Arcodia, M. C., Kirtman, B. P., & Siqueira, L. S. P. (2020). How MJO Teleconnections and ENSO Interference Impacts U.S. Precipitation. J. Climate, 33(11), 4621–4640.
Abstract: A composite analysis reveals how the Madden-Julian oscillation (MJO) impacts North American rainfall through perturbations in both the upper-tropospheric flow and regional low-level moisture availability. Upper-level divergence associated with the MJO tropical convection drives a quasi-stationary Rossby wave response to the midlatitudes. This forces a midlatitude upper-level dipolar geopotential height anomaly that is accompanied by a westward retraction of the jet stream and reduced rainfall over the central-eastern North Pacific. A reverse effect is found as the MJO propagates eastward across the Maritime Continent. These large differences in the extratropical upper-level flow, combined with anomalies in the regional supply of water vapor, have a profound impact on southeastern U.S. rainfall. The low-frequency variability, including that associated with ENSO, can modify the seasonal background flow (e.g., El Nino and La Nina basic states) affecting the distribution, strength, and propagation of the intraseasonal oscillation and the extratropical teleconnection patterns. The combined effects of the ENSO and the MJO signals result in both spatial and temporal patterns of interference and modulation of North American rainfall. The results from this study show that during a particular phase of an active MJO, the extratropical response can considerably enhance or mask the interannual ENSO signal in the United States, potentially resulting in anomalies of the opposite sign than that expected during a specific ENSO phase. Analyses of specific MJO events during an El Nino or La Nina episode reveal significant contributions to extreme events via constructive and destructive interference of the MJO and ENSO signals.
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Bai, K., Chang, N. - B., & Gao, W. (2016). Quantification of relative contribution of Antarctic ozone depletion to increased austral extratropical precipitation during 1979-2013. J. Geophys. Res. Atmos., 121(4), 1459–1474.
Abstract: Attributing the observed climate changes to relevant forcing factors is critical to predicting future climate change scenarios. Precipitation observations in the Southern Hemisphere indicate an apparent moistening pattern over the extratropics during the time period 1979 to 2013. To investigate the predominant forcing factor in triggering such an observed wetting climate pattern, precipitation responses to four climatic forcing factors, including Antarctic ozone, water vapor, sea surface temperature (SST), and carbon dioxide, were assessed quantitatively in sequence through an inductive approach. Coupled time-space patterns between the observed austral extratropical precipitation and each climatic forcing factor were firstly diagnosed by using the maximum covariance analysis (MCA). With the derived time series from each coupled MCA modes, statistical relationships were established between extratropical precipitation variations and each climatic forcing factor by using the extreme learning machine. Based on these established statistical relationships, sensitivity tests were conducted to estimate precipitation responses to each climatic forcing factor quantitatively. Quantified differential contribution with respect to those climatic forcing factors may explain why the observed austral extratropical moistening pattern is primarily driven by the Antarctic ozone depletion, while mildly modulated by the cooling effect of equatorial Pacific SST and the increased greenhouse gases, respectively.
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Bunting, E., Southworth, J., Herrero, H., Ryan, S., & Waylen, P. (2018). Understanding Long-Term Savanna Vegetation Persistence across Three Drainage Basins in Southern Africa. Remote Sensing, 10(7), 1013.
Abstract: Across savanna landscapes of southern Africa, people are strongly tied to the environment, meaning alterations to the landscape would impact livelihoods and socioecological development. Given the human-environment connection, it is essential to further our understanding of the drivers of savanna vegetation dynamics, and under increasing climate variability, to better understand the vegetation-climate relationship. Monthly time series of Advanced Very High-Resolution Radiometer (AVHRR)- and Moderate Resolution Imaging Spectroradiometer (MODIS) derived vegetation indices, available from as early as the 1980s, holds promise for the large-scale quantification of complex vegetation�climate dynamics and regional analyses of landscape change as related to global environmental changes. In this work, we employ time series based analyses to examine landscape-level vegetation greening patterns over time and across a significant precipitation gradient. In this study, we show that climate induced reductions in Normalized Difference Vegetation Index (NDVI; i.e., degradation or biomass decline) have had large spatial and temporal impacts across the Kwando, Okavango, and Zambezi catchments of southern Africa. We conclude that over time there have been alterations in the available soil moisture resulting from increases in temperature in every season. Such changes in the ecosystem dynamics of all three basins has led to system-wide changes in landscape greening patterns.
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Canfield Jr., D. E., Hoyer, M. V., Bachmann, R. W., Bigham Stephens, D., & Ruiz-Bernard, I. (2016). Water quality changes at an Outstanding Florida Water: influence of stochastic events and climate variability. Lake and Reservoir Management, 32(3), 297–313.
