Intrusion Of Stratospheric Air Research Articles

Stratospheric air intrusions promote global-scale new particle formation.

New particle formation in the free troposphere is a major source of cloud condensation nuclei globally. The prevailing view is that in the free troposphere, new particles are formed predominantly in convective cloud outflows. We present another mechanism using global observations. We find that during stratospheric air intrusion events, the mixing of descending ozone-rich stratospheric air with more moist free tropospheric background results in elevated hydroxyl radical (OH) concentrations. Such mixing is most prevalent near the tropopause where the sulfur dioxide (SO2) mixing ratios are high. The combination of elevated SO2 and OH levels leads to enhanced sulfuric acid concentrations, promoting particle formation. Such new particle formation occurs frequently and over large geographic regions, representing an important particle source in the midlatitude free troposphere.

The Generalized Application of a New Surface Pressure Tendency Equation in Synoptic Weather Systems

AbstractThe surface pressure tendency equation (SPTE) is an important theoretical tool in understanding the development of weather systems, with various forms being proposed over the past 100 years. In this study, a new version of the SPTE, which eliminates the explicit or implicit pressure tendency term on the right‐hand side, is applied to three typical synoptic weather systems in terms of tropical cyclones, explosive cyclones anticyclones, and two mesoscale systems in terms of squall lines and supercells based on numerical simulations. Results reveal promising performance of the new equation in understanding the surface pressure tendency of three synoptic systems, showing advantages in uncovering their dominant physical processes as well as inherent discrepancies. For the tropical cyclone, the latent heating is largely responsible for the surface pressure fall, whereas the surface pressure rise of the anticyclone is mainly fueled by the upper‐level advection of potential temperature. The leading factors for the explosive cyclone intensification demonstrate a transition from mid‐level diabatic heating at the early stage to upper‐level potential temperature advection related to stratospheric air intrusion during the later intensification period. For the squall line and supercell, however, local breakdown of hydrostatic balance can be as large as ∼10%, and consequently, caution should be taken when the equation is used in mesoscale systems, especially for the supercell. These results suggest that the new SPTE can be well applied in synoptic weather systems, and can provide new insights into their intensity evolutions and contributions of diverse physical processes.

Extratropical Stratospheric Air Intrusions Over the Western North Pacific and the Genesis of Downstream Monsoon Low‐Pressure Systems

AbstractLow‐pressure systems (LPS) are convectively coupled vortices that contribute nearly half of the summer monsoon rainfall over the Indian subcontinent. About one third of the boreal summer monsoon LPS are caused by downstream amplification of westward propagating disturbances from the western North Pacific (WNP). Analysis of downstream LPS events from 1979 to 2017 reveals that 43% of them are caused by extratropical stratospheric air intrusions over the WNP. Stratospheric air intrusions lead to high tropospheric potential vorticity (PV), and the downstream vortex seeds are observed to initiate and intensify to the southwest of the PV anomalies. The PV anomalies can deform the temperature in its neighborhood and cause adiabatic lifting, which in turn can induce and intensify low‐level cyclonic vortices. The subsequent intensification of the low‐level vortex is aided by deep convection, observed to the southwest of the PV anomaly, through vortex stretching and low‐level PV generation by diabatic heating.

Monitoring Surface 10Be/7Be Directly Reveals Stratospheric Air Intrusion in Sichuan Basin, China

AbstractStratospheric air intrusion can break the balance of atmospheric properties such as chemicals and radiation affecting the atmosphere. The meteoric cosmogenic 7Be and 10Be are mainly produced between the lower stratosphere and the upper troposphere and then adsorbed on aerosols for transport, they are good tracers of the atmospheric mass transport. Here, 7Be and 10Be in aerosols were measured simultaneously by accelerator mass spectrometry, and after removing dust 10Be interference, daily resolution 7Be and 10Be for the whole year in Chengdu (a major city in the Sichuan Basin of China) was obtained. The long‐period tracing of stratospheric air intrusion in the Sichuan Basin area is realized by directly observing the surface 10Be/7Be ratio. This work confirms the influence of stratospheric air intrusion on the surface O3 and atmospheric water vapor in the Sichuan Basin and finds that the stratospheric air intrusion degree in spring and summer is significantly higher than that in autumn and winter. The results indicate that high‐resolution 10Be/7Be can provide effective and refined tracers for the atmospheric vertical motion. The new 7Be and 10Be observation records contribute to evaluating the impact on the environment and climate during the stratospheric air intrusion in the Sichuan Basin.

