations at Kwaialein (9°N, 168°N) for altitudes 25–35 km and rawinsonde observations for Balboa (9°N, 80°W) for pressure levels 50–10 mb, the latter for 1951–79. Since 1951, the period has varied between 21 and 34 months, with an average value near 28 months (2.3 years) at any height, but with slightly greater variability in the lower stratosphere. While the expected downward propagation of easterly and westerly phase was clearly observed, a downward propagation of period is not evident, consistent with the variable structure of the phase descent rates. A systematic modulation of QBO period occurred approximately and inversely in accord with the level of solar activity. Physical mechanisms that might account for the observed variation in QBO period are identified, within the context of assumed dynamical forcing by tropospheric waves. Comprehensive insight into the actual process accounting for the observed period modulation would be gained from improved observational data, including observations of solar ultraviolet behavior.

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RODERICK S. QUIROZ

Abstract

A major warming above the 10-mb level in February 1966 is described with the aid of rocket data from high-latitude stations at Heiss Island (81° N.) and Churchill (59° N.), together with high-level radiosonde reports from Berlin, Germany. At Heiss Island a temperature increase of 85°C is deduced at an altitude of 32 km, preceded by a record wind of nearly 400 kt (at 39 km), verified through thermal wind computations. Extraordinary vertical motions reaching 60 cm sec−1 are calculated from the thermodynamic equation. The warming is shown to have been similar to major warmings of the lower stratosphere in several respects, including the occurrence of 1) high winds related to pressure-gradient intensification several days before the peak temperature and 2) upward vertical motion in high latitudes in response to strong horizontal advection. Rocket soundings extending to the mesopause indicate the occurrence of warming to a height of at least 70 km. The mesospheric data further suggest that prior to warming events the upper polar mesosphere is characteristically cold, in accord with radiative calculations for winter. However, the mesospheric analysis is hampered by poor sampling, and an improved program of observation is needed to clarify the full structure of “stratospheric” warmings.

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Roderick S. Quiroz

Abstract

Knowledge of the air density at altitudes above 30 km is needed for such applications as the calculation of space shuttle reentry heating. A method is described for deriving hemispheric (or global) horizontal density fields at 40–60 km directly from radiance maps based on infrared measurements by such instruments as the Nimbus 4 Satellite Infrared Spectrometer and the Selective Chopper Radiometer. Direct regression of air density with the radiance measured in individual channels of these instruments is investigated. From hydrostatic considerations, maximum density-radiance correlation is expected to occur at about 2.5 scale-heights above the level of maximum temperature-radiance correlation; the latter is found near the peak of the transmittance weighting function for each channel. This expectation is substantially verified with the aid of a statistical sample of rocketsonde temperature and density profiles and radiances computed with the appropriate transmittance data. Regression equations are developed for specifying the density with a standard error within 5–7% of the observed density. For the period of a major stratospheric warming in January–February 1973, sample density maps at 50 km are shown, derived from radiance measurements of the NOAA-2 Vertical Temperature Profile Radiometer. These indicate a density increase by more than 50% near the North Pole, from late January to early February.

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RODERICK S. QUIROZ
and
ALVIN J. MILLER

Abstract

Rocket wind soundings for several stations within 10° latitude of the equator are used to analyze details of the structure of the recently discovered semi-annual wind variation in the equatorial upper stratosphere. The cycle is characterized by winter and summer easterlies and equinoctial westerlies and in 1966 appeared to have maximum amplitude at 45–50 km. Its global extent is confirmed with the aid of rocket data from widely separated longitudes. The semi-annual variation is discussed in relation to the quasi-biennial oscillation, which has maximum amplitude in the lower stratosphere. A possible explanation of the origin of the semi-annual variation is mentioned and attention is called to semi-annual variations in other parameters in the upper atmosphere.

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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 (τ v ) domain 0<τ v <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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