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• For the SH 2019 SSW, the wave driving observed was the highest recorded since 1979. • An enhanced upwelling led to cooling in the tropical stratosphere. • Tropical upper stratospheric water vapor increased while ozone decreased after SSW. The changes in the intensity of Brewer-Dobson circulation (BDC) in the record-breaking Southern Hemisphere sudden stratospheric warming (SH SSW) event in 2019 are investigated in the present study. Wave driving was observed to be at its highest in 2019 SH SSW, despite the event being classified as a minor warming event. The Eliassen-Palm flux divergence, indicative of wave driving, was observed to be increasing before the SSW, and subsiding afterwards. The stratospheric circulation followed the wave driving and intensified along the warming episode. The resulting stratospheric distribution from Aura Microwave Limb Sounder showed a negative ozone anomaly (∼20%) in the tropical lower stratosphere and a downward propagating positive anomaly in the Southern Hemisphere polar stratosphere around the central dates. The water vapor mixing ratio showed an increase of more than 25% in the polar lower stratosphere and 10 % in the tropical upper stratosphere. A cooling of about 5 K was observed in the tropical middle stratosphere. The results indicate that SH SSW can change the intensity of the stratospheric circulation which in turn affects the ozone and water vapor transport from the tropics to the pole. [ABSTRACT FROM AUTHOR]

Abstract Using the ionosonde observations, over Thiruvananthapuram (8.5° N, 77oE, 0.5oN dip lat.), India, for a period of 20 years (1990–2009), the present study reveals the presence of quasi biennial oscillation (QBO) in the pre noon F3 layer occurrence percentage. The presence of a strong QBO modulation in the occurrence of pre noon F3 layers is observed during the period from 1992 to 2000 beyond which it is rather weak/nonexistent. The wavelet periodogram analysis indicates the fact that F3 occurrences are more during the eastward phase of MQBO and less during the westward phase of MQBO. Highlights • Reveal the presence of QBO modulation in the occurrence of pre noon F3 layers. • QBO is present during 1992–2000 beyond which it is rather weak/non existent. • The observations are explained based on the effect of MQBO on F3 generation. [ABSTRACT FROM AUTHOR]

Parameterization schemes of atmospheric normal modes (NMs) and orographic gravity waves (OGWs) have been implemented into the mechanistic Middle and Upper Atmosphere Model (MUAM) simulating atmospheric general circulation. Based on the 12-members ensemble of runs with the MUAM, a composite of the stratospheric warming (SW) has been constructed using the UK Met Office data as the lower boundary conditions. The simulation results show that OGW amplitudes increase at altitudes above 30 km in the Northern Hemisphere after the SW event. At altitudes of about 50 km, OGWs have largest amplitudes over North American and European mountain systems before and during the composite SW, and over Himalayas after the SW. Simulations demonstrate substantial (up to 50–70%) variations of amplitudes of stationary planetary waves (PWs) during and after the SW in the mesosphere-lower thermosphere of the Northern Hemisphere. Westward travelling NMs have amplitude maxima not only in the Northern, but also in the Southern Hemisphere, where these modes have waveguides in the middle and upper atmosphere. Simulated variations of PW and NM amplitudes correspond to changes in the mean zonal wind, EP-fluxes and wave refractive index at different phases of the composite SW events. Inclusion of the parameterization of OGW effects leads to decreases in amplitudes (up to 15%) of almost all SPWs before and after the SW event and their increase (up to 40–60%) after the SW in the stratosphere and mesosphere at middle and high northern latitudes. It is suggested that observed changes in NM amplitudes in the Southern Hemisphere during SW could be caused by divergence of increased southward EP-flux. This EP-flux increases due to OGW drag before SW and extends into the Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Statistical analysis of dates of warming events observed during the years 1981–2016 at different stratospheric altitudes reveals their non-uniform distributions during northern winter months with maxima at the beginning of January, at the end of January – beginning of February and at the end of February. Climatology of zonal-mean zonal wind, deviations of temperature from its winter-averaged values, and planetary wave (PW) characteristics at high and middle northern latitudes in the altitude range from the ground up to 60 km is studied using the database of meteorological reanalysis MERRA. Climatological temperature deviations averaged over the 60–90°N latitudinal bands reveal cooler and warmer layers descending due to seasonal changes during the polar night. PW amplitudes and upward Eliassen-Palm fluxes averaged over 36 years have periodical maxima with the main maximum at the beginning of January at altitudes 40–50 km. During the above-mentioned intervals of more frequent occurrence of stratospheric warming events, maxima of PW amplitudes and Eliassen-Palm fluxes, also minima of eastward winds in the high-latitude northern stratosphere have been found. Climatological intra-seasonal irregularities of stratospheric warming dates could indicate reiterating phases of stratospheric vacillations in different years. [ABSTRACT FROM AUTHOR]