The impact of different atmospheric phenomena to cosmogenic 22Na/7Be ratio

The isotopic ratio of two cosmogenic isotopes, 22Na and 7Be, has been recognized as a possible tracer for atmospheric dynamics. We studied how different atmospheric phenomena affect the 22Na/7Be ratio that are known to affect the ground level 7Be concentrations. The 22Na/7Be ratio was studied in the following context: estimation of aerosol residence time, in the intrusions of stratospheric air after Sudden Stratospheric Warming (SSW) events, seasonal variations due to different atmospheric mixing conditions and finally the interannual variations caused by the large-scale atmospheric circulation such as North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Scandinavian Pattern (SCAND) and Quasi-Biennial Oscillation (QBO). This study utilized airborne radioactivity monitoring data from three Finnish stations located in Rovaniemi (66.51 °N, 25.73 °E), Kajaani (64.08 °N, 27.71 °E) and Kotka (60.48 °N, 26.92 °E). The theoretical calculations were performed to see how the 22Na/7Be ratio changes as a function of altitude during when produced by the galactic cosmic rays. The calculations showed that the 22Na/7Be ratio is higher in the stratosphere and lower in the troposphere. At mid-stratosphere level the ratio was 0.001, at tropopause level approximately 0.0007 and at ground level approximately 0.00045. Due to the different half-lives of 22Na and 7Be the mean atmospheric residence time can be estimefrom the radioactive decay law by assuming an initial activity concentration ratio of 0.0007 and using the measured ground level 22Na/7Be ratios. This resulted in the median atmospheric residence time as 91–95 days. The atmospheric impact on 22Na/7Be ratio was studied at different time scales starting from short-term impact from SSW, the known seasonal cycle and variations at interannual timescale. SSW events caused rapid increases in the ground level 7Be and 22Na concentrations while the impact on 22Na/7Be ratio was relatively small. A clear seasonal cycle in the 22Na/7Be ratio was observed where the 22Na/7Be ratio was at low value during November–February, increased during March–May, stayed at stable high value during June–July and steadily decreased during August–October. The long-term average for 22Na/7Be ratio was established to be 1.1 × 10−4 by using the Kotka data from 1993 to 2020. During 1995–2009, the 22Na/7Be ratio was below the long-term average, and during 2010–2020, generally above. The interannual variations in the 22Na/7Be ratio were studied by using wavelet transform analysis of the Kotka data. The analysis showed 4-6-year and 11-year periodicities. The wavelet coherence analyses with AO, NAO, SCAND, QBO and Southern Oscillation (SO) indices showed that the shorter periodicity was caused by the NAO/AO effects the atmospheric circulation in Scandinavia and hence the transport of the isotopes from upper atmosphere to ground level. The observed coherence with the Southern Oscillation Index (SOI) starting from 2012 onwards appeared at an approximately 3–4year scale while the AO and NAO had a coherence at an approximately 6-year scale. The observed 11-year periodicity was caused by the Solar cycle which modulates the 7Be and 22Na production in the upper atmosphere.

