Climate Variability And Predictability Research Articles

Tropical Widening: From Global Variations to Regional Impacts

AbstractOver the past 15 years, numerous studies have suggested that the sinking branches of Earth’s Hadley circulation and the associated subtropical dry zones have shifted poleward over the late twentieth century and early twenty-first century. Early estimates of this tropical widening from satellite observations and reanalyses varied from 0.25° to 3° latitude per decade, while estimates from global climate models show widening at the lower end of the observed range. In 2016, two working groups, the U.S. Climate Variability and Predictability (CLIVAR) working group on the Changing Width of the Tropical Belt and the International Space Science Institute (ISSI) Tropical Width Diagnostics Intercomparison Project, were formed to synthesize current understanding of the magnitude, causes, and impacts of the recent tropical widening evident in observations. These working groups concluded that the large rates of observed tropical widening noted by earlier studies resulted from their use of metrics that poorly capture changes in the Hadley circulation, or from the use of reanalyses that contained spurious trends. Accounting for these issues reduces the range of observed expansion rates to 0.25°–0.5° latitude decade‒1—within the range from model simulations. Models indicate that most of the recent Northern Hemisphere tropical widening is consistent with natural variability, whereas increasing greenhouse gases and decreasing stratospheric ozone likely played an important role in Southern Hemisphere widening. Whatever the cause or rate of expansion, understanding the regional impacts of tropical widening requires additional work, as different forcings can produce different regional patterns of widening.

Trends and interannual variability of extreme rainfall indices over Ghana, West Africa

Rainfall plays an important role in the socio-economic development of any nation. Below or above normal rainfall amounts have serious consequences on key socio-economic sectors. This is particularly true for countries such as Ghana where rainfall plays a key role in the agriculture and energy sectors. In this study, the Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS)-homogenized daily rainfall series was used to determine the variability of ten extreme rainfall indices recommended by the World Meteorological Organization-Commission for Climatology (WMO-CCL) and the research project on Climate Variability and Predictability (CLIVAR). The trends of these indices and their links to SST anomalies at oceanic basins were also explored in this study. To understand the variability at interannual to decadal time scales and links with SST forcings, the sum of the first three principal components of the indices were correlated with SST anomalies at oceanic basins. The 35 years mean of frequency indices, CDD, CWD, R10mm and R20mm were found to be in a range of 10–125, 6–14, 30–60 and 8–24 days per year, respectively. On the other hand, the mean over the same period of intensity indices PRCPTOT, R95p, R99p, SDII, RX1day and RX5day were in the range of 900–1700 mm, 200–400 mm, 40–130 mm, 9–13 mm, 30–100 mm and 90–180 mm per year, respectively. The maximum of temporally averaged intensity indices covers southwestern Ghana, while the minimum of the indices lies over northwestern and eastern coasts. A significant decreasing trend in wet indices were observed over the Volta Lake and central portions of the country (7.5°N to 9.5°N), whereas low positive trends were observed over the Northern parts of the country. Wet indices over the country showed significant positive correlations with the Atlantic Ocean SST and negative correlations with the Pacific and Indian basins SSTs. Specifically, the NINO3.4 revealed significant negative correlations with the wet indices over the west-central portions of the country. IOD was observed to have a dipole effect on rainfall indices with the central and southern parts generally covered by negative correlations, while Northern and coastal regions showed positive correlations. The impacts of Atlantic SST on wet rainfall indices are significant over most parts of the country. These results have implications on the improvement of seasonal forecast of the Ghanaian rainfall and its extremes and also provide prior knowledge for better understandings of multidecadal modulations of global interannual teleconnections.

Multidisciplinary investigations of the Northern Atlantic and Arctic in 71th cruise of R/V «Akademik Mstislav Keldysh»

The article briefly shows the results of the expedition, expanding Russia’s contribution to the international program CLIVAR (Climate Variability and Predictability), aimed at studying and predicting climate change. The geological part of the expedition is aimed at studying the sedimentary system of the North Atlantic and the Arctic. During the voyage, a unique material was received, requiring additional analysis and further publication.