We report measurements of atomic sodium, iron and temperature in the mesosphere and lower thermosphere (MLT) made by ground-based lidars at the ALOMAR observatory (69°N, 16°E) during a major sudden stratospheric warming (SSW) event that occurred in January 2009. The high resolution temporal observations allow the responses of the Na and Fe layers to the SSW at high northern latitudes to be investigated. A significant cooling with temperatures as low as 136 K around 90 km was observed on 22–23 January 2009, along with substantial depletions of the Na and Fe layers (an ~80% decrease in the column abundance with respect to the mean over the observation period). The Whole Atmosphere Community Climate Model (WACCM) incorporating the chemistry of Na, Fe, Mg and K, and nudged with reanalysis data below 60 km, captures well the timing of the SSW, although the extent of the cooling and consequently the depletion in the Na and Fe layers is slightly underestimated. The model also predicts that the perturbations to the metal layers would have been observable even at equatorial latitudes. The modelled Mg layer responds in a very similar way to Na and Fe, whereas the K layer is barely affected by the SSW because of the enhanced conversion of K + ions to K atoms at the very low temperatures. [ABSTRACT FROM AUTHOR]

Using 8 years (May 2006 to March 2014) of high resolution and high accuracy GPS radiosonde observations available from a tropical station Gadanki (13.5°N, 79.2°E), India, we have investigated the climatology of gravity wave energy and zonal momentum fluxes in the lower stratosphere. We also obtained best fit spectrum model for the gravity waves (GWs) for this tropical station. In general, strong annual variation in the energy and momentum flux with maximum during Indian summer monsoon is observed in the lower stratospheric region (18–25 km). By considering different source spectra, we have applied Gravitywave Regional or Global RAy Tracer (GROGRAT) model run on monthly basis using the source spectrum values at different altitudes on the ERA-Interim background fields to obtain the kinetic energy and zonal momentum fluxes for each of the spectra considered. These simulated fluxes are compared with the observed fluxes to arrive at the best fit spectrum model. It is found that the spectrum which represents the convection transient mountain mechanism that is purely anti-symmetric and anisotropic in nature is the best fit model for Gadanki location. This information would be useful in parameterization of the GWs in numerical models over Indian region. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to study the response of the ionospheric F-region using GPS-TEC measurements at equatorial and low latitude regions over the Brazilian sector during an sudden stratospheric warming (SSW) event in the year 2006. In this work, we present vertical total electron content (VTEC) and phase fluctuations derived from GPS network in Brazil. The continuous wavelet transform (CWT) was employed to check the periodicities of the ∆VTEC during the SSW event. The results show a strong decrease in VTEC and ∆VTEC values in the afternoon over low latitudes from DOY 05–39 (during the SSW event) mainly after the second SSW temperature peak. The ionospheric ∆VTEC pattern over Brazilian sector shows diurnal and semidiurnal oscillations during the 2006 SSW event. In addition, for the first time, variations in ∆VTEC (low latitude stations) with periods of about 02–08 day have been reported during an SSW event. Using GPS stations located in the Brazilian sector, it is reported for the first time that equatorial ionospheric irregularities were not suppressed by the SSW event. [ABSTRACT FROM AUTHOR]

When a stratospheric satellite travels by prevailing winds in the stratosphere, its cross-track displacement needs to be controlled to keep a constant latitude orbital flight. To design the orbit control system, a 6 degree-of-freedom (DOF) model of the satellite is established based on the second Lagrangian formulation, it is proven that the input/output feedback linearization theory cannot be directly implemented for the orbit control with this model, thus three subsystem models are deduced from the 6-DOF model to develop a sequential nonlinear control strategy. The control strategy includes an adaptive controller for the balloon-tether subsystem with uncertain balloon parameters, a PD controller based on feedback linearization for the tether-sail subsystem, and a sliding mode controller for the sail-rudder subsystem with uncertain sail parameters. Simulation studies demonstrate that the proposed control strategy is robust to uncertainties and satisfies high precision requirements for the orbit flight of the satellite. [ABSTRACT FROM AUTHOR]

