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John L. McBride
,
B. W. Gunn
,
G. J. Holland
,
T. D. Keenan
,
N. E. Davidson
, and
William M. Frank

Abstract

Line integral techniques are used to calculate vertically integrated heat and moisture budgets over the Gulf of Carpentaria during Phase II of the Australian Monsoon Experiment (AMEX). The budget area is an array of six radiosondes in a monsoon environment, and the calculations are performed every 6 hours over a period of 33 days.

During convective outbreaks the integrated heating and drying of the large scale by the cumulonimbus activity has a magnitude of the order of 10°C day−1. The heat and moisture sources are dominated by the flux divergence terms, which account for over 90% of the variance. The observed warming is as large as ±1°C day−1 but is diurnally dominated and does not correspond to the latent heat release. The integrated moisture convergence has a high correlation with latent heat release but not with the measured moisture storage. The convective heat source is also highly correlated with middle tropospheric vertical velocity.

Mean budgets are presented for each of the four diurnal observation times. Also, budgets were run with each station, in turn, excluded from the sonde array to determine sensitivity of the results to the data network.

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Vladimir M. Kattsov
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John E. Walsh
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William L. Chapman
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Veronika A. Govorkova
,
Tatyana V. Pavlova
, and
Xiangdong Zhang

Abstract

The state-of-the-art AOGCM simulations have recently (late 2004–early 2005) been completed for the Intergovernmental Panel on Climate Change (IPCC) in order to provide input to the IPCC’s Fourth Assessment Report (AR4). The present paper synthesizes the new simulations of both the twentieth- and twenty-first-century arctic freshwater budget components for use in the IPCC AR4, and attempts to determine whether demonstrable progress has been achieved since the late 1990s. Precipitation and its difference with evapotranspiration are addressed over the Arctic Ocean and its terrestrial watersheds, including the basins of the four major rivers draining into the Arctic Ocean: the Ob, the Yenisey, the Lena, and the Mackenzie. Compared to the previous [IPCC Third Assessment Report (TAR)] generation of AOGCMs, there are some indications that the models as a class have improved in simulations of the Arctic precipitation. In spite of observational uncertainties, the models still appear to oversimulate area-averaged precipitation over the major river basins. The model-mean precipitation biases in the Arctic and sub-Arctic have retained their major geographical patterns, which are at least partly attributable to the insufficiently resolved local orography, as well as to biases in large-scale atmospheric circulation and sea ice distribution. The river discharge into the Arctic Ocean is also slightly oversimulated. The simulated annual cycle of precipitation over the Arctic Ocean is in qualitative agreement between the models as well as with observational and reanalysis data. This is also generally the case for the seasonality of precipitation over the Arctic Ocean’s terrestrial watersheds, with a few exceptions. Some agreement is demonstrated by the models in reproducing positive twentieth-century trends of precipitation in the Arctic, as well as positive area-averaged PE late-twentieth-century trends over the entire terrestrial watershed of the Arctic Ocean.

For the twenty-first century, three scenarios are considered: A2, A1B, and B1. Precipitation over the Arctic Ocean and its watersheds increases through the twenty-first century, showing much faster percentage increases than the global mean precipitation. The arctic precipitation changes have a pronounced seasonality, with the strongest relative increase in winter and fall, and the weakest in summer. The river discharge into the Arctic Ocean increases for all scenarios from all major river basins considered, and is generally about twice as large as the increase of freshwater from precipitation over the Arctic Ocean (70°–90°N) itself. The across-model scatter of the precipitation increase for each scenario is significant, but smaller than the scatter between the climates of the different models in the baseline period.

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William J. Randel
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Byron A. Boville
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John C. Gille
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Paul L. Bailey
,
Steven T. Massie
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J. B. Kumer
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J. L. Mergenthaler
, and
A. E. Roche

Abstract

Global variability and budgets of stratospheric nitrous oxide (N2O) are studied using output from a stratospheric version of the NCAR Community Climate Model. The model extends over 0–80 km, incorporating an N2O-like tracer with tropospheric source and upper-stratospheric photochemical sink, the latter parameterized using linear damping rates obtained from detailed two-dimensional model calculations. Results from the model over several seasonal cycles are compared with observations of N2O from the Cryogenic Limb Array Etalon Spectrometer instrument on the Upper Atmosphere Research Satellite. The model produces N2O structure and variability that is in reasonable agreement with the observations. Global budgets of stratospheric N2O are furthermore analyzed using model output, based on the transformed Eulerian-mean, zonal-mean framework. These budgets are used to quantify the importance of planetary wave constituent transport in the stratosphere, for both slow seasonal variations and fast planetary wave events. These results demonstrate that such wave fluxes act to form and sharpen the strong subtropical N2O gradients observed in satellite measurements.

