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G. S. Kent
,
C. R. Trepte
,
U. O. Farrukh
, and
M. P. McCormick

Abstract

Aerosol extinction data obtained by the Stratospheric Aerosol Measurement II (SAM II) satellite instrument during the 1979/80 Northern Hemisphere winter season have been analyzed in relation to the cyclonic polar vortex. A synoptic approach has been employed to study the behavior of aerosol extinction ratio and optical depth between altitudes of 8 and 30 km as a tracer of mean atmospheric motions in and near the polar vortex. As the polar vortex intensifies, a gradient of extinction ratio is established across the polar-night jet stream, which is associated with subsidence within the vortex. Maximum subsidence occurs at the center of the vortex. Calculated descent rates relative to isentropic surfaces are of the order of 8 × 10−4 m s−1 near 20 km, at the center of the vortex between September and December. Below an altitude of 14 km, taken as the base of the vortex, and outside the vortex, horizontal movements occur freely, masking any systematic vertical motions. Extinction enhancements by polar stratospheric clouds and changes produced by sudden warmings in the second half of winter have prevented a similar study for this period. An estimate of the aerosol mass transferred downward through the base of the vortex for the entire season is 7000 tonnes. Comparison of the inferred stratospheric motions with earlier studies using radioactive tracers shows good agreement.

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Kelly Mahoney
,
Chesley McColl
,
Douglas M. Hultstrand
,
William D. Kappel
,
Bill McCormick
, and
Gilbert P. Compo

Abstract

Accurate estimation of the potential “upper limit” for extreme precipitation is critical for dam safety and water resources management, as dam failures pose significant risks to life and property. Methods used to estimate the theoretical upper limit of precipitation are often outdated and in need of updating. The rarity of extreme events means that old storms with limited observational data are often used to define the upper bound of precipitation. Observations of many important old storms are limited in spatial and temporal coverage, and sometimes of dubious quality. This reduces confidence in flood hazard assessments used in dam safety evaluations and leads to unknown or uncertain societal risk. This paper describes a method for generating and applying ensembles of high-resolution, state-of-the-art numerical model simulations of historical past extreme precipitation events to meet contemporary stakeholder needs. The method was designed as part of a research-to-application-focused partnership project to update state dam safety rules in Colorado and New Mexico. The results demonstrated multiple stakeholder and user benefits that were applied directly into storm analyses utilized for extreme rainfall estimation, and diagnostics were developed and ultimately used to update Colorado state dam safety rules, officially passed in January 2020. We discuss how what started as a prototype research foray to meet a specific user need may ultimately inform wider adoption of numerical simulations for water resources risk assessment, and how the historical event downscaling method performed offers near-term, implementable improvements to current dam safety flood risk estimates that can better serve society today.

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P. B. Russell
,
M. P. McCormick
,
T. J. Swissler
,
J. M. Rosen
,
D. J. Hofmann
, and
L. R. McMaster

Abstract

A large satellite validation experiment was conducted at Poker Flat, Alaska, 16–19 July 1979. Instruments included the SAM II and SAGE satellite sensors, dustsondes impactors, a fitter collector and an airborne lidar. We show that the extinction profiles that were measured independently by SAM II and SAGE agree with each other. We then use a generalized optical model (which agrees with the Poker Flat optical absorption and relative size distribution measurements) to derive extinction profiles from the other measurements. Extinction profiles thus derived from the dustsonde, fitter and lidar measurements agree with the satellite-measured extinction profiles to within the combined uncertainties. (Individual 1 σ uncertainties are, at most heights, roughly 7 to 20% each for the satellite, dustsonde and filter measurements, 30 to 60% for the lidar measurements, and 10 to 20% for the process of converting one measured parameter to another using the optical model.)

The wire impactor-derived results are also consistent with the other results, but the comparison is coarse because of the relatively large uncertainties (±35% to a factor of 4) in impactor-derived mass, extinction, N 0.15 and N 0.25 (Nx is the number of particles per unit volume with radius greater than x μm.) These uncertainties apply to background stratospheric aerosol size distributions, and result primarily from relatively small uncertainties (±8 to ±20% for confidence limits of 95%) in radii assigned to impacted particles, combined with the steepness of background size distributions in the radius range that contributes most to mass, extinction, N 0.15 and N 0.25. Polar nephelometer-measured asymmetry parameters (0.4 to 0.6) agree with a previous balloon photometer inference, but are significantly less than the value (∼0.7) obtained from Mie scattering calculations assuming either model or measured size distributions.

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M. P. McCormick
,
Patrick Hamill
,
T. J Pepin
,
W. P. Chu
,
T. J Swissler
, and
L. R. McMaster

The potential climatological and environmental importance of the stratospheric aerosol layer has prompted great interest in measuring the properties of this aerosol. In this paper we report on two recently deployed NASA satellite systems (SAM II and SAGE) that are monitoring the stratospheric aerosol. The satellite orbits are such that nearly global coverage is obtained. The instruments mounted in the spacecraft are sun photometers that measure solar intensity at specific wavelengths as it is moderated by atmospheric particulates and gases during each sunrise and sunset encountered by the satellites. The data obtained are “inverted” to yield vertical aerosol and gaseous (primarily ozone) extinction profiles with 1 km vertical resolution. Thus, latitudinal, longitudinal, and temporal variations in the aerosol layer can be evaluated. The satellite systems are being validated by a series of ground truth experiments using airborne and ground lidar, balloon-borne dustsondes, aircraft-mounted impactors, and other correlative sensors. We describe the SAM II and SAGE satellite systems, instrument characteristics, and mode of operation; outline the methodology of the experiments; and describe the ground truth experiments. We present preliminary results from these measurements.

