Stratospheric Wind Research Articles

Identification of blasting sources in the Dobrogea seismogenic region, Romania using seismo-acoustic signals

In order to discriminate between quarry blasts and earthquakes observed in the Dobrogea seismogenic region, a seismo-acoustic analysis was performed on 520 events listed in the updated Romanian seismic catalogue from January 2011 to December 2012. During this time interval, 104 seismo-acoustic events observed from a distance between 110 and 230 km and backazimuth interval of 110–160° from the IPLOR infrasound array were identified as explosions by associating with infrasonic signals. WinPMCC software for interactive analysis was applied to detect and characterize infrasonic signals in terms of backazimuth, speed and frequency content. The measured and expected values of both backazimuths and arrival times for the study events were compared in order to identify the sources of infrasound. Two predominant directions for seismo-acoustic sources’ aligning were observed, corresponding to the northern and central parts of Dobrogea, and these directions are further considered as references in the process of discriminating explosions from earthquakes. A predominance of high-frequency detections (above 1 Hz) is also observed in the infrasound data. The strong influence of seasonally dependent stratospheric winds on the IPLOR detection capability limits the efficiency of the discrimination procedure, as proposed by this study.

Seasonal changes in atmospheric noise levels and the annual variation in pigeon homing performance.

Repeated releases of experienced homing pigeons from single sites were conducted between 1972 and 1974 near Cornell University in upstate New York and between 1982 and 1983 near the University of Pittsburgh in western Pennsylvania, USA. No annual variation in homing performance was observed at these sites in eastern North America, in contrast to results from a number of similar experiments in Europe. Assuming pigeons home using low-frequency infrasonic signals (~0.1-0.3Hz), as has been previously proposed, the annual and geographic variability in homing performance within the northern hemisphere might be explained, to a first order, by seasonal changes in low-frequency atmospheric background noise levels related to storm activity in the North Atlantic Ocean, and by acoustic waveguides formed between the surface and seasonally reversing stratospheric winds. In addition, increased dispersion among departure bearings of test birds on some North American release days was possibly caused by infrasonic noise from severe weather events during tornado and Atlantic hurricane seasons.

Predictability of the stratospheric polar vortex breakdown: An ensemble reforecast experiment for the splitting event in January 2009

AbstractA series of ensemble reforecast experiments is conducted to investigate the predictability and the occurrence mechanism of a stratospheric sudden warming occurred in late January 2009, which is a typical polar vortex splitting event. To fully examine the rapid vortex splitting evolution and predictability variation, ensemble forecasts are carried out every day during January 2009. The vortex splitting event is reliably predicted by forecasts initialized after 6 days prior to the vortex breakup. It is also found that the propagating property of planetary waves within the stratosphere is a key to the successful prediction for the vortex splitting event. Planetary waves incoming from the troposphere are reflected back into the troposphere for failed forecasts, whereas they are absorbed within the stratosphere for succeeded forecasts. Composite analysis reveals the following reflection process of planetary waves for the failed forecast: Upward propagation of planetary wave activity from a tropospheric blocking over Alaska is weaker during initial prediction periods; then, the deceleration of the zonal wind in the upper stratosphere becomes weaker over Europe, which produces a preferable condition for the wave reflection; hence, subsequently incoming wave activity from the troposphere over Europe is reflected back over the Siberia inducing the eastward phase tilt of planetary waves, which shuts down the further upward propagation of planetary waves leading to the vortex splitting. Thus, this study shows that the stratospheric condition would be another important control factor for the occurrence of the vortex splitting event, besides anomalous tropospheric circulations enforcing upward propagation of planetary waves.