Unraveling the process of aerosols secondary formation and removal based on cosmogenic beryllium-7 and beryllium-10

The secondary formation and diffusion processes of aerosol are extraordinarily complex and significantly impact the environment and human health. Therefore, exploring the process of aerosol formation and diffusion based on independent new tracer has always been a concern. The 7Be and 10Be, which are generated only by the action of cosmic rays, are chemically stable and adsorbed on aerosol for transmission, so they have the potential characteristics of aerosol tracers. Here, we obtained the daily resolution atmospheric 7Be, 10Be, and 10Be/7Be without dust interference in Xi'an autumn and winter (heavy pollution period in a typical polluted area) by accelerator mass spectrometry. It is found that during the rapid formation of secondary aerosols (SA) under the stable 10Be/7Be ratio, which indicates the stable atmospheric vertical structure, the concentration of 7Be and 10Be is significantly negatively correlated (R2 > 0.9) with the aerosol concentration. Therefore, SA relative content in aerosols can be estimated by the dilution amount of 7Be and 10Be to reveal the secondary-formation process of aerosol (33% average contribution to aerosols during the winter heavy air pollution period). Furthermore, we also revealed the physical removal process of aerosols based on 7Be, 10Be, and 10Be/7Be, including precipitation removal and diffusion of vertical atmospheric movement caused by stratospheric air intrusion. In summary, meteoric cosmogenic 7Be and 10Be will provide a new way to study the secondary chemical formation and physical removal of aerosols.

Extreme wet seasons – their definition and relationship with synoptic-scale weather systems

Abstract. An extreme aggregation of precipitation on the seasonal timescale, leading to a so-called extreme wet season, can have substantial environmental and socio-economic impacts. This study has a twofold aim: first to identify and statistically characterize extreme wet seasons around the globe and second to elucidate their relationship with specific weather systems. Extreme wet seasons are defined independently at every grid point of ERA-Interim reanalyses as the consecutive 90 d period with the highest accumulated precipitation in the 40-year period of 1979–2018. In most continental regions, the extreme seasons occur during the warm months of the year, especially in the midlatitudes. Nevertheless, colder periods might be also relevant, especially in coastal areas. All identified extreme seasons are statistically characterized in terms of climatological anomalies of the number of wet days and of daily extreme events. Results show that daily extremes are decisive for the occurrence of extreme wet seasons in regions of frequent precipitation, e.g., in the tropics. This is in contrast to arid regions where wet seasons may occur only due to anomalously frequent wet days. In the subtropics and more precisely within the transitional zones between arid areas and regions of frequent precipitation, both an anomalously high occurrence of daily extremes and of wet days are related to the formation of extreme wet seasons. A novel method is introduced to define the spatial extent of regions affected by a particular extreme wet season and to relate extreme seasons to four objectively identified synoptic-scale weather systems, which are known to be associated with intense precipitation: cyclones, warm conveyor belts, tropical moisture exports and breaking Rossby waves. Cyclones and warm conveyor belts contribute particularly strongly to extreme wet seasons in most regions of the globe. But interlatitudinal influences are also shown to be important: tropical moisture exports, i.e., the poleward transport of tropical moisture, can contribute to extreme wet seasons in the midlatitudes, while breaking Rossby waves, i.e., the equatorward intrusion of stratospheric air, may decisively contribute to the formation of extreme wet seasons in the tropics. Three illustrative examples provide insight into the synergetic effects of the four identified weather systems on the formation of extreme wet seasons in the midlatitudes, the Arctic and the (sub)tropics.

Multiplatform observations of stratosphere-troposphere exchange over the Bharati (69.41° S, 76° E), Antarctica during ISEA-35

This paper deals with the observations of stratospheric ozone intruding into the troposphere over the Bharati (69.41° S, 76.19° E) station in Antarctica, made during 35th Indian Scientific Expeditions to Antarctica (ISEA-35) during jet stream conditions. High-resolution multiplatform measurements from radiosonde coupled with ozonesonde, Very High-Frequency (VHF) radar and Micro-Limb Sounder (MLS) and Indian National Satellite System (INSAT-3D) satellite measurements are used for the present study. The most significant observation is that there is an increase of ozone by 30 ppbv in the upper troposphere and decrease by 100–110 ppbv in the lower stratosphere and this condition persisted for three successive days. The wind shows the presence of jet-stream in the vicinity of tropopause, enhancing the turbulence due to wind shear during the event of stratospheric intrusion. Further, the vertical velocity shows the presence of strong updrafts and downdrafts in the vicinity of tropopause which manifests the tropopause oscillation. Global analysis of satellite and reanalysis data also indicates the horizontal intrusion of stratospheric air from the mid-latitude to upper troposphere over the Bharati station. These observations constitute the first multi-instrumented, experimental evidence of stratospheric intrusions over the coastal Antarctica. These results are presented and discussed in the light of present understanding of turbulence and tropopause oscillation.

