Abstract: The interannual, equatorial Pacific, 20 degrees C isotherm depth variability since 1980 is dominated by two empirical orthogonal function (EOF) modes: the "tilt" mode, having opposite signs in the eastern and western equatorial Pacific and in phase with zonal wind forcing and El Nino-Southern Oscillation (ENSO) indices, and a second EOF mode of one sign across the Pacific. Because the tilt mode is of opposite sign in the eastern and western equatorial Pacific while the second EOF mode is of one sign, the second mode has been associated with the warm water volume (WWV), defined as the volume of water above the 20 degrees C isotherm from 5 degrees S to 5 degrees N, 120 degrees E to 80 degrees W. Past work suggested that the WWV led the tilt mode by about 2-3 seasons, making it an ENSO predictor. But after 1998 the lead has decreased and WWV-based predictions of ENSO have failed. The authors constructed a sea level-based WWV proxy back to 1955, and before 1973 it also exhibited a smaller lead. Analysis of data since 1980 showed that the decreased WWV lead is related to a marked increase in the tilt mode contribution to the WWV and a marked decrease in second-mode EOF amplitude and its contribution. Both pre-1973 and post-1998 periods of reduced lead were characterized by "mean" La Nina-like conditions, including a westward displacement of the anomalous wind forcing. According to recent theory, and consistent with observations, such westward displacement increases the tilt mode contribution to the WWV and decreases the second-mode amplitude and its WWV contribution.

Abstract: Drought index is a useful tool to assess and respond to drought. However, current drought indices could not fully reveal land use effects and they have limitations in applications. Besides, El Niño Southern Oscillation (ENSO), strongly influences the climate of Florida. Hence, understanding ENSO patterns on a regional scale and developing a new land use drought index suitable for Florida are critical in agriculture and water resources planning and management. This paper presents a 32 km high resolution land use adapted drought index, which relies on five types of land uses (lake, urban, forest, wetland, and agriculture) in Florida. The land uses were obtained from National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) data from 1979 to 2002. The results showed that Bowen ratio responded to land use and could be used as an indicator to monitor drought events. Then, an innovative regional land use drought index was developed from the normalized Bowen ratio, which could reflect not only the level of severity during drought events resulting from land use effects, but also La Niña driven drought impacts. The proposed new index may help scientists answer the critical questions about drought effect on various land uses and potential feedbacks of changes in land use and land cover to climate.

Abstract: Much of the year-to-year climate variability on the Earth is associated with El Nino and the Southern Oscillation (ENSO). This variability is generated ˜ primarily by a coupled ocean-atmosphere instability near the eastern edge of the western equatorial Pacific warm pool. Here, I discuss the physics of this variability, including its phase locking to the seasonal cycle. ENSO growth typically occurs from April/May to November, and by July the perturbation is usually strong enough that it persists to the beginning of the following year, when ENSO events usually end. Consequently, predicting ENSO is easy from July to February but is more challenging across the April/May transition to the next event. I discuss precursors of this transition and recent results from dynamical and statistical models used for ENSO forecasting.

Abstract: Agriculture is an economic activity directly affected by drought. With the constant increase of food demand and the need for high efficiency in food production, drought effects gain attention. The Agricultural Reference Index for Drought (ARID) was developed to quantify drought and better understand its effect on agriculture. ARID values range from 0 to 1 where zero is transpiration occurring at potential rate and one is full water deficit. El Niño Southern Oscillation (ENSO) is the main factor of climate variability around the world and affects the climate of two states located in midlatitudes, Florida, USA and Rio Grande do Sul, Brazil. An historical assessment of the relationship between ARID and ENSO will assist with establishing the role played by ENSO in the seasonal variation of soil moisture, which is critical to drought forecasting based on ENSO. The main objectives of this study were to investigate ARID's temporal and spatial variability in Florida and Rio Grande do Sul, and provide an assessment of ENSO-induced potential anomalies in ARID. Daily ARID values in Florida were calculated using data obtained from the National Weather Service COOP (Cooperative Observer Program) weather stations. In Rio Grande do Sul, ARID was calculated using daily weather data from the Instituto Nacional de Meteorologia (INMET) weather stations, Brazil. Daily ARID values were compiled into monthly averages and categorized according to ENSO phase based on the Multivariate ENSO Index (MEI). Results showed that typical ARID values for both regions vary throughout the year. The highest values were observed in the warm season due to increased evapotranspiration. During this period, ARID values varied from 0.3 to 0.8 in Florida and 0.2 to 0.7 in Rio Grande do Sul. In the cold period, South Florida had the highest ARID values, varying from 0.3 to 0.7, while for the rest of state and Rio Grande do Sul the values varied from 0 to 0.5. ENSO showed stronger influence from November to March in Florida, and November and May in Rio Grande do Sul. For both regions, El Niño caused ARID values below normal, indicating higher soil moisture while during La Niña the values were above normal. This study contributes to establish historical ARID records across the southeastern United States and southern Brazil, and can assist farmers to adjust management practices according to expected water stress conditions.