Assessment of climate change for extreme precipitation indices: A case study from the central United States

Five extreme precipitation indicators were calculated on an annual basis for 1890 through 2013 and analysed to determine spatial patterns and temporal trends in the frequency and magnitude of observed extreme precipitation events in Kansas located in the central United States. Indicators were selected from the list of the World Meteorological Organization–Commission for Climatology (WMO–CCL) and the Research Programme on Climate Variability and Predictability (CLIVAR). The indicators included the number of days with precipitation greater than or equal to 10 mm/day (R10), maximum number of consecutive dry days (CDD; days with precipitation lower that 1 mm), maximum 5‐day precipitation total (R5D), and simple daily intensity index (SDII) which is the annual precipitation total divided by number of days with precipitation greater than or equal to 1 mm, and the fraction of annual total precipitation due to events exceeding the 95th percentile (R95T) based on the period 1961–1990. Positive trends in the results were found for a majority of stations for R10, R5D, SDII, and R95T. Consecutive dry days was the only index that had a negative trend at a majority of stations. Spatial pattern analysis indicates greater changes in frequencies and magnitudes for eastern Kansas. Results from this study highlight observed climate shifts in precipitation patterns with a tendency towards greater and more frequent extreme precipitation in eastern Kansas and a tendency towards drier conditions in western Kansas. These hydroclimatic adjustments can produce costly impacts in areas that include flood management, hydraulic structures, water availability throughout the year, agricultural production, ecosystems, and human health.

Recent changes in daily climate extremes in a serious water shortage metropolitan region, a case study in Jing-Jin-Ji of China

Extreme climate index is one of the useful tools to monitor and detect climate change. The primary objective of this study is to provide more comprehensively the changes in precipitation and temperature extremes for the period of 1959–2015 in the Jing-Jin-Ji metropolitan region of China, including Beijing city, Tianjin city and Hebei province, which will hopefully provide scientific understanding of the precipitation and temperature-related natural hazards such as flood, drought and heat wave. Daily precipitation and temperature from 26 surface meteorological stations over the study area were used to calculate 14 extreme precipitation indices (EPIs) and 17 extreme temperature indices (ETIs) generated by the joint World Meteorological Organization Commission for Climatology (CCI)/World Climate Research Programme (WCRP) project on Climate Variability and Predictability (CLIVAR) Expect Team on Climate Change Detection, Monitoring and Indices (ETCCDMI). The EPIs and ETIs were generated using the RClimRex software, and the trends were analyzed using the Mann-Kendall non-parametric test and the Thiel-Sen’s slope estimator. The results showed the following: (1) The spatiotemporal variability for daily climate extremes varied for both the EPIs and ETIs between 1959 and 2015. In the case of the EPIs, most of the indices were negative trend-dominated, and for the ETIs, 13 ETIs were positive trend-dominated, and six ETIs were negative trend-dominated. (2) Six types of precipitation intensity EPIs including the R10mm–R250mm were especially defined to detect impacts of climate change on the precipitation events. The results showed that the spatial distributions of increasing trends for these EPIs were similar, mainly located at the south of the Hebei province. (3) In general, the trend magnitudes of fixed-threshold extreme indices were smaller than those of station-related thresholds and non-threshold extreme indices for both the EPIs and ETIs. (4) The spatial distributions of positive and negative trends for both the EPIs and ETIs were scattered. For several indices such as the ID0, SU25, WSDI and TX90p, stations that had statistically significant increasing/decreasing trends at 5% significance level were detected mainly located at the north of the Jing-Jin-Ji metropolitan region. More works on the physical mechanisms behind the varied changes and scattered spatial distributions of trends in the Jing-Jin-Ji metropolitan region are recommended as an extension of this study.

