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Robert Nissen
,
Roland List
,
David Hudak
,
Greg M. McFarquhar
,
R. Paul Lawson
,
N. P. Tung
,
S. K. Soo
, and
T. S. Kang

Abstract

For nonconvective, steady light rain with rain rates <5 mm h−1 the mean Doppler velocity of raindrop spectra was found to be constant below the melting band, when the drop-free fall speed was adjusted for pressure. The Doppler radar–weighted raindrop diameters varied from case to case from 1.5 to 2.5 mm while rain rates changed from 1.2 to 2.9 mm h−1. Significant changes of advected velocity moments were observed over periods of 4 min.

These findings were corroborated by three independent systems: a Doppler radar for establishing vertical air speed and mean terminal drop speeds [using extended Velocity Azimuth Display (EVAD) analyses], a Joss–Waldvogel disdrometer at the ground, and a Particle Measuring System (PMS) 2-DP probe flown on an aircraft. These measurements were supported by data from upper-air soundings. The reason why inferred raindrop spectra do not change with height is the negligible interaction rate between raindrops at low rain rates. At low rain rates, numerical box models of drop collisions strongly support this interpretation. It was found that increasing characteristic drop diameters are correlated with increasing rain rates.

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J. S. Kimball
,
M. Zhao
,
A. D. McGuire
,
F. A. Heinsch
,
J. Clein
,
M. Calef
,
W. M. Jolly
,
S. Kang
,
S. E. Euskirchen
,
K. C. McDonald
, and
S. W. Running

Abstract

Northern ecosystems contain much of the global reservoir of terrestrial carbon that is potentially reactive in the context of near-term climate change. Annual variability and recent trends in vegetation productivity across Alaska and northwest Canada were assessed using a satellite remote sensing–based production efficiency model and prognostic simulations of the terrestrial carbon cycle from the Terrestrial Ecosystem Model (TEM) and BIOME–BGC (BioGeoChemical Cycles) model. Evidence of a small, but widespread, positive trend in vegetation gross and net primary production (GPP and NPP) is found for the region from 1982 to 2000, coinciding with summer warming of more than 1.8°C and subsequent relaxation of cold temperature constraints to plant growth. Prognostic model simulation results were generally consistent with the remote sensing record and also indicated that an increase in soil decomposition and plant-available nitrogen with regional warming was partially responsible for the positive productivity response. Despite a positive trend in litter inputs to the soil organic carbon pool, the model results showed evidence of a decline in less labile soil organic carbon, which represents approximately 75% of total carbon storage for the region. These results indicate that the regional carbon cycle may accelerate under a warming climate by increasing the fraction of total carbon storage in vegetation biomass and more rapid turnover of the terrestrial carbon reservoir.

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Brian Eder
,
Daiwen Kang
,
S. Trivikrama Rao
,
Rohit Mathur
,
Shaocai Yu
,
Tanya Otte
,
Ken Schere
,
Richard Wayland
,
Scott Jackson
,
Paula Davidson
,
Jeff McQueen
, and
George Bridgers

The National Air Quality Forecast Capability (NAQFC) currently provides next-day forecasts of ozone concentrations over the contiguous United States. It was developed collaboratively by NOAA and Environmental Protection Agency (EPA) in order to provide state and local agencies, as well as the general public, air quality forecast guidance. As part of the development process, the NAQFC has been evaluated utilizing strict monitor-to-gridcell matching criteria, and discrete-type statistics of forecast concentrations. While such an evaluation is important to the developers, it is equally, if not more important, to evaluate the performance using the same protocol as the model's intended application. Accordingly, the purpose of this article is to demonstrate the efficacy of the NAQFC from the perspective of a local forecaster, thereby promoting its use. Such an approach has required the development of a new evaluation protocol: one that examines the ability of the NAQFC to forecast values of the EPA's Air Quality Index (AQI) rather than ambient air concentrations; focuses on the use of categorical-type statistics related to exceedances and nonexceedances; and, most challenging, examines performance, not based on matched grid cells and monitors, but rather over a “local forecast region,” such as an air shed or metropolitan statistical area (MSA). Results from this approach, which is demonstrated for the Charlotte, North Carolina, MSA and subsequently applied to four additional MSAs during the summer of 2007, reveal that the quality of the NAQFC forecasts is generally comparable to forecasts from local agencies. Such findings will hopefully persuade forecasters, whether they are experienced with numerous tools at their disposal or inexperienced with limited resources, to utilize the NAQFC as forecast guidance.

