Evolution Of Atmospheric Circulation Research Articles

The indicative significance of grain size end-members and quartz surface microtextural features in Beglitsa loess sections at the Sea of Azov

The loess accumulation processes in the Azov Sea region leaves a record of atmospheric circulation trends in southern Russia, which can be used to explore aeolian dynamics and atmospheric circulation evolution. However, the historical aeolian transportation and accumulation processes of the loess deposits in this region remain controversial, which limits our understanding of aeolian dust dynamics. In the present study, based on grain size analysis and scanning electron microscopy imaging, grain size end-member and microtextural characteristics of loess sediments in the Beglitsa section of the Sea of Azov were studied to reveal their sedimentary environments and processes. According to the results, the Beglitsa section exhibits typical characteristics of aeolian sediment. EM analysis revealed that the Sea of Azov loess is composed of materials from both distant and proximal sources transported by high-altitude westerly and mesoscale regional winds, respectively. Particle shape and morphology indicated that the Azov loess materials have experienced wind and flow action. The application of the two methods revealed that the formation of the Azov loess is a complex process from source to sink. It results from the combined effects of high-altitude westerly winds, low-altitude local wind systems, and near-surface air flow in the course of development, which is also influenced by sea-level rise and fall. The results of the present study lay a foundation for the interpretation of historical aeolian dynamics and environmental significance of the Azov loess.

Summer Russian Heat Waves Linked to Arctic Sea Ice Anomalies in 2010 and 2016

Abstract This study investigates dominant features of the atmospheric circulation evolution associated with extreme heat waves (HWs) in Russia during the summers of 2010 and 2016, respectively, and their possible association with Arctic sea ice loss. Results show that a region of Russia (20°–70°E, 45°–65°N) experienced a lasting 44-day HW event from 4 July to 16 August 2010 and a 26-day HW event from 2 to 27 August 2016. The associated atmospheric circulation anomalies are characterized by the summer Arctic cold anomaly in the mid- to low troposphere and an anticyclonic circulation anomaly over the Ural Mountains. Simulation experiments forced by summer Arctic sea ice anomalies reproduce the major characteristics of observational associations. Observations and numerical simulations indicate that summer Arctic sea ice anomaly is conducive to the formation of the summer Arctic cold anomaly, which is often accompanied by the enhanced baroclinicity in most of the Arctic troposphere and increased and decreased meridional temperature gradient in the high and midlatitudes, respectively. Such a configuration strengthens westerly winds over most of the Arctic and weakens zonal westerly over the southern Ural Mountains. This anomalous zonal wind pattern establishes the background conditions for the sustained positive geopotential height anomaly in the mid- to low troposphere that dynamically facilitates the prevalence of Russian HW events. Moreover, when compared with 2016, the weaker meridional potential vorticity gradient anomaly in the summer of 2010 prolonged the persistence of Ural blocking, which may lead to longer HW events in Russia.

Classification and mechanism of spring and summer floods in northern Xinjiang from 2006 to 2011

AbstractThe significant socioeconomic impact of extreme flooding provides an incentive to improve our understanding of flood drivers. In this study, floods that occurred in northern Xinjiang from 2006 to 2011 were divided into three categories: rainstorm‐type, warming‐type, and mixed‐type. These three types of floods primarily occurred from April to July, with most occurring in May and June. Through analysis of the atmospheric circulation evolution process of the three types of floods, it can be concluded that when a rainstorm‐type flood occurs, northern Xinjiang is affected by an anomalous cyclone that forms in front of the strengthened trough over northern Europe. Anomalous cyclones provide favorable conditions for precipitation, which is conducive to rainstorm‐type floods. As for the warming‐type flood event, northern Xinjiang is affected by an anomalous anticyclone formed by the eastward movement of the blocking system in the middle of the Eurasian continent. Before the third type of mixed flood event occurred, northern Xinjiang was affected by an anomalous cyclone formed by energy propagation along the northwesterly wind belt. In addition, the energy propagating along the westerly wind belt along the southern road is conducive to the formation of a high‐pressure ridge in southern Xinjiang. In addition, the analysis of temperature conditions indicates that the daily maximum temperature showed a warming trend from 5 to 1 day before the warming‐type and mixed‐type flood event occurred. These results provide valuable insights for flood risk management by identifying atmospheric circulation patterns and temperature conditions associated with floods in northern Xinjiang.