Spatial and temporal analysis of extreme bioclimate conditions in Vojvodina, Northern Serbia

ABSTRACTSeveral indices, with focus on extreme climate and bioclimate events have been calculated and their trends (over 1961 to 2014) analyzed in order to identify possible changes in temperature‐related climate extremes over Vojvodina region, Northern Serbia. Physiologically equivalent temperature (PET) has been used for the assessment of bioclimatological extremes in Vojvodina. A number of indices for temperature extremes have been defined by CLIVAR (Climate Variability and Predictability) and they are modified in order to detect extremes in bioclimatological variables (PET). In this study, we used 11 PET indices. The results indicate that the whole area is dominated by significant increase in the frequency of warm conditions and significant decrease in the cold conditions. These results could indicate that the warming in Vojvodina could be due to the more pronounced and higher frequency of warm bioclimatological extreme conditions. The frequency and the duration of heat waves are increasing for the whole area, while the decrease in number and duration of cold waves is not so pronounced.

Spatiotemporal variability of extreme precipitation in Shaanxi province under climate change

Extreme climate index is one of the useful tools to monitor and detect climate change. The primary objective of this study is to provide a more comprehensively the changes in extreme precipitation between the periods of 1954–1983 and 1984–2013 in Shaanxi province under climate change, which will hopefully provide a scientific understanding of the precipitation-related natural hazards such as flood and drought. Daily precipitation from 34 surface meteorological stations were used to calculated 13 extreme precipitation indices (EPIs) generated by the joint World Meteorological Organization Commission for Climatology (CCI)/World Climate Research Programme (WCRP) project on Climate Variability and Predictability (CLIVAR) expect Team on climate change Detection, Monitoring and Indices (ETCCDMI). Two periods including 1954–1983 and 1984–2013 were selected and five types of precipitation days (R10mm-R100mm) were defined, to provide more evidences of climate change impacts on the extreme precipitation events, and specially, to investigate the changes in different types of precipitation days. The EPIs were generated using RClimRex software, and the trends were analyzed using Mann-Kendall nonparametric test and Sen’s slope estimator. The relationships between the EPIs and the impacts of climate anomalies on typical EPIs were investigated using correlation and composite analysis. The mainly results include: 1) Thirteen EPIs, except consecutive dry day (CDD), were positive trends dominated for the period of 1984–2013, but the trends were not obvious for the period of 1954–1983. Most of the trends were not statistically significant at 5 % significance level. 2) The spatial distributions of stations that exhibited positive and negative trends were scattered. However, the stations that had negative trends mainly distributed in the north of Shaanxi province, and the stations that had positive trends mainly located in the south. 3) The percentage of stations that had positive trends had increased from the period of 1954–1983 to 1984–2013 for all the 13 EPIs except CDD, indicating the possible climate change impacts on extreme precipitation events. 4) The correlations between annual total wet-day precipitation (PRCPTOT) and other 12 EPIs varied for different indices and stations. The composite analysis found that El Nino Southern Oscillation (ENSO) exerted greater impacts on PRCPTOT than other EPIs and greater in the Guanzhong Plain (GZP) than Qinling-Dabashan Mountains (QDM) and Shanbei Plateau (SBP) of Shaanxi province.

Study of Daily Extreme Temperature Indices over Sutlej Basin, N-W Himalayan Region, India

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 <p>A detailed analysis of extreme temperature indices for the period of 1970-2005 is conducted over Sutlej river basin located in North-West Himalayan region. For this purpose, daily records of maximum and minimum temperature data were procured from Bhakara Beas Management Board, India for four stations. These stations are installed at varying height from 518m to 976m under different physiographic and climatic conditions. Fourteen extreme indices for temperature as specified by the World Meteorological Organization (WMO) Commission for Climatology (CCL)/Climate Variability and Predictability (CLIVAR) Expert Team on Climate Change Detection, Monitoring and Indices (ETCCDMI) are derived with the aid of RClimDex software.  Linear Regression (LR) method is employed for detecting annual as well as monthly trends in extreme indices of temperature over the period of thirty six years (1970-2005). Large spatial and inter-annual variability in trends of extreme indices is observed. However, a rise in diurnal temperature range is observed for the basin as a whole. This may be attributed to the decrease observed in maximum T<sub>Min</sub> (TXn) and warm nights (TN90p) coupled with the increase in maximum T<sub>Max</sub> (TXx).</p>
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Dissolved Fe and Al in the upper 1000 m of the eastern Indian Ocean: A high‐resolution transect along 95°E from the Antarctic margin to the Bay of Bengal