Interannual variability in effective diffusivity in the upper troposphere/lower stratosphere from reanalysis data

The effective diffusivity based on passive tracer advection is used to evaluate the long‐term mixing properties for the period 1980–2012 in the lower stratosphere and upper troposphere (UTLS) using data from the ERA‐Interim reanalysis. The regions of strongest interannual variability in effective diffusivity coincide with the regions of strong climatological mixing, such as the winter and spring midlatitude stratosphere, the polar lowermost stratosphere and around the edge of the subtropical jets (especially in summer). The annular modes dominate the variability in the winter polar vortices, and the Quasi‐Biennial Oscillation in the tropical stratosphere. El Niño/Southern Oscillation modulates the strength of mixing across the subtropical jets, and has a significant impact on mixing in the summer subtropical lower stratosphere. Long‐term trends show a vertical shift in the mixing consistent with the effect of ozone depletion on the zonal wind in the austral summer polar stratosphere. Other significant trends include increased mixing in the austral surf zone and a dipolar pattern in the boreal summer and autumn, with mixing increased on the equatorward part of the subtropical jet and reduced just above. The results are highly consistent with those from the JRA‐55 reanalysis when the same horizontal resolution is used. The calculations are also qualitatively consistent with effective diffusivity obtained directly from the potential vorticity field and, in the UTLS, they are broadly consistent with those obtained from the ozone field.

An Abel transform for deriving line‐of‐sight wind profiles from LEO‐LEO infrared laser occultation measurements

AbstractWe have developed a formula for the retrieval of the line‐of‐sight (l.o.s.) wind speed from future low Earth orbit (LEO) satellite‐to‐satellite infrared laser occultation measurements. The formula involves an Abelian integral transform akin to the Abel transform widely used for deriving refractive index from bending angle in Global Navigation Satellite System radio occultation measurements. Besides the Abelian integral transform, the formula is derived from a truncated series expansion of the volume absorption coefficient as a function of frequency and includes a simple absorption‐line‐asymmetry correction term. A first‐order formulation (referred to as the standard formula) is complemented by higher‐order terms that can be used for high‐accuracy computations. Under the assumptions of spherical symmetry and perfect knowledge of spectroscopy, the residual l.o.s. wind error from using the standard formula rather than the high‐accuracy formula is assessed to be small compared to that anticipated from measurement errors in a real experiment. Applying the new formula just in standard form to future infrared laser transmission profiles would therefore enable the retrieval of l.o.s. stratospheric wind profiles with an accuracy limited mainly by measurement errors, residual spectroscopic errors, and deviations from spherical symmetry.

Quasi-biennial oscillation signal detected in the stratospheric zonal wind at 55–65°N

AbstractTo investigate the impacts of the quasi-biennial oscillation (QBO) on high-latitude circulation and the Arctic vortex, stratospheric zonal wind at 55–65°N is analyzed. The seasonal cycle, solar cycle, and linear trend in the zonal wind at these latitudes are analyzed and removed, and the QBO signal is retrieved from the monthly zonal wind for the period 1979–2014. The zonal wind has a strong decreasing trend in winter, with a maximum decrease (less than −0.35 m s−1 yr−1) occurring within 70–100°E. The zonal wind has an in-phase response of 1.6 m s−1 to the solar cycle, with a maximum within 100–140°E. A clear QBO signal is detected in the zonal wind during the period 1979–2014, with an amplitude of 2.5 m s−1 and a period of 30 months. The latitudinal distribution of the QBO signal is inhomogeneous, with a maximum within 120–180°E and a minimum within 25–45°E.

Multi-instrument gravity-wave measurements over Tierra del Fuego and the Drake Passage – Part 1: Potential energies and vertical wavelengths from AIRS, COSMIC, HIRDLS, MLS-Aura, SAAMER, SABER and radiosondes

