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  • Author or Editor: L. J. Allison x
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David M. Wright
,
Derek J. Posselt
, and
Allison L. Steiner

Abstract

High-resolution Weather Research and Forecasting Model (WRF) simulations are used to explore the sensitivity of Great Lakes lake-effect snowfall (LES) to changes in lake ice cover and surface temperature. A control simulation with observed ice cover is compared with three sensitivity tests: complete ice cover, no lake ice, and warmer lake surface temperatures. The spatial pattern of unfrozen lake surfaces determines the placement of LES, and complete ice cover eliminates it. Removal of ice cover and an increase in lake temperatures result in an expansion of the LES area both along and downwind of the lake shore, as well as an increase in snowfall amount. While lake temperatures and phase determine the amount and spatial coverage of LES, the finescale distribution of LES is strongly affected by the interaction between lake surface fluxes, the large-scale flow, and the local lake shore geography and inland topography. As a consequence, the sensitivity of LES to topography and shore geometry differs for lakes with short versus long overwater fetch. These simulations indicate that coarse-resolution models may be able to realistically reproduce the gross features of LES in future climates, but will miss the important local-scale interactions that determine the location and intensity of LES.

Full access
C. Prabhakara
,
V. V. Salomonson
,
B. J. Conrath
,
J. Sterania
, and
L. J. Allison

Abstract

Remote soundings of total ozone made by the Infrared Interferometer Spectrometer onboard the Nimbus 3 satellite, during June and July 1969, show the presence of ozone minima over northeast India and north Africa where summertime upper air high pressure systems exist. The easterly jet stream is revealed by ozone maxima observed along its path over southeast Asia and Africa during the summer monsoon period.

Full access
Robin L. Tanamachi
,
Stephen J. Frasier
,
Joseph Waldinger
,
Allison LaFleur
,
David D. Turner
, and
Francesc Rocadenbosch

Abstract

During spring 2016 and spring 2017, a vertically pointing, S-band Frequency Modulated Continuous Wave radar (UMass FMCW) was deployed in northern Alabama under the auspices of the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)-Southeast. In total, ~14 weeks of data were collected, in conditions ranging from quiescent clear skies to severe thunderstorms. The principal objective of these deployments was to characterize the boundary layer evolution near the VORTEX-Southeast domain. In this paper, we describe intermediate results in service of this objective. Specifically, we describe updates to the UMass FMCW system, document its deployments for VORTEX-Southeast, and apply four automated algorithms: 1) a dealiasing algorithm to the Doppler velocities, 2) a fuzzy logic scatterer classification scheme to separate precipitation from nonprecipitation observations, 3) a brightband/melting-layer identification algorithm for stratiform precipitation, and 4) an extended Kalman filter–based convective boundary layer depth (mixing height) measurement algorithm for nonprecipitation observations. Results from the latter two applications are qualitatively verified against retrieved soundings from a collocated thermodynamic profiling system.

Open access
Peiyun Zhu
,
Susan J. Cheng
,
Zachary Butterfield
,
Gretchen Keppel-Aleks
, and
Allison L. Steiner

Abstract

Clouds can modify terrestrial productivity by reducing total surface radiation and increasing diffuse radiation, which may be more evenly distributed through plant canopies and increase ecosystem carbon uptake (the “diffuse fertilization effect”). Previous work at ecosystem-level observational towers demonstrated that diffuse photosynthetically active radiation (PAR; 400–700 nm) increases with cloud optical thickness (COT) until a COT of approximately 10, defined here as the “low-COT regime.” To identify whether the low-COT regime also influences carbon uptake on broader spatial and longer temporal time scales, we use global, monthly data to investigate the influence of COT on carbon uptake in three land-cover types: shrublands, forests, and croplands. While there are limitations in global gross primary production (GPP) products, global COT data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) reveal that during the growing season tropical and subtropical regions more frequently experience a monthly low-COT regime (>20% of the time) than other regions of the globe. Contrary to ecosystem-level studies, comparisons of monthly COT with monthly satellite-derived solar-induced chlorophyll fluorescence and modeled GPP indicate that, although carbon uptake generally increases with COT under the low-COT regime, the correlations between COT and carbon uptake are insignificant (p > 0.05) in shrublands, forests, and croplands at regional scales. When scaled globally, vegetated regions under the low-COT regime account for only 4.9% of global mean annual GPP, suggesting that clouds and their diffuse fertilization effect become less significant drivers of terrestrial carbon uptake at broader spatial and temporal scales.