AbstractA high‐resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along ~95°E in the upper 1000 m of the eastern Indian Ocean from the Antarctic margin (66°S) to the Bay of Bengal (18°N) during the U.S. Climate Variability and Predictability (CLIVAR) CO2 Repeat Hydrography I08S and I09N sections (February–April 2007). In the Southern Ocean, low concentrations of dAl (<1 n M) reflect the negligible dust inputs impacting the water masses subducted in the circumpolar domain. The low dAl concentrations characterizing the Southern Ocean terminate near 45°S, probably because of the advection of subtropical water masses that received dust and sedimentary inputs in their formation region. Our subsurface dFe data near the southern Kerguelen Plateau were significantly higher than historical observations in other Indian sectors of the Southern Ocean. We surmise that the offshore advection of dFe‐rich waters along the western flank of the southern Kerguelen plateau and enhanced vertical mixing could contribute to this elevated subsurface dFe inventory. Elevated subsurface particulate and dFe levels downstream of the northern Kerguelen Plateau may reflect long‐range lateral transport from the plateau's sediments and/or remineralization inputs. At the northern edge of the south Indian subtropical gyre, the deposition of Australian dust, possibly combined with the advection of dAl‐enriched waters from the Indonesian Throughflow, creates a region of elevated dAl in the upper 400 m but without a corresponding enrichment in dFe. In the northern Indian Ocean, the South Equatorial Current constitutes a remarkable biogeochemical front separating the oxygen‐rich and dFe‐poor subtropical gyre waters from the dFe‐rich and oxygen‐depleted waters of the northern Indian Ocean. By tracing the accumulation of macronutrients and dFe along the advective pathway of Indian Central Water, we show that the central waters of the northern Indian Ocean receive excess dFe in addition to that produced by remineralization inputs. The resuspension of shelf sediments and release of pore waters probably contribute to the elevated dFe and dAl levels observed below the highly stratified upper layers of the Bay of Bengal.

The climate of the Mediterranean region: research progress and climate change impacts

This special issue was proposed at the second MedCLIVAR conference (which was held in Madrid, Spain, 26–29 September 2012) and has received a wide range of contributions covering different and complementary topics: paleo-climate, present climate variability and trends, extremes, climate projections, and impacts of future climate change on the regional environment and societies. All these topics (see Lionello et al. 2012b, for a synthesis) are subject of a rapidly evolving research, which has the sensitivity of the Mediterranean region to climate change as a main motivation. In fact, in the last decades in the Mediterranean region, temperatures have risen faster than the global average and model projections agree on its future warming and drying, with a likely increase of heat waves and dry spells. Further, countries around the Mediterranean basin are characterized by strong differences, as shown by various socioeconomic and environmental indicators, such as per capita gross domestic product (GDP), energy supply, CO2 emissions, and water availability. Environmental issues are exacerbated by societal aspect, as the whole region is densely populated with many Middle East and North African (MENA) countries expected to double their population by the mid-twenty-first century. A growing dependence on irrigation in MENA countries will likely increase their economic and social vulnerability, because of future reduced total water availability and rapidly growing competing urban water demands. This issue is an outcome of the work carried on within the MedCLIVAR network. It describes recent progresses on the understanding of the climate of the Mediterranean region and the impacts of its future evolution on the environment and people. MedCLIVAR (Mediterranean CLImate VARiability) has been running continuously for about 10 years. It was initially proposed at the 2003 European Geosciences Union assembly in Nice (France), endorsed by the international Climate Variability and Predictability (CLIVAR) office in 2005, and supported by the European Science Foundation for the period 2006–2011. This special issue is the latest contribution to the MedCLIVAR dissemination activity, which has already produced three books (Lionello et al. 2006; Vicente-Serrano and Trigo 2011; Lionello 2012) and 4 special issues (Lionello et al. 2008; Jones et al. 2011; Lionello 2012; P. Lionello (&) DISTeBA, University of Salento, CMCC – Centro EuroMediterraneo sui Cambiamenti Climatici, via per Monteroni 165, Block M, 73100 Lecce, Italy e-mail: piero.lionello@unisalento.it