Abstract. Gravity waves in the terrestrial atmosphere are a vital geophysical process, acting to transport energy and momentum on a wide range of scales and to couple the various atmospheric layers. Despite the importance of these waves, the many studies to date have often exhibited very dissimilar results, and it remains unclear whether these differences are primarily instrumental or methodological. Here, we address this problem by comparing observations made by a diverse range of the most widely used gravity-wave-resolving instruments in a common geographic region around the southern Andes and Drake Passage, an area known to exhibit strong wave activity. Specifically, we use data from three limb-sounding radiometers (Microwave Limb Sounder, MLS-Aura; HIgh Resolution Dynamics Limb Sounder, HIRDLS; Sounding of the Atmosphere using Broadband Emission Radiometry, SABER), the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS-RO constellation, a ground-based meteor radar, the Advanced Infrared Sounder (AIRS) infrared nadir sounder and radiosondes to examine the gravity wave potential energy (GWPE) and vertical wavelengths (λz) of individual gravity-wave packets from the lower troposphere to the edge of the lower thermosphere ( ∼ 100 km). Our results show important similarities and differences. Limb sounder measurements show high intercorrelation, typically > 0.80 between any instrument pair. Meteor radar observations agree in form with the limb sounders, despite vast technical differences. AIRS and radiosonde observations tend to be uncorrelated or anticorrelated with the other data sets, suggesting very different behaviour of the wave field in the different spectral regimes accessed by each instrument. Evidence of wave dissipation is seen, and varies strongly with season. Observed GWPE for individual wave packets exhibits a log-normal distribution, with short-timescale intermittency dominating over a well-repeated monthly-median seasonal cycle. GWPE and λz exhibit strong correlations with the stratospheric winds, but not with local surface winds. Our results provide guidance for interpretation and intercomparison of such data sets in their full context.

Variability of Madden Julian Oscillations (MJO) observed over southern India using radiosonde observations

In the present work, characteristics of 30–50 day oscillations (referred to as the MJO) in tropospheric and lower stratospheric wind and temperature have been studied using long-term high resolution radiosonde observations at a tropical station, Gadanki (13.5°N, 79.2°E) for the period 2006–2012. Wind and temperature perturbations showed clear features of the MJO with higher amplitudes between 10 and 18km altitude. Interestingly, the MJO signal is confined vertically to different altitudes in different seasons. Variability in the perturbations of wind and temperature similar to that of outgoing long-wave radiation (OLR) with a few cases showing an out of phase relation. The amplitudes of these oscillations are larger in the winter and pre-monsoon seasons than in the monsoon season where the largest amplitudes are confined below the Tropical Easterly Jet (~16km). There also exists a large inter-annual variability in the MJO. Spatio-temporal variability of OLR not only showed the features of the MJO but also northward and eastward propagation in the monsoons and winter seasons, respectively, in a few cases. It is found that convection leads the MJO in the zonal wind by 8–12 days in all the seasons except in winter. One intriguing result observed is the vitiation of the MJO pattern by the presence of strong wind shears during monsoon season. We expect this study would be helpful in representing the MJO features in the vertical in the general circulation models (GCMs) which is still a major challenge.

Gravity waves observation of wind field in stratosphere based on a Rayleigh Doppler lidar.

Simultaneous wind and temperature measurements in stratosphere with high time-spatial resolution for gravity waves study are scarce. In this paper we perform wind field gravity waves cases in the stratosphere observed by a mobile Rayleigh Doppler lidar. This lidar system with both wind and temperature measurements were implemented for atmosphere gravity waves research in the altitude region 15-60 km. Observations were carried out for two periods of time: 3 months started from November 4, 2014 in Xinzhou, China (38.425°N,112.729°E) and 2 months started from October 7, 2015 in Jiuquan, China (39.741°N, 98.495°E) . The mesoscale fluctuations of the horizontal wind velocity and the two dimensional spectra analysis of these fluctuations show the presence of dominant oscillatory modes with wavelength of 4-14 km and period of around 10 hours in several cases. The simultaneous temperature observations make it possible to identify gravity wave cases from the relationships between different variables: temperature and horizontal wind. The observed cases demonstrate the Rayleigh Doppler Lidar's capacity to study gravity waves.

Studying Earth in the New Millennium: NASA Jet Propulsion Laboratory's Contributions to Earth Science and Applications Space Agencies

The NASA Jet Propulsion Laboratory (JPL) is a national research facility that carries out cuttingedge earth science missions. JPL developed the first U.S. Earth-orbiting science spacecraft and is a pioneer in the use of remote sensing for science of the oceans, atmosphere, and solid earth. Explorer I was the first U.S. Earth-orbiting spacecraft. It followed the Soviet Sputniks 1 and 2 but carried James Van Allen's Geiger counter, which upended space physics with the discovery of the radiation belts now named for him [1]. Explorer I also carried a micrometeoroid detector. JPL developed atmospheric temperature instruments for the Nimbus series of weather satellites, built microwave and infrared instruments to help gain an understanding of stratospheric ozone depletion, ocean circulation, and surface winds, and flew Seasat, which carried the first civilian synthetic aperture radar. This article gives a general overview of recent, current, and near-future earth science missions led by JPL, highlighting a few of the many measurements that are transforming our understanding of the processes governing the Earth's atmosphere, oceans, land surfaces, and climate.

