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Annarita Mariotti

Abstract

An observational analysis of Mediterranean Sea water cycle variability based on recently available datasets provides new insights on the long-term changes that affected the region since the 1960s. Results indicate an overall increase in evaporation during 1958–2006, with a decrease up until the mid-1970s and an increase thereafter. Precipitation variability is characterized by substantial interdecadal variations and a negative long-term trend. Evaporation increase, primarily driven by SST variability, together with precipitation decrease resulted in a substantial increase in the loss of freshwater from the Mediterranean Sea toward the overlying atmosphere. An increase in the freshwater deficit is consistent with observed Mediterranean Sea salinity tendencies and has broad implications for the Mediterranean water cycle and connected systems.

These observational results are in qualitative agreement with simulated Mediterranean Sea water cycle behavior from a large ensemble of models from the Coupled Model Intercomparison Project Phase 3 (CMIP3). However, simulated anomalies are about one order of magnitude smaller than those observed. This inconsistency and the large uncertainties associated with the observational rates of change highlight the need for more research to better characterize and understand Mediterranean water cycle variations in recent decades, and to better simulate the crucial underlying processes in global models.

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Maria Vittoria Struglia, Annarita Mariotti, and Angelo Filograsso

Abstract

River discharge across the Mediterranean catchment basin is investigated by means of an extensive dataset of historical monthly time series to represent at-best discharge into the sea. Results give an annual mean river discharge into the Mediterranean of 8.1 × 103 m3 s−1, or at most a value that should not exceed 10.4 × 103 m3 s−1. The seasonal cycle has an amplitude of 5 × 103 m3 s−1, with a dry season in midsummer and a peak flow in early spring. Dominant contributions are from Europe with a climatological annual mean of 5.7 × 103 m3 s−1. Discharge in the Adriatic Sea, the Gulf of Lion, and the Aegean Sea together account for 62% of Mediterranean discharge, which mostly occurs in the Adriatic (2.7 × 103 m3 s−1).

The North Atlantic Oscillation (NAO) impacts Mediterranean discharge primarily in winter, with most river discharges across the Mediterranean catchment being anticorrelated with the NAO. Related winter anomalies are about 10%–20% of the winter means. During the period 1960–90, Mediterranean winter discharge as a whole may have undergone year-to-year NAO-related variations of up to 26% of the seasonal mean, while about 17% on decadal time scales. These variations are expected to have occurred mostly in the Gulf of Lion and the Adriatic Sea, together with the Balearic Sea, where the impact of the NAO is greatest.

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Ning Zeng, Jin-Ho Yoon, Annarita Mariotti, and Sean Swenson

Abstract

In an approach termed the PER method, where the key input variables are observed precipitation P and runoff R and estimated evaporation, the authors apply the basin water budget equation to diagnose the long-term variability of the total terrestrial water storage (TWS). Unlike the typical offline land surface model estimate where only atmospheric variables are used as input, the direct use of observed runoff in the PER method imposes an important constraint on the diagnosed TWS. Although there is a lack of basin-scale observations of evaporation, the tendency of E to have significantly less variability than the difference between precipitation and runoff (PR) minimizes the uncertainties originating from estimated evaporation. Compared to the more traditional method using atmospheric moisture convergence (MC) minus R (MCR method), the use of observed precipitation in the PER method is expected to lead to general improvement, especially in regions where atmospheric radiosonde data are too sparse to constrain the atmospheric model analyzed MC, such as in the remote tropics.

TWS was diagnosed using the PER method for the Amazon (1970–2006) and the Mississippi basin (1928–2006) and compared with the MCR method, land surface model and reanalyses, and NASA’s Gravity Recovery and Climate Experiment (GRACE) satellite gravity data. The seasonal cycle of diagnosed TWS over the Amazon is about 300 mm. The interannual TWS variability in these two basins is 100–200 mm, but multidecadal changes can be as large as 600–800 mm. Major droughts, such as the Dust Bowl period, had large impacts, with water storage depleted by 500 mm over a decade. Within the short period 2003–06 when GRACE data were available, PER and GRACE show good agreement both for seasonal cycle and interannual variability, providing potential to cross validate each other. In contrast, land surface model results are significantly smaller than PER and GRACE, especially toward longer time scales. While the authors currently lack independent means to verify these long-term changes, simple error analysis using three precipitation datasets and three evaporation estimates suggest that the multidecadal amplitude can be uncertain up to a factor of 2, while the agreement is high on interannual time scales. The large TWS variability implies the remarkable capacity of land surface in storing and taking up water that may be underrepresented in models. The results also suggest the existence of water storage memories on multiyear time scales, significantly longer than typically assumed seasonal time scales associated with surface soil moisture.