Intense Precipitation Events Associated with Landfalling Tropical Cyclones in Response to a Warmer Climate and Increased CO2

Abstract In this work the authors investigate possible changes in the intensity of rainfall events associated with tropical cyclones (TCs) under idealized forcing scenarios, including a uniformly warmer climate, with a special focus on landfalling storms. A new set of experiments designed within the U.S. Climate Variability and Predictability (CLIVAR) Hurricane Working Group allows disentangling the relative role of changes in atmospheric carbon dioxide from that played by sea surface temperature (SST) in changing the amount of precipitation associated with TCs in a warmer world. Compared to the present-day simulation, an increase in TC precipitation was found under the scenarios involving SST increases. On the other hand, in a CO2-doubling-only scenario, the changes in TC rainfall are small and it was found that, on average, TC rainfall tends to decrease compared to the present-day climate. The results of this study highlight the contribution of landfalling TCs to the projected increase in the precipitation changes affecting the tropical coastal regions.

Sensitivity of Tropical Cyclone Rainfall to Idealized Global-Scale Forcings*

Abstract Heavy rainfall and flooding associated with tropical cyclones (TCs) are responsible for a large number of fatalities and economic damage worldwide. Despite their large socioeconomic impacts, research into heavy rainfall and flooding associated with TCs has received limited attention to date and still represents a major challenge. The capability to adapt to future changes in heavy rainfall and flooding associated with TCs is inextricably linked to and informed by understanding of the sensitivity of TC rainfall to likely future forcing mechanisms. Here a set of idealized high-resolution atmospheric model experiments produced as part of the U.S. Climate Variability and Predictability (CLIVAR) Hurricane Working Group activity is used to examine TC response to idealized global-scale perturbations: the doubling of CO2, uniform 2-K increases in global sea surface temperature (SST), and their combined impact. As a preliminary but key step, daily rainfall patterns of composite TCs within climate model outputs are first compared and contrasted to the observational records. To assess similarities and differences across different regions in response to the warming scenarios, analyses are performed at the global and hemispheric scales and in six global TC ocean basins. The results indicate a reduction in TC daily precipitation rates in the doubling CO2 scenario (on the order of 5% globally) and an increase in TC rainfall rates associated with a uniform increase of 2 K in SST (both alone and in combination with CO2 doubling; on the order of 10%–20% globally).

Trends in daily temperature and precipitation extremes over Georgia, 1971–2010

Annual changes to climate extreme indices in Georgia (Southern Caucasus) from 1971 to 2010 are studied using homogenized daily minimum and maximum temperature and precipitation series. Fourteen extreme temperature and 11 extreme precipitation indices are selected from the list of core climate extreme indices recommended by the World Meteorological Organization – Commission for Climatology (WMO-CCL) and the research project on Climate Variability and Predictability (CLIVAR) of the World Climate Research Programme (WCRP). Trends in the extreme indices are studied for 10 minimum and 11 maximum temperature and 24 precipitation series for the period 1971–2010. Between 1971 and 2010 most of the temperature extremes show significant warming trends. In 2010 there are 13.3 fewer frost days than in 1971. Within the same time frame there are 13.6 more summer days and 7.0 more tropical nights. A large number of stations show significant warming trends for monthly minimum and maximum temperature as well as for cold and warm days and nights throughout the study area, whereas warm extremes and night-time based temperature indices show greater trends than cold extremes and daytime indices. Additionally, the warm spell duration indicator indicates a significant increase in the frequency of warm spells between 1971 and 2010. Cold spells show an insignificant increase with low spatial coherence. Maximum 1-day and 5-day precipitation, the number of very heavy precipitation days, very wet and extremely wet days as well as the simple daily intensity index all show an increase in Georgia, although all trends manifest a low spatial coherence. The contribution of very heavy and extremely heavy precipitation to total precipitation increased between 1971 and 2010, whereas the number of wet days decreases.

