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Steven A. Mauget and Eugene C. Cordero

Abstract

In Part I of this paper, the optimal ranking regime (ORR) method was used to identify intradecadal to multidecadal (IMD) regimes in U.S. climate division temperature data during 1896–2012. Here, the method is used to test for annual and seasonal precipitation regimes during that same period. Water-year mean streamflow rankings at 125 U.S. Hydro-Climatic Data Network gauge stations are also evaluated during 1939–2011. The precipitation and streamflow regimes identified are compared with ORR-derived regimes in the Pacific decadal oscillation (PDO), the Atlantic multidecadal oscillation (AMO), and indices derived from gridded SST anomaly (SSTA) analysis data. Using a graphic display approach that allows for the comparison of IMD climate regimes in multiple time series, an interdecadal cycle in western precipitation is apparent after 1980, as is a similar cycle in northwestern streamflow. Before 1980, IMD regimes in northwestern streamflow and annual precipitation are in approximate antiphase with the PDO. One of the clearest IMD climate signals found in this analysis are post-1970 wet regimes in eastern U.S streamflow and annual precipitation, as well as in fall [September–November (SON)] precipitation. Pearson correlations between time series of annual and seasonal precipitation averaged over the eastern United States and SSTA analysis data show relatively extensive positive correlations between warming tropical SSTA and increasing fall precipitation. The possible Pacific and northern Atlantic roots of the recent eastern U.S. wet regime, as well as the general characteristics of U.S. climate variability in recent decades that emerge from this analysis and that of Part I, are discussed.

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Eugene C. Cordero and Terrence R. Nathan

Abstract

The effects of wave and zonal mean ozone heating on the evolution of the quasi-biennial oscillation (QBO) are examined using a two-dimensional mechanistic model of the equatorial stratosphere. The model atmosphere is governed by coupled equations for the zonal mean and (linear) wave fields of ozone, temperature, and wind, and is driven by specifying the amplitudes of a Kelvin wave and a Rossby–gravity wave at the lower boundary. Wave–mean flow interactions are accounted for in the model, but not wave–wave interactions.

A reference simulation (RS) of the QBO, in which ozone feedbacks are neglected, is carried out and the results compared with Upper Atmosphere Research Satellite observations. The RS is then compared with three model experiments, which examine separately and in combination the effects of wave ozone and zonal mean ozone feedbacks. Wave–ozone feedbacks alone increase the driving by the Kelvin and Rossby–gravity waves by up to 10%, producing stronger zonal wind shear zones and a stronger meridional circulation. Zonal mean–ozone feedbacks (ozone QBO) alone decrease the magnitude of the temperature QBO by up to 15%, which in turn affects the momentum deposition by the wave fields. Overall, the zonal mean–ozone feedbacks increase the magnitude of the meridional circulation by up to 30%. The combined effects of wave–ozone and ozone QBO feedbacks generally produce a larger response then either process alone. Moreover, these combined ozone feedbacks produce a temperature QBO amplitude that is up to 30% larger than simulations without the feedbacks. Correspondingly, significant changes are also observed in the zonal wind and ozone QBOs. When ozone feedbacks are included in the model, the Kelvin and Rossby–gravity wave amplitudes can be reduced by ∼10% and still produce a QBO similar to simulations without ozone.

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Steven A. Mauget and Eugene C. Cordero

Abstract

The optimal ranking regime (ORR) method was used to identify intradecadal to multidecadal (IMD) time windows containing significant ranking sequences in U.S. climate division temperature data. The simplicity of the ORR procedure’s output—a time series’ most significant nonoverlapping periods of high or low rankings—makes it possible to graphically identify common temporal breakpoints and spatial patterns of IMD variability in the analyses of 102 climate division temperature series. This approach is also applied to annual Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) climate indices, a Northern Hemisphere annual temperature (NHT) series, and divisional annual and seasonal temperature data during 1896–2012. In addition, Pearson correlations are calculated between PDO, AMO, and NHT series and the divisional temperature series. Although PDO phase seems to be an important influence on spring temperatures in the northwestern United States, eastern temperature regimes in annual, winter, summer, and fall temperatures are more coincident with cool and warm phase AMO regimes. Annual AMO values also correlate significantly with summer temperatures along the Eastern Seaboard and fall temperatures in the U.S. Southwest. Given evidence of the abrupt onset of cold winter temperatures in the eastern United States during 1957/58, possible climate mechanisms associated with the cause and duration of the eastern U.S. warming hole period—identified here as a cool temperature regime occurring between the late 1950s and late 1980s—are discussed.

