Search Results

You are looking at 1 - 8 of 8 items for

  • Author or Editor: G. E. Hunt x
  • All content x
Clear All Modify Search
M. E. Voice and B. G. Hunt

Abstract

A semi-spectral model formulation has been tested for short-term numerical weather prediction in the Southern Hemisphere: The model configuration consisted of 5 levels in the vertical with 15 zonal waves and 30 grid points from pole to equator. Several two-day forecasts were verified and examined for synoptic accuracy and spectral performance. The semi-spectral technique produced credible and useful NWP results, competitive with standard grid point methods. An extended integration to 8 days demonstrated the stability of the model. The same model with a higher vertical resolution of 18 levels was briefly tested. Comparison with the 5-level version revealed only small improvements in forecasting accuracy and highlighted data limitations in the Southern Hemisphere.

Full access
G. E. Hunt and I. P. Grant

Abstract

The classical methods that have been devised to analyze theoretically the transfer of radiation in plane parallel atmospheres may produce an analytic solution provided that the medium is assumed to be homogeneous. Even then, when the results have been expressed in terms of tabulated functions, practical computations are difficult and tedious. It is therefore essential to employ numerical methods for solving realistic radiative transfer problems.

We briefly describe a method of computation that uses discrete space techniques depending on concepts of invariance. The solution algorithms compute internal and external light fields for inhomogeneous plane parallel atmospheres with arbitrary internal, external source distributions and scattering diagrams. The stability and errors of our algorithms are susceptible to mathematical analysis and make it possible to identify the critical parameters in the calculation with precision.

To illustrate our techniques, we briefly discuss the practical problem of making theoretical predictions of the spectral properties of ice clouds at selected spectral intervals between 2.6–150 μ in the infrared. The predictions are consistent with recent measurements.

Full access
Kieran M. R. Hunt, Andrew G. Turner, Peter M. Inness, David E. Parker, and Richard C. Levine

Abstract

ERA-Interim reanalysis data from the past 35 years have been used with a newly developed feature tracking algorithm to identify Indian monsoon depressions originating in or near the Bay of Bengal. These were then rotated, centralized, and combined to give a fully three-dimensional 106-depression composite structure—a considerably larger sample than any previous detailed study on monsoon depressions and their structure. Many known features of depression structure are confirmed, particularly the existence of a maximum to the southwest of the center in rainfall and other fields and a westward axial tilt in others. Additionally, the depressions are found to have significant asymmetry owing to the presence of the Himalayas, a bimodal midtropospheric potential vorticity core, a separation into thermally cold (~−1.5 K) and neutral (~0 K) cores near the surface with distinct properties, and the center has very large CAPE and very small CIN. Variability as a function of background state has also been explored, with land–coast–sea, diurnal, ENSO, active–break, and Indian Ocean dipole contrasts considered. Depressions are found to be markedly stronger during the active phase of the monsoon, as well as during La Niña. Depressions on land are shown to be more intense and more tightly constrained to the central axis. A detailed schematic diagram of a vertical cross section through a composite depression is also presented, showing its inherent asymmetric structure.

Full access
R. W. Saunders, L. L. Stowe, G. E. Hunt, and C. F. England

Abstract

Daily averaged and instantaneous values or the Earth's radiation budget have been computed from the satellite measurements of reflected solar and emitted terrestrial radiation with MEUGSAT 1, Nimbus 7 ERB and TIROS-N scanning radiometers. The estimates have been compared for 12 selected 2.5° × 2.5° latitude-longitude moons for 14 October 1979. The METEOSAT daily mean values were used to study the effects of diurnal variations because observations were available nearly every hour of the day. The comparisons between the three independent data sets is discussed and an assessment is made of the relative importance of diurnal variations and anisotropic scattering models. A cheek was made on the inferred broad-band MEUOSAT fluxes by a direct comparison with coincident Nimbus 7 ERB measurements.

Full access
R. W. Saunders, N. R. Ward, C. F. England, and G. E. Hunt

TIROS–N Advanced Very High Resolution Radiometer (AVHRR) imagery has been used to study the temperature structure of the sea surface around the British Isles. We have combined the satellite imagery from both TIROS–N, METEOSAT, and conventional synoptic data to obtain a calibration for both 11 μm infrared channels, which gave sea surface temperatures accurate to ± 1 K. The changes in the sea surface temperature around the British Isles for 12 July 1979 are shown well by the satellite data. In particular, we have made a study of an anomalously warm patch in the North Sea that appeared at local noon over an area where the surface winds were weak, inhibiting surface mixing.