Quantifying the Impact of Atmospheric Deposition on the Biogeochemistry of Fe and Al in the Upper Ocean: A Decade of Collaboration with the US CLIVAR-CO2 Repeat Hydrography Program

The aerosol deposition of continental material and its partial dissolution in the surface ocean exerts an important control on the distribution of iron and other potentially limiting trace metal (TM) micronutrients in the open ocean. This dust deposition has implications for the regulation of global climate through the coupling of biolimiting TM cycles, marine productivity, and the global carbon cycle. Thus, it is important to determine the locations of dust deposition in the open ocean and to quantify the magnitude and subsequent dissolution of the dust. At present, there are too few dust deposition estimates and solubility measurements in the open ocean to adequately constrain this key source term in global biogeochemical models. While early sampling efforts were invaluable in highlighting the importance of TMs in regulating nutrient cycling and phytoplankton productivity in vast ocean regions, they lacked the spatial resolution and global coverage required to constrain model simulations and identify features that illuminate the processes controlling TM distributions. Starting in 2003, the US Climate Variability and Predictability (CLIVAR)-CO2 Repeat Hydrography Program provided an hour of ship time for dedicated TM sampling at every degree of latitude or longitude along selected cruise tracks. The principal goals for CLIVAR TM sampling were to produce a high-resolution dissolved iron (Fe) and aluminum (Al) data set with global coverage to better understand upper-ocean Fe biogeochemistry, determine patterns of atmospheric dust deposition based on surface dissolved Al levels, and improve our estimates of the fractional solubility of aerosol TMs using a dedicated shipboard aerosol sampling program. This paper describes recent advances in our understanding of dust deposition and the solubility of aerosol material resulting from 10 years of collaborative work under the US CLIVAR-CO2 Repeat Hydrography Program.

Pacific Ocean aerosols: Deposition and solubility of iron, aluminum, and other trace elements

The deposition of aerosols to the open ocean and the mechanisms controlling trace element solubility are important factors in the biogeochemical cycling of biolimiting elements, including iron, with implications for the global carbon cycle. During 2004–2006, 24-hour integrated aerosol samples were collected on two Climate Variability and Predictability (CLIVAR)-CO2 Repeat Hydrography cruises in the Pacific Ocean. The cruise sections traversed the North Pacific Ocean along 30°N (Section P02) and the eastern Pacific along 150°W (Section P16). This dataset includes analyses of aerosol particle chemistry as well as iron, aluminum, and manganese solubility in ultrapure deionized water and iron solubility in filtered surface seawater, measured using a rapid, flow-through extraction technique. The atmospheric concentrations of soluble aerosol iron were not significantly different using these extraction solutions (Wilcoxon signed rank, p=0.076). However, aerosol iron fractional solubility was higher in ultrapure deionized water than in filtered surface seawater (Wilcoxon signed rank, p=0.009). The median fractional solubility of aerosol iron in ultrapure water was 9.2% (3.2–29.1%) and 6.4% (0.5–81.1%) in seawater. Soluble aerosol Fe(II) accounted for 1.7% of the total aerosol Fe and 26.2% of the seawater soluble aerosol iron. The fractional solubility of aerosol iron did not increase with distance from Asian source regions nor was solubility related to the concentration of aerosol Fe in the atmosphere.

Factors Associated with Decadal Variability in Great Plains Summertime Surface Temperatures

Abstract Decadal variability of summertime Great Plains surface temperature is probed from the perspective of the Great Plains low-level jet (GPLLJ). GPLLJ variability modes 2 and 5 are shown to be most influential on the evolution and magnitude of Great Plains surface temperature anomalies over the latter half of the twentieth century, including the development of the summertime warming hole and are further linked to the Pacific decadal oscillation (PDO) and Atlantic multidecadal oscillation (AMO), respectively. The connection between GPLLJ variability and Great Plains surface temperature is strongest when the PDO and AMO are oppositely phased, and in the case of the warming hole, a preference for a positive (negative) PDO (AMO). The influence of remote SST variability on the central U.S. warming hole is broadly consistent with previous modeling studies. However, the pivotal role that GPLLJ variability plays in linking the hemispheric-wide SST variability (through the AMO and PDO) to the regional warming hole is an expanded and clarified perspective. These findings unify the results of recent studies from the U.S. Climate Variability and Predictability (CLIVAR) Drought Working Group and have implications for decadal climate prediction efforts.

