Biomass Burning and Gas Flares create the extreme West African Aerosol Plume Which Perturbs the Hadley Circulation and thereby Changes Europe’s Winter Climate

Three significant changes have occurred in the winter climate in Europe recently: increased UK flooding; Iberian drought; and warmer temperatures north of the Alps. The literature links all three to a persistent, significant increase in sea level pressure over Southern Europe, the Mediterranean, Iberia and the Eastern Atlantic (SEMIEA) which changes the atmospheric circulation system: forcing cold fronts to the north away from Iberia; and creating a south westerly flow around the northern perimeter of the high-pressure region bringing warmer, moist air from the subtropical Atlantic to the UK and Europe which increases precipitation in the UK and raises the temperature in Europe. I use the Last Millennium Ensemble, MERRA-2 and Terra-NCEP data to demonstrate that the extreme, anthropogenic, West African aerosol Plume (WAP) which only exists from December to April perturbs the northern, regional Hadley Circulation creating the high pressure in the SEMIEA. I also show that the anthropogenic WAP has only existed in its extreme form in recent decades as the two major sources of the WAP aerosols: biomass burning; and gas flaring have both increased significantly since 1950 due to: a four-fold increase in population; and gas flaring rising from zero to 7.4 billion m3/annum and note that this time span coincides with the changes in the three elements of the winter climate of Europe. I also suggest that it may be possible to eliminate the WAP and return the winter climate of Europe to its natural state after the crucial first step of recognising the cause of the changes is taken.

Development of longitudinal dunes under Pangaean atmospheric circulation

As a result of the large difference in heat capacity between land and ocean, global climate and atmospheric circulation patterns in the supercontinent Pangaea were significantly different from today. Modelling experiments have suggested the seasonal overturning of cross-equatorial Hadley circulation; however, there are large discrepancies between model-generated surface wind patterns and the reported palaeo-wind directions from aeolian dune records. Here, we present the results of measurements of spatial distribution of dune slip-face azimuths recorded in Lower Jurassic aeolian sandstones over a wide area of the western United States (palaeolatitude: ~19°–27° N). The azimuth data of dune slip-faces reveal a bi-directional and oblique angular pattern that resembles the internal structures of modern longitudinal dunes. Based on the spatial pattern of slip-face directions and outcrop evidences, we suggest most of Lower Jurassic aeolian sandstones to be NNE–SSW- to NNW–SSE- oriented longitudinal dunes, which likely formed as the result of a combination of westerly, northwesterly, and northeasterly palaeo-winds. The reconstructed palaeo-wind pattern at ~19°–27° N appears to be consistent with the model-generated surface wind pattern and its seasonal turnover. The reconstructed palaeo-wind patterns also suggest an influence of orbitally induced changes in atmospheric pressure configuration in Pangaea.

Trends in the frequency of cyclonic disturbances and their intensification over Indian seas

Trends in cyclonic disturbances for the period 1891-1997 were studied over Bay of Bengal and Arabian Sea. It is noticed that there is a significant decreasing trend at 99% level of confidence in the frequency of storms. The slopes of decreasing trend in cyclonic activity over Bay of Bengal and that over Arabian Sea were found to be maximum during last four decades. Weakening of Hadley circulation due to upper tropospheric warming may be one of the cause of this decreasing trend. There appears to be decrease in intensification of cyclonic disturbances in recent period.

