Simulation of the mid-Pliocene Warm Period using HadGEM3: Experimental design and results from model-model and model-data comparison

Here we present the experimental design and results from a new mid-Pliocene simulation using the latest version of the UK’s physical climate model, HadGEM3-GC31-LL, conducted under the auspices of CMIP6/PMIP4/PlioMIP2. Although two other paleoclimate simulations have been recently run using this model, they both focused on more recent periods within the Quaternary and therefore this is the first time this version of the UK model has been run this far back in time. The mid-Pliocene Warm Period, ~3 Ma, is of particular interest because it represents a time period when the Earth was in equilibrium with CO2 concentrations roughly equivalent to those of today, providing a possible analogue for current and future climate change. The implementation of the Pliocene boundary conditions is firstly described in detail, based on the PRISM4 dataset, including CO2, ozone, orography, ice mask, lakes, vegetation fractions and vegetation functional types. These were incrementally added into the model, to change from a preindustrial setup to Pliocene conditions. The results of the simulation are then presented, which are firstly compared with the model’s pre-industrial simulation, secondly with previous versions of the same model and with available proxy data, and thirdly with all other models included in PlioMIP2. Firstly, the comparison with preindustrial suggests that the Pliocene simulation is consistent with current understanding and existing work, showing warmer and wetter conditions, and with the greatest warming occurring over high latitude and polar regions. The global mean surface air temperature anomaly at the end of the Pliocene simulation is 5.1 °C, which is the 2nd highest of all models included in PlioMIP2 and is consistent with the fact that HadGEM3-GC31-LL has one of the highest Effective Climate Sensitivities of all CMIP6 models. Secondly, the comparison with previous generation models and with proxy data suggests a clear increase in global sea surface temperatures as the model has undergone development. Up to a certain level of warming, this results in a better agreement with available proxy data, and the “sweet spot” appears to be the previous CMIP5 generation of the model, HadGEM2-AO. The most recent simulation presented here, however, appears to show poorer agreement with the proxy data compared with HadGEM2, and may be overly sensitive to the Pliocene boundary conditions resulting in a climate that is too warm. Thirdly, the comparison with other models from PlioMIP2 further supports this conclusion, with HadGEM3-GC31-LL being one of the warmest and wettest models in all of PlioMIP2 and, if all the models are ordered according to agreement with proxy data, HadGEM3-GC31-LL ranks approximately halfway among them.

Atmospheric effects in Scotland of the AD 1783–84 Laki eruption in Iceland

Daily weather diaries and meteorological records from Scotland reveal complex weather patterns following the 1783–84 fissure eruption of the Laki volcano, Iceland. Four diarists in eastern and northern Scotland describe the near-simultaneous occurrence of discrete groups of days characterised by ‘foggy’, ‘gloomy’ and ‘hazy’ conditions during June and July 1783. The weather records suggest that an ash-rich portion of the initial plume may have arrived synchronously across eastern Scotland on June 15th, 5 days after the first eruption in Iceland, and lingered for between 5 and 7 days. Following a 3-day interval of fine weather, a sulphurous haze arrived on June 24th and persisted for the rest of the summer. As the summer progressed air pollution episodes became shorter, less frequent and more influenced by air pressure fluctuations. The effect of the eruption on Scotland’s climate is unclear although a negative air temperature anomaly of 1.5°C to 2.5°C below the decadal average occurred in September 1783 lasting for 16 days at Dalkeith and 33 days at Fochabers. The 1783–84 winter in Scotland was one of the coldest in recent centuries and was accompanied by prolonged snow and frost through the first 4 months of 1784. During this period, temperatures in eastern Scotland averaged 2.0°C to 2.6°C below the decadal average. The duration and amplitude of post-eruption negative temperature anomalies appear to have been strongly associated with synoptic air pressure and wind flow patterns and not simply related to volcanically-forced cooling. This challenges the hypothesis that the Laki eruptions were responsible for the sustained lowering of air temperatures over the three successive winters of 1783–84, 1784–85 and 1785–86.