Full access
Allison L. Steiner
,
Dori Mermelstein
,
Susan J. Cheng
,
Tracy E. Twine
, and
Andrew Oliphant

Abstract

Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

Full access
T. T. Wilheit
,
J. S. Theon
,
W. E. Shenk
,
L. J. Allison
, and
E. B. Rodgers

Abstract

The Electrically Scanned Microwave Radiometer (ESMR) on the Nimbus 5 satellite measures the microwave radiation emitted by the earth and the atmosphere in a wavelength band centered at 1.55 cm. The ESMR scans perpendicularly to the spacecraft suborbital track from 50° left to 50° right in 78 steps every 4 s, producing an image which has a spatial resolution of 25 km at nadir.

At these wavelengths, the emissivity of the earth and atmosphere varies considerably more than at infrared wavelengths. Thus the contrast in radiance between land surfaces, which have high emissivities, and ocean surfaces, which have low emissivities, makes continents and islands readily distinguishable. There is a minimum of interference from clouds since most non-raining clouds are virtually transparent at these wavelengths. However, atmospheric moisture does modify the radiation emitted by the surface and when cloud droplets reach precipitable size, they enhance the radiation considerably over surfaces of low emissivity (e.g., over oceans), making it possible to map areas of rainfall as well as regions of heavy cloudiness.

In this application the ESMR images are meteorologically useful in determining the extent, structure and, qualitatively, the intensity of rainfall. It is then possible, over oceans, to determine the location of frontal rain, rain/snow boundaries, and the structure of tropical storms. Because of the generally high emissivities of land surfaces and the wide range of values they assume, interpretation of atmospheric parameters over land is not possible at present.

Full access
Yumin Moon
,
Daehyun Kim
,
Allison A. Wing
,
Suzana J. Camargo
,
Ming Zhao
,
L. Ruby Leung
,
Malcolm J. Roberts
,
Dong-Hyun Cha
, and
Jihong Moon

Abstract

This study evaluates tropical cyclone (TC) rainfall structures in the CMIP6 HighResMIP global climate model (GCM) simulations against satellite rainfall retrievals. We specifically focus on TCs within the deep tropics (25°S–25°N). Analysis of TC rain rate composites indicates that in comparison to the satellite observations at the same intensity, many HighResMIP simulations tend to overproduce rain rates around TCs, in terms of both maximum rain rate magnitude and area-averaged rain rates. In addition, as model horizontal resolution increases, the magnitude of the peak rain rate appears to increase. However, the area-averaged rain rates decrease with increasing horizontal resolution, partly due to the TC eyewall being located closer to the TC center, thus occupying a smaller area and contributing less to the area-averaged rain rates. The effect of ocean coupling is to lower the TC rain rates, bringing them closer to the satellite observations, due to reduced horizontal moisture flux convergence and surface latent heat flux beneath TCs. Examination of horizontal rain rate distributions indicates that vertical wind shear–induced rainfall asymmetries in HighResMIP-simulated TCs are qualitatively consistent with the observations. In addition, a positive relationship is observed between the area-averaged inner-core rainfall and TC intensification likelihoods across the HighResMIP simulations, as GCM simulations producing stronger TCs more frequently have the greater rainfall close to the center, in agreement with previous theoretical and GCM simulation results.

Free access
Shuguang Liu
,
Ben Bond-Lamberty
,
Lena R. Boysen
,
James D. Ford
,
Andrew Fox
,
Kevin Gallo
,
Jerry Hatfield
,
Geoffrey M. Henebry
,
Thomas G. Huntington
,
Zhihua Liu
,
Thomas R. Loveland
,
Richard J. Norby
,
Terry Sohl
,
Allison L. Steiner
,
Wenping Yuan
,
Zhao Zhang
, and
Shuqing Zhao

