Mihai Dima

University of Bucharest | Unibuc · Department of Matter Structure, Earth and Atmospheric Physics, and Astrophysics

The proximity of the states of climatic tipping components to bifurcation points, which could mark the emergence of rapid and irreversible transitions, is a subject of major concern in the context of anthropogenic influence on climate. Among such systems, the Atlantic Meridional Overturning Circulation has one of the largest climatic impact and it...

Due to its involvement in numerous feedbacks, sea ice plays a crucial role not only for polar climate but also at global scale. We analyse state-of-the-art observed, reconstructed, and modelled sea-ice concentration (SIC) together with sea surface temperature (SST) to disentangle the influence of different forcing factors on the variability of thes...

The Atlantic Meridional Overturning Circulation (AMOC) is a tipping component of the climate system, with a quasi-global impact. Several numerical and observational studies emphasized two modes of AMOC variability, characterized by two distinct Atlantic sea surface temperature patterns. One is associated with centennial changes, the Trend Mode, and...

Study region Europe, with a particular focus on the Czech Republic, Poland, Spain, and Norway. Study focus Long-lasting droughts have become a semi-permanent feature of the European climate, especially over the last two decades. These prolonged droughts are usually driven by persistent sea surface temperature anomalies over the Pacific and Atlanti...

The Atlantic Meridional Overturning Circulation (AMOC), a tipping component of the climate system, is projected to slowdown during the 21st century in response to increased atmospheric CO 2 concentration. The rate and start of the weakening are associated with relatively large uncertainties. Observed sea surface temperature-based reconstructions in...

Megadroughts are notable manifestations of the American Southwest, but not so much of the European climate. By using long-term hydrological and meteorological observations, as well as paleoclimate reconstructions, here we show that central Europe has experienced much longer and severe droughts during the Spörer Minimum (~AD 1400-1480) and Dalton Mi...

Variations of the global sea level pressure (SLP) field reflect atmospheric and oceanic influences and have a profound influence on temperature, precipitation and the global carbon cycle. The impact of various forcing factors on this field was investigated mainly based on numerical simulations. Alternatively, here we identify and quantify the influ...

Teleconnections refer to links between regions that are distant to each other, but nevertheless exhibit some relation. The study of such teleconnections is a well-known task in climate research. Climate simulation shall model known teleconnections. Detecting teleconnections in climate simulations is a crucial aspect in judging the quality of the si...

Due to the complexity of the physical processes responsible for cloud formation and to the relatively short satellite database of continuous data records, cloud behavior in a warming climate remains uncertain. Identifying physical links between climate modes and clouds would contribute not only to a better understanding of the physical processes go...

Traditional analyses of geoscientific data and their features require a lot of manual scripting to organize various tools and software libraries. We present a tool developed to cover the typical workflow of the task of analyzing dependencies between regions of the climate system. We propose an interactive visual analysis tool that uses a series of...

The impact of large-scale modes on Iraq climate is investigated here based on winter and spring fields of temperature and precipitation. The temperature data (1971–2010) was recorded at 8 stations whereas the precipitation fields (1981–2010) were recorded at 18 locations. Empirical orthogonal function analyses were performed in order to characteriz...

We investigate the connections of the North Atlantic and Indian Ocean sectors with Iraq winter/summer temperature and precipitation. Canonical Correlation Analyses (CCAs) are performed in order to identify potential links between Iraq climate and the atmospheric circulation over these two regions. Regression maps of 200 hPa and 500 hPa geopotential...

Bivalve shells are reliable bio-archives for sub-annual to multi-decadal climate reconstructions. The well-established and calibrated bivalve species Arctica islandica is long-lived (500 years), abundant in the fossil record and widely distributed in the North Atlantic. The reconstruction of atmosphere-ocean phenomena, such as NAO, has been demonst...

As a key persistent component of the atmospheric dynamics, the North Atlantic blocking activity has been linked to extreme climatic phenomena in the European sector. It has also been linked to Atlantic multidecadal ocean variability, but its potential links to rapid oceanic changes have not been investigated. Using a global ocean-sea ice model forc...

One of the main sources of uncertainty in climate projections is represented by clouds, which have a profound influence on the Earth’s radiation budget through the feedbacks in which they are involved. The improvement of clouds representation in General Circulation Models relies largely on constraints derived from observations and on correct identi...

A significant increase in sea surface temperature (SST) is observed over the mid-latitude western boundary currents (WBCs) during the past century. However, the mechanism for this phenomenon remains poorly understood due to limited observations. In the present paper, several coupled parameters (i.e., sea surface temperature (SST), ocean surface hea...

