G. Zittis

On the linkage between the Asian summer monsoon and tropopause fold activity over the eastern Mediterranean and the Middle East

A climatology of tropopause folds occurring over the Eastern Mediterranean and the Middle East (EMME) has been established using the ERA-Interim reanalyses for the years 1979–2012. The methodology employs an algorithm that detects folds at grid points where the vertical profile features multiple crossings of the dynamical tropopause and allows their classification according to their vertical extent. Our results confirm the findings of an earlier 1 year climatology that recognized a global “hot spot” of summertime fold activity between the eastern Mediterranean and central Asia, in the vicinity of the subtropical jet. Two distinct maxima of activity are identified over Turkey and Iran-Afghanistan where fold frequency exceeds 25%. Occasionally, medium and deep folds form over the two regions at surprisingly low latitudes. This summertime peak in fold activity diverges from the zonal mean seasonal cycle over the subtropics and is driven by the South Asian Monsoon. Starting in late spring, the EMME is gradually brought under the influence of the zonally asymmetric background state induced by the monsoon. As areas of sharply sloping isentropes develop especially over the eastern Mediterranean and Iran-Afghanistan, subsidence and fold formation are favored. Further investigation of the reanalysis data provided empirical evidence that the monsoon also drives the interannual variability of EMME fold activity. An upward trend in fold activity is identified, especially in May, attributed to the recent advanced monsoon onset and the deepening convective activity throughout summer, which promotes upper-level baroclinicity over the EMME and favors folding.

High-Resolution Simulations of Recent Past Extreme Precipitation Events Over Cyprus

Besides global warming, climate change is expected to influence precipitation amounts and distribution. While global climate projections typically address the long-term, and weather forecasts the short to medium range up to weeks, decision-makers and stakeholders also need guidance on inter-annual to decadal time scales. In this context, the BINGO H2020 project aims both at reducing the uncertainty of near-term climate predictions and developing response strategies. One of the main objectives is to provide decadal predictions with a specific focus on extreme events. The projected precipitation distribution will eventually drive hydrological impact models. In this study we present the dynamical downscaling of the ERA-Interim (EI) dataset for validation purposes. Extreme rainfall periods were identified and simulated in very high horizontal resolution (up to 4 km) using the WRF model. In a later stage, future periods of extreme precipitation or droughts will be identified from the output of the MiKlip decadal prediction system and will be downscaled in order to assess the climate change impact on water resources in Cyprus. Our simulations seem to capture reasonably well rainfall during an extreme event (November 2014) over the eastern Mediterranean. It is also found to improve the EI precipitation that was found to be underestimated.

Land-atmosphere coupling: The feedback of soil moisture on surface temperature in the Eastern Mediterranean and Middle East

Future climate projections suggest that beside changes in mean climate there will also be shifts in extremes (i.e. droughts, floods, heat waves), partly due to enhanced interannual variability. In the already warm Eastern Mediterranean and Middle East (EMME) it is crucial to investigate possible changes in extreme temperature and try to understand all the relative mechanisms and feedbacks that cause or intensify severe heat events. One of these feedbacks is the soil moisture – atmosphere interaction. In general, when there is no sufficient water content in the soil, evapotranspiration is low, leading to higher near surface air temperatures, due to less evaporative cooling. In the present study, we explore this interaction, for the summer season. We identify sub-regions sensitive to this feedback in the EMME domain using the classical hydrology framework which defines evapotranspiration regimes as a function of soil moisture and latent heat flux. Moreover, we use the correlation of temperature and evapotranspiration as a diagnostic of this coupling. The data used cover the period 1951–2099 and come from the Hadley Centre’s regional climate model PRECIS, driven by the A1B emissions scenario. Finally, we discuss possible alterations of the relationship between soil moisture and surface temperature throughout the twenty-first century.

Air Pollution from Space

Diofantos G. Hadjimitsis, Rodanthi-Elisavet Mamouri, Argyro Nisantzi, Natalia Kouremerti, Adrianos Retalis, Dimitris Paronis, Filippos Tymvios, Skevi Perdikou, Souzana Achilleos, Marios A. Hadjicharalambous, Spyros Athanasatos, Kyriacos Themistocleous, Christiana Papoutsa, Andri Christodoulou, Silas Michaelides, John S. Evans, Mohamed M. Abdel Kader, George Zittis, Marilia Panayiotou, Jos Lelieveld and Petros Koutrakis

Exploration of 12-km ERA-Interim Simulations from CORDEX Over the Levant

We investigate the performance of the 12-km horizontal resolution simulations that are increasingly becoming available from the CORDEX simulations, as part of the Phase I CORDEX regional climate model runs (which mainly contain climate downscaling simulations at a grid spacing of about 50 km). In this preliminary work we evaluate 12-km CORDEX simulations driven by the ERA-Interim re-analyses for the period 1980–2010 with a focus in the Levant, broadly defined as the region encompassing the eastern Mediterranean. The 12-km modelled climatology, variability and trends of temperature and precipitation are compared with station measurements from different locations in the region and their performance is assessed. Biases of a few degrees are assigned to the model while the inter-annual variability and longer-term trends is reproduced nicely.