Abstract

Half of Earth’s land surface has been altered by human activities, creating various consequences on the climate and weather systems at local to global scales, which in turn affect a myriad of land surface processes and the adaptation behaviors. This study reviews the status and major knowledge gaps in the interactions of land and atmospheric changes and present 11 grand challenge areas for the scientific research and adaptation community in the coming decade. These land-cover and land-use change (LCLUC)-related areas include 1) impacts on weather and climate, 2) carbon and other biogeochemical cycles, 3) biospheric emissions, 4) the water cycle, 5) agriculture, 6) urbanization, 7) acclimation of biogeochemical processes to climate change, 8) plant migration, 9) land-use projections, 10) model and data uncertainties, and, finally, 11) adaptation strategies. Numerous studies have demonstrated the effects of LCLUC on local to global climate and weather systems, but these putative effects vary greatly in magnitude and even sign across space, time, and scale and thus remain highly uncertain. At the same time, many challenges exist toward improved understanding of the consequences of atmospheric and climate change on land process dynamics and services. Future effort must improve the understanding of the scale-dependent, multifaceted perturbations and feedbacks between land and climate changes in both reality and models. To this end, one critical cross-disciplinary need is to systematically quantify and better understand measurement and model uncertainties. Finally, LCLUC mitigation and adaptation assessments must be strengthened to identify implementation barriers, evaluate and prioritize opportunities, and examine how decision-making processes work in specific contexts.

Full access
Adam J. Clark
,
Israel L. Jirak
,
Timothy A. Supinie
,
Kent H. Knopfmeier
,
Jake Vancil
,
David Jahn
,
David Harrison
,
Allison Lynn Brannan
,
Christopher D. Karstens
,
Eric D. Loken
,
Nathan A. Dahl
,
Makenzie Krocak
,
David Imy
,
Andrew R. Wade
,
Jeffrey M. Milne
,
Kimberly A. Hoogewind
,
Pamela L. Heinselman
,
Montgomery Flora
,
Joshua Martin
,
Brian C. Matilla
,
Joseph C. Picca
,
Patrick S. Skinner
, and
Patrick Burke
Open access
John E. Yorks
,
Jun Wang
,
Matthew J. McGill
,
Melanie Follette-Cook
,
Edward P. Nowottnick
,
Jeffrey S. Reid
,
Peter R. Colarco
,
Jianglong Zhang
,
Olga Kalashnikova
,
Hongbin Yu
,
Franco Marenco
,
Joseph A. Santanello
,
Tammy M. Weckwerth
,
Zhanqing Li
,
James R. Campbell
,
Ping Yang
,
Minghui Diao
,
Vincent Noel
,
Kerry G. Meyer
,
James L. Carr
,
Michael Garay
,
Kenneth Christian
,
Angela Bennedetti
,
Allison M. Ring
,
Alice Crawford
,
Michael J. Pavolonis
,
Valentina Aquila
,
Jhoon Kim
, and
Shobha Kondragunta

Abstract

A SmallSat mission concept is formulated here to carry out Time-varying Optical Measurements of Clouds and Aerosol Transport (TOMCAT) from space while embracing low-cost opportunities enabled by the revolution in Earth science observation technologies. TOMCAT’s “around-the-clock” measurements will provide needed insights and strong synergy with existing Earth observation satellites to 1) statistically resolve diurnal and vertical variation of cirrus cloud properties (key to Earth’s radiation budget), 2) determine the impacts of regional and seasonal planetary boundary layer (PBL) diurnal variation on surface air quality and low-level cloud distributions, and 3) characterize smoke and dust emission processes impacting their long-range transport on the subseasonal to seasonal time scales. Clouds, aerosol particles, and the PBL play critical roles in Earth’s climate system at multiple spatiotemporal scales. Yet their vertical variations as a function of local time are poorly measured from space. Active sensors for profiling the atmosphere typically utilize sun-synchronous low-Earth orbits (LEO) with rather limited temporal and spatial coverage, inhibiting the characterization of spatiotemporal variability. Pairing compact active lidar and passive multiangle remote sensing technologies from an inclined LEO platform enables measurements of the diurnal and vertical variability of aerosols, clouds, and aerosol-mixing-layer (or PBL) height in tropical-to-midlatitude regions where most of the world’s population resides. TOMCAT is conceived to bring potential societal benefits by delivering its data products in near–real time and offering on-demand hazard-monitoring capabilities to profile fire injection of smoke particles, the frontal lofting of dust particles, and the eruptive rise of volcanic plumes.

Open access