Gridded Satellite Sounding Retrievals in Operational Weather Forecasting: Product Description and Emerging Applications

The National Aeronautics and Space Administration (NASA) Short-term Prediction Research and Transition Center (SPoRT) has been part of a collaborative effort within the National Oceanic and Atmospheric Administration (NOAA) Joint Polar Satellite System (JPSS) Proving Ground and Risk Reduction (PGRR) Program to develop gridded satellite sounding retrievals for the operational weather forecasting community. The NOAA Unique Combined Atmospheric Processing System (NUCAPS) retrieves vertical profiles of temperature, water vapor, trace gases, and cloud properties derived from infrared and microwave sounder measurements. A new, optimized method for deriving NUCAPS level 2 horizontally and vertically gridded products is described here. This work represents the development of approaches to better synthesize remote sensing observations that ultimately increase the availability and usability of NUCAPS observations. This approach, known as “Gridded NUCAPS”, was developed to more effectively visualize NUCAPS observations to aid in the quick identification of thermodynamic spatial gradients. Gridded NUCAPS development was based on operations-to-research feedback and is now part of the operational National Weather Service display system. In this paper, we discuss how Gridded NUCAPS was designed, how relevant atmospheric fields are derived, its operational application in pre-convective weather forecasting, and several emerging applications that expand the utility of NUCAPS for monitoring phenomena such as fire weather, the Saharan Air Layer, and stratospheric air intrusions.

Structure and evolution of intense austral cut‐off lows

AbstractThis study examines the three‐dimensional structure and evolution of the 200 most intense Cut‐off Lows (COLs) in the Southern Hemisphere (SH). This is done using feature tracking and cyclone‐centred compositing based on the ERA‐Interim reanalysis. Composites confirm the existence of a well‐defined tropospheric moist cold core co‐located with warm dry air in the lower stratosphere. Such cores are surrounded by regions of strong temperature gradients (frontal zones) which move downstream throughout the life cycle. The stratospheric air intrusion into the troposphere is identified in vertical cross‐sections of potential vorticity and ozone, a process referred to as tropopause folding. Precipitation occurs ahead of the COLs because of the low (high)‐level convergence (divergence) and strong upward motion. The maximum precipitation is observed during decay, indicating a possible link between COLs and surface cyclones. Composites conditioned on relative vorticity and precipitable water suggest these variables may be related to precipitation. The COLs exhibit a westward tilt during their early stages but they change to a barotropic state in the mature stage. Finally, the main characteristics of the COLs are summarised by categories which discriminate different intensities, indicating there are differences in the structure of COLs with consequences for precipitation. These efforts aim to provide new insights into the development of COLs in the SH which could aid in identifying and forecasting their various types and associated precipitation patterns.

Analysis of the Anomalous Signals near the Tropopause before the Overshooting Convective System Onset over the Tibetan Plateau

