A single-particle soot photometer (SP2) was flown on a NASA WB-57F high-altitude research aircraft in November 2004 from Houston, Texas. The SP2 uses laser-induced incandescence to detect individual ...black carbon (BC) particles in an air sample in the mass range of approx.3-300 fg (approx.0.15-0.7 microns volume equivalent diameter). Scattered light is used to size the remaining non-BC aerosols in the range of approx.0.17-0.7 microns diameter. We present profiles of both aerosol types from the boundary layer to the lower stratosphere from two midlatitude flights. Results for total aerosol amounts in the size range detected by the SP2 are in good agreement with typical particle spectrometer measurements in the same region. All ambient incandescing particles were identified as BC because their incandescence properties matched those of laboratory-generated BC aerosol. Approximately 40% of these BC particles showed evidence of internal mixing (e.g., coating). Throughout profiles between 5 and 18.7 km, BC particles were less than a few percent of total aerosol number, and black carbon aerosol (BCA) mass mixing ratio showed a constant gradient with altitude above 5 km. SP2 data was compared to results from the ECHAM4/MADE and LmDzT-INCA global aerosol models. The comparison will help resolve the important systematic differences in model aerosol processes that determine BCA loadings. Further intercomparisons of models and measurements as presented here will improve the accuracy of the radiative forcing contribution from BCA.
At low latitudes, cirrus are ubiquitous and can be in excess of 100 C colder than the surface, limiting the amount of sunlight absorbed by the earth s atmosphere and surface, and reducing its loss of ...heat. Here we present aircraft measurements within cirrus over southern Florida indicating that ice crystals have smaller sizes and are more reflective than is assumed in most current climate models. If the measurements are generally representative of low-latitude cirrus, they point to a first-order correction to represenntions of how these clouds affect the earth's climate.
Evolution of a florida cirrus anvil GARRETT, T. J; NAVARRO, B. C; MINNIS, P ...
Journal of the atmospheric sciences,
07/2005, Letnik:
62, Številka:
7
Journal Article
Recenzirano
Abstract
This paper presents a detailed study of a single thunderstorm anvil cirrus cloud measured on 21 July 2002 near southern Florida during the Cirrus Regional Study of Tropical Anvils and Cirrus ...Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE). NASA WB-57F and University of North Dakota Citation aircraft tracked the microphysical and radiative development of the anvil for 3 h. Measurements showed that the cloud mass that was advected downwind from the thunderstorm was separated vertically into two layers: a cirrus anvil with cloud-top temperatures of −45°C lay below a second, thin tropopause cirrus (TTC) layer with the same horizontal dimensions as the anvil and temperatures near −70°C. In both cloud layers, ice crystals smaller than 50 μm across dominated the size distributions and cloud radiative properties. In the anvil, ice crystals larger than 50 μm aggregated and precipitated while small ice crystals increasingly dominated the size distributions; as a consequence, measured ice water contents and ice crystal effective radii decreased with time. Meanwhile, the anvil thinned vertically and maintained a stratification similar to its environment. Because effective radii were small, radiative heating and cooling were concentrated in layers approximately 100 m thick at the anvil top and base. A simple analysis suggests that the anvil cirrus spread laterally because mixing in these radiatively driven layers created horizontal pressure gradients between the cloud and its stratified environment. The TTC layer also spread but, unlike the anvil, did not dissipate—perhaps because the anvil shielded the TTC from terrestrial infrared heating. Calculations of top-of-troposphere radiative forcing above the anvil and TTC showed strong cooling that tapered as the anvil evolved.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Large particles containing nitric acid (HNO3) were observed in the 1999/2000 Arctic winter stratosphere. These in situ observations were made over a large altitude range (16 to 21 kilometers) and ...horizontal extent (1800 kilometers) on several airborne sampling flights during a period of several weeks. With diameters of 10 to 20 micrometers, these sedimenting particles have significant potential to denitrify the lower stratosphere. A microphysical model of nitric acid trihydrate particles is able to simulate the growth and sedimentation of these large sizes in the lower stratosphere, but the nucleation process is not yet known. Accurate modeling of the formation of these large particles is essential for understanding Arctic denitrification and predicting future Arctic ozone abundances.
On-orbit firings of both liquid and solid rocket motors provide localized disturbances to the plasma in the upper atmosphere. Large amounts of energy are deposited to ionosphere in the form of ...expanding exhaust vapors which change the composition and flow velocity. Charge exchange between the neutral exhaust molecules and the background ions (mainly O + ) yields energetic ion beams. The rapidly moving pickup ions excite plasma instabilities and yield optical emissions after dissociative recombination with ambient electrons. Line-of-sight techniques for remote measurements rocket burn effects include direct observation of plume optical emissions with ground and satellite cameras, and plume scatter with UHF and higher frequency radars. Long range detection with HF radars is possible if the burns occur in the dense part of the ionosphere. The exhaust vapors initiate plasma turbulence in the ionosphere that can scatter HF radar waves launched from ground transmitters. Solid rocket motors provide particulates that become charged in the ionosphere and may excite dusty plasma instabilities. Hypersonic exhaust flow impacting the ionospheric plasma launches a low-frequency, electromagnetic pulse that is detectable using satellites with electric field booms. If the exhaust cloud itself passes over a satellite, in situ detectors measure increased ion-acoustic wave turbulence, enhanced neutral and plasma densities, elevated ion temperatures, and magnetic field perturbations. All of these techniques can be used for long range observations of plumes in the ionosphere. To demonstrate such long range measurements, several experiments were conducted by the Naval Research Laboratory including the Charged Aerosol Release Experiment, the Shuttle Ionospheric Modification with Pulsed Localized Exhaust experiments, and the Shuttle Exhaust Ionospheric Turbulence Experiments.