A significant change in temperature in the tropopause and stratosphere, from pole to the tropics, was observed during a major Sudden Stratospheric Warming (SSW) occurring in January 2009. The SSW event strongly modified the pattern of polar and tropical stratospheric circulation. After termination of SSW, a new pattern emerged that prevailed for ~ 2–3 months. After SSW, a clear descending cold phase completely replaced the warm phase in the polar regions. During the warm phase, temperature increased to ~ 40 °C in stratosphere (> 30 km altitude) in the polar region (80°N–90°N), then it dropped down to − 80 °C during the cold phase. Interestingly, new warm anomalies appeared over the tropical region during the cold phase at polar regions. Possible implications of these unusually warm and cold phases are demonstrated in this study. These phases altered significantly the cold point tropopause temperature and its height. SSW also affected the tropical atmospheric stability. Cross equatorial response (from northern to southern hemisphere) up to 40°S was observed in the form of persisting anomalies as a consequence of the SSW event. [ABSTRACT FROM AUTHOR]

Droughts and floods are natural phenomena that occur when water availability is significantly below or above normal levels over a specific period. In recent years, the Gan River Basin has frequently been threatened by droughts and floods, and it is important to evaluate the characteristics of dry/wet conditions for better water resource management and disaster mitigation in this region. On the basis of precipitation and temperature data for the period 1964–2013 from 40 meteorological stations across the basin, the variability of dry/wet conditions was analyzed using the standardized precipitation evapotranspiration index (SPEI). In addition, the standardized streamflow index (SSI) and large-scale atmospheric circulation patterns calculated from NCEP/NCAR reanalysis data were used to further explore and evaluate temporal variations, spatial patterns, and possible mechanism responsible for the formation of dry/wet conditions in the basin. The results indicated that robust coefficients between monthly SSI and SPEI exist at multiple timescales. The best correlation coefficients were found at timescales of 2–3 months, which better reflect the intensity and magnitude of seasonal dry/wet conditions. Application of a 3-month SPEI for the dry (July–September) and wet (April–June) seasons indicated that severe dry/wet episodes were easy to occur in the northern part of the basin. The difference between composites of anomalous dry/wet seasons shows that both a positive height anomaly at 500 hPa and a very little water vapor flux influence the basin during the dry season of anomalous years, which can lead to the occurrence of drought events in the basin. However, during the wet season of anomalous years, geopotential height anomalies caused by areas of high pressure in the south (South China Sea) and areas of low pressure in the north (Mongolia), are responsible for the transport of copious amounts of water vapor from both the Bay of Bengal and the South China Sea. Under these conditions, the negative values of water vapor flux divergence dominate the basin and bring abundant precipitation, which often causes calamitous flood events. [ABSTRACT FROM AUTHOR]

Abstract: The low latitude ionosphere is highly variable over a large range of temporal and spatial scales even during geomagnetically quiet periods, largely as a result of electrodynamic plasma drift effects. Several recent experimental and modeling studies have investigated the electrodynamic response of the low latitude ionosphere to high latitude and lower atmospheric wave activity, particularly during sudden stratospheric warmings. In this work, we review some recent results on the short-term variability of equatorial vertical plasma drifts measured mostly at the Jicamarca Radio Observatory and their effects on equatorial short-scale spread F irregularities. We show that lunar tidal semidiurnal and diurnal effects, which have been largely ignored in most studies, can play significant roles in low latitude ionospheric variability. [Copyright &y& Elsevier]

Abstract: The interannual variability of the springtime transition date of the stratospheric circulation is analyzed on the basis of the data assimilated in the UK Met Office and NCEP/NCAR models. As a proxy for the zonal mean flow we use the geostrophic wind calculated at 65.7N from geopotential heights of the 10hPa pressure level. The results show that the springtime transition date depends on the planetary-wave activity in the stratosphere and there is a tendency to the later date with a rate of about 4 days per decade. The significant correlation between the interannual variability of the spring transition date and amplitudes of stationary planetary wave with zonal wave number 1 is found. A noticeable dependence of the breakup date on the NAM index and the QBO phase is observed. [Copyright &y& Elsevier]