Atmospheric Circulation Anomalies and Key Physical Processes behind Two Categories of Anomalous Eurasian Spring Snowmelt

Abstract Eurasian spring snowmelt plays an important role in the subsequent climate and hydrological cycle, however, the understanding of snowmelt itself and its causes remains insufficient. This study explored the basic characteristics of spring snowmelt in the eastern Europe–western Siberia (EEWS) region by classifying snowmelt anomalies into two categories based on the different factors that dominate spring snowmelt, and then investigated the associated atmospheric circulation anomalies and local physical processes. The first category of anomalous snowmelt (category 1) is controlled by both the initial snow mass and the later snowmelt process, while the second category of anomalous snowmelt (category 2) is mainly linked to the later snowmelt process. Specifically, category 1 is characterized by an anomalous trough in EEWS in winter, where water vapor transported and converged, accompanied by anomalous upward motion, which promotes snowfall and snow accumulation, providing initial conditions conducive to snowmelt. In April, this region is controlled by an anomalous ridge, with significant warm advection anomalies and subsidence promoting surface warming, thereby accelerating snow melting. In contrast, the winter circulation anomalies are insignificant in category 2, while the anomalous ridge in April is stronger than in category 1, accompanied by more intense snowmelt processes. In addition, from the surface energy balance perspective, atmospheric downward sensible heat transport is an important factor influencing the anomalous snowmelt in category 1, while shortwave radiation plays a secondary role. Conversely, the snowmelt in category 2 is dominated by shortwave radiation forcing, but the sensible heat effect is slightly weaker. Significance Statement Eurasian spring snowmelt significantly impacts the subsequent climate and hydrological cycle, but the understanding of snowmelt itself and its causes is still inadequate. The purpose of this study is to explore the monthly evolution of atmospheric circulation associated with anomalous snowmelt and its local physical processes associated by categorizing them based on snowmelt characteristics. Category 1 is jointly affected by winter snow accumulation and later warming, while category 2 is dominated by strong snowmelt process in late spring. These two categories are accompanied by different winter and spring circulation configurations. Our results provide a basis for further investigation of snowmelt precursor signals.

Provenance variations of the loess deposits in the East Asian monsoon boundary zone, Northeast China: Response to the variations of climate and wind regimes

Provenance studies are critical for the paleoclimatic reconstruction of loess. However, very little information is available about the provenance variations of the loess in the monsoon boundary zone, limiting our understanding of aeolian dust dynamics, the evolution of atmospheric circulation and driving mechanisms on the glacial-interglacial timescale. To this end, the integration of grain size end-member modeling, machine learning, sediment fingerprinting and wavelet transform analysis is performed for the Harbin loess in Northeast China to understand the long-term provenance variations, atmospheric circulation evolutions and forcing mechanisms. The results show the Harbin loess comprises three grain size end-members, EM1 (7.81 μm), EM2 (27.2 μm) and EM3 (54.41 μm), and they correspond to the background of atmospheric dust, the intensity of the southwesterly and of the East Asian Winter Monsoon (EAWM), respectively, indicating the three transport dynamics of dust delivered to this region. The quantitative source reconstruction indicates that the loess experienced the dramatic source variations, characterized by an abrupt termination of the dust contribution from the Hulun Buir Sandy Land at ∼ 250 ka, and by variations in the relative contribution of the dust sources (i.e., Songnen Sandy Land, Horqin Sandy Land, Onqin Daga Sandy Land, and to a lesser extent, Hulun Buir Sandy Land) during the glacial-interglacial cycles. The comparisons between the indicators, e.g., EM2, the deep-sea oxygen isotopes and the rate of dust accumulation in the North Pacific, combined with wavelet transform analysis indicating a dramatic shift of orbital cycles from the significant 100-kyr and 41-kyr cycles to a weakened 100-kyr cycle, suggest that the weakened EAWM induced by both reduced the Northern Hemisphere ice volume and summer solar radiation, accounted for a termination of the Hulun Buir Sandy Land as the loess source. However, the change in wind regimes due to the glacial-interglacial cycles, and climate change (e.g., enhanced aridification) are the dominant forcing for the variations in the relative contribution of the dust sources to the Harbin loess.

