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Arnold A. Barnes Jr.

Equipment developments under the AFCRL radar meteor trail project are reviewed. Winds and densities in the 80–100 km altitude region obtained at AFCRL, Eglin AFB, Stanford, and Durham are briefly compared with results from other radar meteor stations. A comprehensive list of over 40 meteor trail stations is provided.

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Elizabeth A. Barnes and Randal J. Barnes

Abstract

Two common approaches for estimating a linear trend are 1) simple linear regression and 2) the epoch difference with possibly unequal epoch lengths. The epoch difference estimator for epochs of length M is defined as the difference between the average value over the last M time steps and the average value over the first M time steps divided by NM, where N is the length of the time series. Both simple linear regression and the epoch difference are unbiased estimators for the trend; however, it is demonstrated that the variance of the linear regression estimator is always smaller than the variance of the epoch difference estimator for first-order autoregressive [AR(1)] time series with lag-1 autocorrelations less than about 0.85. It is further shown that under most circumstances if the epoch difference estimator is applied, the optimal epoch lengths are equal and approximately one-third the length of the time series. Additional results are given for the optimal epoch length at one end when the epoch length at the other end is constrained.

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Elizabeth A. Barnes and Lorenzo Polvani

Abstract

This work documents how the midlatitude, eddy-driven jets respond to climate change using model output from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The authors consider separately the North Atlantic, the North Pacific, and the Southern Hemisphere jets. The analysis is not limited to annual-mean changes in the latitude and speed of the jets, but also explores how the variability of each jet changes with increased greenhouse gases.

All jets are found to migrate poleward with climate change: the Southern Hemisphere jet shifts poleward by 2° of latitude between the historical period and the end of the twenty-first century in the representative concentration pathway 8.5 (RCP8.5) scenario, whereas both Northern Hemisphere jets shift by only 1°. In addition, the speed of the Southern Hemisphere jet is found to increase markedly (by 1.2 m s−1 between 850 and 700 hPa), while the speed remains nearly constant for both jets in the Northern Hemisphere.

More importantly, it is found that the patterns of jet variability are a strong function of the jet position in all three sectors of the globe, and as the jets shift poleward the patterns of variability change. Specifically, for the Southern Hemisphere and the North Atlantic jets, the variability becomes less of a north–south wobbling and more of a pulsing (i.e., variation in jet speed). In contrast, for the North Pacific jet, the variability becomes less of a pulsing and more of a north–south wobbling. These different responses can be understood in terms of Rossby wave breaking, allowing the authors to explain most of the projected jet changes within a single dynamical framework.

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Chengji Liu and Elizabeth A. Barnes

Abstract

Isentropic mixing is an important process for the distribution of chemical constituents in the mid- to high latitudes. A modified Lagrangian framework is applied to quantify the mixing associated with two distinct types of Rossby wave breaking (i.e., cyclonic and anticyclonic). In idealized numerical simulations, cyclonic wave breaking (CWB) exhibits either comparable or stronger mixing than anticyclonic wave breaking (AWB). Although the frequencies of AWB and CWB both have robust relationships with the jet position, this asymmetry leads to CWB dominating mixing variability related to the jet shifting. In particular, when the jet shifts poleward the mixing strength decreases in areas of the midlatitude troposphere and also decreases on the poleward side of the jet. This is due to decreasing CWB occurrence with a poleward shift of the jet. Across the tropopause, equatorward of the jet, where AWB mostly occurs and CWB rarely occurs, the mixing strength increases as AWB occurs more frequently with a poleward shift of the jet. The dynamical relationship above is expected to be relevant both for internal climate variability, such as the El Niño–Southern Oscillation (ENSO) and the annular modes, and for future climate change that may drive changes in the jet position.

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Bryn Ronalds and Elizabeth A. Barnes

Abstract

Previous studies have suggested that, in the zonal mean, the climatological Northern Hemisphere wintertime eddy-driven jet streams will weaken and shift equatorward in response to Arctic amplification and sea ice loss. However, multiple studies have also pointed out that this response has strong regional differences across the two ocean basins, with the North Atlantic jet stream generally weakening across models and the North Pacific jet stream showing signs of strengthening. Based on the zonal wind response with a fully coupled model, this work sets up two case studies using a barotropic model to test a dynamical mechanism that can explain the differences in zonal wind response in the North Pacific versus the North Atlantic. Results indicate that the differences between the two basins are due, at least in part, to differences in the proximity of the jet streams to the sea ice loss, and that in both cases the eddies act to increase the jet speed via changes in wave breaking location and frequency. Thus, while baroclinic arguments may account for an initial reduction in the midlatitude winds through thermal wind balance, eddy–mean flow feedbacks are likely instrumental in determining the final total response and actually act to strengthen the eddy-driven jet stream.