Abstract: A significant inter-annual decrease in polar mesosphere ice-particles, i.e., PMSE and PMC, during 2010–2011 is compared with earlier austral summers, in particular with 2009–2010. The first IAP iron lidar temperature measurement at Davis (68.6°S), Antarctica from 14 December 2010 are used to assess thermal effects of atmospheric processes on the mesopause region. We report low average temperatures of ∼125K measured by Fe-lidar near 90km when the PMSE season commenced, whereas temperatures were warmer in 2010–2011 compared to 2009–2010 at altitudes where PMSE normally occur (around 86km). Summer mesopause region temperature anomalies are derived using Aura MLS records. We reveal that the late break-down of the Antarctic stratospheric polar vortex on 5 January 2010, coupled with enhanced early summer mesospheric zonal wind field, provide a barrier to upward propagation of atmospheric gravity waves to be the main mechanism for the observed warm early summer season below the mesopause. The mesopause in 2010–2011 was unusually high and cold. We conclude that the timing of the annual break-down of the southern polar stratospheric vortex as manifest in zonal winds at 30hPa impacts mesosphere temperature and ice-particle formation early in the austral summer. [Copyright &y& Elsevier]

Abstract: The present study demonstrates how the relationship between the high latitude northern hemispheric major sudden stratospheric warming (SSW) events of 2006 and 2009 and low-latitude mesospheric tidal variability in zonal winds observed by the MF radar at Tirunelveli (8.7°0N, 77.8°E) exists. It is found that the ozone mixing ratio increases at low latitudes during the SSW and it could probably be due to the SSW induced reversal of meridional circulation towards southward, which may aid the transport of ozone from high to low latitudes, but prevent the same from low to high latitudes. As semi-diurnal tide is produced due to solar insolation absorption of ozone and the increase in the ozone mixing ratio could be a reason for the increase in the semi-diurnal tidal amplitude. The variabilities of diurnal tide appear to be governed mostly by variation of specific humidity at 300hPa over equator and intraseasonal variability dominates the variabilities in both the parameters. [Copyright &y& Elsevier]

Abstract: Several major stratospheric sudden warmings (SSWs) characterized by a rapid vertical displacement of the winter polar stratopause are simulated in the National Center for Atmospheric Research''s Whole Atmosphere Community Climate Model. The stratopause descends into the mid-stratosphere at the onset of the SSW, and then abruptly reforms near 70km. The SSWs are accompanied by a strong equatorward and downward residual circulation between 40 and 60km. The descent occurs mainly through the core of the highly displaced vortex, and is accompanied by an intrusion of air rich in carbon monoxide (CO) from the mesosphere into the mid-stratosphere. Around the periods when the stratopause undergoes rapid vertical displacement, the simulation shows that the air of mesospheric origin is being cut off and remains distinct from surrounding stratospheric air masses for at least a month after SSW onset. Such mesospheric cut-off intrusion of CO-rich appears to be a defining signature of winters with major SSWs. Due to its strong temperature dependency, the secondary ozone maximum (between 90 and 110km) abruptly decreases in amplitude at the time of the high-altitude stratopause reformation that influences the thermal structure at these altitudes. The vertical location of the tertiary ozone maximum (between 70 and 75km) shows significant variations in response to the changing vertical motion during SSW. [Copyright &y& Elsevier]

Abstract: Sea level changes in the two regions of the East China, separated by 30°N, were investigated based on the data of sea level anomalies (SLA) from Oct, 1992 to May, 2007. In the past 14years, the rising rates have reached to 0.338 and 0.237cm/yr in the two regions of East China Sea, respectively. The magnitudes of SLA increase or decrease in the East China Sea related to ENSO events are ±2cm. Interannual components of SOI and SLA are positively correlated in the Southern East China Sea (SECS), while with completely opposite phase in the Yangtze River Estuary and its adjacent sea (YRE), both significant at the 95% confidence level. This implies that the interannual changes of sea level in the East China Sea are dominated by ENSO events, and the dynamical mechanism between ENSO events and SLA in the two regions differs from each other. Wind stresses in the two regions have a strong response to ENSO events but opposite phase relationship with SOI, and local winds in the direction of 60° and 25° east by south over the YRE and SECS respectively affect the interannual changes of SLA the most strongest (both significant with anti-phase relationship at the 95% confidence level). The divergence zone in the East China Sea is wiggling from 30°N to 37°N. This change affects the wind field of the East China Sea strongly through atmospheric circulation, and in return makes the wind stress anomalies and SLA in the two regions response differently to ENSO events. To sum up, both ENSO and wind stress make contribution to the sea-level change over the East China Sea. Sea surface wind responds well to ENSO, indicating that ENSO could affect the sea level of the East China Sea through the mechanism of wind stress transfer. Because the local wind fields are closely related to the atmospheric circulation, the response of SLA to ENSO events is related to the location of divergence zone of atmospheric circulation over the East China Sea. [Copyright &y& Elsevier]