Abstract: The Santa Fe Lake System (SFS) is an Outstanding Florida Water system in northern peninsular Florida and receives special protection from governmental agencies to prevent impairment of water quality from anthropogenic activities. Since 1986, periods of sudden nutrient increases and declines have occurred along with changes in water clarity documented within a 28-year monthly database. Changes were linked to stochastic events such as an influx of gulls in 1986, the adjacent 5100-ha Dairy Road forest fire in 2007, 3 Category 3 hurricanes that struck Florida in 2004, and droughts. However, increasing trends at SFS were also observed for the yearly measured minimum water chemistry values, as were synchronous changes in these baseline conditions at other nearby lakes, suggesting the lakes were being impacted by a regional environmental factor. These changes corresponded to a period of decreasing precipitation and were related to climate variability, perhaps reflecting phase changes in the Atlantic Multidecadal Oscillation. The possible mechanism for the observed changes most likely relates to alterations in regional precipitation/evaporation rates and resulting changes in groundwater chemistry and hydrology. Long-term trends in water quality at SFS may reverse if Florida enters a long-term period of increasing precipitation.
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Chang, N. - B., Imen, S., Bai, K., & Jeffrey Yang, Y. (2017). The impact of global unknown teleconnection patterns on terrestrial precipitation across North and Central America. Atmospheric Research, 193, 107–124.
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Chang, N. - B., Yang, Y. J., Imen, S., & Mullon, L. (2017). Multi-scale quantitative precipitation forecasting using nonlinear and nonstationary teleconnection signals and artificial neural network models. Journal of Hydrology, 548, 305–321.
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Chang, N. B., Imen, S., & Bai, K. (2015). Impacts of Global Non-leading Teleconnection Signals on Terrestrial Precipitation across the United States. In Proceedings of SPIE (Vol. 9610).
Abstract: Identification of teleconnection patterns at a local scale is challenging, largely due to the coexistence of non-stationary and non-linear signals embedded within the ocean-atmosphere system. This study develops a method to overcome the problem of non-stationarity and nonlinearity and investigates how the non-leading teleconnection signals as well as the known teleconnection patterns can affect precipitation over three pristine sites in the United States. It is presented here that the oceanic indices which affect precipitation of specific site do not have commonality in different seasons. Results also found cases in which precipitation is significantly affected by the oceanic regions of two oceans within the same season. We attribute these cases to the combined physical oceanic-atmospheric processes caused by the coupled effects of oceanic regions. Interestingly, in some seasons, different regions in the South Pacific and Atlantic Oceans show more salient effects on precipitation compared to the known teleconnection patterns. Results highlight the importance of considering the seasonality scale and non-leading teleconnection signals in climate prediction.
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Chen, R., Ebrahimi, H., & Jones, W. L. (2017). Creating a Multidecadal Ocean Microwave Brightness Dataset: Three-Way Intersatellite Radiometric Calibration Among GMI, TMI, and WindSat. IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing, 10(6), 2623–2630.
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Cocke, S., Boisserie, M., & Shin, D. - W. (2013). A coupled soil moisture initialization scheme for the FSU/COAPS climate model. Inverse Problems in Science and Engineering, 21(3), 420–437.
Abstract: We developed a coupled soil initialization scheme for the Florida State University/Center for Ocean-Atmosphere Prediction Studies (FSU/COAPS) climate model, which is coupled to the Community Land Model version 2. This method indirectly initializes the land surface component of the climate model by assimilating precipitation in the atmospheric component. A continuous assimilation is performed while the land and atmosphere components exchange fluxes, thus keeping the coupled model in a physically consistent state, obviating the need for any correction. Comparison with in situ observations in Illinois and Oklahoma shows very good agreement with the initialized soil moisture profile. A global comparison of the initialized land surface model with the Global Soil Wetness Project 2 multi-model analysis also shows very good agreement. Short-term climate forecasts (2 weeks to 2 months), performed in conjunction with the Global Land Atmosphere Coupling Experiment, Part 2, show that initialized soil moisture conditions improve surface temperature forecasts.
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Correa-Metrio, A., Vélez, M. I., Escobar, J., St-Jacques, J. - M., López-Pérez, M., Curtis, J., et al. (2016). Mid-elevation ecosystems of Panama: future uncertainties in light of past global climatic variability. J. Quaternary Sci., 31(7), 731–740.
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Deitch, M., Sapundjieff, M., & Feirer, S. (2017). Characterizing Precipitation Variability and Trends in the World's Mediterranean-Climate Areas. Water, 9(4), 259.
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Du, Y., Ramirez, C. E., & Jaffé, R. (2018). Fractionation of Dissolved Organic Matter by Co-Precipitation with Iron: Effects of Composition. Environ. Process., 5(1), 5–21.
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Dumitru, O. A., Forray, F. L., Fornós, J. J., Ersek, V., & Onac, B. P. (2017). Water isotopic variability in Mallorca: a path to understanding past changes in hydroclimate. Hydrol. Process., 31(1), 104–116.
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Ebrahimi, H., Chen, R., & Jones, W. L. (2017). Calibration of Millimeter Wave Sounder Radiometers on Polar Orbiting Satellites. IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing, 10(6), 2849–2854.
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Engström, J., & Keellings, D. (2018). Drought in the Southeastern USA: an assessment of downscaled CMIP5 models. Clim. Res., 74(3), 251–262.
