Monica Ionita

Prediction of Spring Elbe Discharge Based on Stable Teleconnections with Winter Global Temperature and Precipitation

Abstract The predictability of Elbe streamflow anomalies during spring is examined using previous winter sea surface temperature (SST), temperature over land (TT), and precipitation (PP) anomalies. Based on running correlation analysis, the authors identify several regions where the spring streamflow anomalies are stable correlated with SST, TT, and PP anomalies from the previous winter. During the period 1902–71 the Elbe spring streamflow is stable correlated with previous winter PP anomalies from its catchment area, with TT anomalies from the Black Sea–Caspian Sea region, northwestern Europe, and northern Canada as well as with SST anomalies from the tropical Pacific, the Indian Ocean, and several regions of the North Pacific and the North Atlantic. An index based on winter SST, TT, and PP anomalies from these regions is highly significantly correlated with spring streamflow anomalies during this period. Based on SST, TT, and PP anomalies from stable correlated regions, a forecast scheme is developed an...

Intensification and poleward shift of subtropical western boundary currents in a warming climate

A significant increase in sea surface temperature (SST) is observed over the midlatitude 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 heat fluxes, ocean water velocity, ocean surface winds and sea level pressure (SLP)) are analyzed to identify the dynamic changes of the WBCs. Three types of independent data sets are used, including reanalysis products, satellite-blended observations. and climate model outputs from the fifth phase of the Climate Model Intercomparison Project (CMIP5). Based on these broad ranges of data, we find that the WBCs (except the Gulf Stream) are intensifying and shifting toward the poles as long-term effects of global warming. An intensification and poleward shift of near-surface ocean winds, attributed to positive annular mode-like trends, are proposed to be the forcing of such dynamic changes. In contrast to the other WBCs, the Gulf Stream is expected to be weaker under global warming, which is most likely related to a weakening of the Atlantic Meridional Overturning Circulation (AMOC). However, we also notice that the natural variations of WBCs might conceal the long-term effect of global warming in the available observational data sets, especially over the Northern Hemisphere. Therefore, long-term observations or proxy data are necessary to further evaluate the dynamics of the WBCs.

Multidecadal variability of summer temperature over Romania and its relation with Atlantic Multidecadal Oscillation

We investigate the multidecadal variability of summer temperature over Romania as measured at 14 meteorological stations with long-term observational records. The dominant pattern of summer temperature variability has a monopolar structure and shows pronounced multidecadal variations. A correlation analysis reveals that these multidecadal variations are related with multidecadal variations in the frequency of four daily atmospheric circulation patterns from the North Atlantic region. It is found that on multidecadal time scales, negative summer mean temperature (TT) anomalies are associated with positive sea level pressure (SLP) anomalies centered over the northern part of the Atlantic Ocean and Scandinavia and negative SLP anomalies centered over the northern part of Africa. It is speculated that a possible cause of multidecadal fluctuations in the frequency of these four patterns are the sea surface temperature (SST) anomalies associated to the Atlantic Multidecadal Oscillation (AMO). These results have implications for predicting the evolution of summer temperature over Romania on multidecadal time scales.

Interannual Variability of Rhine River Streamflow and Its Relationship with Large-Scale Anomaly Patterns in Spring and Autumn

AbstractInterannual-to-decadal variability of Rhine River streamflow and their relationship with large-scale climate anomaly patterns for spring [March–May (MAM)] and autumn [September–November (SON)] are investigated through a statistical analysis of observed streamflow data and global climate anomaly fields. A wavelet analysis reveals that spring streamflow variability is nonstationary with enhanced variability in the 8–16-yr band from 1860 to 1900 and in the 2–8 and 16–30 yr after 1960. A composite analysis reveals that streamflow anomalies during spring are related to a sea surface temperature (SST) pattern that resembles the corresponding El Nino–Southern Oscillation (ENSO) SST pattern. The corresponding atmospheric circulation pattern favors enhanced moisture advection over the Rhine catchment area during positive streamflow anomalies. During autumn, the streamflow variability follows a distribution similar to spring streamflow, but with a strong peak in the 30–60-yr band. Autumn streamflow anomalie...