Impacts of parameterized orographic drag on the Northern Hemisphere winter circulation.

A recent intercomparison exercise proposed by the Working Group for Numerical Experimentation (WGNE) revealed that the parameterized, or unresolved, surface stress in weather forecast models is highly model‐dependent, especially over orography. Models of comparable resolution differ over land by as much as 20% in zonal mean total subgrid surface stress (τtot). The way τtot is partitioned between the different parameterizations is also model‐dependent. In this study, we simulated in a particular model an increase in τtot comparable with the spread found in the WGNE intercomparison. This increase was simulated in two ways, namely by increasing independently the contributions to τtot of the turbulent orographic form drag scheme (TOFD) and of the orographic low‐level blocking scheme (BLOCK). Increasing the parameterized orographic drag leads to significant changes in surface pressure, zonal wind and temperature in the Northern Hemisphere during winter both in 10 day weather forecasts and in seasonal integrations. However, the magnitude of these changes in circulation strongly depends on which scheme is modified. In 10 day forecasts, stronger changes are found when the TOFD stress is increased, while on seasonal time scales the effects are of comparable magnitude, although different in detail. At these time scales, the BLOCK scheme affects the lower stratosphere winds through changes in the resolved planetary waves which are associated with surface impacts, while the TOFD effects are mostly limited to the lower troposphere. The partitioning of τtot between the two schemes appears to play an important role at all time scales.

Reconstructing the plinian and co-ignimbrite sources of large volcanic eruptions: A novel approach for the Campanian Ignimbrite.

The 39 ka Campanian Ignimbrite (CI) super-eruption was the largest volcanic eruption of the past 200 ka in Europe. Tephra deposits indicate two distinct plume forming phases, Plinian and co-ignimbrite, characteristic of many caldera-forming eruptions. Previous numerical studies have characterized the eruption as a single-phase event, potentially leading to inaccurate assessment of eruption dynamics. To reconstruct the volume, intensity, and duration of the tephra dispersal, we applied a computational inversion method that explicitly accounts for the Plinian and co-ignimbrite phases and for gravitational spreading of the umbrella cloud. To verify the consistency of our results, we performed an additional single-phase inversion using an independent thickness dataset. Our better-fitting two-phase model suggests a higher mass eruption rate than previous studies, and estimates that 3/4 of the total fallout volume is co-ignimbrite in origin. Gravitational spreading of the umbrella cloud dominates tephra transport only within the first hundred kilometres due to strong stratospheric winds in our best-fit wind model. Finally, tephra fallout impacts would have interrupted the westward migration of modern hominid groups in Europe, possibly supporting the hypothesis of prolonged Neanderthal survival in South-Western Europe during the Middle to Upper Palaeolithic transition.

Using Sounds from the Ocean to Measure Winds in the Stratosphere

Stratospheric winds deflect acoustic waves from the oceans. With the right data and the math to analyze them, these waves tell us about the weather aloft.

Total Ozone Content Trend during the Last Decade over Western Indian Tropical Station i.e. Udaipur