This study investigates the anomalous signals near the tropopause before the overshooting convective system (OCS) onset over the Tibetan Plateau (TP). It is found that the tropopause height is stable at the maximum height for the 7th day and the 5th day before the OCS onset. It then decreases significantly one day before and on the day of the OCS onset. The upward motion in the troposphere is the strongest for the 5th day before the OCS onset. From one day before and after the OCS onset, there are strong ascending motions at 500–300 hPa but weak descending motions near the tropopause. It is proposed that the descending of the tropopause height on the day of the OCS onset is caused by frequent tropopause fold events over the eastern TP associated with frequent cold trough intrusion from the north and the southeastward movement of upper-level westerly jet stream. The decrease of the tropopause height is accompanied by the intrusion of stratospheric air with higher potential vorticity (PV). Positive potential vorticity anomalies on 350 K isentropic surface can be noted in the region where the tropopause height decreases one day before and on the day of the OCS onset. With the deepening of the tropopause fold on the day of the OCS onset, there is not only downward motion near the tropopause in the area behind of the fold but also upward motion in the troposphere beneath the folding region. In addition, the upward displacement of isentropic surfaces leads to an upper-level cold pool, which causes a reduction in static stability beneath the PV anomaly on the day of the OCS onset. The upper-level PV anomalies and their associated strong instability in the middle troposphere can trigger convective activities by the release of potential instability on the day of the OCS onset. The overshooting convection is more likely to occur due to lower tropopause height, although upward motion in the troposphere is not the strongest.

Long‐Term Observations of Stratosphere‐Troposphere Exchange Using MST Radar and Aura MLS Measurements Over a Tropical Station Gadanki

AbstractThis paper presents the climatology of stratospheric intrusion into the troposphere during the Indian Summer Monsoon (ISM) observed using the mesosphere‐stratosphere‐troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). The most significant and new observation is the presence of enhanced signal‐to‐noise ratio (SNR) of 3 dB and half‐power full spectral width of >0.2 m s−1 in the vicinity of tropopause during the ISM. Downdrafts (updrafts) are dominated in the vicinity of tropopause from April to June (July to March). The result of stratospheric air intrusion is also supported with 10 years of ozone measurements obtained from Aura‐Microwave Limb Sounder (MLS) and 5 years of in situ ozonesonde observations. Detailed analysis shows that the horizontal advection along with turbulence in the vicinity of tropopause caused by the tropical easterly jet and tropopause altitude variability is the prime candidate for stratosphere to troposphere transport of ozone. In contrast, the tropical tropopause temperature plays a significant role in the troposphere to stratosphere transport of water vapor during the ISM. The significance of the present study is to qualitatively constitute the climatology of these exchange processes over Gadanki using Indian MST radar.

On the determining factors in cases of moderate to heavy precipitation in Tehran

Investigating the factors responsible for heavy precipitation events is important because of the financial and non-financial losses they often cause. Based on the ERA-Interim reanalysis and a numerical mesoscale forecasting model (WRF), the effects of four factors on significant precipitations in Tehran are studied. The four factors are upper-level potential vorticity (PV) anomalies, and mid-tropospheric PV anomalies as two meteorological factors; and the Alborz and Zagros mountains as two external factors. A factor separation analysis is applied to six days that are representative (most similar) of the six circulation types (CTs) previously identified for moderate to heavy precipitations in Tehran. The independent contribution of the upper-level PV anomaly to precipitation in each of the selected days of the second to the sixth CT is higher than 60%; hence, the upper-level tropospheric flow provided the main precipitation forcing factor, with much less contribution from the thermodynamic factor of the mid-level troposphere. Regarding the two orographic external factors, the higher positive impact on Tehran precipitation is found for the Alborz mountains. This is related to synoptic-scale weather systems that induce a northerly low-level flow towards the Alborz mountains. Moreover, in all the studied cases, except the fifth CT, the independent impact of the Zagros mountains on Tehran precipitation is positive. In all of the selected days except that of the first CT, the main factor responsible for precipitation is the intrusion of dry and cold stratospheric air associated with a large positive PV anomaly (streamer) at upper-tropospheric levels. For the first CT, further quest is necessary to find out the main factor.