A diagnostic study on the energetic aspects of weak/strong spell of north east monsoon

An attempt has been made to study dynamics of consecutive weak/strong spell of north east monsoon for the years, 2009 and 2010 from an energetics aspect. For that different energy terms, their generation and conversion among different energy terms have been computed for consecutive weak and strong phases during Oct to Dec of the above two years over a limited region between 70 °E to 85 °E, 5 °N to 20 °N. These computations are based on daily NCEP 2.5° × 2.5° data for the same period. The transition from weak phase to strong phase of north east monsoon (NEM) observed to be associated with an enhancement in conversion of zonal available potential energy (Az) to zonal kinetic energy (Kz), implying a strengthening of Hadley circulation, favouring the above transition. It is also observed that the transition from weak phase to strong phase is associated with enhanced Baroclinic energy conversion

Evaluating the large-scale hydrological cycle response within the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2) ensemble

The mid-Pliocene (∼3 Ma) is one of the most recent warm periods with high CO2 concentrations in the atmosphere and resulting high temperatures, and it is often cited as an analog for near-term future climate change. Here, we apply a moisture budget analysis to investigate the response of the large-scale hydrological cycle at low latitudes within a 13-model ensemble from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2). The results show that increased atmospheric moisture content within the mid-Pliocene ensemble (due to the thermodynamic effect) results in wetter conditions over the deep tropics, i.e., the Pacific intertropical convergence zone (ITCZ) and the Maritime Continent, and drier conditions over the subtropics. Note that the dynamic effect plays a more important role than the thermodynamic effect in regional precipitation minus evaporation (PmE) changes (i.e., northward ITCZ shift and wetter northern Indian Ocean). The thermodynamic effect is offset to some extent by a dynamic effect involving a northward shift of the Hadley circulation that dries the deep tropics and moistens the subtropics in the Northern Hemisphere (i.e., the subtropical Pacific). From the perspective of Earth's energy budget, the enhanced southward cross-equatorial atmospheric transport (0.22 PW), induced by the hemispheric asymmetries of the atmospheric energy, favors an approximately 1∘ northward shift of the ITCZ. The shift of the ITCZ reorganizes atmospheric circulation, favoring a northward shift of the Hadley circulation. In addition, the Walker circulation consistently shifts westward within PlioMIP2 models, leading to wetter conditions over the northern Indian Ocean. The PlioMIP2 ensemble highlights that an imbalance of interhemispheric atmospheric energy during the mid-Pliocene could have led to changes in the dynamic effect, offsetting the thermodynamic effect and, hence, altering mid-Pliocene hydroclimate.

The Connection Between the Hadley Circulation and Meridional Structure of Tropical SST during ENSO from 1950 to 1977

The connection between the meridional structure of tropical sea surface temperature (SST) and the Hadley circulation (HC) under the effect of ENSO (El Niño Southern Oscillation) from 1950 to 1977 is studied. We decompose the HC and zonal mean SST into equatorially symmetric (HES for HC, SES for SST) and asymmetric variations (HEA for HC, SEA for SST) to discuss the modulation of their connection by ENSO. During El Niño events from 1950 to 1977, the HC is less sensitive to the different SST meridional structures and expressed by response ratio. The ratio in La Niña and neutral events is around 4, which is equivalent to the result in the climatology. The reason for the decreased ratio during El Niño events is explored. The interdecadal variation in the linkage between the HC and tropical SST is due to a clear interdecadal shift in the impacts of ENSO on the tropical Indian Ocean (TIO) SST. For the period 1950–1977, when El Niño events occur, larger SST warming amplitude is observed over the northern TIO (0°–15°N, 50°–100°E). However, the southern TIO (15°S–0°, 50°–100°E) shows greater warming amplitude during 1980–2016. The anomalous SST variation over the TIO linked to El Niño events alters the meridional SST distribution, inducing anomalies in the meridional circulation. These results can help us to understand the interdecadal modulation by ENSO of the relationship between tropical SST and the HC.