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Annarita Mariotti, Maria Vittoria Struglia, Ning Zeng, and K-M. Lau

Abstract

The hydrological cycle in the Mediterranean region is analyzed focusing on climatology and interannual to interdecadal variability, in particular long-term changes related to the well-established North Atlantic Oscillation (NAO) teleconnection. Recent atmospheric reanalyses and observational datasets are used: precipitation, evaporation, and moisture flux from 50 yr of NCEP's and 15 yr of ECMWF's reanalyses; precipitation from the Climate Prediction Center Merged Analysis of Precipitation (CMAP) and the East Anglia University Climate Research Unit (CRU) datasets; and evaporation from the University of Wisconsin—Milwaukee (UWM) Comprehensive Ocean–Atmosphere Data Set (COADS). A budget analysis is performed to study contributions to the freshwater flux into the Mediterranean Sea, including atmospheric as well as river discharge inputs. The total river discharge is derived using historical time series from Mediterranean Hydrological Cycle Observing System (MED-HYCOS) and Global Runoff Data Center (GRDC) archives.

Mediterranean-averaged precipitation during the period 1979–93 has an annual mean ranging among datasets from 331 to 477 mm yr−1, with a seasonal cycle amplitude of ∼700 mm yr−1. Evaporation is estimated in the range of 934–1176 mm yr−1 with a seasonal cycle amplitude of ∼1000 mm yr−1. The excess of evaporation over precipitation gives an annual mean Mediterranean Sea water loss ranging among datasets approximately from 500 to 700 mm yr−1. The annual mean river discharge is 100 mm yr−1, somewhat smaller than previous estimates using similar approaches. Water loss to the atmosphere and riverine inputs combined lead to an estimated Mediterranean freshwater deficit of about 500 mm yr−1, consistent with most oceanographically based estimates of the water flux from the Atlantic Ocean at the Gibraltar Strait.

On interannual to interdecadal timescales, during the period 1948–98, the Mediterranean atmospheric winter water deficit is positively correlated with the NAO and has been increasing due to the long-term positive anomalies of the NAO since the early 1970s. Precipitation, which is also significantly correlated with the NAO, appears to be mostly responsible for this since no significant correlation is found for evaporation. Over the 50-yr period the Mediterranean atmospheric water deficit increased by about 24% in the winter season, and by 9% annually. Given the pattern of the NAO-related precipitation anomalies, this change is likely to have occurred primarily north of 35°N. The results presented here suggest that in response to the changes in the freshwater flux significant variations in the characteristics of Mediterranean waters and the Gibraltar flux may also have occurred during this period, mostly driven by the influence of the NAO.

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Annarita Mariotti, Carlos R. Mechoso, Bernard Legras, and Vincent Daniel

Abstract

The ozone evolution in the lower stratosphere of the Southern Hemisphere during the period 5–10 August 1994 is analyzed. The analysis focuses on the ozone “collar” (the band of maximum values in ozone mixing ratio around the Antarctic ozone “hole” at these altitudes) and the development of “collar filaments.” Ozone mixing ratios provided by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite and by an ER-2 aircraft participating in the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft campaign are compared with values at corresponding locations in high-resolution isentropic maps obtained by using the numerical scheme of “contour advection with surgery” (CAS).

The CAS reconstructed ozone maps provide a view of the way in which air masses are exported from the outskirts of the collar to form the “tongues” of higher mixing ratios observed at lower latitudes on MLS synoptic maps. There is an overall consistency between the datasets insofar as the collar location is concerned. This location seems to be primarily defined by the local properties of the flow. Nevertheless the CAS reconstructed collar tends to become weaker than that depicted by MLS data. By means of radiative calculation estimates, it is argued that diabatic descent may be responsible for maintaining the ozone concentration approximately constant in the collar while filaments isentropically disperse collarlike mixing ratios from this region toward lower latitudes.

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Annarita Mariotti, John Dunne, Jason Link, Hendrik Tolman, Kevin Garrett, Derrick Snowden, and Timothy Schneider

2018 NOAA GENERAL MODELING MEETING AND FAIR

What: Nearly 200 scientists and managers from government, academia, and private industry convened for this inaugural event to learn about unified modeling across the National Oceanic and Atmospheric Administration (NOAA) for weather, climate, fisheries, oceans, and coasts across all relevant disciplines, share ideas on how to advance activities, and network with other modeling professionals.

When: 10–12 September 2018

Where: NOAA Center for Weather and Climate Prediction, College Park, MD

The 2018 NOAA Modeling Meeting and Fair 1 brought together experts across many different modeling disciplines to share lessons learned,

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Annarita Mariotti, Siegfried Schubert, Kingtse Mo, Christa Peters-Lidard, Andy Wood, Roger Pulwarty, Jin Huang, and Dan Barrie

Having the capacity to monitor droughts in near–real time and providing accurate drought prediction from weeks to seasons in advance can greatly reduce the severity of social and economic damage caused by drought, a leading natural hazard for North America. The congressional mandate to establish the National Integrated Drought Information System (NIDIS; Public Law 109–430) in 2006 was a major impulse to develop, integrate, and provide drought information to meet the challenges posed by this hazard. Significant progress has been made on many fronts. On the research front, efforts by the broad scientific community have resulted in improved understanding of

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Eric F. Wood, Siegfried D. Schubert, Andrew W. Wood, Christa D. Peters-Lidard, Kingtse C. Mo, Annarita Mariotti, and Roger S. Pulwarty