Predicting the June 2013 European Flooding Based on Precipitation, Soil Moisture, and Sea Level Pressure

AbstractOver recent decades Europe has experienced heavy floods, with major consequences for thousands of people and billions of euros worth of damage. In particular, the summer of 2013 flood in central Europe showed how vulnerable modern society is to hydrological extremes and emphasized once more the need for improved forecast methods of such extreme climatic events. Based on a multiple linear regression model, it is shown here that 55% of the June 2013 Elbe River extreme discharge could have been predicted using May precipitation, soil moisture, and sea level pressure. Moreover, the model was able to predict more than 75% of the total Elbe River discharge for June 2013 (in terms of magnitude) by also incorporating the amount of precipitation recorded during the days prior to the flood, but the predicted discharge for the June 2013 event was still underestimated by 25%. Given that all predictors used in the model are available at the end of each month, the forecast scheme can be used to predict extreme ...

Holocene winter climate variability in Central and Eastern Europe

Among abundant reconstructions of Holocene climate in Europe, only a handful has addressed winter conditions, and most of these are restricted in length and/or resolution. Here we present a record of late autumn through early winter air temperature and moisture source changes in East-Central Europe for the Holocene, based on stable isotopic analysis of an ice core recovered from a cave in the Romanian Carpathian Mountains. During the past 10,000 years, reconstructed temperature changes followed insolation, with a minimum in the early Holocene, followed by gradual and continuous increase towards the mid-to-late-Holocene peak (between 4-2 kcal BP), and finally by a decrease after 0.8 kcal BP towards a minimum during the Little Ice Age (AD 1300–1850). Reconstructed early Holocene atmospheric circulation patterns were similar to those characteristics of the negative phase of the North Atlantic Oscillation (NAO), while in the late Holocene they resembled those prevailing in the positive NAO phase. The transition between the two regimes occurred abruptly at around 4.7 kcal BP. Remarkably, the widespread cooling at 8.2 kcal BP is not seen very well as a temperature change, but as a shift in moisture source, suggesting weaker westerlies and increased Mediterranean cyclones penetrating northward at this time.

Interannual to multidecadal Euro‐Atlantic blocking variability during winter and its relationship with extreme low temperatures in Europe

The dominant modes of blocking frequency variability in the Atlantic-European region are evaluated for the 1871–2010 period. An Empirical Orthogonal Function (EOF) analysis of a two-dimensional blocking indicator field reveals three dominant EOFs, describing about 35% of interannual to multidecadal blocking variability. The first EOF captures an out-of-phase blocking frequency anomaly over Greenland and Western Europe regions. The corresponding principal component time series is strongly correlated with the North Atlantic Oscillation index but shows also significant correlations with indices of the East Atlantic, Scandinavian, and East Atlantic-Western Russia patterns. The second EOF shows a dominant center over the North Sea region as well as a less pronounced center with anomalies of the same sign over southeastern Greenland. The multidecadal variations of this mode of blocking variability are related with a basin wide North Atlantic sea surface temperature anomaly which projects partly on the Atlantic Multidecadal Oscillation (AMO). The third mode is an east-west dipole of blocking frequency anomalies from Scandinavian and southern Greenland regions and shows enhanced variability at ~20 year time scales. The coherent variations of the time coefficients of this pattern with open solar flux suggest a possible solar influence on blocking variability at these time scales. Furthermore, the dominant patterns of blocking variability are related with distinct anomaly patterns in the occurrence of extreme low temperature events over Europe at interannual to multidecadal time scales. AMO as well as the solar signals was detected also in the corresponding extreme low temperature blocking patterns. We argue that multivariate analysis of blocking indicators gives additional information about blocking and related extreme climate phenomena variability and predictability comparative with classical sectorial approach.

Evaluation of Labrador Sea Water formation in a global Finite-Element Sea-Ice Ocean Model setup, based on a comparison with observational data