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Marie C. McGraw and Elizabeth A. Barnes

ABSTRACT

Arctic–midlatitude teleconnections are complex and multifaceted. By design, targeted modeling studies typically focus only on one direction of influence—usually, the midlatitude atmospheric response to a changing Arctic. The two-way, coupled feedbacks between the Arctic and the midlatitude circulation on submonthly time scales are explored using a regularized regression model formulated around Granger causality. The regularized regression model indicates that there are regions in which Arctic temperature drives a midlatitude circulation response, and regions in which the midlatitude circulation drives a response in the Arctic; however, these regions rarely overlap. In many regions, on submonthly time scales, the midlatitude circulation drives Arctic temperature variability, highlighting the important role the midlatitude circulation can play in impacting the Arctic. In particular, the regularized regression model results support recent work that indicates that the observed high pressure anomalies over Eurasia drive a significant response in the Arctic on submonthly time scales, rather than being driven by the Arctic.

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Cheng-Hsuan Lyu, William L. Barnes, and Robert A. Barnes

Abstract

This work presents the first on-orbit calibration results using the Moon, the Sun, and cold deep space as inputs to the Visible and Infrared Scanner (VIRS) on board the Tropical Rainfall Measuring Mission (TRMM) satellite. The authors have developed lunar reflectance curves using VIRS data for phase angles ranging from 1.6° to 82°. Comparisons with modeled reflectance curves show that the VIRS lunar data are as predicted. Specifically, the six-parameter model of Helfenstein and Veverka provides a good description of the VIRS 0.62-μm data. The lunar reflectance data will be used to discern long-term changes in VIRS response. Solar calibrations, performed using an onboard solar diffuser, show fluctuations of the VIRS responsivity of less than 1.3% and no indication of any systematic change during 11 months. Using the deep-space calibration implemented via a spacecraft maneuver on three different dates—7 January, 8 January, and 2 September 1998—the authors have measured the dependence of the scan mirror reflectance with angle of incidence for the VIRS thermal bands. These results have replaced the scan modulation curves adopted from the prelaunch measurements. From the on-orbit calibration results, it appears that the TRMM/VIRS is functioning as predicted by the prelaunch calibration and characterization tests and that there has been no discernable change in sensor performance during the first 11 months of operation.

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Elizabeth A. Barnes, Nicholas W. Barnes, and Lorenzo M. Polvani

Abstract

Stratospheric ozone is expected to recover by the end of this century because of the regulation of ozone-depleting substances by the Montreal Protocol. Targeted modeling studies have suggested that the climate response to ozone recovery will greatly oppose the climate response to rising greenhouse gas (GHG) emissions. However, the extent of this cancellation remains unclear since only a few such studies are available. Here, a much larger set of simulations performed for phase 5 of the Coupled Model Intercomparison Project is analyzed, which includes ozone recovery. It is shown that the closing of the ozone hole will cause a delay in summertime [December–February (DJF)] Southern Hemisphere climate change between now and 2045. Specifically, it is found that the position of the jet stream, the width of the subtropical dry zones, the seasonality of surface temperatures, and sea ice concentrations all exhibit significantly reduced summertime trends over the first half of the twenty-first century as a consequence of ozone recovery. After 2045, forcing from GHG emissions begins to dominate the climate response. Finally, comparing the relative influences of future GHG emissions and historic ozone depletion, it is found that the simulated DJF tropospheric circulation changes between 1965 and 2005 (driven primarily by ozone depletion) are larger than the projected changes in any future scenario over the entire twenty-first century.

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Yean Lee and Arnold A. Barnes Jr.

Abstract

A simplified analytical model is developed to analyze the removal of A12O3 particles from the TITAN rocket exhaust cloud. The model incorporates the physical processes of deposition and impact collection and includes consideration of particle size spectra. Results of computations are in good agreement with the measurements and show that sedimentation plays the most important role in the removal of the mass of material in the elevated ground cloud within the first hour after launch. The model allows for easy estimates of airborne concentrations and sedimentation when relevant sounding, exhaust mass and estimates of initial particle size distribution data are available.

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Charles A. Doswell III and Stanley L. Barnes

Abstract

No abstract available.

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