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W. D. Scott
,
D. Lamb
, and
D. Duffy

Past studies of the reactions between anhydrous NH3 and anhydrous SO2 have suggested that two distinct products are formed. These products are stable below about 10C, are pale yellow or white solids, and have NH3:SO2 stoichiometric ratios of 1:1 and 2:1, respectively. The present work corroborates these results and presents quantitative measurements of the equilibrium total vapor pressure over the products at temperatures between −10 and −70C. Infrared spectra of the vapor infer that the products dissociate reversibly on sublimation into their components, NH3 and SO2. One white product was formed which exerted an extremely low vapor pressure at low temperatures. Regions of temperature minima would be preferred for its formation in the atmosphere. This stable product may appear at some stage in the formation of the ammonium sulfate layer in the lower stratosphere.

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Dennis Lamb
and
William D. Scott

Abstract

The formation of multiple layers of adsorbed water molecules on the basal and prism faces of ice may be responsible for the remarkable temperature dependence of all growth variables (linear growth rate, step velocity, and mean migration distance). This effect results from an increased residence time of molecules in the adsorbed state as the melting point is approached. A quantitative treatment based on the Brunauer, Emmett and Teller model of multi-layer adsorption exemplifies these concepts and appears to explain the measured trends with temperature. When the theoretical treatment is used in conjunction with a growth model based on the propagation of spiral steps, reasonable values for the condensation coefficient emerge. The alternation of the primary habit of ice crystals with temperature is explained when the theoretical treatment is applied to the basal and prism faces, respectively.

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D. Lamb
and
Peter V. Hobbs

Abstract

No abstract available.

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J. D. Fuentes
,
D. D. Baldocchi
, and
B. Lamb
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D. L. Sisterson
,
R. A. Peppler
,
T. S. Cress
,
P. J. Lamb
, and
D. D. Turner
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D. Lamb
,
K. W. Nielsen
,
H. E. Klieforth
, and
J. Hallett

Abstract

Investigations of the structure and organization of synoptic-scale storms over the Sierra Nevada Mountain Range during two successive winters (1971–73) were made with a modified B-26 aircraft. Measurements of liquid water content, temperature and dew point were made along horizontal traverses in a vertical plane oriented roughly perpendicular to the main crest and extending from Lake Tahoe to Sacramento, Calif. It is shown that the spatial distribution of liquid water is linked to the gross terrain features, as is the surface distribution of precipitation. The main centers of cloud liquid water content tend to form 40–75 km upwind of the main crest in highly convective cells.

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Esther D. Mullens
,
Lance M. Leslie
, and
Peter J. Lamb

Abstract

Ice storms are an infrequent but significant hazard in the U.S southern Great Plains. Common synoptic profiles for freezing precipitation reveal advection of low-level warm moist air from the Gulf of Mexico (GOM), above a shallow Arctic air mass ahead of a midlevel trough. Because the GOM is the proximal basin and major moisture source, this study investigates impacts of varying GOM sea surface temperature (SST) on the thermodynamic evolution of a winter storm that occurred during 28–30 January 2010, with particular emphasis on the modulation of freezing precipitation. A high-resolution, nested ARW sensitivity study with a 3.3-km inner domain is performed, using six representations of GOM SST, including control, climatological mean, uniform ±2°C from control, and physically constrained upper- and lower-bound basin-average anomalies from a 30-yr dataset. The simulations reveal discernable impacts of SST on the warm-layer inversion, precipitation intensity, and low-level dynamics. Whereas total precipitation for the storm increased monotonically with SST, the freezing-precipitation response was more varied and nonlinear, with the greatest accumulation decreases occurring for the coolest SST perturbation, particularly at moderate precipitation rates. Enhanced precipitation and warm-layer intensity promoted by warmer SST were offset for the highest perturbations by deepening of the weak 850-hPa low circulation and faster eastward progression associated with enhanced baroclinicity and diabatic generation of potential vorticity. Air-parcel trajectories terminating within the freezing-precipitation region were examined to identify airmass sources and modification. These results suggest that GOM SST can affect the severity of concurrent ice-storm events in the southern Great Plains, with warmer basin SST potentially exacerbating the risk of damaging ice accumulations.