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Eugene C. Cordero, Terrence R. Nathan, and Robert S. Echols

Abstract

An equatorial beta-plane model of the middle atmosphere is used to analytically examine the effects of radiative cooling and ozone heating on the spatial and temporal evolution of the quasi-biennial oscillation (QBO). Under the assumption that the diabatic heating is weak and the background fields of wind, temperature, and ozone are slowly varying, a perturbation analysis yields expressions describing the vertical spatial modulation of Kelvin and Rossby–gravity waves in the presence of ozone. These expressions show that wave-induced changes in the diabatic heating arising from the advection of basic-state ozone reduce the local radiative damping rate by up to 15% below 35 km. In a one-dimensional model of the QBO, eddy ozone heating increases the amplitude of the zonal wind QBO by 1–2 m s−1 and increases the oscillation period by about two months. The significance of these results to the observed QBO is discussed.

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Eugene C. Cordero, Anne Marie Todd, and Diana Abellera

Global warming has become one of the most important scientific, political, and social issues of our era. In designing an effective mitigation strategy, it is clear that public education must play an important role. This study looks at various components of climate change literacy within a cohort of university students and investigates the impact of action-oriented learning on student understanding. Results from questionnaires given to primarily nonscience students enrolled in weather and climate courses are used to examine student knowledge of climate change. In agreement with prior research, this study finds that significant student misconceptions exist regarding the causes of global warming and the relationship between global warming and ozone depletion. Most students seem to connect global warming only with visible pollution, such as exhaust from either a car or factory, while discounting more indirect emissions such as from electricity use and through product or food consumption. The authors then explore how a learning activity designed around the “ecological footprint” affects student ideas about their personal energy use and connections with global warming. The results show that a relatively simple learning activity that personally engages the student improves understanding of the connection between personal energy use and global warming. This work suggests that similar curricula, employing methods of personal engagement and social activism, be further developed to aid in the teaching of climate change.

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Eugene C. Cordero, Anne Marie Todd, and Diana Abellera
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Steven A. Mauget, Eugene C. Cordero, and Patrick T. Brown

Abstract

An analysis method previously used to detect observed intra- to multidecadal (IMD) climate regimes was adapted to compare observed and modeled IMD climate variations. Pending the availability of the more appropriate phase 5 Coupled Model Intercomparison Project (CMIP-5) simulations, the method is demonstrated using CMIP-3 model simulations. Although the CMIP-3 experimental design will almost certainly prevent these model runs from reproducing features of historical IMD climate variability, these simulations allow for the demonstration of the method and illustrate how the models and observations disagree. This method samples a time series’s data rankings over moving time windows, converts those ranking sets to a Mann–Whitney U statistic, and then normalizes the U statistic into a Z statistic. By detecting optimally significant IMD ranking regimes of arbitrary onset and varying duration, this process generates time series of Z values that are an adaptively low-passed and normalized transformation of the original time series. Principal component (PC) analysis of the Z series derived from observed annual temperatures at 92 U.S. grid locations during 1919–2008 shows two dominant modes: a PC1 mode with cool temperatures before the late 1960s and warm temperatures after the mid-1980s, and a PC2 mode indicating a multidecadal temperature cycle over the Southeast. Using a graphic analysis of a Z error metric that compares modeled and observed Z series, the three CMIP-3 model simulations tested here are shown to reproduce the PC1 mode but not the PC2 mode. By providing a way to compare grid-level IMD climate response patterns in observed and modeled data, this method can play a useful diagnostic role in future model development and decadal climate forecasting.

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Dustin F. P. Grogan, Terrence R. Nathan, Robert S. Echols, and Eugene C. Cordero

Abstract

An equatorial β-plane model of the tropical stratosphere is used to examine the effects of ozone on Kelvin, Rossby–gravity, equatorial Rossby, inertia–gravity, and smaller-scale gravity waves. The model is composed of coupled equations for wind, temperature, and ozone volume mixing ratio, which are linearized about a zonally averaged background state. Using the Wentzel–Kramers–Brillouin (WKB) formalism, equations are obtained for the vertical spatial scale, spatial damping rate, and amplitude of the waves. These equations yield an analytical expression for the ozone-modified wave driving of the zonal-mean circulation. The expression for the wave driving provides an efficient parameterization that can be implemented into models that are unable to spontaneously generate the ozone-modified, convectively coupled waves that drive the quasi-biennial and semiannual oscillations of the tropical stratosphere.

The effects of ozone on the wave driving, which are strongly modulated by the Doppler-shifted frequency, are maximized in the upper stratosphere, where ozone photochemistry and vertical ozone advection combine to augment Newtonian cooling. The ozone causes a contraction in spatial scale and an increase in the spatial damping rate. In the midstratosphere to lower mesosphere, the ozone-induced increase in wave driving is about 10%–30% for all wave types, but it can be as large as about 80% over narrow altitude regions and for specific wave types. In the dynamically controlled lower stratosphere, vertical ozone advection dominates over meridional ozone advection and opposes Newtonian cooling, causing, on average, a 10%–15% reduction in the damping rate.

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