Full access
H. J. S. Fernando, E. R. Pardyjak, S. Di Sabatino, F. K. Chow, S. F. J. De Wekker, S. W. Hoch, J. Hacker, J. C. Pace, T. Pratt, Z. Pu, W. J. Steenburgh, C. D. Whiteman, Y. Wang, D. Zajic, B. Balsley, R. Dimitrova, G. D. Emmitt, C. W. Higgins, J. C. R. Hunt, J. C. Knievel, D. Lawrence, Y. Liu, D. F. Nadeau, E. Kit, B. W. Blomquist, P. Conry, R. S. Coppersmith, E. Creegan, M. Felton, A. Grachev, N. Gunawardena, C. Hang, C. M. Hocut, G. Huynh, M. E. Jeglum, D. Jensen, V. Kulandaivelu, M. Lehner, L. S. Leo, D. Liberzon, J. D. Massey, K. McEnerney, S. Pal, T. Price, M. Sghiatti, Z. Silver, M. Thompson, H. Zhang, and T. Zsedrovits

Abstract

Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.

Full access
Annmarie G. Carlton, Joost de Gouw, Jose L. Jimenez, Jesse L. Ambrose, Alexis R. Attwood, Steven Brown, Kirk R. Baker, Charles Brock, Ronald C. Cohen, Sylvia Edgerton, Caroline M. Farkas, Delphine Farmer, Allen H. Goldstein, Lynne Gratz, Alex Guenther, Sherri Hunt, Lyatt Jaeglé, Daniel A. Jaffe, John Mak, Crystal McClure, Athanasios Nenes, Thien Khoi Nguyen, Jeffrey R. Pierce, Suzane de Sa, Noelle E. Selin, Viral Shah, Stephanie Shaw, Paul B. Shepson, Shaojie Song, Jochen Stutz, Jason D. Surratt, Barbara J. Turpin, Carsten Warneke, Rebecca A. Washenfelder, Paul O. Wennberg, and Xianling Zhou

Abstract

The Southeast Atmosphere Studies (SAS), which included the Southern Oxidant and Aerosol Study (SOAS); the Southeast Nexus (SENEX) study; and the Nitrogen, Oxidants, Mercury and Aerosols: Distributions, Sources and Sinks (NOMADSS) study, was deployed in the field from 1 June to 15 July 2013 in the central and eastern United States, and it overlapped with and was complemented by the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. SAS investigated atmospheric chemistry and the associated air quality and climate-relevant particle properties. Coordinated measurements from six ground sites, four aircraft, tall towers, balloon-borne sondes, existing surface networks, and satellites provide in situ and remotely sensed data on trace-gas composition, aerosol physicochemical properties, and local and synoptic meteorology. Selected SAS findings indicate 1) dramatically reduced NOx concentrations have altered ozone production regimes; 2) indicators of “biogenic” secondary organic aerosol (SOA), once considered part of the natural background, were positively correlated with one or more indicators of anthropogenic pollution; and 3) liquid water dramatically impacted particle scattering while biogenic SOA did not. SAS findings suggest that atmosphere–biosphere interactions modulate ambient pollutant concentrations through complex mechanisms and feedbacks not yet adequately captured in atmospheric models. The SAS dataset, now publicly available, is a powerful constraint to develop predictive capability that enhances model representation of the response and subsequent impacts of changes in atmospheric composition to changes in emissions, chemistry, and meteorology.

Open access
C. P. Weaver, X.-Z. Liang, J. Zhu, P. J. Adams, P. Amar, J. Avise, M. Caughey, J. Chen, R. C. Cohen, E. Cooter, J. P. Dawson, R. Gilliam, A. Gilliland, A. H. Goldstein, A. Grambsch, D. Grano, A. Guenther, W. I. Gustafson, R. A. Harley, S. He, B. Hemming, C. Hogrefe, H.-C. Huang, S. W. Hunt, D.J. Jacob, P. L. Kinney, K. Kunkel, J.-F. Lamarque, B. Lamb, N. K. Larkin, L. R. Leung, K.-J. Liao, J.-T. Lin, B. H. Lynn, K. Manomaiphiboon, C. Mass, D. McKenzie, L. J. Mickley, S. M. O'neill, C. Nolte, S. N. Pandis, P. N. Racherla, C. Rosenzweig, A. G. Russell, E. Salathé, A. L. Steiner, E. Tagaris, Z. Tao, S. Tonse, C. Wiedinmyer, A. Williams, D. A. Winner, J.-H. Woo, S. WU, and D. J. Wuebbles

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the different groups, simulated global climate change causes increases of a few to several parts per billion (ppb) in summertime mean maximum daily 8-h average O3 concentrations over substantial regions of the country. The different modeling experiments in general do not, however, simulate the same regional patterns of change. These differences seem to result largely from variations in the simulated patterns of changes in key meteorological drivers, such as temperature and surface insolation. How isoprene nitrate chemistry is represented in the different modeling systems is an additional critical factor in the simulated O3 response to climate change.

Full access