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Esther D. Mullens
,
Lance M. Leslie
, and
Peter J. Lamb

Abstract

Winter storms in the southern United States can significantly impact infrastructure and the economy. In this study, National Centers for Environmental Information Storm Event Database and local climate summaries, are used to develop a spatial climatology of freezing precipitation (freezing rain and ice pellets) and snow over the southern Great Plains, 1993–2011. Principal component analysis is performed on the 500-hPa height field, at the approximate onset time of precipitation, for 33 freezing precipitation and 42 snow case studies, to differentiate common synoptic flow fields associated with precipitation type. The five leading patterns for each precipitation type are retained. Composites of temperature, moisture, pressure, and wind fields are constructed and extended 24 h before and after precipitation initiation to track the storm system evolution. Many 500-hPa flow fields are similar for both precipitation types. However, snow-dominant events have stronger and/or more frequent surface cyclone development. Freezing precipitation is associated with the southward propagation of an Arctic anticyclone well ahead of precipitation, weak or absent surface cyclone formation, and a more western trough axis. High-impact ice storms in the region often have slow-moving upper-level flow, persistent isentropic ascent over a surface quasi-stationary front with strongly positive moisture anomalies, and warm layer airmass trajectories originating over the Gulf of Mexico. The results here are based on a relatively small sample size. However, this work is intended to be useful for forecasters, in particular as a pattern recognition aid in predicting the evolution of precipitation within southern Great Plains winter storms.

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D. Finn
,
B. Lamb
,
M. Y. Leclerc
,
S. Lovejoy
,
S. Pecknold
, and
D. Schertzer

Abstract

A codimension multifractal methodology was used to analyze and to model scalar concentration fluctuations within sulfur hexafluoride tracer gas plumes from a line source in atmospheric surface-layer flows. Correspondence was exhibited between the double trace moments parameters α and C 1 of the codimension methodology and the experimentally measured plume concentration characteristics of peak-to-mean ratio and concentration fluctuation intensity. Data series were generated using an extremal Levy, stochastic multifractal model, with the experimental α and C 1 as inputs. Uncertainties in experimentally determined plume characteristic values overlapped the uncertainties in model-simulated values. The utility of the procedure includes 1) characterizing the state of scalar turbulent mixing, 2) helping to evaluate and to model hazardous plume concentrations, and 3) being able to estimate the probability of realizing extreme events at timescales of observation beyond or at magnitudes in excess of those present in the actual observations.

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J. D. Fuentes
,
M. Lerdau
,
R. Atkinson
,
D. Baldocchi
,
J. W. Bottenheim
,
P. Ciccioli
,
B. Lamb
,
C. Geron
,
L. Gu
,
A. Guenther
,
T. D. Sharkey
, and
W. Stockwell

Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of hydrocarbons to the atmosphere. In this manuscript, the state of the science concerning biosynthesis, transport, and chemical transformation of hydrocarbons emitted by the terrestrial biosphere is reviewed. In particular, the focus is on isoprene, monoterpenes, and oxygenated hydrocarbons. The generated science during the last 10 years is reviewed to explain and quantify hydrocarbon emissions from vegetation and to discern impacts of biogenic hydrocarbons on local and regional atmospheric chemistry. Furthermore, the physiological and environmental processes controlling biosynthesis and production of hydrocarbon compounds are reported on. Many advances have been made on measurement and modeling approaches developed to quantify hydrocarbon emissions from leaves and forest ecosystems. A synthesis of the atmospheric chemistry of biogenic hydrocarbons and their role in the formation of oxidants and aerosols is presented. The integration of biogenic hydrocarbon kinetics and atmospheric physics into mathematical modeling systems is examined to assess the contribution of biogenic hydrocarbons to the formation of oxidants and aerosols, thereby allowing us to study their impacts on the earth's climate system and to develop strategies to reduce oxidant precursors in affected regions.

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