Hydration of the lower stratosphere by ice crystal geysers over land convective systems

Abstract. The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to Mesoscale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of the instrument show the presence of accumulation of enhanced water vapour layers between the tropopause at 370 K and the 420 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets above the tropopause by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers exceeds frequently by 1–3 ppmv the average 6 ppmv saturation ratio at the tropopause and by up to 7 ppmv in the extreme case of local storm in coincidence with the presence of ice crystals. The presence of such layers strongly suggests hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like increase of water vapour up to 19 km seen by the high-resolution hygrometer during the season of maximum temperature of the tropopause, suggests that the above hydration mechanism may contribute to the summer maximum moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause might be an important contributor to the stratospheric water vapour budget.

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Hydration of the lower stratosphere by ice crystal geysers over land convective systems

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-15463-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 15463-15490 ◽

Cited By ~ 1

Author(s):

S. Khaykin ◽

J.-P. Pommereau ◽

L. Korshunov ◽

V. Yushkov ◽

J. Nielsen ◽

...

Keyword(s):

Water Vapour ◽

Lower Stratosphere ◽

Monsoon Season ◽

Satellite Observation ◽

Fast Response ◽

Vertical Resolution ◽

Ice Crystal ◽

Lyman Alpha ◽

Convective Systems ◽

Mesoscale Convective

Abstract. The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to MesoScale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of this instrument show the presence of enhanced water vapour layers between the tropopause at 370 K and the 450 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images, over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets up to 18.5 km by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers, up to 8 ppmv higher than that of saturation at the tropopause, and the coincidence with the presence of ice crystals strongly suggest hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like structure of the water vapour seen by the high-resolution hygrometer in contrast to smooth profiles reported by a coarse vertical-resolution satellite observation, suggests that the hydration mechanism described above may be responsible for the known summer seasonal increase of moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause may be an important contributor to the stratospheric water vapour budget.

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Annual cycle of water vapour in the lower stratosphere over the Indian Peninsula derived from Cryogenic Frost-point Hygrometer observations

10.5194/acp-2018-630 ◽

2018 ◽

Author(s):

Maria Emmanuel ◽

Sukumarapillai V. Sunilkumar ◽

Muhsin Muhammed ◽

Buduru Suneel Kumar ◽

Nagendra Neerudu ◽

...

Keyword(s):

Water Vapour ◽

Summer Monsoon ◽

Lower Stratosphere ◽

Indian Subcontinent ◽

Monsoon Season ◽

Deep Convection ◽

Equatorial Station ◽

Post Monsoon ◽

Frost Point ◽

Stratospheric Water Vapour

Abstract. In situ measurements of lower stratospheric water vapour employing Cryogenic Frost point Hygrometer (CFH) over two tropical stations, Trivandrum (8.53 °N, 76.87 °E) and Hyderabad (17.47 °N, 78.58 °E) over the Indian subcontinent are conducted as part of Tropical Tropopause Dynamics (TTD) monthly campaigns under GARNETS program. The annual variation of lower stratosphere (LS) water vapour clearly depicts the so called tape recorder effect at both the stations. The ascent rate of water vapour compares well with the velocity of Brewer-Dobson circulation and is slightly higher over the equatorial station when compared to the off-equatorial station. The column integrated water vapour in the LS varies in the range 1.5 to 4 g/m2 with low values during winter and high values during summer monsoon and post monsoon seasons and its variability shows the signatures of local dynamics. The variation in water vapour mixing ratio (WVMR) at the cold point tropopause (CPT) exactly follows the variation in CPT temperature. The difference in WVMR between the stations shows a semi-annual variability in the altitude region 18–20 km region with high values of WVMR during summer monsoon and winter over Hyderabad and during pre-monsoon and post-monsoon over Trivandrum. This difference is related to the influence of the variations in local CPT temperature and deep convection. The monsoon dynamics has a significant role in stratospheric water vapour distribution in summer monsoon season.

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An overview of the SCOUT-AMMA stratospheric aircraft, balloons and sondes campaign in West Africa, August 2006: rationale, roadmap and highlights

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-19713-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 19713-19781 ◽

Cited By ~ 5

Author(s):

F. Cairo ◽

J. P. Pommereau ◽

K. S. Law ◽

H. Schlager ◽

A. Garnier ◽

...

Keyword(s):

West Africa ◽

Large Scale ◽

Lower Stratosphere ◽

Chemical Species ◽

Upper Troposphere ◽

Convective Systems ◽

Mesoscale Convective ◽

Aerosol Dust ◽

D 20 ◽

The Impact

Abstract. A multi-platform field measurement campaign involving aircraft and balloons took place over West Africa between 26 July and 25 August 2006, in the frame of the concomitant AMMA Special Observing Period and SCOUT-O3 African tropical activities. Specifically aiming at sampling the upper troposphere and lower stratosphere, the high-altitude research aircraft M55 Geophysica was deployed in Ouagadougou (12.3° N, 1.7° W), Burkina Faso, in conjunction with the German D-20 Falcon, while a series of stratospheric balloon and sonde flights were conducted from Niamey (13.5° N, 2.0° E), Niger. The stratospheric aircraft and balloon flights intended to gather experimental evidence for a better understanding of large scale transport, assessing the effect of lightning on NOx production, and studying the impact of intense mesoscale convective systems on water, aerosol, dust and chemical species in the upper troposphere and lower stratosphere. The M55 Geophysica carried out five local and four transfer flights between southern Europe and the Sahel and back, while eight stratospheric balloons and twenty-nine sondes were flown from Niamey. These experiments allowed a characterization of the tropopause and lower stratosphere of the region. We provide here an overview of the campaign activities together with a description of the general meteorological situation during the flights and a summary of the observations accomplished.