Abstract: This study assesses the relation between the year-to-year variability of the semidiurnal tides (SDT) observed at high latitudes of both hemispheres and the global stratospheric stationary planetary wave (SPW) with zonal wavenumber S=1 (SPW1) derived from the UKMO temperature data. No significant positive correlation can be identified between the interannual variability of the Northern Hemisphere (NH) SDT and the Southern Hemisphere (SH) SPW1 for austral late-winter months. In contrast, a good consistency is evident for the interannual variations between the SDT observed at Rothera (68°S, 68°W) and the Arctic SPW1 for NH mid-winter months. Since it has been observed that during austral summer the non-migrating SDT often plays a significant role at the latitude of Rothera, a physical link between the SH SDT and the NH SPW is suggested. This asymmetry in the interhemispheric link is also noted in a recent study. [Copyright &y& Elsevier]

Abstract: This paper summarizes the results of our research in sporadic E-layer (Es) dynamics with planetary wave periods (2–32 days) in the Northern Hemisphere and its connection with equatorial stratospheric quasi-biennial oscillation (QBO). The interpolation of averaged daily values of Es highest frequency (), amplitudes of 2–32-day oscillations and filtered 16-day oscillations is conducted on the basis of measurement data for 1965–1989 from the world ionosonde network. Averaged monthly values of the zonal wind in the equatorial stratosphere at the 19–31km height interval are used as the index of quasi-biennial oscillation of atmospheric circulation. A correlation analysis between the annual averaged values of index and the interpolated values of and 4–24-day oscillations showed significant correlation in the sector of longitude from 30° to 270° (to the East of Greenwich) and latitude from 15°N to 75°N. We have developed an original algorithm for detecting a spatial motion in scalar field of any interpolated geophysical parameter in a specific local area. The algorithm is used to obtain zonal and meridional projections of local displacement of the 4–24-day wave perturbation field in the Northern Hemisphere. A connection between the annual prevailing directions of 4–24-day wave perturbations and the QBO phase (eastern or western) of atmospheric circulation is revealed on the basis of correlation analysis. The strongest correlation is discovered in the area around 60° N, 120° E in the case of filtered 16-day f o Es oscillation field. [Copyright &y& Elsevier]

Abstract: The height–season and year-to-year regularities of parameters of first and second spatial harmonics determine the structure of the stratosphere and mesosphere circulation and its variability. In the period 1992–2002 at heights 0–55km, the amplitudes and phases of the first and second spatial harmonics in the field of temperature, geopotential height, zonal and meridional wind were calculated by the method of harmonic decomposition. Dispersion (standard or mean square deviation) of their day-to-day and year-to-year variations was calculated by their wavelength constants. Height and season patterns of variability have been estimated. The difference in height–longitude variability for wave numbers m =1 and 2 has been discovered. At the same time, the intensity of wave disturbances for m =1 is less than for m =2 excluding the polar areas, where a significant variability appears at the heights 0–55km. There is also a tendency for the intensity of year-to-year variations to decrease in comparison with day-to-day variations. In cold and warm periods the amplitude of perturbation waves with m =2 both for day-to-day and year-to-year variations is greater than for waves with m =1. Transient height areas in the interval of 20–30km are more distinct for day-to-day variations of polar area. The mean square deviation (RMS) of the first harmonic of the zonal and meridional winds is less than that of the second harmonic and its year-to-year variability is less than day-to-day one. The amplitude of the first harmonic of zonal and meridional wind is higher than the amplitude of the second harmonic, and the day-to-day variability is greater than the year-to-year variability for the Northern hemisphere. The heterogeneous height and latitude structure is a characteristic of the year-to-year variation of the phase of the second harmonic. It could be caused by a non-steady state of the second harmonic. [Copyright &y& Elsevier]

