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L. F. HUBERT and A. F. KRUEGER

Abstract

Satellite photographs of horizontal eddy patterns are presented and the conditions associated with their formation are discussed. It is shown that some map be purely mechnnical eddies produced by an obstacle (islands) in the flow, others may be the result of inertial oscillation, and others may be produced by inertial instability. Gravity waves on a low inversion are suggested to be the key mechanism producing instability.

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A. F. KRUEGER and T. I. GRAY JR.

Abstract

The large-scale air-sea interaction over the equatorial Pacific proposed by Bjerknes is investigated. It was found from a study of the Canton Island record that ocean temperature, rainfall, trade wind flow, and equivalent potential temperature are related and undergo long-term variations with periods in excess of a year. Similar changes occur in the high troposphere.

Satellite cloud observations, however, indicate important longitudinal variations near the Equator. During the abnormal rainy season of 1965–66 at Canton Island, the amount of cloudiness remained low over the eastern equatorial Pacific despite above-normal sea-surface temperatures. This suggests a continuation of the widespread subsidence usually present over this region, which is apparently part of a large-scale semipermanent zonal circulation.

Satellite observations further show that there are three major “centers of action” (standing eddies) in the vicinity of the Equator. Probably the major part of the condenstion heating necessary for the Hadley circulation occurs in these areas.

This study also indicates a possible relation between equatorial rainfall in the central Pacific and the strength of the Northern Hemisphere westerlies as suggested by Bjerknes. In addition, rainfall appears to vary inversely with the eddy kinetic energy over the Northern Hemisphere suggesting an inverse relation with the large-scale planetary waves in the Northern Hemisphere.

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M. A. Shapiro, T. Hampel, and A. J. Krueger

Abstract

Analyses of research aircraft observation, satellite total columnar ozone retrievals and synoptic upper-air soundings are used to describe the structure of Arctic jetstreams and their associated frontal zones and tropopause folds. These analyses document the presence of major tropopause folding events within the Arctic that occur at the flanks of large-scale (∼2000 km) polar vortices. One example shows a polar vortex and its associated tropopause fold and Arctic front that migrated from the high Canadian Arctic southward into midlatitudes over central North America. The frigid cold-air outbreak associated with this migration was an important component in the record setting daily minimum temperatures that were recorded from the Great Lakes to southern Florida. Total columnar ozone measurements from the Total Ozone Mapping Spectrometer (TOMS) are shown to identify the location of polar vortices and the mesoscale (∼200 km) ozone gradients at the flanks of these vortices which coincide with regions of Arctic tropopause folding and associated stratospheric-tropospheric exchange (ST) processes. A major modification to earlier models of the meridional structure of the tropopause and primary wind systems is proposed. The model introduces the Arctic jetstream and its associated tropopause fold as a primary wind system and vehicle for ST-exchange. The model also uses the ST-discontinuity in potential vorticity to define the pole-to-equator structure of the tropopause.

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ARTHUR F. KRUEGER, JAY S. WINSTON, and DONALD A. HAINES

Abstract

Computations of atmospheric energy and several of its transformation terms from data extending back to October 1958 have been carried out using the National Meteorological Center's ADP analyses. From these calculations the annual variation of the atmosphere's energy cycle has been estimated. In addition, some yearly differences for the colder half of the year are described.

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L. F. Hubert, A. F. Krueger, and J. S. Winston

Abstract

No abstract available.

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Steven K. Krueger, Chwen-Wei Su, and Patrick A. McMurtry

Abstract

A model used to study entrainment and mixing of thermodynamic properties in the stratus-topped boundary layer has been extended to represent these processes in cumulus clouds. The new model, called the “explicit mixing parcel model” (EMPM), depicts finescale internal structure of a rising thermal in a cumulus cloud using a 1D domain. The EMPM links the conventional parcel model, which has no internal structure, and multidimensional cloud models, which resolve cloud-scale structure produced by large eddies. In the EMPM, the internal structure evolves as a consequence of a sequence of discrete entrainment events and an explicit representation of turbulent mixing based on Kerstein’s linear eddy model. In this version of the EMPM, subgrid-scale (eddy) diffusion is found to be adequate for representing the effects of the smallest turbulent eddies. In addition, a simple parameterization is used to determine the local condensation or evaporation rates. If the grid size is reduced so that the Kolmogorov scale is resolved and a droplet growth model is incorporated, the EMPM can predict the local microphysical environments of individual cloud droplets.

To evaluate its entrainment parameterization, the EMPM was used to predict the bulk properties of Hawaiian cumulus cloud main turrets observed by aircraft. All of the quantities required by the EMPM except for the entrained blob size were obtained from the observations. Profiles of in-cloud means and variances of thermodynamic properties calculated by the EMPM for entrained blob sizes of 50 m, 100 m, and 200 m and by a parcel model with instantaneous mixing were compared to those observed. The observed mean conserved scalar profiles are reproduced by both mixing representations, but the observed mean liquid water mixing ratio and buoyancy profiles, all of the observed variance profiles, and the observed nonbuoyancy level are better reproduced by the EMPM. For entrained blob sizes of 100 m and 200 m, undiluted cloud base air reaches the inversion base in the EMPM, as was observed. These results indicate that the EMPM’s entrainment parameterization is adequate for these cloud turrets, and that the characteristic entrained blob size is about 100 m. The model results also demonstrate that the finescale structure represented by the EMPM’s 1D domain can be directly compared to high-frequency aircraft measurements.