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An introduction to the SCOUT-AMMA stratospheric aircraft, balloons and sondes campaign in West Africa, August 2006: rationale and roadmap

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-2237-2010 ◽

2010 ◽

Vol 10 (5) ◽

pp. 2237-2256 ◽

Cited By ~ 55

Author(s):

F. Cairo ◽

J. P. Pommereau ◽

K. S. Law ◽

H. Schlager ◽

A. Garnier ◽

...

Keyword(s):

West Africa ◽

Large Scale ◽

Lower Stratosphere ◽

Chemical Species ◽

Upper Troposphere ◽

Convective Systems ◽

Mesoscale Convective ◽

Aerosol Dust ◽

D 20 ◽

The Impact

Abstract. A multi-platform field measurement campaign involving aircraft and balloons took place over West Africa between 26 July and 25 August 2006, in the frame of the concomitant AMMA Special Observing Period and SCOUT-O3 African tropical activities. Specifically aiming at sampling the upper troposphere and lower stratosphere, the high-altitude research aircraft M55 Geophysica was deployed in Ouagadougou (12.3° N, 1.7° W), Burkina Faso, in conjunction with the German D-20 Falcon, while a series of stratospheric balloons and sonde flights were conducted from Niamey (13.5° N, 2.0° E), Niger. Altogether, these measurements were intended to provide experimental evidence for a better understanding of large scale transport, assessing the effect of lightning on NOx production, and studying the impact of intense mesoscale convective systems on water, aerosol, dust and chemical species in the upper troposphere and lower stratosphere. The M55 Geophysica carried out five local and four transfer flights between southern Europe and the Sahel and back, while eight stratospheric balloons and twenty-nine sondes were flown from Niamey. These experiments allowed a characterization of the tropopause and lower stratosphere of the region. The paper provides an overview of SCOUT-AMMA campaign activities together with a description of the meteorology of the African monsoon and the situation prevailing during the flights and a brief summary of the observations accomplished.

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Combined use of Raman Lidar and DIAL measurements and MESO-NH model simulations for the characterization of complex water vapour field structures, their genesis and their role in the activation of Mesoscale Convective Systems

10.5194/egusphere-egu21-9297 ◽

2021 ◽

Author(s):

Paolo Di Girolamo ◽

Marie-Noelle Bouin ◽

Cyrille Flamant ◽

Donato Summa ◽

Benedetto De Rosa ◽

...

Keyword(s):

Water Vapour ◽

Heavy Precipitation ◽

Mesoscale Convective Systems ◽

Mixing Ratio ◽

Raman Lidar ◽

Convective Systems ◽

Combined Use ◽

Lidar Measurements ◽

Mesoscale Convective ◽

Precipitation Events

As part of the Cevennes-Vivarais site, the University of Basilicata Raman lidar system BASIL (Di Girolamo et al., 2009, 2012, 2916) was deployed in Candillargues (C&#233;vennes-Vivarais Southern France Lat: 43&#176;37&#8242; N; Long: 04&#176;04&#8242; E; Elev: 1 m) and operated throughout the duration of HyMeX-SOP 1 (September-November 2012), providing high-resolution and accurate measurements, both in daytime and night-time, of atmospheric temperature, water vapour mixing ratio and particle backscattering and extinction coefficient at three wavelengths.Measurements carried out by BASIL on 28 September 2012 reveal a water vapour field characterized by a quite complex vertical structure. Reported measurements were run in the time interval between two consecutive heavy precipitation events, from 15:30 UTC on 28 September to 03:30 UTC on 29 September 2012. Throughout most of this observation period, lidar measurements reveal the presence of four distinct humidity layers.The present research effort aims at assessing the origin and transport path of the different humidity filaments observed by BASIL on this day. The analysis approach relies on the comparison between Raman lidar measurements and MESO-NH and NOAA-HYSPLIT model simulations. Back-trajectory analyses from MESO-NH reveal that air masses ending in Candillargues at different altitudes levels are coming and are originated from different geographical regions.The four distinct humidity layers observed by BASIL are also identified in the water vapour mixing ratio profiles collected by the air-borne DIAL LEANDRE 2 on-board of the French research aircraft ATR42. The exact correspondence, in terms of back-trajectories computation and water budget, between the humidity layers observed by BASIL and those identified in LEANDRE2 measurements has been verified based on a dedicated simulation effort.In this research work we also try to identify the presence of dry layers and cold pools and assess their role in the genesis of the mesoscale convective systems and the heavy precipitation events observed on 29 September 2012 based on the combined use of water vapour mixing ratio and temperature profile measurements from BASIL and water vapour mixing ratio profile measurements from LEANDRE 2, again supported by MESO-NH simulations.