Role of eccentricity in early Holocene African and Asian summer monsoons

The effect of precession on paleoclimate changes depends on eccentricity. However, whether and to what degree eccentricity relates to millennial-scale monsoonal changes remain unclear. By investigating climate simulations with a fixed precession condition of 9 ka before the present, we explored the potential influence of eccentricity on early-Holocene changes in the Afro–Asian summer monsoons. Compared with the lower eccentricity of the present day, higher eccentricity in the early Holocene strengthened the continental summer monsoons, Pacific anticyclone, and Hadley circulation, particularly over the ocean. Over Africa, the eccentricity-induced “dry-gets-wetter” condition could be related to the Green Sahara, suggesting a superimposed effect of precession. Over the western Pacific, the tropical response to eccentricity may have been competitive in terms of what an extremely high obliquity may have caused. A downscaled modulation of eccentricity in relation to precession and obliquity cannot be ignored when paleomonsoon records are studied. Regarding early-Holocene monsoonal changes in South Asia, however, a high eccentricity may have had only a secondary effect on enhancing the monsoonal precipitation in the southern edge of the Tibetan Plateau, exhibiting the weak power of candle-like heating. This suggested that sizable monsoonal changes over the northern Indian Ocean and India–Pakistan region are unrelated to early-Holocene eccentricity.

Biomass Burning and Gas Flares Create the Extreme West African Aerosol Plume Which Perturbs the Hadley Circulation and Thereby Changes Europe’s Winter Climate

Three significant changes have occurred in the winter climate in Europe recently: increased UK flooding; Iberian drought; and warmer temperatures north of the Alps. The literature links all three to a persistent, significant increase in sea level pressure over Southern Europe, the Medi-terranean, Iberia and the Eastern Atlantic (SEMIEA) which changes the atmospheric circulation system: forcing cold fronts to the north away from Iberia; and creating a south westerly flow around the northern perimeter of the high-pressure region bringing warmer, moist air from the subtropical Atlantic to the UK and Europe which increases precipitation in the UK and raises the temperature in Europe. I use the Last Millennium Ensemble, MERRA-2 and Terra-NCEP data to demonstrate that the extreme, anthropogenic, West African aerosol Plume (WAP) which only exists from December to April perturbs the northern, regional Hadley Circulation creating the high pressure in the SEMIEA. I also show that the anthropogenic WAP has only existed in its extreme form in recent decades as the two major sources of the WAP aerosols: biomass burning; and gas flaring have both increased significantly since 1950 due to: a four-fold increase in population; and gas flaring rising from zero to 7.4 billion m3/annum and note that this time span coincides with the changes in the three elements of the winter climate of Europe. I also suggest that it may be possible to eliminate the WAP and return the winter climate of Europe to its natural state after the crucial first step of recognising the cause of the changes is taken.

Energetic constraints on the time-dependent response of the ITCZ to volcanic eruptions

Energetic constraints on the time-dependent response of the intertropical convergence zone (ITCZ) to volcanic eruptions are analyzed using the Community Earth System Model Last Millennium Ensemble project. The energetic constraints are found to vary during the first few years, governed by conjoined variations of the energy budgets of the stratosphere, troposphere, and oceans. Specifically, following eruptions, sulfate aerosols heat the stratosphere by long-wave absorption and cool the surface by shortwave reflection, leading to contrasting energy transport anomalies in the stratosphere and troposphere, which are of comparable strength during the first year. Similar contrasting responses are also seen by the mean and eddy components of atmospheric energy transport (AET). Consequently, ocean energy transport (OET) dominates the anomalous total interhemispheric energy transport during the first year. However, wind-driven OET, generally assumed to constrain shifts of the ITCZ, has a negligible role in the transient ocean response. Consistent with theory, anomalous cross-equatorial tropospheric energy transport, dominated by the anomalous Hadley circulation, is strongly negatively correlated with ITCZ shifts. However, due to the strong anomalous stratospheric energy fluxes, the commonly used energy flux equator (derived from net AET) is a poor predictor of transient ITCZ shifts following eruptions. El Niño-like conditions typically appear during the second year after eruptions, and La Niña-like conditions after the third year. These variations modulate ITCZ shifts in a complex manner, via changes in surface conditions and in associated energy transport variations in the atmosphere and oceans.