In this study we have examined the spatial and temporal variability of mean temperature (0C) and precipitation (mm) in winter (DJF) and spring (MAM) in Iraq. The data used were recorded at 12 stations for temperature and 18stations for precipitation over the period 1981-2010. An empirical orthogonal function (EOFs) and principal component (PCs) ana...

Fram Strait sea ice export from the Arctic represents a key source of fresh water for the North Atlantic. Although it may have strong influence on the ocean circulation, its causes and consequences are not yet fully understood. Using a global ocean-sea ice model with an increased resolution over the Arctic, here it is shown that enhanced blocking a...

Over the past decades Europe has experienced heavy floods with major consequences for thousands of people and billions of Euros worth of damage. In particular, the summer 2013 flood in Central Europe showed how vulnerable modern society is to hydrological extremes and emphasizes once more the need for improved forecast methods of such extreme clima...

The most intense El Niño episodes in more than a century occurred after the 1970s climate shift. Previous studies show that the characteristics of the El Niño-Southern Oscillation (ENSO) phenomenon changed synchronously with the shift, but the associated causes are not fully understood. An analysis of the observed tropical Pacific sea surface tempe...

Bivalve shells are reliable bio-archives for sub-annual to multi-decadal climate reconstructions. The well-established and calibrated bivalve species Arctica islandica is long-lived (400 yrs), abundant in the fossil record and widely distributed in the North Atlantic. The reconstruction of atmosphere-ocean phenomena, such as NAO, has been demonstra...

Interannual to decadal variability of European summer drought and its relationship with global sea surface temperature (SST) is investigated using the newly developed self calibrated Palmer drought severity index (scPDSI) and global sea surface temperature (SST) field for the period 1901–2002. A European drought severity index defined as the averag...

The internal variability of the global meridional overturning circulation (GMOC) in long-term integration of the earth system model Community Earth System Models (COSMOS) is examined in this study. Two distinct modes of the GMOC, which are closely linked to the Southern Hemisphere westerly winds (SWW) anomalies, are found to vary on multidecadal an...

The second half of the 20th century showed a series of decadal-scale anomalies of salinity, temperature and sea ice cover in the northern North Atlantic. One pronounced event, the 'great salinity anomaly' (GSA) is observed in the late 1060s and the early 1970s (Dickson et al., 1988). This anomaly can be linked to the sea ice volume out of the Arcti...

On the basis of the multidecadal component of a Fram Strait sea ice export reconstruction and on a sea surface temperature proxy for changes in the ocean circulation, a bifurcation diagram for two cycles of the Atlantic Ocean multidecadal oscillation is constructed. It suggests a hysteresis behavior that is consistent with nonlinear convective adju...

Interannual and seasonal predictability of Danube river discharge is investigated using three model types: 1) time series models 2) linear regression models of discharge with large-scale climate mode indices and 3) models based on stable teleconnections. All models are calibrated using discharge and climatic data for the period 1901-1977 and valida...

Through its nonlinear dynamics and involvement in past abrupt climate shifts the thermohaline circulation (THC) represents a key element for the understanding of rapid climate changes. The expected THC weakening under global warming is characterized by large uncertainties, and it is therefore of significant importance to identify ocean circulation...

Near-shore waters along the northwest African margin are characterized by coastal upwelling and represent one of the world's major upwelling regions. Sea surface temperature (SST) records from Moroccan sediment cores, extending back 2500 years, reveal anomalous and unprecedented cooling during the 20th century, which is consistent with increased up...

Instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century. Unlike for temperature, continuous salinity observations in the surface ocean are scarce prior to 1970, and the magnitude of salinity changes during the twentieth century is largely unknown. Surface ocean salinity is a major...

This study focuses on analyzing the statistical behavior of Elbe river streamflow and the identification of the main circulation patterns associated with extreme events in Elbe's catchment area, on seasonal timescale. To identify the threshold, which defines an extreme event, we have made use of Peak over Threshold method and the 90% and 95% percen...

Instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century. Unlike for temperature, continuous salinity observations in the surface ocean are scarce prior to 1970, and the magnitude of salinity changes during the twentieth century is largely unknown. Surface ocean salinity is a major...

Dansgaard-Oeschger and Heinrich events are the most pronounced climatic changes over the last 120,000years. Although many of their properties were derived from climate reconstructions, the associated physical mechanisms are not yet fully understood. These events are paced by a ~1,500-year periodicity whose origin remains unclear. In a conceptual mo...