Nitric acid–containing particles with diameters of 10–20 μm were detected inside the Arctic polar vortex in the period January to March 2000. We present the results of a unique three‐dimensional ...microphysical simulation of these large HNO3‐containing particles covering the entire Arctic vortex. The model describes the simultaneous growth, evaporation, sedimentation, and advection of several thousand individual nitric acid hydrate particles over their complete lifetime. We compare modeled and observed particle size distributions as a test of different particle nucleation mechanisms. The model is able to produce particles with sizes typical of those observed and broadly reproduces the change in particle characteristics through the winter assuming nitric acid trihydrate (NAT) particle growth. The possibility that the observed large nitric acid–containing particles were composed of nitric acid dihydrate (NAD) cannot be excluded within the uncertainty of the HNO3 field above the aircraft. The formation of nitric acid hydrate particles on synoptic ice clouds may be a source of some of the observed large nitric acid–containing particles. However, a direct, but highly selective, nucleation of NAT or NAD particles over wide regions appears to be necessary to explain the observations.
In situ observations in a tropical subvisible cirrus cloud during the Costa Rica Aura Validation Experiment on 2 February 2006 show the presence of condensed-phase nitric acid. The cloud was observed ...near the tropopause at altitudes of 16.3-17.7 km in an extremely cold (183-191 K) and dry 5 ppm H2O) air mass. Relative humidities with respect to ice ranged from 150-250% throughout most of the cloud. Optical particle measurements indicate the presence of ice crystals as large as 90 microns in diameter. Condensed RN031H20 molar ratios observed in the cloud particles were 1-2 orders of magnitude greater than ratios observed previously in cirrus clouds at similar RN03 partial pressures. Nitric acid trihydrate saturation ratios were 10 or greater during much of the cloud encounter, indicating that RN03 may be present in the cloud particles as a stable condensate and not simply physically adsorbed on or trapped in the particles.
Convective generation of cirrus near the tropopause Garrett, T. J.; Heymsfield, A. J.; McGill, M. J. ...
Journal of Geophysical Research - Atmospheres,
16 November 2004, Letnik:
109, Številka:
D21
Journal Article
Recenzirano
During the July 2002 CRYSTAL‐FACE field program based from Key West, Florida, aircraft measurements showed that long‐lived thin tropopause cirrus (TTC) layers were often present above thunderstorm ...anvils. This paper describes these clouds and explores their possible origins. Measurements showed that the horizontal dimensions of TTC layers were nearly identical to convectively formed anvils beneath, but that TTC did not appear to have originated from convective detrainment. Rather, they appeared to have formed in stably stratified air derived from high altitudes near the tropopause. TTC were separated vertically from the top of the anvil by ∼1 km, they lacked precipitation particles, and they were strongly depleted in HDO, all of which indicate in situ formation. However, compared to surrounding clear air near the tropopause, TTC were enriched in moisture and trace gases. The degree of enrichment was consistent with mixing of air near the tropopause with the same convective air mass that produced the anvil. Unlike surrounding air, TTC had embedded a monochromatic gravity wave with a wavelength of 2 km and an amplitude of several hundred meters. This evidence, supported by a photograph from CRYSTAL‐FACE, leads to the conjecture that TTC originate as stratiform pileus clouds that form near the tropopause ahead of vigorous convective uplift. We hypothesize that the pileus are penetrated by the convection, moistened through turbulent mixing, and once the convection subsides, they are sustained by radiative cooling due to the presence of the anvil layer beneath.
Persistent contrails are a common feature of the upper troposphere. We describe two methods for intercomparing and evaluating RH
i measurements in a persistent contrail with calculated or expected ...values. The methods were applied to measurements made in the upper troposphere on board an NASA WB-57F aircraft while sampling its own contrail. Included in the analysis are measurements of water vapor pressure, temperature, ice particle number and size, and nitric oxide (NO). The systematic use of these contrail-sampling methods in future studies will improve our understanding of contrail microphysics and the performance of fast-response water and temperature measurements.
Simulations of the development of the chemical composition of the Arctic stratosphere for spring 2000 are made with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations are ...performed for the entire Northern Hemisphere on four isentropic levels (400–475 K). The initialization in early February is based on observations made from satellite, balloon and ER‐2 aircraft platforms. Tracer‐tracer correlations from balloon‐borne cryosampler (Triple) and ER‐2 measurements, as well as tracer‐PV correlations, are used to derive a comprehensive hemispherical initialization of all relevant chemical trace species. Since significant denitrification has been observed on the ER‐2 flights, a parameterization of the denitrification is derived from NOy and N2O observations on board the ER‐2 aircraft and the temperature history of the air masses under consideration. Over the simulation period from 10 February to 20 March, a chemical ozone depletion of up to 60% was derived for 425–450 K potential temperature. Maximum vortex‐averaged chemical ozone loss rates of 50 ppb d−1 or 4 ppb per sunlight hour were simulated in early March 2000 at the 425 and 450 K potential temperature levels. We show comparisons between the measurements and the simulations for the location of the ER‐2 flight paths in late February and March and the location of the Triple balloon flight. The simulated tracer mixing ratios are in good agreement with the measurements. It was not possible to reproduce the exact details of the inorganic chlorine compounds. The simulation agrees with ClOx observations on the Triple balloon flight but overestimates for the ER‐2 flights. The simulated ozone depletion agrees with estimates from other observations in the 425 and 450 K levels, but is underestimated on the 475 K level.
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