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T. Matthews
,
L. B. Perry
,
I. Koch
,
D. Aryal
,
A. Khadka
,
D. Shrestha
,
K. Abernathy
,
A. C. Elmore
,
A. Seimon
,
A. Tait
,
S. Elvin
,
S. Tuladhar
,
S. K. Baidya
,
S. D. Birkel
,
S. Kang
,
T. C. Sherpa
,
A. Gajurel
, and
P. A. Mayewski
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T. Matthews
,
L. B. Perry
,
I. Koch
,
D. Aryal
,
A. Khadka
,
D. Shrestha
,
K. Abernathy
,
A. C. Elmore
,
A. Seimon
,
A. Tait
,
S. Elvin
,
S. Tuladhar
,
S. K. Baidya
,
M. Potocki
,
S. D. Birkel
,
S. Kang
,
T. C. Sherpa
,
A. Gajurel
, and
P. A. Mayewski

Abstract

As the highest mountain on Earth, Mount Everest is an iconic peak that offers an unrivalled natural platform for measuring ongoing climate change across the full elevation range of Asia’s water towers. However, Everest’s extreme environment challenges data collection, particularly on the mountain’s upper slopes, where glaciers accumulate mass and mountaineers are most exposed. Weather stations have operated on Everest before, including the world’s previous highest, but coverage has been sparse in space and time. Here we describe the installation of a network of five automatic weather stations (AWSs), including the two highest stations on Earth (8,430 and 7,945 m MSL) which greatly improves monitoring of this iconic mountain. We highlight sample applications of the new data, including an initial assessment of surface energy fluxes at Camp II (6,464 m MSL) and the South Col (7,945 m MSL), which suggest melt occurs at both sites, despite persistently below-freezing air temperatures. This analysis indicates that melt may even be possible at the 8,850 m MSL summit, and prompts a reevaluation of empirical temperature index models used to simulate glacier melt in the Himalayas that focus only on air temperature. We also provide the first evaluation of numerical weather forecasts at almost 8,000 m MSL and use of model output statistics to reduce forecast error, showcasing an important opportunity to improve climber safety on Everest. Looking forward, we emphasize the considerable potential of these freely available data for understanding weather and climate in the Himalayas and beyond, including tracking the behavior of upper-atmosphere winds, which the AWS network is uniquely positioned to monitor.

Free access
D. Kim
,
K. Sperber
,
W. Stern
,
D. Waliser
,
I.-S. Kang
,
E. Maloney
,
W. Wang
,
K. Weickmann
,
J. Benedict
,
M. Khairoutdinov
,
M.-I. Lee
,
R. Neale
,
M. Suarez
,
K. Thayer-Calder
, and
G. Zhang

Abstract

The ability of eight climate models to simulate the Madden–Julian oscillation (MJO) is examined using diagnostics developed by the U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group. Although the MJO signal has been extracted throughout the annual cycle, this study focuses on the boreal winter (November–April) behavior. Initially, maps of the mean state and variance and equatorial space–time spectra of 850-hPa zonal wind and precipitation are compared with observations. Models best represent the intraseasonal space–time spectral peak in the zonal wind compared to that of precipitation. Using the phase–space representation of the multivariate principal components (PCs), the life cycle properties of the simulated MJOs are extracted, including the ability to represent how the MJO evolves from a given subphase and the associated decay time scales. On average, the MJO decay (e-folding) time scale for all models is shorter (∼20–29 days) than observations (∼31 days). All models are able to produce a leading pair of multivariate principal components that represents eastward propagation of intraseasonal wind and precipitation anomalies, although the fraction of the variance is smaller than observed for all models. In some cases, the dominant time scale of these PCs is outside of the 30–80-day band.

Several key variables associated with the model’s MJO are investigated, including the surface latent heat flux, boundary layer (925 hPa) moisture convergence, and the vertical structure of moisture. Low-level moisture convergence ahead (east) of convection is associated with eastward propagation in most of the models. A few models are also able to simulate the gradual moistening of the lower troposphere that precedes observed MJO convection, as well as the observed geographical difference in the vertical structure of moisture associated with the MJO. The dependence of rainfall on lower tropospheric relative humidity and the fraction of rainfall that is stratiform are also discussed, including implications these diagnostics have for MJO simulation. Based on having the most realistic intraseasonal multivariate empirical orthogonal functions, principal component power spectra, equatorial eastward propagating outgoing longwave radiation (OLR), latent heat flux, low-level moisture convergence signals, and vertical structure of moisture over the Eastern Hemisphere, the superparameterized Community Atmosphere Model (SPCAM) and the ECHAM4/Ocean Isopycnal Model (OPYC) show the best skill at representing the MJO.