Evolution of atmospheric circulation across the Cretaceous–Paleogene (K–Pg) boundary interval in low-latitude East Asia

Abstract The Cretaceous–Paleogene (K–Pg) boundary interval is an important time interval for deep-time paleoclimatic research, and most records of this interval are derived from marine sections. In this study, we conduct high-resolution magnetic and geochemical analyses in a terrestrial sedimentary succession from the Nanxiong Basin (Southeast China). We combine this data with previous work to compare these results with global marine and other terrestrial records. We find that the magnetic and geochemical parameters record a sequence of global climatic changes across the K–Pg boundary interval. Moreover, during the Maastrichtian cold “greenhouse” time interval, the climate changes in the studied area are consistent with the benthic foraminiferal δ18O record from the North Atlantic, and we observe no correlation between the δ13Ccarb and δ18Ocarb; in contrast, during the Danian “greenhouse” time interval, the climate changes in the studied area are consistent with the benthic foraminiferal δ18O records from both the Pacific and the North Atlantic, and we observe a positive correlation between δ13Ccarb and δ18Ocarb. We suggest that the observed changes are likely linked to the transformation of atmospheric circulation in low-latitude East Asia. These new insights have implications for “global monsoon” research and understanding the causes of the mass extinction

Autumn Cold Surge Paths over North China and the Associated Atmospheric Circulation

Using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, we tracked the paths of 46 autumn cold surges affecting North China from 1961 to 2014, and classified them by clustering analysis, thereby investigating their changes and associated atmospheric circulation evolution. Our results indicate that autumn cold surges affecting North China can be classified into three types according to their paths: the north type, west type, and northwest type, with occurrences of 12, 16, and 18 respectively. Different types of cold surges have different atmospheric circulation characteristics. The north type is associated with a blocking type of atmospheric circulation pattern, with an enhanced stretching northeast ridge over the Ural Mountains and a transverse trough over Lake Baikal. However, the northwest type is characterized by a ridge–trough–ridge wave-train pattern that is located over the Barents Sea, West Siberian Plain, and Sakhalin Island, respectively. The west-type cold surge is related to a conversion type: a blocking system over the Ural Mountains forms four days before the cold surge occurrence, after which it becomes a wave-train type. The atmospheric signals detected prior to the occurrences of the three types of cold surges are also explored. The main signal of the north-path cold surges is that the energy propagates eastward from the Azores Islands to the Ural Mountains, and then forms a blocking high over the Urals. However, for the northwest-path cold surges, there is a weak trough over the Ural Mountains that gradually strengthens because the blocking high collapses over the Norwegian Sea. The key signal of the formation of the west-path cold surges is a blocking high over the Norwegian Sea’s continuous enhancement and extension to Novaya Zemlya, which results in a transmission of energy to the Ural Mountains and leads to the formation of a blocking system over here. When the above-mentioned different types of atmospheric circulation characteristics appear, the type of cold surge path and its impact area can be potentially forecasted in advance, which may reduce the losses that result from cold surges.

Seasonal evolution of C2N2, C3H4, and C4H2 abundances in Titan’s lower stratosphere

Aims. We study the seasonal evolution of Titan’s lower stratosphere (around 15 mbar) in order to better understand the atmospheric dynamics and chemistry in this part of the atmosphere. Methods. We analysed Cassini/CIRS far-IR observations from 2006 to 2016 in order to measure the seasonal variations of three photochemical by-products: C4H2, C3H4, and C2N2. Results. We show that the abundances of these three gases have evolved significantly at northern and southern high latitudes since 2006. We measure a sudden and steep increase of the volume mixing ratios of C4H2, C3H4, and C2N2 at the south pole from 2012 to 2013, whereas the abundances of these gases remained approximately constant at the north pole over the same period. At northern mid-latitudes, C2N2 and C4H2 abundances decrease after 2012 while C3H4 abundances stay constant. The comparison of these volume mixing ratio variations with the predictions of photochemical and dynamical models provides constraints on the seasonal evolution of atmospheric circulation and chemical processes at play.