Abstract: Yellowstone National Park has been an important location for paleoecologic studies that focus on the use of charcoal data to reconstruct past fire activity and on the role of climate variations in shaping past vegetation and fire regimes. One hypothesis, which has been explored in other parts of the western U.S., is the idea that present-day summer-dry and summer-wet precipitation regimes were intensified during the early Holocene as a result of greater-than-present summer insolation and its effect on atmospheric circulation patterns. In Yellowstone, this hypothesis was previously examined at two sites, one in summer-wet and one in summer-dry precipitation regions. The records showed variation in both fire and vegetation history that supported the hypothesis. We present a fire and vegetation history from Blacktail Pond, located in Pseudotsuga parkland in the transitional region. The Blacktail Pond data indicate the following ecological history: prior to 12,000 cal yr BP, the site supported tundra vegetation and fire episodes were infrequent. Between 12,000 and 11,000 cal yr BP, Picea–Pinus parkland was established and fire activity increased; these changes are consistent with increasing temperature, as a result of rising summer insolation. From 11,000 to 7600 cal yr BP, the presence of a closed forest of Pinus and some Picea is attributed to high levels of winter moisture, but high fire activity indicates that summers were drier than at present. After 7600 cal yr BP, the presence of forest and steppe vegetation in combination with high fire activity suggest that middle-Holocene conditions were warm and dry. The decrease in Picea and Betula in the last 4000 cal yr indicates continued drying in the late Holocene, although fire-episode frequency was relatively high until 2000 cal yr BP. The pollen data at Blacktail Pond and other low-elevation sites in the northern Rocky Mountains suggest a widespread vegetation response in summer-wet regions to effectively wetter conditions in the early Holocene and decreased moisture in the middle and late Holocene. In contrast, the more-variable fire history among the three sites implies either that (1) summer moisture stress and fire conditions are related to year-round moisture balance and not well predicted by the hypothesis, (2) the transitional area between summer-wet and summer-dry precipitation regimes experienced complicated shifts in effective moisture through time, and/or (3) fire-episode data have a limited source area that makes it difficult to separate local influences from regional climate changes in understanding long-term variations in fire-episode frequency. [Copyright &y& Elsevier]

Abstract: Wintertime temperature and ozone in the Northern Hemisphere stratosphere vary significantly between years. Largely random, those variations are marked by compensating changes at high and low latitudes, a feature that reflects the residual mean circulation of the stratosphere. Interannual changes of temperature and ozone each track anomalous forcing of the residual circulation. This relationship is shown to be obeyed even over the Arctic, where transport is augmented by heterogeneous chemical processes that destroy ozone. Chlorine activation obeys a similar relationship, reflecting feedback between changes of the residual circulation and anomalous photochemistry. Changes of stratospheric dynamical and chemical structure are found be accompanied by coherent changes in the troposphere. Vertically extensive, they reflect inter-dependent changes in the stratosphere and troposphere, which are coupled by the residual circulation through transfers of mass. The corresponding structure is shown to share major features with empirical modes of interannual variability associated with the AO and its cousin, the NAO. A 3D model of dynamics and photochemistry is used to simulate anomalous temperature and ozone. Driven by anomalous wave activity representative of that observed, the model reproduces the salient structure of observed interannual changes. Anomalous temperature and ozone follow in the integrations from anomalous downwelling, which, under disturbed conditions, renders temperature over the Arctic anomalously warm, and from anomalous poleward transport, which renders Arctic ozone anomalously rich. Accompanying random interannual changes in the observed record was a systematic decline of Northern Hemisphere temperature and ozone during the 1980s and early 1990s. Comprising decadal trends, these systematic changes are shown to have the same essential structure and seasonality as random changes, which, in turn, vary coherently with anomalous forcing of the residual circulation. Implications of the findings to the interpretation of stratospheric trends are discussed in light of anomalous residual motion, photochemistry, and feedback between them. [Copyright &y& Elsevier]

Abstract: We here present a synchronization of the NGRIP, GRIP, and GISP2 ice cores based mainly on volcanic events over the period 14.9–32.45ka b2k (before AD 2000), corresponding to Marine Isotope Stage 2 (MIS 2) and the end of MIS 3. The matching provides a basis for applying the recent NGRIP-based Greenland Ice Core Chronology 2005 (GICC05) time scale to the GRIP and GISP2 ice cores, thereby making it possible to compare the synchronized palaeoclimate profiles of the cores in detail and to identify relative accumulation differences between the cores. Based on the matching, a period of anomalous high accumulation rates in the GISP2 ice core is detected within the period 16.5–18.3ka b2k. The and profiles of the three cores are presented on the common GICC05 time scale and generally show excellent agreement across the stadial–interstadial transitions and across the two characteristic dust events in Greenland Stadial 3. However, large differences between the and profiles of the three cores are seen in the same period as the 7–9% increase in the GISP2 accumulation rate. We conclude that changes of the atmospheric circulation are likely to have occurred in this period, altering the spatial gradients in Greenland and resulting in larger variations between the records. [Copyright &y& Elsevier]

