Correlation among cirrus ice content, water vapor and temperature in the TTL as observed by CALIPSO and Aura/MLS

Flury, Thomas; Wu, Dong L.; Read, W. G.

doi:10.5194/acp-12-683-2012

Cited by 24 publications

(33 citation statements)

References 27 publications

(32 reference statements)

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“…Their results show that aerosols were predominantly moved poleward and show no signs of mixing back to their tropical origin in the lower stratosphere. Flury et al (2012) showed that total water (ice and vapor) is roughly constant in the tropical tropopause layer (TTL) at 100 hPa on seasonal time scales. However, the temperature determines the balance between ice in cirrus clouds and water vapour.…”

Section: T Flury Et Al: Variability Of the Brewer-dobson Circulationmentioning

confidence: 99%

“…To compare our observations with the QBO we use the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis daily zonal wind data, which are retrieved on 17 pressure levels from 1000 hPa to 10 hPa. The method used to determine vertical and meridional speeds of the BDC is similar to the one introduced by Schoeberl et al (2008) and Flury et al (2012). We calculate the time lagged correlation in the H 2 O time series between two different levels.…”

Section: T Flury Et Al: Variability Of the Brewer-dobson Circulationmentioning

confidence: 99%

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Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

Flury

Read

2013

Atmos. Chem. Phys.

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Abstract. We use Aura/MLS stratospheric water vapour (H2O) measurements as tracer for dynamics and infer interannual variations in the speed of the Brewer–Dobson circulation (BDC) from 2004 to 2011. We correlate one-year time series of H2O in the lower stratosphere at two subsequent pressure levels (68 hPa, ~18.8 km and 56 hPa, ~19.9 km at the Equator) and determine the time lag for best correlation. The same calculation is made on the horizontal on the 100 hPa (~16.6 km) level by correlating the H2O time series at the Equator with the ones at 40° N and 40° S. From these lag coefficients we derive the vertical and horizontal speeds of the BDC in the tropics and extra-tropics, respectively. We observe a clear interannual variability of the vertical and horizontal branch. The variability reflects signatures of the Quasi Biennial Oscillation (QBO). Our measurements confirm the QBO meridional circulation anomalies and show that the speed variations in the two branches of the BDC are out of phase and fairly well anti-correlated. Maximum ascent rates are found during the QBO easterly phase. We also find that transport of H2O towards the Northern Hemisphere (NH) is on the average two times faster than to the Southern Hemisphere (SH) with a mean speed of 1.15 m s−1 at 100 hPa. Furthermore, the speed towards the NH shows much more interannual variability with an amplitude of about 21% whilst the speed towards the SH varies by only 10%. An amplitude of 21% is also observed in the variability of the ascent rate at the Equator which is on the average 0.2 mm s−1.

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Section: T Flury Et Al: Variability Of the Brewer-dobson Circulationmentioning

confidence: 99%

Section: T Flury Et Al: Variability Of the Brewer-dobson Circulationmentioning

confidence: 99%

Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

Flury

Read

2013

Atmos. Chem. Phys.

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“…There is now evidence from several studies (Boehm and Verlinde, 2000;Immler et al, 2008;Fujiwara et al, 2009;Virts et al, 2010;Flury et al, 2012) that there is a correlation between cold anomalies in the TTL and cirrus clouds. From recent studies on cirrus clouds in the TTL using the lidar in space onboard CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation), the vertical motions in the regions of cirrus cloud occurrence were estimated (Virts et al, 2010).…”

Section: Large-scale Dynamicsmentioning

confidence: 99%

“…Here, we again use a lognormally distributed aerosol with modal diameter L m = 0.5 µm, a geometrical standard deviation of σ L = 1.4 and a total number concentration of N IN = 7 L −1 (see e.g. DeMott et al, 2003). The nucleation threshold is size-dependent, i.e.…”

Section: Ttl Ice Crystal Numbers From Heterogeneous and Homogeneous Nmentioning

confidence: 99%

Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Spichtinger

Krämer²

2013

Atmos. Chem. Phys.

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Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s −1 ) and faster (> 1 cm s −1 ) largescale updraughts, respectively. This statistical analysis shows that about 80 % of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20 % stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

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“…Also, we characterize the impact of orbital sampling on derived lower-stratospheric tropical vertical velocities. These velocities are computed by correlating the lag of the water vapor "tape recorder" signal between adjacent levels (Niwano et al, 2003;Flury et al, 2012;Jiang et al, 2015). As such, they are likely an upper bound on the actual velocity (Schoeberl et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Case studies of the impact of orbital sampling on stratospheric trend detection and derivation of tropical vertical velocities: solar occultation vs. limb emission sounding

et al. 2016

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Abstract. This study investigates the representativeness of two types of orbital sampling applied to stratospheric temperature and trace gas fields. Model fields are sampled using real sampling patterns from the Aura Microwave Limb Sounder (MLS), the HALogen Occultation Experiment (HALOE) and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The MLS sampling acts as a proxy for a dense uniform sampling pattern typical of limb emission sounders, while HALOE and ACE-FTS represent coarse nonuniform sampling patterns characteristic of solar occultation instruments. First, this study revisits the impact of sampling patterns in terms of the sampling bias, as previous studies have done. Then, it quantifies the impact of different sampling patterns on the estimation of trends and their associated detectability. In general, we find that coarse nonuniform sampling patterns may introduce non-negligible errors in the inferred magnitude of temperature and trace gas trends and necessitate considerably longer records for their definitive detection. Lastly, we explore the impact of these sampling patterns on tropical vertical velocities derived from stratospheric water vapor measurements. We find that coarse nonuniform sampling may lead to a biased depiction of the tropical vertical velocities and, hence, to a biased estimation of the impact of the mechanisms that modulate these velocities. These case studies suggest that dense uniform sampling such as that available from limb emission sounders provides much greater fidelity in detecting signals of stratospheric change (for example, fingerprints of greenhouse gas warming and stratospheric ozone recovery) than coarse nonuniform sampling such as that of solar occultation instruments.

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Correlation among cirrus ice content, water vapor and temperature in the TTL as observed by CALIPSO and Aura/MLS

Cited by 24 publications

References 27 publications

Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Case studies of the impact of orbital sampling on stratospheric trend detection and derivation of tropical vertical velocities: solar occultation vs. limb emission sounding

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