A Cold Event in Asia during January–February 2012 and Its Possible Association with Arctic Sea Ice Loss

Abstract Through both observational analyses and simulation experiments, this study investigates the intraseasonal evolution of atmospheric circulation anomalies associated with a persistent cold event in the Asian continent during late January–early February 2012, and the possible association with Arctic sea ice loss and Arctic atmospheric circulation during the preceding summer. The results suggest that the northeastern Pacific–Aleutian region and central Eurasia are two critical areas where the atmospheric circulation evolution contributed to the development of this cold event. A persistent increase in sea level pressure (SLP) over the Aleutian region was a predominant feature prior to the cold event, and then decreasing SLP over this region was concurrent with both occurrence of a polar blocking high aloft and rapid strengthening of the Siberian high, triggering outbreaks of Arctic air over the Asian continent. Consequently, the influence of the Aleutian region on this cold event (i.e., the downstream effect of the atmospheric circulation) played a critical role. Simulation experiments demonstrate that Arctic atmospheric circulation conditions in the summer of 2011 significantly enhanced a negative feedback of Arctic sea ice loss on atmospheric circulation over the Aleutian region and central Eurasia during the ensuing wintertime, which could have led to the favorable atmospheric circulation that facilitated the occurrence of cold events resembling the one in 2012. This study also implies that the Aleutian low and disturbances in the midlatitudes over the northeastern Pacific may provide precursors that could increase skill in predicting the intraseasonal evolution of extreme cold events over Eurasia.

Review of Qinghai-Tibet Plateau Impacting on Atmospheric Circulation

It is of great importance for the global atmospheric circulation evolution about Qinghai-Tibet Plateau, Uplift, dynamic and thermodynamic in the qinghai-tibet plateau affect together atmospheric circulation in the plateau region, Asia and even in the northern hemisphere. Firstly，we summarize the research progress in the impact of plateau uplift on atmospheric circulation, a view is that the qinghai-tibet plateau uplift has a critical value that impacts on the atmosphere when the plateau uplift exceeds the critical height, another view is it that sea and land distribution is the basic situation of modern atmospheric circulation factors and decisive. Then, we discuss about the impact of dynamic action on atmospheric circulation, basically using numerical simulation method to study the influence of plateau on atmospheric circulation by removing directly to terrain. Finally, we analyzed the impact of thermal action on atmospheric circulation, plateau is always as heat source in summer, point out the relationship between the heating effect and South Asia high pressure change and some of the monsoon outbreaks associated with plateau spring ground heating. Plateau snow cover on reflection of solar radiation that is also an important factor to affect the underlying surface heat condition.

Responses of the summer Asian-Pacific zonal thermal contrast and the associated evolution of atmospheric circulation to transient orbital changes during the Holocene.

This study investigates the response of large-scale atmospheric circulation over the Asian-Pacific sector and precipitation over eastern China to transient orbital changes during the Holocene summer using an intermediate-complexity climate model. Corresponding to variations in the incoming solar radiation, the eddy sea level pressure (SLP) exhibited an out-of-phase relationship between the North Pacific and the Eurasian landmass that was similar to the present-day Asia-Pacific Oscillation (APO) pattern and was defined as the paleo-APO. Its index presented an increasing trend, which implies the enhancement of a zonal thermal contrast between Asia and the North Pacific. Associated with the strengthening of the paleo-APO was the westward shift in North Pacific high pressure. Accordingly, there was less/more summer precipitation over both the middle reach of the Yangtze River and Southwest China/over North China. The high-resolution stalagmite δ18O records further support this decrease in the model precipitation. Along with the strengthening of paleo-APO from the early Holocene to the present, the eddy SLP anomalies exhibited a decreasing/increasing trend over the Eurasian landmass/the North Pacific, with a phase change of approximately 4.5 ka BP, and they both moved westward. Meanwhile, a less rainfall belt over eastern China exhibited northward propagation from southern China.