A Numerical Study of Aviation Turbulence Encountered on 13 February 2013 over the Yellow Sea between China and the Korean Peninsula

AbstractAt 0247 UTC 13 February 2013, a South Korean commercial aircraft encountered moderate-level clear-air turbulence at ~24 000 ft (~7.3 km) over the Yellow Sea (121.25°E, 38.55°N) en route from Incheon, South Korea, to Tianjin, China. Two crew members were severely injured by this event. To investigate the possible mechanisms of this event, a high-resolution numerical simulation using the Weather Research and Forecasting Model was conducted. In the synoptic-scale flow pattern, one of two bifurcated jet streams passed over the Yellow Sea, and strong horizontal and vertical gradients of the wind occurred on the northern edge of the jet stream near the flight route. An upper-level frontal system on the cyclonic shear side of the jet intensified as it moved northward toward a strengthening upper-level trough in northeastern China. The developed jet–frontal system induced strong vertical wind shear and tropopause folding, which extended down to about z = 5 km, near the observed turbulence region. Despite a relatively high stability with an intrusion of stratospheric air with tropopause folding, the strong vertical wind shear led to a small Richardson number in the incident region, which in turn induced the aviation turbulence through the Kelvin–Helmholtz instability. Although small-scale mountain waves were evident during the passage of flight before the incident time, breaking of these waves was not likely the key factor for the observed turbulence, given that the wave amplitudes were weak and that the strong zonal wind on the upstream of the mountain waves prohibited wave saturation and breakdown.

A decadal time series of water vapor and D / H isotope ratios above Zugspitze: transport patterns to central Europe

Abstract. We present vertical soundings (2005–2015) of tropospheric water vapor (H2O) and its D ∕ H isotope ratio (δD) derived from ground-based solar Fourier transform infrared (FTIR) measurements at Zugspitze (47° N, 11° E, 2964 m a.s.l.). Beside water vapor profiles with optimized vertical resolution (degrees of freedom for signal, DOFS, = 2.8), {H2O, δD} pairs with consistent vertical resolution (DOFS = 1.6 for H2O and δD) applied in this study. The integrated water vapor (IWV) trend of 2.4 [−5.8, 10.6] % decade−1 is statistically insignificant (95 % confidence interval). Under this caveat, the IWV trend estimate is conditionally consistent with the 2005–2015 temperature increase at Zugspitze (1.3 [0.5, 2.1] K decade−1), assuming constant relative humidity. Seasonal variations in free-tropospheric H2O and δD exhibit amplitudes of 140 and 50 % of the respective overall means. The minima (maxima) in January (July) are in agreement with changing sea surface temperature of the Atlantic Ocean. Using extensive backward-trajectory analysis, distinct moisture pathways are identified depending on observed δD levels: low column-based δD values (δDcol < 5th percentile) are associated with air masses originating at higher latitudes (62° N on average) and altitudes (6.5 km)than high δD values (δDcol > 95th percentile: 46° N, 4.6 km). Backward-trajectory classification indicates that {H2O, δD} observations are influenced by three long-range-transport patterns towards Zugspitze assessed in previous studies: (i) intercontinental transport from North America (TUS; source region: 25–45° N, 70–110° W, 0–2 km altitude), (ii) intercontinental transport from northern Africa (TNA; source region: 15–30° N, 15° W–35° E, 0–2 km altitude), and (iii) stratospheric air intrusions (STIs; source region: > 20° N, above zonal mean tropopause). The FTIR data exhibit significantly differing signatures in free-tropospheric {H2O, δD} pairs (5 km a.s.l.) – given as the mean with uncertainty of ±2 standard error (SE) – for TUS (VMRH2O = 2.4 [2.3, 2.6] × 103 ppmv, δD = −315 [−326, −303] ‰), TNA (2.8 [2.6, 2.9] × 103 ppmv, −251 [−257, −246] ‰), and STIs (1.2 [1.1, 1.3] × 103 ppmv, −384 [−397, −372] ‰). For TUS events, {H2O, δD} observations depend on surface temperature in the source region and the degree of dehydration having occurred during updraft in warm conveyor belts. During TNA events (dry convection of boundary layer air) relatively moist and weakly HDO-depleted air masses are imported. In contrast, STI events are associated with import of predominantly dry and HDO-depleted air masses. These long-range-transport patterns potentially involve the import of various trace constituents to the central European free troposphere, i.e., import of pollution from North America (e.g., aerosol, ozone, carbon monoxide), Saharan mineral dust, stratospheric ozone, and other airborne species such as pollen. Our results provide evidence that {H2O, δD} observations are a valuable proxy for the transport of such tracers. To validate this finding, we consult a database of transport events (TNA and STI) covering 2013–2015 deduced by data filtering from in situ measurements at Zugspitze and lidar profiles at nearby Garmisch. Indeed, the FTIR data related to these verified TNA events (27 days) exhibit characteristic fingerprints in IWV (5.5 [4.9, 6.1] mm) and δDcol (−266 [−284, −247] ‰), which are significantly distinguishable from the rest of the time series (4.3 [4.1, 4.5] mm, −316 [−324, −308] ‰). This holds true for 136 STI days considering uncertainties of ±1 SE (4.2 [4.0, 4.3] mm, −322 [−327, −316] ‰) with respect to the remainder (4.6 [4.5, 4.8] mm, −302 [−307, −297] ‰). Furthermore, deep stratospheric intrusions to the Zugspitze summit (in situ humidity and beryllium-7 data filtering) show a significantly lower mean value (−334 [−337, −330] ‰) of lower-tropospheric δD (3–5 km a.s.l.) than the rest of the 2005–2015 time series (−284 [−286, −282] ‰) considering uncertainty of ±2 SE. Our results show that consistent {H2O, δD} observations at Zugspitze can serve as an operational indicator for long-range-transport events potentially affecting regional climate and air quality, as well as human health in central Europe.