The physical processes associated with the 70-yr period climate mode, known as the Atlantic multidec- adal oscillation (AMO), are examined. Based on analyses of observational data, a deterministic mechanism relying on atmosphere-ocean-sea ice interactions is proposed for the AMO. Variations in the thermohaline circulation are reflected as uniform s...

Near-shore waters along the northwest African margin are characterized by coastal upwelling and represent one of the world's major upwelling regions. Sea surface temperature (SST) records from Moroccan sediment cores, extending back 2500 years, reveal anomalous and unprecedented cooling during the 20th century, which is consistent with increased up...

It is shown that spring Danube flow anomalies are significantly related to winter SST anomalies from several key regions. These areas are identified through stable teleconnections between flow and SST. A forecast scheme is developed and applied to predict flow anomalies using SST anomalies from these key regions. Small potential predictability of w...

Proxy data can bring observed climate variability of the last 100 years into a long-term context. We identify regions of the Northern Hemisphere where the teleconnection patterns of the Arctic Oscillation are stationary. Our method provides a systematic way to examine optimal sites for the reconstruction of climate modes based on paleoclimatic arch...

Statistical analyses of long-term instrumental and proxy data emphasize a distinction between two quasi-decadal modes of climate variability. One mode is linked to atmosphere–ocean interactions ('the internal mode') and the other one is associated with the solar sunspots cycle ('the solar mode'). The distinct signatures of these two modes are also...

The Rarotonga coral Sr/Ca time series (Linsley et al. in Science 290:1145–1148, 2000) provides a near-monthly resolved proxy record of South Pacific climate variability over the last ~300years. Here we show that two distinct interdecadal, quasi-periodic time components with periods of ~80 and ~25years can be identified in this time series by Singul...

Based on analysis of observational data we show that the impact of the North Atlantic Oscillation (NAO) and El Niño–Southern Oscillation (ENSO) on the Danube river flow variability shows important decadal variations. A lag-correlation analysis reveals that winter SST from tropical Pacific and some regions from the North Atlantic are significantly c...

The signature of solar irradiance variations on decadal-to-centennial climate variability is analysed by means of statistical analysis of long-term instrumental, historical, and proxy data sets. Solar variations associated with the Schwabe, Hale, and Gleissberg cycles are detected by their spatial patterns in sea-surface temperature and sea-level p...

The notion of mode interaction is proposed as a deterministic concept for understanding climatic modes at various time-scales. This concept is based on the distinction between fundamental modes relying on their own physical mechanisms and derived modes that emerge from the interaction of two other modes. The notion is introduced and applied to inte...

The notion of mode interaction is proposed as a deterministic concept for understanding climatic modes at various timescales. This concept is based on the distinction between fundamental modes relying on their own physical mechanisms and derived modes that emerge from the interaction of two other modes. The notion is introduced and applied to inter...

Sediment records from the Cariaco Basin and Greenland ice core records provide a millennial record of ocean-atmosphere variability in the North Atlantic Basin. These records with yearly resolution provide strong decadal to centennial climate variabilty. Here, the distinct modes of documented variability sea surface temperature and pressure are foun...

The decadal variability (>5 years) of the Danube river flow in the lower basin and its connection with the North Atlantic Oscillation (NAO) is analysed for the period 1931–95. Associated linkages with precipitation (PP) in the European sector, global sea surface temperature (SST) and atmospheric circulation for the period 1931–81, and the 500 hPa g...

We investigate the structure of the Northern Hemisphere atmospheric circulation anomaly patterns associated with the dominant mode of interannual variability in the Tropical Pacific and the dominant mode of quasi-decadal variability in the Atlantic basin. There is evidence that the superposition of the atmospheric patterns associated with these mod...

Recent studies suggest that, interannual, decadal, and quasibidecadal periodicities dominate global sea surface temperature and sea level pressure variability over past hundred years. In this study, we present evidence that the quasibidecadal mode of variability can be considered in a first order approximation as resulting from a linear interaction...

Observational data are used to emphasise a 5- to 7-yr lag between the main modes of variability in the midlatitudes and in the Tropics. Considering this finding a mechanism for quasidecadal variability based on Tropics-midlatitudes and ocean-atmosphere interaction is described. It appears that the signal associated with the SST anomalies in the nor...

The role of anomalous Indian Ocean sea surface temperature (SST) in forcing east African rainfall anomalies during December-January 1997/98 has been investigated by means of atmospheric model response experiments. It is shown that the strong precipitation anomalies that led to severe flooding over eastern equatorial Africa can be directly related t...