Atmospheric Circulation Characteristics Favoring Dust Outbreaks over the Solar Village, Central Saudi Arabia*

Abstract This study examines the atmospheric circulation characteristics of dust outbreaks (DOs) over the central Arabian Peninsula. Based on a 12-yr (1999–2011) Aerosol Robotic Network (AERONET) database over the Solar Village in Saudi Arabia and criteria pertinent to the aerosol optical depth at 500 nm and the Ångström exponent, 177 DOs have been identified. Factor and cluster analysis are further applied on the 1000- and 700-hPa geopotential height daily patterns of the days preceding the onset of the DOs and the days of the DOs’ initiation, revealing four main types (clusters) of the atmospheric circulation evolution leading to DOs. During the winter season, the anticyclonic circulation intensifies over the Middle East causing the strengthening of the pressure gradient over the Arabian Peninsula, inducing northerly winds over the study region, thereby favoring dust entrainment in the atmosphere (cluster 1, 16 DOs, 9%). The passage of midlatitude cyclones over the northern or central Arabian Peninsula is frequently accompanied by postfrontal northerly winds also promoting the presence of DOs in the region (cluster 2, 41 DOs, 23%). The DOs during spring are likely favored by the enhancement of convective activity, as the thermal low over the Arabian Peninsula further influences the dynamics of the upper troposphere (cluster 3, 73 DOs, 41%). During summer the pressure gradient over the study region is greatly enhanced due to the extension of the subtropical Azores anticyclone over the Mediterranean. The latter is the main driver triggering the DOs in this cluster category (cluster 4, 46 DOs, 27%).

Atmospheric circulation evolution related to desert‐dust episodes over the Mediterranean

Cases of atmospheric circulation evolution favouring the occurrence of desert aerosol episodes (DAEs) over the broader Mediterranean region were investigated using an objective and dynamic algorithm, with daily satellite data for the period 2000–2013. After identifying strong and extreme DAEs, at a 1°×1° geographical‐cell level, 255 dust aerosol episode days (DAEDs) and 148 cases of consecutive DAEDs, namely desert aerosol episode cases (DAECs), are defined. For each DAEC, the evolution of the lower tropospheric circulation 1 and 2 days before, during the initiation and after the cessation of the DAEC, is considered. S‐mode factor analysis and k‐means cluster analysis are applied on mean sea‐level pressure and 700 hPa geopotential height fields obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis Project, classifying the 148 cases of atmospheric‐circulation evolution into six homogeneous and discrete clusters. The mean intra‐annual variation of the DAECs reveals a primary maximum in May (18.9%), and their mean annual number is equal to 11.4 DAECs. On a seasonal basis, the highest percentage of the DAECs is found in spring (51.4%). Maximum duration of the DAECs is 7 days, with 58.8% lasting 1 day. Annually, the mean monthly number of the DAEs varies from 35.8 (September) to 58.0 (April). The western parts of the Mediterranean are affected by the DAEs when cyclonic conditions prevail in the western Mediterranean and northwestern Africa. In contrast, the central and eastern parts of the study region are affected by dust storms when a low‐pressure system in the central Mediterranean or central Europe and an anticyclone in the eastern Mediterranean prevail. As to the mean regional intensity (aerosol optical depth at 550 nm) the strong DAEs vary from 0.67 to 0.77, while the extremes vary from 1.14 to 2.06. Generally, strong DAEs are more frequent than extremes (in five out of six clusters).

Clima e incendios forestales en Cantabria: evolución y tendencias recientes

Wildfires are a frequent event in Cantabria, but their seasonality does not match the typical warm season maximum generalized in most of the Iberian Peninsula. They occur at the end of the winter and the beginning of the spring (January to March), being mostly anthropogenically triggered, in conjunction with “Suradas”, a windstorm which combines high winds and low humidity. In this contribution temporal trends of several climatic variables from meteorological observatories located in Cantabria and nearby regions are analyzed since 1961 during the highest risk period in order to assess to what extent the occurrence of wildfires may be linked to the recent climatic variability. Our results show that the regional climate has become warmer and drier, due to the combined effects of increases in temperatures and the decrease in relative humidity and precipitation, variables that are likely to play an important role in drought and fire proneness. However, the exception is the frequency of “Suradas”, which have reduced. Those regional climatic trends are strongly linked to the recent evolution of atmospheric circulation at regional and hemispheric scale. The higher frequency of anticyclonic cells over the Iberian Peninsula, and conversely, the reduction of the number of Atlantic baroclinic disturbances are consistent with the temporal evolution of the North Atlantic Oscillation.

