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T. Y. Tang
,
Y. Hsueh
,
Y. J. Yang
, and
J. C. Ma

Abstract

Hydrographic observations and current measurements with a Shipboard Acoustic Doppler Current Profiler over the continental shelf–slope junction northeast of Taiwan during 10–17 August 1994 allow the construction of the mesoscale flow pattern generated by the collision of the Kuroshio and a stretch of the continental shelf that has turned to run nearly east–west. The pattern is made up of a deflected Kuroshio mainstream to the east, an intrusion of Kuroshio water onto the continental shelf region, a counterclockwise circulation over Mien-Hwa Canyon (MHC) immediately northeast of Taiwan, a deep southwestward countercurrent along the northern wall of MHC, and a seaward outflow of continental shelf water around the northern coast of Taiwan. The hydrography features a cold dome over the west side of MHC that consisted of subsurface Kuroshio water. A temperature–salinity plot of all the station data shows the incorporation in the neighborhood of Taiwan of continental shelf water into the Kuroshio.

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H.-Y. Ma
,
X. Ji
,
J. D. Neelin
, and
C. R. Mechoso

Abstract

The present study examines the mechanisms for the connection between the precipitation variability in eastern Brazil and the South Atlantic convergence zone (SACZ) convective margin (eastern Brazil/SACZ convective margin) and the variability of low-level inflow on interannual time scales during austral summer. The authors' methodology is based on the analysis of observational datasets and simulations by the University of California, Los Angeles (UCLA) atmospheric general circulation model (AGCM) coupled to the Simplified Simple Biosphere Model.

It is demonstrated that the inflow variability is associated with the leading mode of wind variability over subtropical South America, and the connection is established through the mechanism of an analytic prototype for convective margin shifts proposed in previous studies. Over the eastern Brazil/SACZ convective margin, the weaker (stronger) convection tends to occur together with stronger (weaker) low-level inflows in reference to the mean easterly trades. By changing the “ventilation” effect, stronger (weaker) inflows with low moist static energy from the Atlantic Ocean suppress (promote) convection. The causal relationship is verified by AGCM mechanism-testing experiments performed in perpetual-February mode, in which low-level, nondivergent wind perturbations are imposed in a region overlapping eastern Brazil and the western Atlantic Ocean. With solely the imposed-wind perturbations acting on the moisture advection in the model equation, the AGCM can reproduce the precipitation variability in the eastern Brazil/SACZ convective margin. The capability of the AGCM in capturing such precipitation sensitivity to the low-level inflow variability also suggests that the mechanism can be applied to other regions of convective margins or to other time scales.

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Hsi-Yen Ma
,
C. Roberto Mechoso
,
Yongkang Xue
,
Heng Xiao
,
J. David Neelin
, and
Xuan Ji

Abstract

An evaluation is presented of the impact on tropical climate of continental-scale perturbations given by different representations of land surface processes (LSPs) in a general circulation model that includes atmosphere–ocean interactions. One representation is a simple land scheme, which specifies climatological albedos and soil moisture availability. The other representation is the more comprehensive Simplified Simple Biosphere Model, which allows for interactive soil moisture and vegetation biophysical processes.

The results demonstrate that such perturbations have strong impacts on the seasonal mean states and seasonal cycles of global precipitation, clouds, and surface air temperature. The impact is especially significant over the tropical Pacific Ocean. To explore the mechanisms for such impact, model experiments are performed with different LSP representations confined to selected continental-scale regions where strong interactions of climate–vegetation biophysical processes are present. The largest impact found over the tropical Pacific is mainly from perturbations in the tropical African continent where convective heating anomalies associated with perturbed surface heat fluxes trigger global teleconnections through equatorial wave dynamics. In the equatorial Pacific, the remote impacts of the convection anomalies are further enhanced by strong air–sea coupling between surface wind stress and upwelling, as well as by the effects of ocean memory. LSP perturbations over South America and Asia–Australia have much weaker global impacts. The results further suggest that correct representations of LSP, land use change, and associated changes in the deep convection over tropical Africa are crucial to reducing the uncertainty of future climate projections with global climate models under various climate change scenarios.

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E.A. Terray
,
M.A. Donelan
,
Y.C. Agrawal
,
W.M. Drennan
,
K.K. Kahma
,
A.J. Williams
,
P.A. Hwang
, and
S.A. Kitaigorodskii

Abstract

The dissipation of kinetic energy at the surface of natural water bodies has important consequences for many Physical and biochemical processes including wave dynamics, gas transfer, mixing of nutrients and pollutants, and photosynthetic efficiency of plankton. Measurements of dissipation close to the surface obtained in a large lake under conditions of strong wind forcing are presented that show a layer of enhanced dissipation exceeding wall layer values by one or two orders of magnitude. The authors propose a scaling for the rate of dissipation based on wind and wave parameters, and conclude that the dissipation rate under breaking waves depends on depth, to varying degrees, in three stages. Very near the surface, within one significant height, the dissipation rate is high (an order of magnitude greater than that predicted by wall layer theory) and roughly constant. Below this is an intermediate region where the dissipation decays as z −2. The thickness of this layer (relative to the significant wave height) is proportional to the energy flux from breaking normalized by pu 3 *, which for young waves is proportional to wave age. At sufficient depth the dissipation rate asymptotes to values commensurate with a traditional wall layer. The total energy flux into the water column can be an order of magnitude greater than the conventional estimate of pu 3 */2 and depends strongly on wave age. Thew results imply a pronounced shift in our approach to estimating kinetic energy dissipation in wave-stirred regions and in the modeling of various physical, chemical, and biological processes.