This study focuses on multi-year change in Total Ozone Content (TOC) values measured simultaneously by ground based instrument, i.e., MICROTOPS-II sun photometer and space based TOMS satellite experiment during the last decade, i.e., the period from 2002 to 2009 in the outskirts of the semi-arid and semi-urban tropical region of Udaipur (24.6°N, 74°E; 580 m asl), India. The negative declining trend in TOC value has been detected about 2 DU/decade by using Linear Regression Analysis (LRA) of the monthly averaged TOC levels. The LRA presents the best statistically significant percentage level (p) of greater than 99%. From the comparison of present result with the observations reported over mid, high and polar latitude sites, long-term TOC variability from tropical site is found to be the lowest, followed by their intermediate range from 10 to 30 DU/ decade over mid latitude sites and the highest range from 30 to 50 DU/decade over high to polar latitude. In order to establish the possible linking of reduction in TOC level per decade with other stratospheric dynamic parameters and atmospheric UV aerosols parameter, inter-annual change in average monthly TOC level has shown a strong correlation coefficient (r) of the order of 0.73 (p > 99.9990) with the stratospheric temperature, followed by its observed lower r value of 0.25 (p = 99%) for stratospheric zonal wind and then a significant correlation (r = 0.17; p = 95%) for AI 300 nm (Aerosols Index 300 nm) parameter. The variation of monthly mean meridional wind component does not illustrate a statistically significant correlation (r = 0.13; p < 80%) with their respective multi-year change in mean monthly TOC values. The consequence of such reduction of TOC per decade may be identified as the result of expected enhancement in incident ground UV-radiation level. At the same time, the harmful influence of increasing the UV level seems to be counteracted and reduced with the evidence of observed higher level of AI at 300 nm as high as 3 in the summer months over selected tropical environmental site.

Do split and displacement sudden stratospheric warmings have different annular mode signatures?

AbstractSudden stratospheric warmings (SSWs) contribute to intraseasonal tropospheric forecasting skill due to their surface impacts. Recent studies suggest these impacts depend upon whether the polar vortex splits or is displaced during the SSW. We analyze the annular mode signatures of SSWs in a 1000 year IPSL‐CM5A‐LR simulation. Although small differences in the mean surface Northern Annular Mode (NAM) index following splits and displacements are found, the sign is not consistent for two independent SSW algorithms, and over 50 events are required to distinguish the responses. We use the wintertime correlation between extratropical lower stratospheric wind anomalies and the surface NAM index as a metric for two‐way stratosphere‐troposphere coupling and find that the differences between splits and displacements, and between classification methodologies, can be simply understood in terms of their mean stratospheric wind anomalies. Predictability studies should therefore focus on understanding the factors that determine the persistence of these anomalies following SSWs.

Influence of subtropical Rossby wave trains on planetary wave activity over Antarctica in September 2002

At the beginning of September 2002, strong convection processes over south-eastern Indonesia and over south-eastern Africa have been observed. Due to the strong upper tropospheric divergent outflow, two Rossby wave trains (RWTs) were generated. Their south-eastward propagation was controlled by the mean background flow. These two wave trains are visible in observations. It is hypothesised that these wave trains cause enhanced planetary wave activity fluxes which are a result of an amplified planetary wave 2 in the upper troposphere/lower stratosphere over Antarctica. Such a change of the planetary wave structure was diagnosed in September 2002, prior to the first observed major sudden stratospheric warming event on the Southern Hemisphere. A simplified version of GCM ECHAM4 is used to evaluate the hypothesis. Sensitivity experiments were performed for a mean background flow similar to September 2002. Furthermore, the wave maker approach was used to generate Rossby waves in the subtropical upper troposphere at two distinct locations which are corresponding to the observed regions of divergent outflow. As a main result, after about 2 weeks of model integration with wave maker forcing, we find two RWTs with a south-eastward propagation inducing a polar amplification of planetary wave 2 in the upper troposphere and lower/middle stratosphere. The poleward wave activity flux is enhanced in comparison to the control run without any wave maker forcing. The convergence of the Eliassen–Palm flux causes a 25% deceleration of zonal mean zonal wind in the model stratosphere but no wind reversal. Sensitivity runs support the robustness of these results. The obtained model results highlight the mechanism and confirm the hypothesis that enhanced planetary wave activity in austral polar region in 2002 is caused by enhanced subtropical forcing of two RWTs.

Total ozone variations and trends during the period 1979–2014

Variations and trends in the total ozone (TO) content over the period 1979–2014 are studied using monthly mean data from ERA-Interim reanalysis database in different latitudinal belts and TOMS/SBUV/OMI satellite data. We estimated how TO variations, averaged over different latitudinal belts and globally, are modulated by Arctic and Antarctic oscillations, quasi-biennial oscillations of zonal wind in the equatorial stratosphere, El Nino–Southern Oscillation, zonal average meridional heat flux in the lower stratosphere, solar activity (SA), stratospheric content of ozone-depleting substances (ODS), and volcanic aerosol particles. Variations in global TO can be described well using regression dependence on ODS and SA; and certain of the above-mentioned factors should be additionally taken into consideration for a more accurate quantitative description of TO time behavior in certain latitudinal belts.