Abstract

This paper summarizes and synthesizes the research carried out under the NOAA Drought Task Force (DTF) and submitted in this special collection. The DTF is organized and supported by NOAA’s Climate Program Office with the National Integrated Drought Information System (NIDIS) and involves scientists from across NOAA, academia, and other agencies. The synthesis includes an assessment of successes and remaining challenges in monitoring and prediction capabilities, as well as a perspective of the current understanding of North American drought and key research gaps. Results from the DTF papers indicate that key successes for drought monitoring include the application of modern land surface hydrological models that can be used for objective drought analysis, including extended retrospective forcing datasets to support hydrologic reanalyses, and the expansion of near-real-time satellite-based monitoring and analyses, particularly those describing vegetation and evapotranspiration. In the area of drought prediction, successes highlighted in the papers include the development of the North American Multimodel Ensemble (NMME) suite of seasonal model forecasts, an established basis for the importance of La Niña in drought events over the southern Great Plains, and an appreciation of the role of internal atmospheric variability related to drought events. Despite such progress, there are still important limitations in our ability to predict various aspects of drought, including onset, duration, severity, and recovery. Critical challenges include (i) the development of objective, science-based integration approaches for merging multiple information sources; (ii) long, consistent hydrometeorological records to better characterize drought; and (iii) extending skillful precipitation forecasts beyond a 1-month lead time.

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Annarita Mariotti, Cory Baggett, Elizabeth A. Barnes, Emily Becker, Amy Butler, Dan C. Collins, Paul A. Dirmeyer, Laura Ferranti, Nathaniel C. Johnson, Jeanine Jones, Ben P. Kirtman, Andrea L. Lang, Andrea Molod, Matthew Newman, Andrew W. Robertson, Siegfried Schubert, Duane E. Waliser, and John Albers

Abstract

There is high demand and a growing expectation for predictions of environmental conditions that go beyond 0–14-day weather forecasts with outlooks extending to one or more seasons and beyond. This is driven by the needs of the energy, water management, and agriculture sectors, to name a few. There is an increasing realization that, unlike weather forecasts, prediction skill on longer time scales can leverage specific climate phenomena or conditions for a predictable signal above the weather noise. Currently, it is understood that these conditions are intermittent in time and have spatially heterogeneous impacts on skill, hence providing strategic windows of opportunity for skillful forecasts. Research points to such windows of opportunity, including El Niño or La Niña events, active periods of the Madden–Julian oscillation, disruptions of the stratospheric polar vortex, when certain large-scale atmospheric regimes are in place, or when persistent anomalies occur in the ocean or land surface. Gains could be obtained by increasingly developing prediction tools and metrics that strategically target these specific windows of opportunity. Across the globe, reevaluating forecasts in this manner could find value in forecasts previously discarded as not skillful. Users’ expectations for prediction skill could be more adequately met, as they are better aware of when and where to expect skill and if the prediction is actionable. Given that there is still untapped potential, in terms of process understanding and prediction methodologies, it is safe to expect that in the future forecast opportunities will expand. Process research and the development of innovative methodologies will aid such progress.

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Justin Sheffield, Suzana J. Camargo, Rong Fu, Qi Hu, Xianan Jiang, Nathaniel Johnson, Kristopher B. Karnauskas, Seon Tae Kim, Jim Kinter, Sanjiv Kumar, Baird Langenbrunner, Eric Maloney, Annarita Mariotti, Joyce E. Meyerson, J. David Neelin, Sumant Nigam, Zaitao Pan, Alfredo Ruiz-Barradas, Richard Seager, Yolande L. Serra, De-Zheng Sun, Chunzai Wang, Shang-Ping Xie, Jin-Yi Yu, Tao Zhang, and Ming Zhao

Abstract

This is the second part of a three-part paper on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that evaluates the twentieth-century simulations of intraseasonal to multidecadal variability and teleconnections with North American climate. Overall, the multimodel ensemble does reasonably well at reproducing observed variability in several aspects, but it does less well at capturing observed teleconnections, with implications for future projections examined in part three of this paper. In terms of intraseasonal variability, almost half of the models examined can reproduce observed variability in the eastern Pacific and most models capture the midsummer drought over Central America. The multimodel mean replicates the density of traveling tropical synoptic-scale disturbances but with large spread among the models. On the other hand, the coarse resolution of the models means that tropical cyclone frequencies are underpredicted in the Atlantic and eastern North Pacific. The frequency and mean amplitude of ENSO are generally well reproduced, although teleconnections with North American climate are widely varying among models and only a few models can reproduce the east and central Pacific types of ENSO and connections with U.S. winter temperatures. The models capture the spatial pattern of Pacific decadal oscillation (PDO) variability and its influence on continental temperature and West Coast precipitation but less well for the wintertime precipitation. The spatial representation of the Atlantic multidecadal oscillation (AMO) is reasonable, but the magnitude of SST anomalies and teleconnections are poorly reproduced. Multidecadal trends such as the warming hole over the central–southeastern United States and precipitation increases are not replicated by the models, suggesting that observed changes are linked to natural variability.

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