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William C. Macklin
,
Charles A. Knight
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Howard E. Moore
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Nancy C. Knight
,
Walter H. Pollock
,
John N. Carras
, and
Suszanne Thwaiters

Abstract

The deuterium, crystal and air bubble structures of 11 large hailstones from three severe storms have been examined. It is emphasized that there are a number of assumptions underlying the interpretation of such data and these are discussed. In seven of the hailstones the ambient temperatures at which they grew were inferred from the crystal size. The deuterium concentrations and ambient temperatures generally show similar variations and the crystal data thereby provide a useful way of placing an absolute temperature scale against the deuterium values. Throughout most of their growth, the hailstones grew in the updraft between about the ambient temperature levels of –17 to –30°C. The air bubble analyses showed that the hailstones grew near the wet growth limit or slightly wet and heat balance considerations give values of 2–3 g m−3 for the effective liquid water concentrations. On the assumption that the median volume radius of the cloud droplets is 10 µm, the actual liquid water concentrations are then about 4 to 5.5 g m−3.

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William C. Keene
,
James N. Galloway
,
Gene E. Likens
,
Frank A. Deviney
,
Kerri N. Mikkelsen
,
Jennie L. Moody
, and
John R. Maben

Abstract

Precipitation composition was characterized at 14 remote sites between 65°N and 51°S. Anthropogenic sources contributed to non-sea-salt (nss) SO4 2−, NO3 , and NH4 + in North Atlantic precipitation. Biogenic sources accounted for 0.4–3.3 μeq L−1 of volume-weighted-average (VWA) nss SO4 2− in marine precipitation. SO4 2− at the continental sites (2.9–7.7 μeq L−1) was generally higher. VWA NO3 (0.5–1.3 μeq L−1) and NH4 + (0.5–2.6 μeq L−1) at marine-influenced, Southern Hemispheric sites were generally less than those at continental sites (1.4–4.8 μeq L−1 and 2.3–4.2 μeq L−1, respectively). VWA pH ranged from 4.69 to 5.25. Excluding the North Atlantic, nss SO4 2−, NO3 , and NH4 + wet depositions were factors of 4–47, 5–61, and 3–39, respectively, less than those in the eastern United States during 2002–04. HCOOH t (HCOOHaq + HCOO) and CH3COOH t (CH3COOHaq + CH3COO) concentrations and depositions at marine sites overlapped, implying spatially similar source strengths from marine-derived precursors. Greater variability at continental sites suggests heterogeneity in terrestrial source strengths. Seasonality in deposition was driven by variability in precipitation amount, wind velocity, transport, and emissions. Between 1980 and 2009, nss SO4 2− at Bermuda decreased by 85% in response to decreasing U.S. SO2 emissions; trends in NO3 and NH4 + were inconsequential. Corresponding decreases in acidity, as reflected in the significant 30% decline in VWA H+, impacted pH-dependent chemical processes. Comparisons between measurements and models indicate that current predictive capabilities are uncertain by factors of 2 or more.

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Gijs de Boer
,
William Chapman
,
Jennifer E. Kay
,
Brian Medeiros
,
Matthew D. Shupe
,
Steve Vavrus
, and
John Walsh

Abstract

Simulation of key features of the Arctic atmosphere in the Community Climate System Model, version 4 (CCSM4) is evaluated against observational and reanalysis datasets for the present-day (1981–2005). Surface air temperature, sea level pressure, cloud cover and phase, precipitation and evaporation, the atmospheric energy budget, and lower-tropospheric stability are evaluated. Simulated surface air temperatures are found to be slightly too cold when compared with the 40-yr ECMWF Re-Analysis (ERA-40). Spatial patterns and temporal variability are well simulated. Evaluation of the sea level pressure demonstrates some large biases, most noticeably an under simulation of the Beaufort High during spring and autumn. Monthly Arctic-wide biases of up to 13 mb are reported. Cloud cover is underpredicted for all but summer months, and cloud phase is demonstrated to be different from observations. Despite low cloud cover, simulated all-sky liquid water paths are too high, while ice water path was generally too low. Precipitation is found to be excessive over much of the Arctic compared to ERA-40 and the Global Precipitation Climatology Project (GPCP) estimates. With some exceptions, evaporation is well captured by CCSM4, resulting in PE estimates that are too high. CCSM4 energy budget terms show promising agreement with estimates from several sources. The most noticeable exception to this is the top of the atmosphere (TOA) fluxes that are found to be too low while surface fluxes are found to be too high during summer months. Finally, the lower troposphere is found to be too stable when compared to ERA-40 during all times of year but particularly during spring and summer months.

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John E. Yorks
,
Matthew J. McGill
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V. Stanley Scott
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Shane W. Wake
,
Andrew Kupchock
,
Dennis L. Hlavka
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William D. Hart
, and
Patrick A. Selmer

Abstract

The Airborne Cloud–Aerosol Transport System (ACATS) is a Doppler wind lidar system that has recently been developed for atmospheric science capabilities at the NASA Goddard Space Flight Center (GSFC). ACATS is also a high-spectral-resolution lidar (HSRL), uniquely capable of directly resolving backscatter and extinction properties of a particle from a high-altitude aircraft. Thus, ACATS simultaneously measures optical properties and motion of cloud and aerosol layers. ACATS has flown on the NASA ER-2 during test flights over California in June 2012 and science flights during the Wallops Airborne Vegetation Experiment (WAVE) in September 2012. This paper provides an overview of the ACATS method and instrument design, describes the ACATS HSRL retrieval algorithms for cloud and aerosol properties, and demonstrates the data products that will be derived from the ACATS data using initial results from the WAVE project. The HSRL retrieval algorithms developed for ACATS have direct application to future spaceborne missions, such as the Cloud–Aerosol Transport System (CATS) to be installed on the International Space Station (ISS). Furthermore, the direct extinction and particle wind velocity retrieved from the ACATS data can be used for science applications such as dust or smoke transport and convective outflow in anvil cirrus clouds.