Generation of waves by jet-stream instabilities in winter polar stratosphere/mesosphere

In the paper we investigate the manifestation of large-scale and middle-scale atmospheric irregularities observed on stratosphere/mesosphere heights. We consider typical patterns of circulation in stratosphere and lower mesosphere which are formed due to a difference of air potential energy between equatorial and polar latitudes, especially in polar night conditions. On the base of ECMWF Era Interim reanalysis data we consider the dynamics of midlatitude winter jet-streams which transfer heat from low latitudes to polar region and which develop due to equator/pole baroclinic instabilities. We consider typical patterns of general circulation in stratosphere/lower mesosphere and reasons for creation of flaky structure of polar stratosphere. Also we analyze conditions that are favorable for splitting of winter circumpolar vortex during sudden stratosphere warming events and role of phase difference tides in this process. The analysis of vertical structure of the stratosphere wind shows the presence of regions with significant shear of horizontal velocity which favors for inducing of shear-layer instability that appears as gravity wave on boundary surface. During powerful sudden stratosphere warming events the main jet-stream can amplify these gravity waves to very high amplitudes that causes wave overturning and releasing of wave energy into the heat due to the cascade breakdown and turbulence. For the dynamics observed in reanalysis data we consider physical mechanisms responsible for observed phenomena.

Winter–spring anomalies in the stratospheric content of NO2 from ground-based measurement results

According to the results of ground-based spectrometric measurements, significant negative anomalies in the stratospheric content of NO2 were observed at a number of stations in the Northern Hemisphere during winter and spring 2011. These anomalies were accompanied by those in total ozone content (TOC) and stratospheric temperature and were caused by the transport of air masses from the region of the arctic ozone hole. The results of analysis of vertical NO2 profiles obtained at the Zvenigorod Scientific Station showed that a certain contribution to the 2011 negative anomalies of NO2 was made due to a denitrification of the polar stratosphere in the ozone-hole region. The relation between variations in the total content of NO2 and those in the TOC and temperature was analyzed for both the Northern and Southern hemispheres during winter–spring periods. It was found that this relation depends on the phase of the quasi-biennial oscillation in the stratospheric equatorial wind. Such a correlation usually intensifies if only the episodes of negative anomalies caused by the transport of stratospheric air masses from the ozone-hole region are taken into consideration.

Generation of a Quasi-Biennial Oscillation in an NWP Model Using a Stochastic Gravity Wave Drag Parameterization

Abstract Many operational numerical weather prediction (NWP) systems now extend into the stratosphere and are beginning to be used to generate forecasts beyond conventional 5–10-day periods out to seasonal time scales. Past observational and modeling studies have shown that the quasi-biennial oscillation (QBO) in equatorial stratospheric winds can play an important role in stratosphere–troposphere dynamical coupling over these longer time scales. Consequently, stratosphere-resolving NWP models used to generate seasonal forecasts should contain the necessary physics to generate and maintain the QBO. This study describes several key modifications that were necessary to produce a QBO in a high-altitude NWP model, which include an increase in model vertical resolution, implementation of a computationally efficient stochastic gravity wave drag parameterization, and reductions in the amount of horizontal and vertical diffusion in the stratosphere. Results from a 10-yr free-running model simulation with these modifications show that the westerly QBO phase produces lower temperatures and stronger westerly flow in the Northern Hemisphere (NH) winter polar stratosphere compared to the easterly QBO phase. Ensembles of 120-day simulations over the December–March period show that these modifications replace persistent easterly flow in the equatorial lower stratosphere with a more realistic transition from easterly to westerly flow. The resulting changes in planetary wave propagation produce a statistically significant response in the dynamics of the NH extratropical stratosphere consistent with the Holton–Tan relationship. The westerly shift in equatorial winds also produces a significant response in the NH extratropical troposphere, where the sea level pressure differences in winter resemble the positive phase of the northern annular mode.