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I.-S. Kang
,
K. Jin
,
K.-M. Lau
,
J. Shukla
,
V. Krishnamurthy
,
S. D. Schubert
,
D. E. Waliser
,
W. F. Stern
,
V. Satyan
,
A. Kitoh
,
G. A. Meehl
,
M. Kanamitsu
,
V. Ya. Galin
,
Akimasa Sumi
,
G. Wu
,
Y. Liu
, and
J.-K. Kim

Abstract

The atmospheric anomalies for the 1997/98 El Niño–Southern Oscillation (ENSO) period have been analyzed and intercompared using the data simulated by the atmospheric general circulation models (GCMs) of 11 groups participating in the Monsoon GCM Intercomparison Project initiated by the Climate Variability and Prediction Program (CLIVAR)/Asian–Australian Monsoon Panel. Each participating GCM group performed a set of 10 ensemble simulations for 1 September 1996–31 August 1998 using the same sea surface temperature (SST) conditions but with different initial conditions. The present study presents an overview of the intercomparison project and the results of an intercomparison of the global atmospheric anomalies during the 1997/98 El Niño period. Particularly, the focus is on the tropical precipitation anomalies over the monsoon–ENSO region and the upper-tropospheric circulation anomalies in the Pacific–North American (PNA) region.

The simulated precipitation anomalies show that all of the models simulate the spatial pattern of the observed anomalies reasonably well in the tropical central Pacific, although there are large differences in the amplitudes. However, most of the models have difficulty in simulating the negative anomalies over the Maritime Continent during El Niño. The 200-hPa geopotential anomalies over the PNA region are reasonably well reproduced by most of the models. But, the models generally underestimate the amplitude of the PNA pattern. These weak amplitudes are related to the weak precipitation anomalies in the tropical Pacific. The tropical precipitation anomalies are found to be closely related to the SST anomalies not only during the El Niño seasons but also during the normal seasons that are typified by weak SST anomalies in the tropical Pacific. In particular, the pattern correlation values of the 11-model composite of the precipitation anomalies with the observed counterparts for the normal seasons are near 0.5 for the tropical region between 30°S and 30°N.

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F. Vitart
,
C. Ardilouze
,
A. Bonet
,
A. Brookshaw
,
M. Chen
,
C. Codorean
,
M. Déqué
,
L. Ferranti
,
E. Fucile
,
M. Fuentes
,
H. Hendon
,
J. Hodgson
,
H.-S. Kang
,
A. Kumar
,
H. Lin
,
G. Liu
,
X. Liu
,
P. Malguzzi
,
I. Mallas
,
M. Manoussakis
,
D. Mastrangelo
,
C. MacLachlan
,
P. McLean
,
A. Minami
,
R. Mladek
,
T. Nakazawa
,
S. Najm
,
Y. Nie
,
M. Rixen
,
A. W. Robertson
,
P. Ruti
,
C. Sun
,
Y. Takaya
,
M. Tolstykh
,
F. Venuti
,
D. Waliser
,
S. Woolnough
,
T. Wu
,
D.-J. Won
,
H. Xiao
,
R. Zaripov
, and
L. Zhang

Abstract

Demands are growing rapidly in the operational prediction and applications communities for forecasts that fill the gap between medium-range weather and long-range or seasonal forecasts. Based on the potential for improved forecast skill at the subseasonal to seasonal time range, the Subseasonal to Seasonal (S2S) Prediction research project has been established by the World Weather Research Programme/World Climate Research Programme. A main deliverable of this project is the establishment of an extensive database containing subseasonal (up to 60 days) forecasts, 3 weeks behind real time, and reforecasts from 11 operational centers, modeled in part on the The Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) database for medium-range forecasts (up to 15 days).

The S2S database, available to the research community since May 2015, represents an important tool to advance our understanding of the subseasonal to seasonal time range that has been considered for a long time as a “desert of predictability.” In particular, this database will help identify common successes and shortcomings in the model simulation and prediction of sources of subseasonal to seasonal predictability. For instance, a preliminary study suggests that the S2S models significantly underestimate the amplitude of the Madden–Julian oscillation (MJO) teleconnections over the Euro-Atlantic sector. The S2S database also represents an important tool for case studies of extreme events. For instance, a multimodel combination of S2S models displays higher probability of a landfall over the islands of Vanuatu 2–3 weeks before Tropical Cyclone Pam devastated the islands in March 2015.