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Sensitivity of GPS tropospheric estimates to mesoscale convective systems in West Africa

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-9541-2019 ◽

2019 ◽

Vol 19 (14) ◽

pp. 9541-9561 ◽

Cited By ~ 1

Author(s):

Samuel Nahmani ◽

Olivier Bock ◽

Françoise Guichard

Keyword(s):

West Africa ◽

Monsoon Season ◽

Mesoscale Convective Systems ◽

Cold Pool ◽

Small Scale ◽

Strong Impact ◽

Convective Systems ◽

Temporal Sampling ◽

Mesoscale Convective ◽

Convective Cells

Abstract. This study analyzes the characteristics of GPS tropospheric estimates (zenith wet delays – ZWDs, gradients, and post-fit phase residuals) during the passage of mesoscale convective systems (MCSs) and evaluates their sensitivity to the research-level GPS data processing strategy implemented. Here, we focus on MCS events observed during the monsoon season of West Africa. This region is particularly well suited for the study of these events due to the high frequency of MCS occurrences in the contrasting climatic environments between the Guinean coast and the Sahel. This contrast is well sampled with data generated by six African Monsoon Multidisciplinary Analysis (AMMA) GPS stations. Tropospheric estimates for a 3-year period (2006–2008), processed with both the GAMIT and GIPSY-OASIS software packages, were analyzed and intercompared. First, the case of a MCS that passed over Niamey, Niger, on 11 August 2006 demonstrates a strong impact of the MCS on GPS estimates and post-fit residuals when the GPS signals propagate through the convective cells as detected on reflectivity maps from the MIT C-band Doppler radar. The estimates are also capable of detecting changes in the structure and dynamics of the MCS. However, the sensitivity is different depending on the tropospheric modeling approach adopted in the software. With GIPSY-OASIS, the high temporal sampling (5 min) of ZWDs and gradients is well suited for detecting the small-scale, short-lived, convective cells, while the post-fit residuals remain quite small. With GAMIT, the lower temporal sampling of the estimated parameters (hourly for ZWDs and daily for gradients) is not sufficient to capture the rapid delay variations associated with the passage of the MCS, but the post-fit phase residuals clearly reflect the presence of a strong refractivity anomaly. The results are generalized with a composite analysis of 414 MCS events observed over the 3-year period at the six GPS stations with the GIPSY-OASIS estimates. A systematic peak is found in the ZWDs coincident with the cold pool crossing time associated with the MCSs. The tropospheric gradients reflect the path of the MCS propagation (generally from east to west). This study concludes that ZWDs, gradients, and post-fit phase residuals provide relevant and complementary information on MCSs passing over or in the vicinity of a GPS station.

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Corridors of Warm Season Precipitation in the Central United States

Monthly Weather Review ◽

10.1175/mwr3188.1 ◽

2006 ◽

Vol 134 (9) ◽

pp. 2297-2317 ◽

Cited By ~ 99

Author(s):

John D. Tuttle ◽

Chris A. Davis

Keyword(s):

United States ◽

Environmental Factors ◽

Large Scale ◽

Warm Season ◽

Extreme Case ◽

Maximum Rainfall ◽

Convective Systems ◽

Precipitation Forecasting ◽

Central United States ◽

Mesoscale Convective

Abstract During the warm season in the central United States there often exists a corridor of precipitation where a succession of mesoscale convective systems (MCSs) follow similar paths lasting several days. The total cumulative rainfall within a corridor can be substantial while precipitation at nearby regions may be below normal. Understanding the nature of the corridors and the environmental factors important for their formation thus has important implications for quantitative precipitation forecasting and hydrological studies. In this study a U.S. national composite radar dataset and model-analyzed fields are used for the 1998–2002 warm seasons (July–August) to understand the properties of corridors and what environmental factors are important for determining when and where they develop. The analysis is restricted to a relatively narrow longitudinal band in the central United States (95°–100°W), a region where convection often intensifies and becomes highly organized. It is found that ∼68% of MCSs were members of a series and that corridors typically persist for 2–7 days with an extreme case lasting 13 days. Cumulative radar-derived maximum rainfall ranges from 8 to 50 cm, underscoring the fact that corridors can experience excessive rainfall. Combining radar with Rapid Update Cycle model kinematic and thermodynamic fields, 5-yr composites are presented and stratified according to the environmental conditions. While the corridors show the expected association with areas of enhanced CAPE and relatively strong northwesterly/westerly shear, the strongest association is with the northern terminus region of the nocturnal low-level jet (LLJ). Furthermore, the relative intensity of the rainfall is positively correlated with the strength of the LLJ. The LLJ is thought to play a role through enhanced convergence and lifting, moisture transport, and frontogenesis. In the five years analyzed, the large-scale environment varied considerably, but the role of the LLJ in the formation of corridors remained persistent.

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