Pacific Storms Climatology Products (PSCP): Understanding Extreme Events

E xtreme events: the f loods that displace us from our homes, the high waves that wash out coastal roads, or the toppling of trees and power poles from a passing storm. For locations around the Pacific Basin, where remote island chains sit perilously close to sea level and where rainfall is the primary source of water, questions arise concerning the return frequency and duration of such events, and whether or not they are getting more extreme. Understanding the long-term variability and change in coastal climate extremes has grown in public awareness given the potentially severe impacts related to sea-level rise coupled with coastal storms. To reduce vulnerability to the economic, social, and environmental risks associated with these phenomena, decision makers in coastal communities need timely access to accurate and contextually relevant information that affords them an opportunity to plan and respond accordingly. To address this need, the Pacific Storms Climatology Products (PSCP) project—or Pacific Storms— was established under the direction of the NOAA National Climatic Data Center (NCDC). Pacific Storms is focused on improving our understanding of patterns and trends in storm frequency and intensity—“storminess”—within the Pacific Basin. Pacific Storms is exploring how the climate-related processes that govern extreme storm events are expressed within and between three thematic areas: strong winds, heavy rains, and high seas. Theme-specif ic data integration and product development teams were formed to conduct analyses and create a broad suite of derived data products, which are publicly available online (www.pacificstormsclimatology.org). These teams included representatives from NCDC, as well as NOAA’s Center for Operational Products and Services (CO-OPS), Coastal Services Center (CSC), and National Weather Service (NWS), and the University of Hawaii, University of Alaska, University of Guam, and Oregon State University. Sources of information include NOAA’s Integrated Surface Hourly (ISH) mean sea-level pressure and wind speed data, the Global Historical Climate Network-Daily (GHCN-D) precipitation dataset, the National Water Level Observing Network (NWLON) tide gauge records, the University of Hawaii Sea Level Center (UHSLC) Joint Archive for Sea Level research quality dataset and Global Sea Level Observing System (GLOSS)/Climate Variability and Predictability (CLIVAR) “fast delivery” sea level dataset, the National Data Buoy Center (NDBC) wave buoy records, the U.S. Army Corps of Engineers’ Coastal Data Information (CDIP) buoy data, and other data sources. The data analysis and product development framework and guidelines outlined below are innovative in a number of ways. First, they focus on extreme events, and integrate data and products across a range of storm-related phenomena. Furthermore, they also paint a comprehensive picture of changes and variation in extreme-event magnitude and frequency for a mix of theme-specific parameters on seasonal, annual, and interannual time frames. The resulting extremes climatology datasets are unique, as are some of the specific products. Finally, success of the project is fundamentally tied to the collaborative efforts of the data integration and product development teams.

Assessing and Understanding the Impact of Stratospheric Dynamics and Variability on the Earth System

Advances in weather and climate research have demonstrated the role of the stratosphere in the Earth system across a wide range of temporal and spatial scales. Stratospheric ozone loss has been identified as a key driver of Southern Hemisphere tropospheric circulation trends, affecting ocean currents and carbon uptake, sea ice, and possibly even the Antarctic ice sheets. Stratospheric variability has also been shown to affect short-term and seasonal forecasts, connecting the tropics and midlatitudes and guiding storm-track dynamics. The two-way interactions between the stratosphere and the Earth system have motivated the World Climate Research Programme's (WCRP) Stratospheric Processes and their Role in Climate's (SPARC) activity on Modelling the Dynamics and Variability of the Stratosphere-Troposphere System (DynVar) to investigate the impact of stratospheric dynamics and variability on climate. This assessment will be made possible by two new multimodel datasets. First, roughly 10 models with a well-resolved stratosphere are participating in the Coupled Model Intercomparison Project phase 5 (CMIP5), providing the first multimodel ensemble of climate simulations coupled from the stratopause to the sea floor. Second, the Stratosphere Resolving Historical Forecast Project (Strat-HFP) of WCRP's Climate Variability and Predictability (CLIVAR) program is forming a multimodel set of seasonal hind-casts with stratosphere-resolving models, revealing the impact of both stratospheric initial conditions and dynamics on intraseasonal prediction. The CMIP5 and Strat-HFP model datasets will offer an unprecedented opportunity to understand the role of the stratosphere in the natural and forced variability of the Earth system and to determine whether incorporating knowledge of the middle atmosphere improves seasonal forecasts and climate projections.