Intensified impacts of central Pacific ENSO on the reversal of December and January surface air temperature anomaly over China since 1997

The reversal of surface air temperature anomalies (SATA) in winter brings a great challenge for short-term climate prediction and the mechanisms are not well understood. This study found that the reversal of SATA between December and January over China could be demonstrated by the second leading mode of multivariate empirical orthogonal function analysis on the December-January SATA. It further reveals that the central Pacific El Niño-Southern Oscillation (CP ENSO) has contributed more influences on such a reversal of SATA since 1997. CP ENSO shows positive but weak correlations with SATA over China in both December and January during pre-1996, whereas it shows significantly negative and positive correlations with the SATA in December and January, respectively, during post-1997. The CP ENSO-related circulations suggest that the change of the Siberian high plays an essential role in the reversal of SATA since 1997. Sea surface temperature anomalies pattern associated with the CP ENSO leads to a westward-replaced Walker circulation which alters the local meridional circulation and further impacts the Siberian high and SATA over China since 1997. Moreover, the seasonal northward-march of convergence zone from December to January causes northward-replaced west branch of the Walker circulation in January compared with that in December. The west branch of Walker circulation in December and January directly modulates local Hadley and Ferrel circulations, and then causes contrasting Siberian high anomalies through inducing opposite vertical motions anomalies over Siberia. The reversal of SATA between December and January is therefore more frequently observed over China since 1997. The above-mentioned mechanisms are validated by the analysis at pentad time scale and confirmed by numerical simulations.

A new approach to recruitment overfishing diagnosis based on fish condition from survey data

A new approach to recruitment overfishing diagnosis is presented. We hypothesize that condition of recruits should increase when recruitment failures are caused by fishing activity. This would be a consequence of the increase in trophic resource availability, because the population is smaller than that which the ecosystem could support. Temporal series of hake recruit condition were calculated from MEDITS survey data collected in Mediterranean geographical sub-areas (GSAs) 1, 6, 17 and 19 from 1994 to 2015. Multiple linear regressions were used to analyse the relationship between mean annual condition and abundance of recruits and climatic indices in each GSA. Significant correlations were only detected in GSA 6, where 69% of condition variability was explained by the negative correlation with recruit abundance, and with two climatic indices, the Western Mediterranean Oscillation and the standardized air temperature anomaly at surface from the Gulf of Lions. Despite the differences in recruit abundance among GSAs, their mean annual condition oscillated around the same basal value during most of the time series, pointing to density-dependent mortality rates as an important mechanism stabilizing hake recruitment to levels close to the carrying capacity when populations do not suffer recruitment overfishing. This pattern changed when the decreasing recruit abundance trend drove GSA 6 condition values persistently above those of the rest of the GSAs. According to our hypothesis, hake in GSA 6 is in recruitment overfishing.

Fires in ecosystems and influence on the atmosphere

Introduction. Fires in ecosystems, mostly after open burning, affect Ukrainian territory each year causing flora and fauna damage, soil degradation, pollutants emission, which impact air quality and human health. Fires influence the atmosphere by adding burned products and its further direct and indirect effects. Despite majority of fires are open burning, research of forest fire emissions prevail among Ukrainian scientists. Therefore, the study aimed to analyze the influence of all-type fires in Ukrainian ecosystems on substances fluxes to the atmosphere and possible changes of meteorological processes. Data and methodology. The study uses GFED4 data and inventories for analyses of forest and agricultural burned fraction, carbon and dry matter emissions for the period of 1997–2016. Additional data includes absorbed aerosol index derived from OMI (Aura) instrument and ground-based meteorological measurements. Results. Burning fraction indicates the 10 to 30% of area influencing in case of active fires. More than 90% of fires in Ukrainian ecosystems happened on the agricultural lands. The highest trends of active fires appear on the western and northern part of Ukraine, whereas burned fraction on the central territories reached up to 60% decreasing per decade. Most fires happened during two periods: March – April and July – September. The most severe fires occurred in 1999, 2001, 2005, 2007, 2008 and 2012. Average emissions in Ukraine vary from 0.2 to 1.0 g·m2·month-1 for carbon and from 0.001 to 0.003 kg·m2·month-1 for dry matter. There are three localizations of huge burning products emissions, where maximal average values reach 1.8 g·m2·month-1 for carbon and 0.005 kg·m2·month-1 for dry matter. The biggest one occurred in the Polissia forest region. Despite the maximal emission from forest fires, open burning results the biggest coverage and air quality deteriorating. Absorbing aerosol index (AAI) could be good indicator of fires in Ukrainian ecosystems and burning products emissions. Overall, AAI with values more than 0.2 correspond to dry matter emissions of 0.005–0.01 kg·m2·month-1. If AAI exceed 0.4 usual dry matter emissions exceed 0.02 kg·m2·month-1. The study finds local scale changes of air temperature and days with precipitation due to huge burning products emissions. In case of monthly average AAI exceed 1.2 during fires events, positive air temperature anomaly at the ground decrease from 0.7 to 0.1°C. The main reason is absorption of solar radiation in the atmosphere. During the next month after intensive fires in ecosystems, days with precipitation have twofold decrease: from 13-14 to 7 days with precipitation more than 0 mm, and from 2-3 to 1 day with precipitation more than 5 mm. The reason might be changes of cloudiness formation due to elevated concentrations of carbonaceous aerosols. The results obtained for atmospheric changes is planned to be verified and compared using online integrated atmospheric modelling.

