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S. J. Hogan

Abstract

The real and apparent accelerations in the free surface of nonlinear gravity-capillary waves are calculated over a wide range of wavelengths. It is shown that surface tension has hardly any effect on the results previously obtained for pure gravity waves, for wavelengths down to 20 cm in length, over the range of steepness considered. At the other extreme, we present for pure capillary waves, exact analytic results valid for all steepnesses up to and including the highest wave. This yields some intriguing conclusions including the fact that the horizontal component of the real acceleration has the opposite sign over most of the surface of the highest wave to that which it does over the surface of linear waves. We also consider the effect of gravity on this solution as well as the case when both restoring forces are of equal importance.

For short waves considered here, the behavior of all the accelerations in the nonlinear wave is nonsinusoidal with maximum values considerably in excess of those predicted by linear theory.

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S. I. Rasool
and
J. S. Hogan
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J. S. Hogan
,
R. D. Cess
,
T. Encrenaz
, and
D. Gautier

Abstract

Using recently calculated models of the Jovian atmosphere, we have derived a value of 5.0 for the H2/He mixing ratio from the Pioneer 10 infrared radiometer data. We have also computed a far-infrared spectrum corresponding to the thermal profile obtained in the Pioneer S-band occultation experiment. Our computed spectrum strongly suggests a misinterpretation of the data obtained in that experiment.

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S. I. Rasool
,
J. S. Hogan
,
R. W. Stewart
, and
L. H. Russell

Abstract

No abstract available.

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M. Haeffelin
,
S. Crewell
,
A. J. Illingworth
,
G. Pappalardo
,
H. Russchenberg
,
M. Chiriaco
,
K. Ebell
,
R. J. Hogan
, and
F. Madonna
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D. L. Westphal
,
T. R. Holt
,
S. W. Chang
,
N. L. Baker
,
T. F. Hogan
,
L. R. Brody
,
R. A. Godfrey
,
J. S. Goerss
,
J. A. Cummings
,
D. J. Laws
, and
C. W. Hines

Abstract

The Marine Meteorology Division of the Naval Research Laboratory (NRL), assisted by the Fleet Numerical Meteorology and Oceanography Center, has performed global and mesoscale reanalyses to support the study of Gulf War illness. Realistic and quantitatively accurate atmospheric conditions are needed to drive dispersion models that can predict the transport and dispersion of chemical agents that may have affected U.S. and other coalition troops in the hours and days following the demolition of chemical weapons at Khamisiyah, Iraq, at approximately 1315 UTC 10 March 1991. The reanalysis was conducted with the navy’s global and mesoscale analysis and prediction systems: the Navy Operational Global Atmospheric Prediction System and the NRL Coupled Ocean–Atmosphere Mesoscale Prediction System. A comprehensive set of observations has been collected and used in the reanalysis, including unclassified and declassified surface reports, ship and buoy reports, observations from pibal and rawinsonde, and retrievals from civilian and military satellites. The atmospheric conditions for the entire globe have been reconstructed using the global system at the effective spatial resolution of 0.75°. The atmospheric conditions over southern Iraq, Kuwait, and northern Saudi Arabia have been reconstructed using the mesoscale system at the spatial resolutions of 45, 15, and 5 km. In addition to a baseline reanalysis, perturbation analyses were also performed to estimate the atmospheric sensitivity to observational error and analysis error. The results suggest that the reanalysis has bounded the variability and that the actual atmospheric conditions were unlikely to differ significantly from the reanalysis.

The synoptic conditions at and after the time of the detonation were typical of the transitional period after a Shamal and controlled by eastward-propagating small-amplitude troughs and ridges. On the mesoscale, the conditions over the Tigris–Euphrates Valley were further modulated by the diurnal variation in the local circulations between land, the Persian Gulf, and the Zagros Mountains. The boundary layer winds at Khamisiyah were from NNW at the time of the detonation and shifted to WNW in the nocturnal boundary layer. On the second day, a strong high passed north of Khamisiyah and the winds strengthened and turned to the ESE. During the third day, the region was dominated by the approach and passage of a low pressure system and the associated front with the SE winds veering to NW.

A transport model for passive scalars was used to illustrate the sensitivity to the reanalyzed fields of potential areas of contamination. Transport calculations based on various release scenario and reanalyzed meteorological conditions suggest that the mean path of the released chemical agents was southward from Khamisiyah initially, turning westward, and eventually northwestward during the 72-h period after the demolition. Precipitation amounts in the study area were negligible and unlikely to have an effect on the nerve agent.

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R.C.J. Somerville
,
P.H. Stone
,
M. Halem
,
J.E. Hansen
,
J.S. Hogan
,
L.M. Druyan
,
G. Russell
,
A.A. Lacis
,
W.J. Quirk
, and
J. Tenenbaum

Abstract

A model description and numerical results are presented for a global atmospheric circulation model developed at the Goddard Institute for Space Studies (GISS). The model version described is a 9-level primitive-equation model in sigma coordinates. It includes a realistic distribution of continents, oceans and topography. Detailed calculations of energy transfer by solar and terrestrial radiation make use of cloud and water vapor fields calculated by the model. The model hydrologic cycle includes two precipitation mechanisms: large-scale supersaturation and a parameterization of subgrid-scale cumulus convection.