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Feldpausch, T. R., Phillips, O. L., Brienen, R. J. W., Gloor, E., Lloyd, J., Lopez-Gonzalez, G., et al. (2016). Amazon forest response to repeated droughts. Global Biogeochem. Cycles, 30(7), 964–982.
Abstract: The Amazon Basin has experienced more variable climate over the last decade, with a severe and widespread drought in 2005 causing large basin-wide losses of biomass. A drought of similar climatological magnitude occurred again in 2010; however, there has been no basin-wide ground-based evaluation of effects on vegetation. We examine to what extent the 2010 drought affected forest dynamics using ground-based observations of mortality and growth from an extensive forest plot network. We find that during the 2010 drought interval, forests did not gain biomass (net change: -0.43Mgha(-1), confidence interval (CI): -1.11, 0.19, n=97), regardless of whether forests experienced precipitation deficit anomalies. This contrasted with a long-term biomass sink during the baseline pre-2010 drought period (1998 to pre-2010) of 1.33Mgha(-1)yr(-1) (CI: 0.90, 1.74, p<0.01). The resulting net impact of the 2010 drought (i.e., reversal of the baseline net sink) was -1.95Mgha(-1)yr(-1) (CI:-2.77, -1.18; p<0.001). This net biomass impact was driven by an increase in biomass mortality (1.45Mgha(-1)yr(-1) CI: 0.66, 2.25, p<0.001) and a decline in biomass productivity (-0.50Mgha(-1)yr(-1), CI:-0.78, -0.31; p<0.001). Surprisingly, the magnitude of the losses through tree mortality was unrelated to estimated local precipitation anomalies and was independent of estimated local pre-2010 drought history. Thus, there was no evidence that pre-2010 droughts compounded the effects of the 2010 drought. We detected a systematic basin-wide impact of the 2010 drought on tree growth rates across Amazonia, which was related to the strength of the moisture deficit. This impact differed from the drought event in 2005 which did not affect productivity. Based on these ground data, live biomass in trees and corresponding estimates of live biomass in lianas and roots, we estimate that intact forests in Amazonia were carbon neutral in 2010 (-0.07PgCyr(-1) CI:-0.42, 0.23), consistent with results from an independent analysis of airborne estimates of land-atmospheric fluxes during 2010. Relative to the long-term mean, the 2010 drought resulted in a reduction in biomass carbon uptake of 1.1PgC, compared to 1.6PgC for the 2005 event.
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Feng, X., Huang, B., Kirtman, B. P., Kinter, J. L., & Chiu, L. S. (2017). A multi-model analysis of the resolution influence on precipitation climatology in the Gulf Stream region. Clim Dyn, 48(5-6), 1685–1704.
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Fill, J. M., Davis, C. N., & Crandall, R. M. (2019). Climate change lengthens southeastern USA lightning-ignited fire seasons. Glob Chang Biol, 25(10), 3562–3569.
Abstract: Trends in average annual or seasonal precipitation are insufficient for detecting changes in the climatic fire season, especially in regions where the fire season is defined by wet-dry seasonal cycles and lightning activity. Using an extensive dataset (1897-2017) in the Coastal Plain of the southeastern United States, we examined changes in annual dry season length, total precipitation, and (since 1945) the seasonal distribution of thunder-days as a correlate of lightning activity. We found that across the entire region, the dry season has lengthened by as much as 156 days (130% over 120 years), both starting earlier and ending later with less total precipitation. Less rainfall over a longer dry season, with no change in seasonal thunderstorm patterns, likely increases both the potential for lightning-ignited wildfires and fire severity. Global climate change could be having a hitherto undetected influence on fire regimes by altering the synchrony of climatic seasonal parameters.
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Gibbes, C., Southworth, J., Waylen, P., & Child, B. (2014). Climate variability as a dominant driver of post-disturbance savanna dynamics. Applied Geography, 53, 389–401.
Abstract: How do climate variability and climate shifts influence vegetation patterns in dryland ecosystems? A landscape scale assessment of the effect of changes in precipitation on vegetation in three watersheds, spanning four southern African nations is undertaken and tests of statistical significance of vegetation changes developed. Concepts of resilience provide the framework for examining the influence of changes in both the mean and variance of annual precipitation on the ecological systems of southern Africa. They illustrate thresholds of change and their manifestation in the state of savanna ecosystems, which could previously only be postulated. Time series analyses indicate the fundamental role of precipitation mean and variability in modulating the states of savanna ecosystems. Here we show that the savanna dryland ecosystems have overall responded with increasing NDVI measures despite decreased precipitation since the mid to late 1970's. Areas which experienced diminished vegetative cover over time, are related to specific vegetation types, and declines in the variance of precipitation (even in the presence of overall increases in annual mean). The work highlights the importance of
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Guo, L., Cheng, J., Luedeling, E., Koerner, S. E., He, J. - S., Xu, J., et al. (2017). Critical climate periods for grassland productivity on China's Loess Plateau. Agricultural and Forest Meteorology, 233, 101–109.
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