アジア内陸の砂漠堆積物から見る白亜紀“温室期”における大気循環システムの進化

アジア内陸の砂漠堆積物から見る白亜紀“温室期”における大気循環システムの進化

The atmospheric conditions over Europe and the Mediterranean, favoring snow events in Athens, Greece

Abstract. The 3-dimensional structure and the evolution of atmospheric circulation favoring snowfall in Athens are examined. The study refers to 61 snow events, which occurred during the period 1958–2001. For each one of the events, the patterns of MSL pressure, 850 hPa and 500 hPa air temperatures, 500 hPa geopotential height and 1000–500 hPa thickness are constructed for the European region, for the day before (D-1), the first day (D) and the day after the end of the event (END). A statistical methodology involving Factor Analysis and Cluster Analysis is applied to the above data sets and the 61 cases are finally classified into five clusters. These clusters are generally characterized by a north-easterly flow in the lower troposphere over the Athens area. This flow is associated with the presence of a low pressure system around Cyprus and an anticyclone over Europe. The position, the intensity and the trajectories of the surface and the upper air systems during D-1, D and END days are generally different among the five clusters.

Oyashio seasonal intensification and its effect on subsurface temperature variation off the Sanriku coast

The Oyashio seasonal intensification and its effect on subsurface temperature fields off the Sanriku coast are investigated, based on indices of the Oyashio current. These indices include altimeter‐based eddy drifting velocities (EDV) and tide gauge sea levels at Petropavlovsk‐Kamchatsky (PK), where the Oyashio upstream region is located. The annual cycles of EDV, the PK sea levels and the Sverdrup transport for the range of 40–50°N (SV) show similar seasonal features that have (1) maximums in early winter and (2) small secondary local peaks in early summer. These indicate that the Oyashio seasonal variation is mainly governed by the Sverdrup dynamics. The early winter intensification recognized as the general Oyashio seasonal variation involves a large and rapid change from late autumn to early winter, which is roughly explained by the southward shift of westerlies. Its onset timing, which undergoes large year‐to‐year variability, is indeed determined by the timing of the southward migration of the westerly jet. The early summer intensification can also be explained by a barotoropic response to the intraseasonal evolution of atmospheric circulation in the Baiu (rainy) season, which is observed characteristically in East Asia and East Siberia. The seasonal cycle of subsurface temperatures off the Sanriku coast, where the Oyashio water meets the Kuroshio water, shows (1) a minimum in April and (2) a secondary local minimum in July. The cooling cycle is qualitatively explained by lateral heat advection by the Oyashio current.

Initial intensification of East Asian winter monsoon at about 2.75 Ma as seen in the Chinese eolian loess‐red clay deposit

The loess‐paleosol‐red clay sequence in the Chinese Loess Plateau provides a record of the evolution of atmospheric circulation and monsoon climate over East Asia during the last 7–8 Ma. Detailed analyses of the Baishui and Jingchuan sections show that the grain size of eolian loess increased abruptly at about 2.75 Ma, which is accompanied with a reversal of depositional pattern from the red clay to loess‐paleosol deposits, suggesting that the dust transporting circulation was reorganized. This is the earliest clear expression of the East Asian winter monsoon intensification at the Pliocene‐Pleistocene climate transition, coincident with the initiation of major Northern Hemisphere glaciation over the Eurasian Arctic and Northeast Asia, implying that at the early stage of the Pliocene‐Pleistocene global cooling the East Asian winter monsoon circulation had been closely linked with the build up of ice sheet and climate changes over the high latitudes of Northern Hemisphere. The intensified winter monsoon winds would have in turn acted as an important positive feedback in strengthening global cooling by increasing albedo and dust loading.