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E. Kassianov
,
M. Pekour
,
C. Flynn
,
L. K. Berg
,
J. Beranek
,
A. Zelenyuk
,
C. Zhao
,
L. R. Leung
,
P. L. Ma
,
L. Riihimaki
,
J. D. Fast
,
J. Barnard
,
A. G. Hallar
,
I. B. McCubbin
,
E. W. Eloranta
,
A. McComiskey
, and
P. J. Rasch

Abstract

This work is motivated by previous studies of transatlantic transport of Saharan dust and the observed quasi-static nature of coarse mode aerosol with a volume median diameter (VMD) of approximately 3.5 μm. The authors examine coarse mode contributions from transpacific transport of dust to North American aerosol properties using a dataset collected at the high-elevation Storm Peak Laboratory (SPL) and the nearby Atmospheric Radiation Measurement (ARM) Mobile Facility. Collected ground-based data are complemented by quasi-global model simulations and satellite and ground-based observations. The authors identify a major dust event associated mostly with a transpacific plume (about 65% of near-surface aerosol mass) in which the coarse mode with moderate (~3 μm) VMD is distinct and contributes substantially to total aerosol volume (up to 70%) and scattering (up to 40%). The results demonstrate that the identified plume at the SPL site has a considerable fraction of supermicron particles (VMD ~3 μm) and, thus, suggest that these particles have a fairly invariant behavior despite transpacific transport. If confirmed in additional studies, this invariant behavior may simplify considerably parameterizations for size-dependent processes associated with dust transport and removal.

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Q. S. He
,
C. C. Li
,
J. Z. Ma
,
H. Q. Wang
,
G. M. Shi
,
Z. R. Liang
,
Q. Luan
,
F. H. Geng
, and
X. W. Zhou

Abstract

As part of the Tibet Ozone, Aerosol and Radiation (TOAR) project, a micropulse lidar was operated in Naqu (31.5°N, 92.1°E; 4508 m MSL) on the Tibetan Plateau to observe cirrus clouds continuously from 19 July to 26 August 2011. During the experiment, the time coverage of ice clouds only was 15% in the upper troposphere (above 9.5 km MSL). The cirrus top/bottom altitudes (mean values of 15.6/14.7 km) are comparable to those measured previously at tropical sites but relatively higher than those measured at midlatitude sites. The majority of the cloud layers yielded a lidar ratio between 10 and 40 sr, with a mean value of 28 ± 15 sr, characterized by a bimodal frequency distribution. Subvisible, thin, and opaque cirrus formation was observed in 16%, 34%, and 50% of all cirrus cases, respectively. A mean cirrus optical depth of 0.33 was observed over the Tibetan Plateau, slightly higher than those in the subtropics and tropics. With decreasing temperature, the lidar ratio increased slightly, whereas the mean extinction coefficient decreased significantly. The occurrence of clouds is highly correlated with the outgoing longwave radiation and the strong cold perturbations in the upper troposphere. Deep convective activity and Rossby waves are important dynamical processes that control cirrus variations over the Tibetan Plateau, where both anvil cirrus outflowing from convective cumulonimbus clouds and large-scale strong cold perturbations in the upper troposphere should play an important role in cirrus formation.

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Z. Su
,
W. Timmermans
,
Y. Zeng
,
J. Schulz
,
V. O. John
,
R. A. Roebeling
,
P. Poli
,
D. Tan
,
F. Kaspar
,
A. K. Kaiser-Weiss
,
E. Swinnen
,
C. Toté
,
H. Gregow
,
T. Manninen
,
A. Riihelä
,
J.-C. Calvet
,
Y. Ma
, and
J. Wen

Abstract

The Coordinating Earth Observation Data Validation for Reanalysis for Climate Services project (CORE-CLIMAX) aimed to substantiate how Copernicus observations and products can contribute to climate change analyses. CORE-CLIMAX assessed the European capability to provide climate data records (CDRs) of essential climate variables (ECVs), prepared a structured process to derive CDRs, developed a harmonized approach for validating essential climate variable CDRs, identified the integration of CDRs into the reanalysis chain, and formulated a process to compare the results of different reanalysis techniques. With respect to the Copernicus Climate Change Service (C3S), the systematic application and further development of the CORE-CLIMAX system maturity matrix (SMM) and the spinoff application performance metric (APM) were strongly endorsed to be involved in future implementations of C3S. We concluded that many of the current CDRs are not yet sufficiently mature to be used in reanalysis or applied in climate studies. Thus, the production of consistent high-resolution data records remains a challenge that needs more research urgently. Extending ECVs to close climate cycle budgets (e.g., essential water variables) is a next step linking CDRs to sectoral applications.