AMO- and ENSO-Driven Summertime Circulation and Precipitation Variations in North America

Abstract Interannual and multidecadal time-scale anomalies in sea surface temperatures (SST) of the North Atlantic and North Pacific Oceans could result in persistent atmospheric circulation and regional precipitation anomalies for years to decades. Understanding the processes that connect such SST forcings with circulation and precipitation anomalies is thus important for understanding climate variations and for improving predictions at interannual–decadal time scales. This study focuses on the interrelationship between the Atlantic multidecadal oscillation (AMO) and El Niño–Southern Oscillation (ENSO) and their resulting interannual to multidecadal time-scale variations in summertime precipitation in North America. Major results show that the ENSO forcing can strongly modify the atmospheric circulation variations driven by the AMO. Moreover, these modifications differ considerably between the subtropics and the mid- and high-latitude regions. In the subtropics, ENSO-driven variations in precipitation are fairly uniform across longitudes so ENSO effects only add interannual variations to the amplitude of the precipitation anomaly pattern driven by the AMO. In the mid- and high latitudes, ENSO-forced waves in the atmosphere strongly modify the circulation anomalies driven by the AMO, resulting in distinctive interannual variations following the ENSO cycle. The role of the AMO is shown by an asymmetry in precipitation during ENSO between the warm and cold phases of the AMO. These results extend the outcomes of the studies of the recent Climate Variability and Predictability (CLIVAR) Drought Working Group from the AMO and ENSO effects on droughts to understanding of the mechanisms and causal processes connecting the individual and combined SST forcing of the AMO and ENSO with the interannual and multidecadal variations in summertime precipitation and droughts in North America.

The Madden–Julian Oscillation in CCSM4

Abstract This study assesses the ability of the Community Climate System Model, version 4 (CCSM4) to represent the Madden–Julian oscillation (MJO), the dominant mode of intraseasonal variability in the tropical atmosphere. The U.S. Climate Variability and Predictability (CLIVAR) MJO Working Group’s prescribed diagnostic tests are used to evaluate the model’s mean state, variance, and wavenumber–frequency characteristics in a 20-yr simulation of the intraseasonal variability in zonal winds at 850 hPa (U850) and 200 hPa (U200), and outgoing longwave radiation (OLR). Unlike its predecessor, CCSM4 reproduces a number of aspects of MJO behavior more realistically. The CCSM4 produces coherent, broadbanded, and energetic patterns in eastward-propagating intraseasonal zonal winds and OLR in the tropical Indian and Pacific Oceans that are generally consistent with MJO characteristics. Strong peaks occur in power spectra and coherence spectra with periods between 20 and 100 days and zonal wavenumbers between 1 and 3. Model MJOs, however, tend to be more broadbanded in frequency than in observations. Broad-scale patterns, as revealed in combined EOFs of U850, U200, and OLR, are remarkably consistent with observations and indicate that large-scale convergence–convection coupling occurs in the simulated MJO. Relations between MJO in the model and its concurrence with other climate states are also explored. MJO activity (defined as the percentage of time the MJO index exceeds 1.5) is enhanced during El Niño events compared to La Niña events, both in the model and observations. MJO activity is increased during periods of anomalously strong negative meridional wind shear in the Asian monsoon region and also during strong negative Indian Ocean zonal mode states, in both the model and observations.