Potential vorticity patterns in Mediterranean “hurricanes”

AbstractThe potential vorticity (PV) anomalies due to the intrusion of dry stratospheric air and those generated by the tropospheric diabatic latent heating are qualitatively analyzed for five Mediterranean tropical‐like cyclones (also known as Medicanes). Model simulations show the presence of an upper level PV streamer in the early stages of the cyclone, located on the left exit of a jet stream, and a middle‐low level PV anomaly generated by the convection developing around the low‐level vortex. In the mature stage, the upper level PV anomaly around the cyclone evolves differently for each case and appears somehow dependent on the lifetime. Only for the 2006 Medicane, the PV anomalies form an intense PV tower extending continuously from the lower troposphere to the lower stratosphere.

Diurnal variability of the global tropical tropopause: results inferred from COSMIC observations

Short and long-term variability of the tropical tropopause controls the exchange of minor constituents between the troposphere and the stratosphere. We present the diurnal variability of the global tropical tropopause altitude and temperature using 7 years of COSMIC observations. The aim of the study is to extract diurnal tropopause signals and their impact on stratosphere-troposphere exchange processes. The possible role of atmospheric tides and convection in controlling the tropopause characteristics are discussed. The most significant and new observation is that in the deep tropics the cold-point tropopause altitude is higher and temperatue is cooler over the land (ocean) during evening to late evening hours (afternoon to early evening). Lower tropopause altitude allows the stratospheric air intrusion into the troposphere during the day time. The combined effect of diurnal tropopause altitude changes and turbulent mixing increases the possibility of stratospheric intrusions. A warmer forenoon tropopause allows increased injection of water vapor from the troposphere to the lower stratosphere. Over the tropical land (ocean), the zonal mean diurnal amplitude is 130–200 m (140–180 m) for tropopause altitude and 0.6–0.9 K (0.6–0.8 K) for tropopause temperature.