The deep water formation in the Labrador Sea is simulated with the Finite-Element Sea-Ice Ocean Model (FESOM) in a regionally focused, but globally covered model setup. The model has a regional resolution of up to 7 km, and the simulations cover the time period 1958–2009. We evaluate the capability of the model setup to reproduce a realistic deep water formation in the Labrador Sea. Two classes of modeled Labrador Sea Water (LSW), the lighter upper LSW (uLSW) and the denser deep LSW (dLSW), are analyzed. Their layer thicknesses are compared to uLSW and dLSW layer thicknesses derived from observations in the formation region for the time interval 1988–2009. The results indicate a suitable agreement between the modeled and observational derived uLSW and dLSW layer thicknesses except for the period 2003–2007 where deviations in the modeled and observational derived layer thicknesses could be linked to discrepancies in the atmospheric forcing of the model. It is shown that the model is able to reproduce four phases in the temporal evolution of the potential density, temperature, and salinity, since the late 1980s, which are known in observational data. These four phases are characterized by a significantly different LSW formation. The first phase from 1988 to 1990 is characterized in the model by a fast increase in the convection depth of up to 2000 m, accompanied by an increased spring production of deep Labrador Sea Water (dLSW). In the second phase (1991–1994), the dLSW layer thickness remains on a high level for several years, while the third phase (1995–1998) features a gradual decrease in the deep ventilation and the renewal of the deep ocean layers. The fourth phase from 1999 to 2009 is characterized by a slowly continuing decrease of the dLSW layer thickness on a deeper depth level. By applying a composite map analysis between an index of dLSW and sea level pressure over the entire simulation period from 1958 to 2009, it is shown that a pattern which resembles the structure of the North Atlantic Oscillation (NAO) is one of the main triggers for the variability of LSW formation. Our model results indicate that the process of dLSW formation can act as a low-pass filter to the atmospheric forcing, so that only persistent NAO events have an effect, whether uLSW or dLSW is formed. Based on composite maps of the thermal and haline contributions to the surface density flux we can demonstrate that the central Labrador Sea in the model is dominated by the thermal contributions of the surface density flux, while the haline contributions are stronger over the branch of the Labrador Sea boundary current system (LSBCS), where they are dominated by the haline contributions of sea ice melting and formation. Our model results feature a shielding of the central Labrador Sea from the haline contributions by the LSBCS, which only allows a minor haline interaction with the central Labrador Sea by lateral mixing. Based on the comparison of the simulated and measured LSW layer thicknesses as well as vertical profiles of potential density, temperature, and salinity it is shown that the FESOM model is a suitable tool to study the regional dynamics of LSW formation and its impact on a global, not regional restricted, scale.

Evidence of long-term NAO influence on East-Central Europe winter precipitation from a guano-derived δ 15 N record

Currently there is a scarcity of paleo-records related to the North Atlantic Oscillation (NAO), particularly in East-Central Europe (ECE). Here we report δ15N analysis of guano from a cave in NW Romania with the intent of reconstructing past variation in ECE hydroclimate and examine NAO impacts on winter precipitation. We argue that the δ15N values of guano indicate that the nitrogen cycle is hydrologically controlled and the δ15N values likely reflect winter precipitation related to nitrogen mineralization prior to the growing season. Drier conditions indicated by δ15N values at AD 1848–1852 and AD 1880–1930 correspond to the positive phase of the NAO. The increased frequency of negative phases of the NAO between AD 1940–1975 is contemporaneous with higher δ15N values (wetter conditions). A 4‰ decrease in δ15N values at the end of the 1970’s corresponds to a strong reduction in precipitation associated with a shift from negative to positive phase of the NAO. Using the relationship between NAO index and δ15N values in guano for the instrumental period, we reconstructed NAO-like phases back to AD 1650. Our results advocate that δ15N values of guano offer a proxy of the NAO conditions in the more distant past, helping assess its predictability.

Daily to intraseasonal oscillations at Antarctic research station Neumayer

Abstract High temporal resolution (three hours) records of temperature, wind speed and sea level pressure recorded at Antarctic research station Neumayer (70°S, 8°W) during 1982–2011 are analysed to identify oscillations from daily to intraseasonal timescales. The diurnal cycle dominates the three-hourly time series of temperature during the Antarctic summer and is almost absent during winter. In contrast, the three-hourly time series of wind speed and sea level pressure show a weak diurnal cycle. The dominant pattern of the intraseasonal variability of these quantities, which captures the out-of-phase variation of temperature and wind speed with sea level pressure, shows enhanced variability at timescales of ∼ 40 days and ∼ 80 days, respectively. Correlation and composite analysis reveal that these oscillations may be related to tropical intraseasonal oscillations via large-scale eastward propagating atmospheric circulation wave-trains. The second pattern of intraseasonal variability, which captures in-phase variations of temperature, wind and sea level pressure, shows enhanced variability at timescales of ∼ 35, ∼ 60 and ∼ 120 days. These oscillations are attributed to the Southern Annular Mode/Antarctic Oscillation (SAM/AAO) which shows enhanced variability at these timescales. We argue that intraseasonal oscillations of tropical climate and SAM/AAO are related to distinct patterns of climate variables measured at Neumayer.