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P.B. Russell
,
M.P. McCormick
,
T.J. Swissler
,
W.P. Chu
,
J.M. Livingston
,
W.H. Fuller
,
J.M. Rosen
,
D.J. Hofmann
,
L.R. McMaster
,
D.C. Woods
, and
T.J. Pepin

Abstract

We show results from the first set of measurements conducted to validate extinction data from the satellite sensor SAM II. Dustsonde-measured number density profiles and lidar-measured backscattering profiles for two days are converted to extinction profiles using the optical modeling techniques described in the companion Paper I (Russell et al., 1981). At heights ∼2 km and more above the tropopause, the dustsonde data are used to restrict the range of model size distributions, thus reducing uncertainties in the conversion process. At all heights, measurement uncertainties for each sensor are evaluated, and these are combined with conversion uncertainties to yield the total uncertainty in derived data profiles.

The SAM II measured, dustsonde-inferred, and lidar-inferred extinction profiles for both days are shown to agree within their respective uncertainties at all heights above the tropopause. Near the tropopause, this agreement depends on the use of model size distributions with more relatively large particles (radius ≳0.6 μm) than are present in distributions used to model the main stratospheric aerosol peak. The presence of these relatively large particles is supported by measurements made elsewhere and is suggested by in situ size distribution measurements reported here. These relatively large particles near the tropopause are likely to have an important bearing on the radiative impact of the total stratospheric aerosol.

The agreement in this experiment supports the validity of the SAM II extinction data and the SAM II uncertainty estimates derived from an independent error analysis. Recommendations are given for reducing the uncertainties of future correlative experiments.

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M. P. McCormick
,
D. M. Winker
,
E. V. Browell
,
J. A. Coakley
,
C. S. Gardner
,
R. M. Hoff
,
G. S. Kent
,
S. H. Melfi
,
R. T. Menzies
,
C. M. R. Piatt
,
D. A. Randall
, and
J. A. Reagan

The Lidar In-Space Technology Experiment (LITE) is being developed by NASA/Langley Research Center for a series of flights on the space shuttle beginning in 1994. Employing a three-wavelength Nd:YAG laser and a 1-m-diameter telescope, the system is a test-bed for the development of technology required for future operational spaceborne lidars. The system has been designed to observe clouds, tropospheric and stratospheric aerosols, characteristics of the planetary boundary layer, and stratospheric density and temperature perturbations with much greater resolution than is available from current orbiting sensors. In addition to providing unique datasets on these phenomena, the data obtained will be useful in improving retrieval algorithms currently in use. Observations of clouds and the planetary boundary layer will aid in the development of global climate model (GCM) parameterizations. This article briefly describes the LITE program and discusses the types of scientific investigations planned for the first flight.

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The CALIPSO Mission

A Global 3D View of Aerosols and Clouds

D. M. Winker
,
J. Pelon
,
J. A. Coakley Jr.
,
S. A. Ackerman
,
R. J. Charlson
,
P. R. Colarco
,
P. Flamant
,
Q. Fu
,
R. M. Hoff
,
C. Kittaka
,
T. L. Kubar
,
H. Le Treut
,
M. P. Mccormick
,
G. Mégie
,
L. Poole
,
K. Powell
,
C. Trepte
,
M. A. Vaughan
, and
B. A. Wielicki

Aerosols and clouds have important effects on Earth's climate through their effects on the radiation budget and the cycling of water between the atmosphere and Earth's surface. Limitations in our understanding of the global distribution and properties of aerosols and clouds are partly responsible for the current uncertainties in modeling the global climate system and predicting climate change. The CALIPSO satellite was developed as a joint project between NASA and the French space agency CNES to provide needed capabilities to observe aerosols and clouds from space. CALIPSO carries CALIOP, a two-wavelength, polarization-sensitive lidar, along with two passive sensors operating in the visible and thermal infrared spectral regions. CALIOP is the first lidar to provide long-term atmospheric measurements from Earth's orbit. Its profiling and polarization capabilities offer unique measurement capabilities. Launched together with the CloudSat satellite in April 2006 and now flying in formation with the A-train satellite constellation, CALIPSO is now providing information on the distribution and properties of aerosols and clouds, which is fundamental to advancing our understanding and prediction of climate. This paper provides an overview of the CALIPSO mission and instruments, the data produced, and early results.

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C. M. Platt
,
S. A. Young
,
A. I. Carswell
,
S. R. Pal
,
M. P. McCormick
,
D. M. Winker
,
M. DelGuasta
,
L. Stefanutti
,
W. L. Eberhard
,
M. Hardesty
,
P. H. Flamant
,
R. Valentin
,
B. Forgan
,
G. G. Gimmestad
,
H. Jäger
,
S. S. Khmelevtsov
,
I. Kolev
,
B. Kaprieolev
,
Da-ren Lu
,
K. Sassen
,
V. S. Shamanaev
,
O. Uchino
,
Y. Mizuno
,
U. Wandinger
,
C. Weitkamp
,
A. Ansmann
, and
C. Wooldridge

The Experimental Cloud Lidar Pilot Study (ECLIPS) was initiated to obtain statistics on cloud-base height, extinction, optical depth, cloud brokenness, and surface fluxes. Two observational phases have taken place, in October–December 1989 and April–July 1991, with intensive 30-day periods being selected within the two time intervals. Data are being archived at NASA Langley Research Center and, once there, are readily available to the international scientific community.

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