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Joseph G. Alfieri
,
William P. Kustas
,
John H. Prueger
,
Lawrence E. Hipps
,
José L. Chávez
,
Andrew N. French
, and
Steven R. Evett

Abstract

Land–atmosphere interactions play a critical role in regulating numerous meteorological, hydrological, and environmental processes. Investigating these processes often requires multiple measurement sites representing a range of surface conditions. Before these measurements can be compared, however, it is imperative that the differences among the instrumentation systems are fully characterized. Using data collected as a part of the 2008 Bushland Evapotranspiration and Agricultural Remote Sensing Experiment (BEAREX08), measurements from nine collocated eddy covariance (EC) systems were compared with the twofold objective of 1) characterizing the interinstrument variation in the measurements, and 2) quantifying the measurement uncertainty associated with each system. Focusing on the three turbulent fluxes (heat, water vapor, and carbon dioxide), this study evaluated the measurement uncertainty using multiple techniques. The results of the analyses indicated that there could be substantial variability in the uncertainty estimates because of the advective conditions that characterized the study site during the afternoon and evening hours. However, when the analysis was limited to nonadvective, quasi-normal conditions, the response of the nine EC stations were remarkably similar. For the daytime period, both the method of Hollinger and Richardson and the method of Mann and Lenschow indicated that the uncertainty in the measurements of sensible heat, latent heat, and carbon dioxide flux were approximately 13 W m−2, 27 W m−2, and 0.10 mg m−2 s−1, respectively. Based on the results of this study, it is clear that advection can greatly increase the uncertainty associated with EC flux measurements. Since these conditions, as well as other phenomena that could impact the measurement uncertainty, are often intermittent, it may be beneficial to conduct uncertainty analyses on an ongoing basis.

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Francis A. Schiermeier
,
William E. Wilson
,
Francis Pooler
,
Jason K. S. Ching
, and
John F. Clarke

Spurred by the rising sulfate concentrations in the northeastern United States, the Environmental Protection Agency (EPA) has established the Sulfur Transport and Transformation in the Environment (STATE) program to quantitatively determine the impact on local air quality of distant source pollutants and their transformation products. The first major STATE field study was the August 1978 Tennessee Plume Study conducted near the Cumberland Steam Plant in northwestern Tennessee. Representatives from 25 governmental agencies, universities, research institutes, and private contractors participated in this joint meteorological/chemical study in an attempt to define plume transport, dispersion, transformation, and removal rates under various meteorological conditions. A description of the field activities reveals the preplanned experimental guidelines and the flexibility with which the sampling activities were performed. The analytical priorities have since been established and various investigators are performing analyses of the collected data with results to be forthcoming.

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Chad M. Gravelle
,
John R. Mecikalski
,
William E. Line
,
Kristopher M. Bedka
,
Ralph A. Petersen
,
Justin M. Sieglaff
,
Geoffrey T. Stano
, and
Steven J. Goodman

Abstract

With the launch of the Geostationary Operational Environmental Satellite–R (GOES-R) series in 2016, there will be continuity of observations for the current GOES system operating over the Western Hemisphere. The GOES-R Proving Ground was established in 2008 to help prepare satellite user communities for the enhanced capabilities of GOES-R, including new instruments, imagery, and products that will have increased spectral, spatial, and temporal resolution. This is accomplished through demonstration and evaluation of proxy products that use current GOES data, higher-resolution data provided by polar-orbiting satellites, and model-derived synthetic satellite imagery. The GOES-R demonstration products presented here, made available to forecasters in near–real time (within 20 min) via the GOES-R Proving Ground, include the 0–9-h NearCast model, 0–1-h convective initiation probabilities, convective cloud-top cooling, overshooting top detection, and a pseudo–Geostationary Lightning Mapper total lightning tendency diagnostic. These products are designed to assist in identifying areas of increasing convective instability, pre-radar echo cumulus cloud growth preceding thunderstorm formation, storm updraft intensity, and potential storm severity derived from lightning trends. In turn, they provide the warning forecaster with improved situational awareness and short-term predictive information that enhance their ability to monitor atmospheric conditions preceding and associated with the development of deep convection, a time period that typically occurs between the issuance of National Weather Service (NWS) Storm Prediction Center convective watches and convective storm warnings issued by NWS forecast offices. This paper will focus on how this GOES-R satellite convective toolkit could have been used by warning forecasters to enhance near-storm environment analysis and the warning-decision-making process prior to and during the 20 May 2013 Moore, Oklahoma, tornado event.

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