Results are presented both from a comparison of the 13th to the 43rd days (January) of one integration with climatological statistics, and from five short-range forecasting experiments. In the extended integration, the near-equilibrium January-mean model atmosphere exhibits an energy cycle in good agreement with observational estimates, together with generally realistic zonal mean fields of winds, temperature, humidity, transports, diabatic heating, evaporation, precipitation, and cloud cover. In the five forecasting experiments, after 48 hr, the average rms error in temperature is 3.9K, and the average rms error in 500-mb height is 62 m. The model is successful in simulating the 2-day evolution of the major features of the observed sea level pressure and 500-mb height fields in a region surrounding North America.

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Thorwald H. M. Stein
,
Robin J. Hogan
,
Peter A. Clark
,
Carol E. Halliwell
,
Kirsty E. Hanley
,
Humphrey W. Lean
,
John C. Nicol
, and
Robert S. Plant

Abstract

A new frontier in weather forecasting is emerging by operational forecast models now being run at convection-permitting resolutions at many national weather services. However, this is not a panacea; significant systematic errors remain in the character of convective storms and rainfall distributions. The Dynamical and Microphysical Evolution of Convective Storms (DYMECS) project is taking a fundamentally new approach to evaluate and improve such models: rather than relying on a limited number of cases, which may not be representative, the authors have gathered a large database of 3D storm structures on 40 convective days using the Chilbolton radar in southern England. They have related these structures to storm life cycles derived by tracking features in the rainfall from the U.K. radar network and compared them statistically to storm structures in the Met Office model, which they ran at horizontal grid length between 1.5 km and 100 m, including simulations with different subgrid mixing length. The authors also evaluated the scale and intensity of convective updrafts using a new radar technique. They find that the horizontal size of simulated convective storms and the updrafts within them is much too large at 1.5-km resolution, such that the convective mass flux of individual updrafts can be too large by an order of magnitude. The scale of precipitation cores and updrafts decreases steadily with decreasing grid lengths, as does the typical storm lifetime. The 200-m grid-length simulation with standard mixing length performs best over all diagnostics, although a greater mixing length improves the representation of deep convective storms.

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Thorwald H. M. Stein
,
Robin J. Hogan
,
Kirsty E. Hanley
,
John C. Nicol
,
Humphrey W. Lean
,
Robert S. Plant
,
Peter A. Clark
, and
Carol E. Halliwell

Abstract

A set of high-resolution radar observations of convective storms has been collected to evaluate such storms in the Met Office Unified Model during the Dynamical and Microphysical Evolution of Convective Storms (DYMECS) project. The 3-GHz Chilbolton Advanced Meteorological Radar was set up with a scan-scheduling algorithm to automatically track convective storms identified in real time from the operational rainfall radar network. More than 1000 storm observations gathered over 15 days in 2011 and 2012 are used to evaluate the model under various synoptic conditions supporting convection. In terms of the detailed three-dimensional morphology, storms in the 1500-m grid length simulations are shown to produce horizontal structures a factor of 1.5–2 wider compared to radar observations. A set of nested model runs at grid lengths down to 100 m show that the models converge in terms of storm width, but the storm structures in the simulations with the smallest grid lengths are too narrow and too intense compared to the radar observations. The modeled storms were surrounded by a region of drizzle without ice reflectivities above 0 dBZ aloft, which was related to the dominance of ice crystals and was improved by allowing only aggregates as an ice particle habit. Simulations with graupel outperformed the standard configuration for heavy-rain profiles, but the storm structures were a factor of 2 too wide and the convective cores 2 km too deep.

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Robert Wood
,
Matthew Wyant
,
Christopher S. Bretherton
,
Jasmine Rémillard
,
Pavlos Kollias
,
Jennifer Fletcher
,
Jayson Stemmler
,
Simone de Szoeke
,
Sandra Yuter
,
Matthew Miller
,
David Mechem
,
George Tselioudis
,
J. Christine Chiu
,
Julian A. L. Mann
,
Ewan J. O’Connor
,
Robin J. Hogan
,
Xiquan Dong
,
Mark Miller
,
Virendra Ghate
,
Anne Jefferson
,
Qilong Min
,
Patrick Minnis
,
Rabindra Palikonda
,
Bruce Albrecht
,
Ed Luke
,
Cecile Hannay
, and
Yanluan Lin

Abstract

The Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CAP-MBL) deployment at Graciosa Island in the Azores generated a 21-month (April 2009–December 2010) comprehensive dataset documenting clouds, aerosols, and precipitation using the Atmospheric Radiation Measurement Program (ARM) Mobile Facility (AMF). The scientific aim of the deployment is to gain improved understanding of the interactions of clouds, aerosols, and precipitation in the marine boundary layer.

Graciosa Island straddles the boundary between the subtropics and midlatitudes in the northeast Atlantic Ocean and consequently experiences a great diversity of meteorological and cloudiness conditions. Low clouds are the dominant cloud type, with stratocumulus and cumulus occurring regularly. Approximately half of all clouds contained precipitation detectable as radar echoes below the cloud base. Radar and satellite observations show that clouds with tops from 1 to 11 km contribute more or less equally to surface-measured precipitation at Graciosa. A wide range of aerosol conditions was sampled during the deployment consistent with the diversity of sources as indicated by back-trajectory analysis. Preliminary findings suggest important two-way interactions between aerosols and clouds at Graciosa, with aerosols affecting light precipitation and cloud radiative properties while being controlled in part by precipitation scavenging.

The data from Graciosa are being compared with short-range forecasts made with a variety of models. A pilot analysis with two climate and two weather forecast models shows that they reproduce the observed time-varying vertical structure of lower-tropospheric cloud fairly well but the cloud-nucleating aerosol concentrations less well. The Graciosa site has been chosen to be a permanent fixed ARM site that became operational in October 2013.

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