Enhanced ozone values observed in the upper troposphere near intense tropical cyclones have raised the question of the role of stratospheric–tropospheric exchange. The dynamical mechanisms involved in the enhanced ozone values of 6 April 1995 observed at Reunion and associated with the tropical cyclone Marlene could not be explained by ECMWF meteorological analysis with 1.125° horizontal resolution. A previous study based on the ECHAM model has demonstrated the impact of biomass burning, but of limited amplitude (<60–80ppbv max). In this paper, the upper tropospheric ozone enhancement on the periphery of Marlene has been studied with a mesoscale model (MESO-NH). This model is able to reproduce a stratospheric PV filament into the troposphere, crossing the isentropes to the 350K level. The ageostrophic circulation associated with divergence zones that have induced vertical movements has been shown. Further, the influence of vertical wind shear, evident in both the mesoscale analysis and in the idealized HURRICANE tropical cyclone model, also contributes to our understanding of this downward transport process. [Copyright &y& Elsevier]

Abstract: This paper attempts to establish a connection between stratospheric anomalies in the North Pole and rainfall on the Iberian Peninsula through the occurrence of major midwinter warmings (MMWs) and cold events (CEs), taking February as a preliminary approach. We define the MMWs as the warmings which break down the polar vortex, whereas the CEs are the episodes in which the polar vortex remains cold and undisturbed. Both anomalies lead to a wind anomaly around the north polar stratosphere, which is connected with a shortly lagged tropospheric anomaly through a stratosphere–troposphere coupling in winter. A T-mode principal component analysis (PCA) was used as an objective pattern classification method for identifying the main daily surface-level pressure (SLP) patterns for February for the 1961–1990 reference period. Subsequently, those February months with an MMW or a CE influence in the troposphere are identified in the whole study period (1958–2000) by means of the Arctic Oscillation Index (AOI). Thus, performing the same analysis for the selected February months, new principal patterns for detecting changes in surface circulation structure and morphology are obtained. The results show a significant decrease in the westerlies and a southward shift of the storm tracks in Western Europe some weeks after an MMW occurrence, leading to an increase in precipitation in western Iberia and a slight decrease on the eastern Mediterranean fringe. The results are quite the opposite under a CE influence: the westerlies are strengthened and shifted northwards due to the displacement of the Atlantic anticyclone towards Central Europe; dry conditions are established throughout Iberia, except for the Mediterranean fringe, where precipitation shows a considerable increase due to the greater frequency of the northeasterly winds. Finally, an 11-year sunspot cycle–quasi-biennial oscillation (QBO) modulation might be demonstrated in Iberian rainfall in February through the occurrence of these stratospheric anomalies. [Copyright &y& Elsevier]

Abstract: The Late Cenozoic red clay-loess sequence in the Chinese Loess Plateau provides a high-resolution record of paleoclimatic and tectonic changes related to the phased uplift of the Tibetan Plateau. Detailed magnetostratigraphy of a recently recovered 125-m-thick sediment sequence from the central Chinese Loess Plateau shows that the red clay began to accumulate at ca. 8.1Ma, implying a marked drying in the interior of Asian as well as the initial establishment of the East Asian paleomonsoon regime. Prior to 3.8Ma, the ferromagnetic mineral concentrations, as revealed by both magnetic susceptibility and S-ratios, exhibit a cyclic pattern superimposed upon a linear trend. This pattern collapsed immediately after 3.8Ma, suggesting a change in source area. This in turn may have resulted from the reorganization of atmospheric circulation and the onset of the modern Asian monsoon, probably associated with the accelerated uplift of the Tibetan Plateau to a certain threshold elevation. [Copyright &y& Elsevier]

Abstract: We introduce a new index of the leptonic CP phase dependence and derive the maximal condition for this index in a simple and general form. may be realized even in the JPARC experiment. In the case that the 1–3 mixing angle can be observed in the next generation reactor experiments, namely , and nevertheless appearance signal cannot be observed in the JPARC experiment, we conclude that the CP phase δ becomes a value around 135° for without depending the uncertainties of solar and atmospheric parameters. [Copyright &y& Elsevier]