Abstract: Research has shown that there is significant diversity in the location of the maximum sea surface temperature anomaly (SSTA) associated with the El Nio Southern Oscillation (ENSO). In one extreme, warm SSTA peak near the South American coast (often referred to as Eastern Pacific of EP El Nio), and at the other extreme, warm SSTA peak in the central Pacific (Central Pacific or CP El Nio). Due to the differing tropical Pacific SSTA and precipitation structure, there are differing extratropical responses, particularly over North America. Recent work involving the North American Multi-Model Ensemble (NMME) system for intra-seasonal to inter-annual prediction on prediction of the differences between El Nio events found excess warming in the eastern Pacific during CP El Nio events. This manuscript investigates the ensemble and observational agreement of the NMME system when forecasting the North American response to the diversity of ENSO, focusing on regional land-based 2-meter temperature and precipitation. NMME forecasts of North American precipitation and T2m agree with observations more often during EP events. Ensemble agreement of NMME forecasts is regional. For instance, ensemble agreement in Southeast North America demonstrates a strong connection to NINO3 precipitation and SSTA amplitude during warm ENSO events. Ensemble agreement in Northwest North America demonstrates a weak connection to NINO4 precipitation and SSTA amplitude during warm ENSO events. Still other regions do not show a strong connection between ensemble agreement and strength of warm ENSO events.

Abstract: In this chapter we review several climatologically important variables with a history of observation from spaceborne platforms. These include sea surface temperature and wind vectors, altimetric estimates of sea surface height, energy and water vapor fluxes at the sea surface, precipitation over the ocean, and ocean color. We then discuss possible improvements in sampling for climate and climate change definition. Issues of consistency of different data sources, archiving and distribution of these types of data are discussed. The practical prospect of immediate international coordination through the concept of virtual constellations is discussed and applauded.

Abstract: The space-time structure of the daily atmospheric variability in the South American monsoon system has been studied using multichannel singular spectrum analysis of daily outgoing longwave radiation. The three leading eigenmodes are found to have low-frequency variability while four other modes form higher frequency oscillations. The first mode has the same time variability as that of El Nino-Southern Oscillation (ENSO) and exhibits strong correlation with the Pacific sea surface temperature (SST). The second mode varies on a decadal time scale with significant correlation with the Atlantic SST suggesting an association with the Atlantic multidecadal oscillation (AMO). The third mode also has decadal variability but shows an association with the SST of the Pacific decadal oscillation (PDO). The fourth and fifth modes describe an oscillation that has a period of about 165 days and is associated with the North Atlantic oscillation (NAO). The sixth and seventh modes describe an intraseasonal oscillation with a period of 52 days which shows strong relation with the Madden-Julian oscillation. There exists an important difference in the variability of convection between Amazon River Basin (ARB) and central-east South America (CESA). Both regions have similar variations due to ENSO though with higher magnitude in ARB. The AMO-related mode has almost identical variations in the two regions, whereas the PDO-related mode has opposite variations. The interseasonal NAO-related mode also has variations of opposite sign with comparable magnitudes in the two regions. The intraseasonal variability over the CESA is robust while it is very weak over the ARB region. The relative contributions from the low-frequency modes mainly determine the interannual variability of the seasonal mean monsoon although the interseasonal oscillation may contribute in a subtle way during certain years. The intraseasonal variability does not seem to influence the interannual variability in either region.

Abstract: Recent violent and widespread tornado outbreaks in the US, such as occurred in the spring of 2011, have caused devastating societal impact with significant loss of life and property. At present, our capacity to predict US tornado and other severe weather risk does not extend beyond seven days. In an effort to advance our capability for developing a skillful long-range outlook for US tornado outbreaks, here we investigate the spring probability patterns of US regional tornado outbreaks during 1950-2014. Weshow that the four dominant springtime El Nino-Southern Oscillation (ENSO) phases (persistent versus early-terminating El Nino and resurgent versus transitioning La Nina) and the North Atlantic sea surface temperature tripole variability are linked to distinct and significant US regional patterns of outbreak probability. These changes in the probability of outbreaks are shown to be largely consistent with remotely forced regional changes in the large-scale atmospheric processes conducive to tornado outbreaks. An implication of these findings is that the springtime ENSO phases and the North Atlantic SST tripole variability may provide seasonal predictability of US regional tornado outbreaks.