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Tandong Yao
,
Yongkang Xue
,
Deliang Chen
,
Fahu Chen
,
Lonnie Thompson
,
Peng Cui
,
Toshio Koike
,
William K.-M. Lau
,
Dennis Lettenmaier
,
Volker Mosbrugger
,
Renhe Zhang
,
Baiqing Xu
,
Jeff Dozier
,
Thomas Gillespie
,
Yu Gu
,
Shichang Kang
,
Shilong Piao
,
Shiori Sugimoto
,
Kenichi Ueno
,
Lei Wang
,
Weicai Wang
,
Fan Zhang
,
Yongwei Sheng
,
Weidong Guo
,
Ailikun
,
Xiaoxin Yang
,
Yaoming Ma
,
Samuel S. P. Shen
,
Zhongbo Su
,
Fei Chen
,
Shunlin Liang
,
Yimin Liu
,
Vijay P. Singh
,
Kun Yang
,
Daqing Yang
,
Xinquan Zhao
,
Yun Qian
,
Yu Zhang
, and
Qian Li

Abstract

The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years. This paper reviews the latest development in multidisciplinary TP research associated with this warming. The rapid warming facilitates intense and broad glacier melt over most of the TP, although some glaciers in the northwest are advancing. By heating the atmosphere and reducing snow/ice albedo, aerosols also contribute to the glaciers melting. Glacier melt is accompanied by lake expansion and intensification of the water cycle over the TP. Precipitation has increased over the eastern and northwestern TP. Meanwhile, the TP is greening and most regions are experiencing advancing phenological trends, although over the southwest there is a spring phenological delay mainly in response to the recent decline in spring precipitation. Atmospheric and terrestrial thermal and dynamical processes over the TP affect the Asian monsoon at different scales. Recent evidence indicates substantial roles that mesoscale convective systems play in the TP’s precipitation as well as an association between soil moisture anomalies in the TP and the Indian monsoon. Moreover, an increase in geohazard events has been associated with recent environmental changes, some of which have had catastrophic consequences caused by glacial lake outbursts and landslides. Active debris flows are growing in both frequency of occurrences and spatial scale. Meanwhile, new types of disasters, such as the twin ice avalanches in Ali in 2016, are now appearing in the region. Adaptation and mitigation measures should be taken to help societies’ preparation for future environmental challenges. Some key issues for future TP studies are also discussed.

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Sara H. Knox
,
Robert B. Jackson
,
Benjamin Poulter
,
Gavin McNicol
,
Etienne Fluet-Chouinard
,
Zhen Zhang
,
Gustaf Hugelius
,
Philippe Bousquet
,
Josep G. Canadell
,
Marielle Saunois
,
Dario Papale
,
Housen Chu
,
Trevor F. Keenan
,
Dennis Baldocchi
,
Margaret S. Torn
,
Ivan Mammarella
,
Carlo Trotta
,
Mika Aurela
,
Gil Bohrer
,
David I. Campbell
,
Alessandro Cescatti
,
Samuel Chamberlain
,
Jiquan Chen
,
Weinan Chen
,
Sigrid Dengel
,
Ankur R. Desai
,
Eugenie Euskirchen
,
Thomas Friborg
,
Daniele Gasbarra
,
Ignacio Goded
,
Mathias Goeckede
,
Martin Heimann
,
Manuel Helbig
,
Takashi Hirano
,
David Y. Hollinger
,
Hiroki Iwata
,
Minseok Kang
,
Janina Klatt
,
Ken W. Krauss
,
Lars Kutzbach
,
Annalea Lohila
,
Bhaskar Mitra
,
Timothy H. Morin
,
Mats B. Nilsson
,
Shuli Niu
,
Asko Noormets
,
Walter C. Oechel
,
Matthias Peichl
,
Olli Peltola
,
Michele L. Reba
,
Andrew D. Richardson
,
Benjamin R. K. Runkle
,
Youngryel Ryu
,
Torsten Sachs
,
Karina V. R. Schäfer
,
Hans Peter Schmid
,
Narasinha Shurpali
,
Oliver Sonnentag
,
Angela C. I. Tang
,
Masahito Ueyama
,
Rodrigo Vargas
,
Timo Vesala
,
Eric J. Ward
,
Lisamarie Windham-Myers
,
Georg Wohlfahrt
, and
Donatella Zona

Abstract

This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH4) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH4 flux measurements globally, initial results comparing CH4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH4 fluxes across sites ranged from −0.2 ± 0.02 g C m–2 yr–1 for an upland forest site to 114.9 ± 13.4 g C m–2 yr–1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m–2 yr–1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH4 flux across wetland sites globally. Water table position was positively correlated with annual CH4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH4 estimates due to gap-filling and random errors were on average ±1.6 g C m–2 yr–1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH4 flux database, the controls on ecosystem CH4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH4 emissions.

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