Seasonal variation of the O3–CO correlation derived from remote sensing measurements over western Japan

We used a lower tropospheric ozone column (LTOC) and column-averaged dry-air mole fraction of carbon monoxide (XCO) data observed in the area around Saga, which is located in western Japan and is close to the Asian continent, with an aim to investigate whether these data can characterize the seasonal variation of the photochemical ozone (O3) formation in the northeast Asian Pacific rim region. The LTOC data after April 2009 were retrieved from thermal infrared spectra measured by the Thermal and Near Infrared Sensor for Carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse Gases Observing Satellite (GOSAT). The XCO data after July 2011 were obtained from ground-based high-resolution FTS measurements at Saga. The retrieved LTOCs were validated with those derived from a differential absorption lidar for O3 at Saga. The LTOCs showed a distinct seasonal variation that reached a maximum in late spring (May or June) and a local minimum in winter. In addition to the general seasonal pattern, we observed pronounced minimums in July or August. The XCO concentrations showed a maximum in spring and a minimum in summer. These seasonal patterns are consistent with those observed from mountainous sites in Japan. The origins of the air masses reaching Saga were characterized for each season according to backward trajectories, and the factors causing the temporal variations of the LTOCs and the XCO were identified based on the transport paths of the air masses. The enhancement of the LTOC relative to the XCO (ΔO3/ΔCO ratio) reveals significant positive correlations in the spring and summer seasons with slopes of 0.21 and 0.45 ppb/ppb, respectively. The effects of stratospheric air intrusion on the observed ΔO3/ΔCO ratio in spring were investigated using meteorological data (backward trajectory and potential vorticity) and column-averaged hydrogen fluoride data derived from the ground-based FTS measurements. It was found that there was little contribution of the stratospheric intrusion. This suggests that the positive correlations of the ΔO3/ΔCO ratio are likely to be a result of photochemical O3 production in the troposphere.

Stratospheric ozone in boreal fire plumes – the 2013 smoke season over central Europe

Abstract. In July 2013 very strong boreal fire plumes were observed at the northern rim of the Alps by lidar and ceilometer measurements of aerosol, ozone and water vapour for about 3 weeks. In addition, some of the lower-tropospheric components of these layers were analysed at the Global Atmosphere Watch laboratory at the Schneefernerhaus high-altitude research station (2650 m a.s.l., located a few hundred metres south-west of the Zugspitze summit). The high amount of particles confirms our hypothesis that fires in the Arctic regions of North America lead to much stronger signatures in the central European atmosphere than the multitude of fires in the USA. This has been ascribed to the prevailing anticyclonic advection pattern during favourable periods and subsidence, in contrast to warm-conveyor-belt export, rainout and dilution frequently found for lower latitudes. A high number of the pronounced aerosol structures were positively correlated with elevated ozone. Chemical ozone formation in boreal fire plumes is known to be rather limited. Indeed, these air masses could be attributed to stratospheric air intrusions descending from remote high-latitude regions, obviously picking up the aerosol on their way across Canada. In one case, subsidence from the stratosphere over Siberia over as many as 15–20 days without increase in humidity was observed although a significant amount of Canadian smoke was trapped. These coherent air streams lead to rather straight and rapid transport of the particles to Europe.

Excess of ²¹⁰polonium activity in the surface urban atmosphere. Part (1) fluctuation of the ²¹⁰Po excess in the air.

The concentrations of (210)Pb, (210)Bi, and (210)Po in the urban atmosphere of Lodz city were measured from February 2010 to May 2010 and from May 2011 to April 2012. The seasonal changes in the activity ratios for (210)Po/(210)Pb and (210)Bi/(210)Pb indicated that the observed fluctuations were independent of the concentration of tropospheric (210)Pb and its decay products, particularly (210)Po. A simple calculation method was proposed for the estimation of the excess of (210)Po in urban aerosols in relation to the fraction of its activity formed from (210)Pb. On the basis of the results obtained, it was concluded that a substantial part of the (210)Po in urban air did not come from the decay of atmospheric (222)Rn, but rather it was from artificial sources. The highest levels of measured total (210)Po activity were observed during the winter period. This observation suggests that the main source of (210)Po in the investigated region could be related to anthropogenic emissions from domestic heating systems and local coal power plants, rather than from other sources, such as soil resuspension or stratospheric air intrusion as usually suggested in the literature.