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Qiang Fu, M. C. Cribb, H. W. Barker, S. K. Krueger, and A. Grossman

Abstract

A 3D broadband solar radiative transfer scheme is formulated by integrating a Monte Carlo photon transport algorithm with the Fu–Liou radiation model. It is applied to fields of tropical mesoscale convective clouds and subtropical marine boundary layer clouds that were generated by a 2D cloud-resolving model. The effects of cloud geometry on the radiative energy budget are examined by comparing the full-resolution Monte Carlo results with those from the independent column approximation (ICA) that applies the plane-parallel radiation model to each column.

For the tropical convective cloud system, it is found that cloud geometry effects always enhance atmospheric solar absorption regardless of solar zenith angle. In a large horizontal domain (512 km), differences in domain-averaged atmospheric absorption between the Monte Carlo and the ICA are less than 4 W m−2 in the daytime. However, for a smaller domain (e.g., 75 km) containing a cluster of deep convective towers, domain-averaged absorption can be enhanced by more than 20 W m−2. For a subtropical marine boundary layer cloud system during the stratus-to-cumulus transition, calculations show that the ICA works very well for domain-averaged fluxes of the stratocumulus cloud fields even for a very small domain (4.8 km). For the trade cumulus cloud field, the effects of cloud sides and horizontal transport of photons become more significant. Calculations have also been made for both cloud systems including black carbon aerosol and a water vapor continuum. It is found that cloud geometry produces no discernible effects on the absorption enhancement due to the black carbon aerosol and water vapor continuum.

The current study indicates that the atmospheric absorption enhancement due to cloud-related 3D photon transport is small. This enhancement could not explain the excess absorption suggested by recent studies.

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R. J. Alvarez II, L. M. Caldwell, V. H. Li, D. A. Krueger, and C. Y. She

Abstract

Initial measurements of the aerosol backscatter ratio using a new atomic barium filter (FWHM from 2.0–3.0 GHz at 553.7 nm) in conjunction with a narrowband-pulsed dye laser system are reported. Using analog detection and a 0.2 m diameter receiving telescope, variation of about 10 percent are obtained over a range of 0.25–2.0 km with 30 m resolution within two minutes. Dense regions of aerosols (e.g., clouds) as thin as 10 m and at ranges of up to 6.5 km have been observed in the backscattered signal. Under appropriate climate conditions, sequential measurements of backscatter ratio profiles can be used to follow cloud dispersal dynamics. Techniques for improving accuracy and the potential of using this technique for measuring temperatures throughout the troposphere are discussed.

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D. A. Krueger, L. M. Caldwell, C. Y. She, and R. J. Alvarez II

Abstract

A self-consistent method of inverting high spectral resolution, Rayleigh-Mie lidar signals to obtain profiles of atmospheric state variables, as well as aerosol properties, is presented. Assumed are a known air pressure at a reference height, hydrostatic equilibrium, the ideal gas law, and the theoretical temperature and pressure dependence of Rayleigh-Brillouin line shapes. For measurements over several kilometers, variations in the atmospheric pressure must be included in the data analysis. The inversion of the signal is greatly facilitated by making a quadratic expansion of the line shape as a function of atmospheric temperature and pressure that is accurate for temperature ranges of ±30 K and pressure ranges of ±25 kPa around a standard temperature and pressure of 275 K and 76 kPa, respectively. Required measurements are the total lidar signal and signals corresponding to different portions of molecular scattering spectrum. These measurements are made possible by using interference filters and atomic vapor filters, which remove the aerosol contribution. The filters are fully characterized by measuring their transmission functions as a function of frequency. For a typical barium filter such as those considered here, the oven temperature must be controlled to better than 1 K for air temperature determination within 1 K. Specially designed filters will be less sensitive to filter temperature. If the bandwidth of the interference filters used is fairly broad, then the inclusion of rotational Raman scattering is important for accurate lidar inversion. Formulas for determining the vertical profiles of atmospheric temperature, pressure, and density, as well as backscatter ratio, backscatter phase function, extinction ratio, and aerosol extinction coefficient are given and their measurement sensitivities are discussed.

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Liguo Su, Richard L. Collins, David A. Krueger, and Chiao-Yao She

Abstract

A statistical study is presented of the errors in sodium Doppler lidar measurements of wind and temperature in the mesosphere that arise from the statistics of the photon-counting process that is inherent in the technique. The authors use data from the Colorado State University (CSU) sodium Doppler wind-temperature lidar, acquired at a midlatitude site, to define the statistics of the lidar measurements in different seasons under both daytime and nighttime conditions. The CSU lidar measurements are scaled, based on a 35-cm-diameter receiver telescope, to the use of large-aperture telescopes (i.e., 1-, 1.8-, and 3.5-m diameters). The expected biases in vertical heat flux measurements at a resolution of 480 m and 150 s are determined and compared to Gardner and Yang’s reported geophysical values of 2.3 K m s−1. A cross-correlation coefficient of 2%–7% between the lidar wind and temperature estimates is found. It is also found that the biases vary from −4 × 10−3 K m s−1 for wintertime measurements at night with a 3.5-m telescope to −61 K m s−1 for summertime measurements at midday with a 1-m telescope. During winter, at night, the three telescope systems yield biases in their heat flux measurements that are less than 10% of the reported value of the heat flux; and during summer, at night, the 1.8- and 3.5-m systems yield biases in their heat flux measurements that are less than 10% of the geophysical value. While during winter at midday the 3.5-m system yields biases in their heat flux measurements that are less than 10% of the geophysical value, during summer at midday all of the systems yield flux biases that are greater than the geophysical value of the heat flux. The results are discussed in terms of current lidar measurements and proposed measurements at high-latitude sites.

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