What Drives the North Atlantic Oscillation’s Temperature Anomaly Pattern? Part I: The Growth and Decay of the Surface Air Temperature Anomalies

Composite analysis is used to examine the physical processes that drive the growth and decay of the surface air temperature anomaly pattern associated with the North Atlantic Oscillation (NAO). Using the thermodynamic energy equation that the European Centre for Medium-Range Weather Forecasts implements in their reanalysis model, we show that advection of the climatological temperature field by the anomalous wind drives the surface air temperature anomaly pattern for both NAO phases. Diabatic processes exist in strong opposition to this temperature advection and eventually cause the surface air temperature anomalies to return to their climatological values. Specifically, over Greenland, Europe, and the United States, longwave heating/cooling opposes horizontal temperature advection while over northern Africa vertical mixing opposes horizontal temperature advection. Despite the pronounced spatial correspondence between the skin temperature and surface air temperature anomaly patterns, the physical processes that drive these two temperature anomalies associated with the NAO are found to be distinct. The skin temperature anomaly pattern is driven by downward longwave radiation whereas stated above, the surface air temperature anomaly pattern is driven by horizontal temperature advection. This implies that the surface energy budget, although a useful diagnostic tool for understanding skin temperature changes, should not be used to understand surface air temperature changes.

Spatio–Temporal Characterization of Land Surface Air Temperature Anomaly over Nigeria

In this study, seventeen gridded stations across the latitude over Nigeria were selected with a view to determine and characterize land surface air temperature anomaly for both minimum and maximum values. The study intends to present graphic illustrations of spatial and temporal variations of land surface air temperature anomaly within a period 2008 – 2013. Long-term averages of minimum and maximum land surface air temperatures were obtained from National Aeronautic and Space Administration satellite meteorological dataset (1983 – 2007). Also, monthly and annual averages of land surface air temperatures were obtained from tutiempo.net to compute monthly anomaly, annual anomaly and percentage departure of minimum and maximum land surface air temperatures within a period of 2008 – 2013. The results showed that Jos had consistently experienced -10.8 and -4 percent decrease in minimum and maximum LSAT anomaly for the period under review. The implication is that Jos is getting colder than usual. The minimum LSAT anomaly declined by -2.8 percent in Lagos. Other stations across Nigeria showed a considerable percentage increase in minimum LSAT anomaly led by Yola (19.5%), Sokoto (18%) and Katsina (15.5%). Inland stations had percentage increase of minimum LSAT anomaly ranging between 5.8% and 10% except in Osogbo where the percentage increase was 1.8%. Osogbo is a less populated capital city of Osun state with active agricultural activities as heat sink. Percentage increase of minimum LSAT anomaly was not significant in Nigerian coastal areas most especially at Port Harcourt (0.5%). The spatial distribution of maximum LSAT anomaly across Nigerian latitudinal belt, unlike minimum LSAT anomaly, reduced in trend except in Lagos, Makurdi, Abuja, Bida, Minna and Kano. The minimum and maximum anomaly for maximum LSAT was observed at Jos and Makurdi respectively. There are 2 stations to be watched in terms of getting colder in the years to ahead namely Jos and Osogbo while Makurdi and Yola are gradually becoming hotspots.

Evidence for SST-Forced Anomalous Winds Revealed from Simultaneous Radiosonde Launches from Three Ships across the Kuroshio Extension Front

Simultaneous launches of radiosondes were conducted from three research vessels aligned meridionally across a sea surface temperature (SST) front on the flank of the Kuroshio Extension. The soundings carried out every 2 h over 5 days in early July 2012 provided a unique opportunity in capturing unambiguous data on anomalous easterly winds derived from a pronounced meridional SST gradient. The data indicate that a meridional contrast in surface heat fluxes from the underlying ocean enhanced the air temperature anomaly across the SST front, which was observed from the surface up to 300-m altitude. Correspondingly, high and low pressure anomalies that reached 800-m altitude formed on the north and south sides of the SST front, respectively. These temperature and pressure anomalies were maintained even during the passage of synoptic-scale disturbances. Although the free-tropospheric winds are overall westerly, winds below the 1000-m level were easterly due to geostrophic anomalies driven by the northward pressure gradient near the surface. During periods of the northerlies at the surface, especially over the warmer side of the SST front, the wind direction changed in a clockwise direction from 1500 m to the surface, in the opposite sense to the Ekman spiral. The vertical wind shear is apparently in the thermal wind balance ascribed to the meridional contrast in air temperature derived from the SST anomaly.