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Stephen D. Eckermann
,
Dave Broutman
,
Jun Ma
,
James D. Doyle
,
Pierre-Dominique Pautet
,
Michael J. Taylor
,
Katrina Bossert
,
Bifford P. Williams
,
David C. Fritts
, and
Ronald B. Smith

Abstract

On 14 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), aircraft remote sensing instruments detected large-amplitude gravity wave oscillations within mesospheric airglow and sodium layers at altitudes z ~ 78–83 km downstream of the Auckland Islands, located ~1000 km south of Christchurch, New Zealand. A high-altitude reanalysis and a three-dimensional Fourier gravity wave model are used to investigate the dynamics of this event. At 0700 UTC when the first observations were made, surface flow across the islands’ terrain generated linear three-dimensional wave fields that propagated rapidly to z ~ 78 km, where intense breaking occurred in a narrow layer beneath a zero-wind region at z ~ 83 km. In the following hours, the altitude of weak winds descended under the influence of a large-amplitude migrating semidiurnal tide, leading to intense breaking of these wave fields in subsequent observations starting at 1000 UTC. The linear Fourier model constrained by upstream reanalysis reproduces the salient aspects of observed wave fields, including horizontal wavelengths, phase orientations, temperature and vertical displacement amplitudes, heights and locations of incipient wave breaking, and momentum fluxes. Wave breaking has huge effects on local circulations, with inferred layer-averaged westward flow accelerations of ~350 m s−1 h−1 and dynamical heating rates of ~8 K h−1, supporting recent speculation of important impacts of orographic gravity waves from subantarctic islands on the mean circulation and climate of the middle atmosphere during austral winter.

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K.-M. Lau
,
V. Ramanathan
,
G.-X. Wu
,
Z. Li
,
S. C. Tsay
,
C. Hsu
,
R. Sikka
,
B. Holben
,
D. Lu
,
G. Tartari
,
M. Chin
,
P. Koudelova
,
H. Chen
,
Y. Ma
,
J. Huang
,
K. Taniguchi
, and
R. Zhang

Aerosol- and moonsoon-related droughts and floods are two of the most serious environmental hazards confronting more than 60% of the population of the world living in the Asian monsoon countries. In recent years, thanks to improved satellite and in situ observations, and better models, great strides have been made in aerosol and monsoon research, respectively. There is now a growing body of evidence suggesting that interaction of aerosol forcing with monsoon dynamics may alter the redistribution of energy in the atmosphere and at the Earth s surface, thereby influencing monsoon water cycle and climate. In this article, the authors describe the scientific rationale and challenges for an integrated approach to study the interactions between aerosol and monsoon water cycle dynamics. A Joint Aerosol-Monsoon Experiment (JAMEX) is proposed for 2007–11, with enhanced observations of the physical and chemical properties, sources and sinks, and long-range transport of aerosols, in conjunction with meteorological and oceanographic observations in the Indo-Pacific continental and oceanic regions. JAMEX will leverage on coordination among many ongoing and planned national research programs on aerosols and monsoons in China, India, Japan, Nepal, Italy, and the United States, as well as international research programs of the World Climate Research Program (WCRP) and the World Meteorological Organization (WMO).

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Noel E. Davidson
,
Yi Xiao
,
Yimin Ma
,
Harry C. Weber
,
Xudong Sun
,
Lawrie J. Rikus
,
Jeff D. Kepert
,
Peter X. Steinle
,
Gary S. Dietachmayer
,
Charlie C. F. Lok
,
James Fraser
,
Joan Fernon
, and
Hakeem Shaik

Abstract

The Australian Community Climate and Earth System Simulator (ACCESS) has been adapted for operational and research applications on tropical cyclones. The base system runs at a resolution of 0.11° and 50 levels. The domain is relocatable and nested in coarser-resolution ACCESS forecasts. Initialization consists of five cycles of four-dimensional variational data assimilation (4DVAR) over 24 h. Forecasts to 72 h are made. Without vortex specification, initial conditions usually contain a weak and misplaced circulation pattern. Significant effort has been devoted to building physically based, synthetic inner-core structures, validated using historical dropsonde data and surface analyses from the Atlantic. Based on estimates of central pressure and storm size, vortex specification is used to filter the analyzed circulation from the original analysis, construct an inner core of the storm, locate it to the observed position, and merge it with the large-scale analysis at outer radii.

Using all available conventional observations and only synthetic surface pressure observations from the idealized vortex to correct the initial location and structure of the storm, the 4DVAR builds a balanced, intense 3D vortex with maximum wind at the radius of maximum wind and with a well-developed secondary circulation. Mean track and intensity errors for Australian region and northwest Pacific storms have been encouraging, as are recent real-time results from the Australian National Meteorological and Oceanographic Centre. The system became fully operational in November 2011. From preliminary diagnostics, some interesting structure change features are illustrated. Current limitations, future enhancements, and research applications are also discussed.

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