Abstract: Analyses of simulations of the last glacial maximum (LGM) made with 17 atmospheric general circulation models (AGCMs) participating in the Paleoclimate Modelling Intercomparison Project, and a high-resolution (T106) version of one of the models (CCSR1), show that changes in the elevation of tropical snowlines (as estimated by the depression of the maximum altitude of the 0°C isotherm) are primarily controlled by changes in sea-surface temperatures (SSTs). The correlation between the two variables, averaged for the tropics as a whole, is 95%, and remains >80% even at a regional scale. The reduction of tropical SSTs at the LGM results in a drier atmosphere and hence steeper lapse rates. Changes in atmospheric circulation patterns, particularly the weakening of the Asian monsoon system and related atmospheric humidity changes, amplify the reduction in snowline elevation in the northern tropics. Colder conditions over the tropical oceans combined with a weakened Asian monsoon could produce snowline lowering of up to 1000m in certain regions, comparable to the changes shown by observations. Nevertheless, such large changes are not typical of all regions of the tropics. Analysis of the higher resolution CCSR1 simulation shows that differences between the free atmospheric and along-slope lapse rate can be large, and may provide an additional factor to explain regional variations in observed snowline changes. [Copyright &y& Elsevier]

Abstract: High resolution oxygen isotope profiles of aragonitic bivalve shells (Astarte borealis) collected alive in different years are used to trace hydrographical changes on the Laptev Sea shelf, which are mainly forced by changes in riverine freshwater discharge and arctic atmospheric circulation patterns. By merging individual isotope profiles, a high resolution time series of relative changes in bivalve δ 18O is obtained for the eastern Laptev Sea for the period 1969 to 1998. The resulting pattern in the δ 18O time series reflects seasonal bottom-water salinity changes in the Laptev Sea, which is dominated by the peak input of freshwater discharged by the Lena River onto the Laptev Sea shelf during summer. The relative changes in summer bottom-water salinity, deduced from the δ 18O values in the bivalves and the discharge anomaly of the Lena River, show a significant negative correlation. It is therefore suggested that the annual and subdecadal variations of the riverine freshwater and its influence on the shelf hydrography are imprinted in the bivalve shells. Moreover, we note that extreme summer precipitation anomalies in the Lena River catchment area affect the river discharge characteristics, events which are detectable in the δ 18O time series. This all implies that δ 18O records of bivalve shells have the potential to build long-term records of atmospheric-forced changes in arctic circulation. [Copyright &y& Elsevier]

We present a global climatology of aerosol parameters derived recently by optical inversion of extinction profiles measured by the SAGE II experiment. The aerosol parameters of interest are the particle number density and the modal radius and width of the particle size distribution supposed to be lognormal. We further derived the surface area density from those three aerosol parameters and compared our results with data retrieved from in situ measurements. In several cases, we found an underestimation for SAGE II derived values with respect to corresponding in situ values. This discrepancy between both data sets is discussed and interpreted in terms of fundamental limitations of aerosol remote sounding in the UV–Vis range. [Copyright &y& Elsevier]

During the second mission of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) from August 8 to 16, 1997, over 45,000 altitude profiles of infrared spectra were collected. A variety of atmospheric trace gases have been retrieved. Due to its unprecedented spatial and temporal resolution CRISTA data is especially suited to study variability on small scales. Variability of selected trace gases is presented in terms of standard deviations from the zonal means in 5° latitude bands: altitude range is about 15–50 km for the mixing ratios of O3, N2O, CH4, CFC 11, and HNO3. Results are compared to CIRA 1996, Part III, and agreements or disagreements are discussed. Variability is found to be not constant, but quite variable itself. It is generally higher in winter than in summer. Beyond that there are considerable variations of standard deviations with latitude and with altitude. They show interesting peculiarities that will be discussed. The results indicate that most part of the data variability are atmospheric fluctuations rather than measurement errors. [Copyright &y& Elsevier]

Tropospheric and stratospheric radar wind data obtained at Jicamarca, Peru´ (11.95°S, 76.87°W) during August 17–26, 1998 have been used to estimate the momentum flux of short-period (T<2 h) wind fluctuations together with the estimation uncertainties. As a result of our study we conclude that momentum flux estimates exceeding the measurement uncertainties can be obtained after about one day of integration. [Copyright &y& Elsevier]

Balloonborne measurements of the polar conductivity and the vertical electric field were carried out over a period of 1984–1994 from Hyderabad, Central India. The conductivity values show positive correlation with solar activity between 20 and 35 km. Between 5 and 20 km the conductivity values show an anti-correlation with solar activity. The vertical electric field does not show solar cycle effect. However, the electric field and the conductivity show a semi-diurnal variation at balloon float altitude. [Copyright &y& Elsevier]