scholarly journals On the Susceptibility of Cold Tropical Cirrus to Ice Nuclei Abundance

2016 ◽  
Vol 73 (6) ◽  
pp. 2445-2464 ◽  
Author(s):  
Eric J. Jensen ◽  
Rei Ueyama ◽  
Leonhard Pfister ◽  
Thaopaul V. Bui ◽  
R. Paul Lawson ◽  
...  
Keyword(s):  
High Frequency ◽  
Regional Distribution ◽  
Ice Nucleation ◽  
Small Scale ◽  
Height Distribution ◽  
Microphysical Properties ◽  
Ice Nuclei ◽  
High Frequency Waves ◽  
The Impact

Abstract Numerical simulations of cirrus formation in the tropical tropopause layer (TTL) during boreal wintertime are used to evaluate the impact of heterogeneous ice nuclei (IN) abundance on cold cloud microphysical properties and occurrence frequencies. The cirrus model includes homogeneous and heterogeneous ice nucleation, deposition growth/sublimation, and sedimentation. Reanalysis temperature and wind fields with high-frequency waves superimposed are used to force the simulations. The model results are constrained by comparison with in situ and satellite observations of TTL cirrus and relative humidity. Temperature variability driven by high-frequency waves has a dominant influence on TTL cirrus microphysical properties and occurrence frequencies, and inclusion of these waves is required to produce agreement between the simulated and observed abundance of TTL cirrus. With homogeneous freezing only and small-scale gravity waves included in the temperature curtains, the model produces excessive ice concentrations compared with in situ observations. Inclusion of relatively numerous heterogeneous ice nuclei (NIN ≥ 100 L−1) in the simulations improves the agreement with observed ice concentrations. However, when IN contribute significantly to TTL cirrus ice nucleation, the occurrence frequency of large supersaturations with respect to ice is less than indicated by in situ measurements. The model results suggest that the sensitivity of TTL cirrus extinction and ice water content statistics to heterogeneous ice nuclei abundance is relatively weak. The simulated occurrence frequencies of TTL cirrus are quite insensitive to ice nuclei abundance, both in terms of cloud frequency height distribution and regional distribution throughout the tropics.

scholarly journals Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

2009 ◽  
Vol 9 (5) ◽  
pp. 20631-20675 ◽  
Author(s):  
E. J. Jensen ◽  
L. Pfister ◽  
T.-P. Bui ◽  
P. Lawson ◽  
D. Baumgardner
Keyword(s):  
Ice Nucleation ◽  
Nucleation Theory ◽  
Ice Crystal ◽  
Tropical Tropopause Layer ◽  
Microphysical Properties ◽  
Tropical Tropopause ◽  
Ice Nuclei ◽  
Ice Crystal Size ◽  
Homogeneous Freezing

Abstract. In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remote-sensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L−1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.

scholarly journals Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen

2012 ◽  
Vol 12 (5) ◽  
pp. 2541-2550 ◽  
Author(s):  
B. G. Pummer ◽  
H. Bauer ◽  
J. Bernardi ◽  
S. Bleicher ◽  
H. Grothe
Keyword(s):  
Radiative Forcing ◽  
Pollen Grains ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Distribution Area ◽  
Ice Cloud ◽  
Ice Nuclei ◽  
Nucleation Activity ◽  
Ice Nucleation Activity ◽  
The Impact

Abstract. The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behaviour. The average freezing temperatures in laboratory experiments range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been separated from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromolecules located on the pollen. Once extracted, they can be distributed further through the atmosphere than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our experiments lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compounds.

scholarly journals Factors that influence surface PM<sub>2.5</sub> values inferred from satellite observations: perspective gained for the US Baltimore–Washington metropolitan area during DISCOVER-AQ

2014 ◽  
Vol 14 (4) ◽  
pp. 2139-2153 ◽  
Author(s):  
S. Crumeyrolle ◽  
G. Chen ◽  
L. Ziemba ◽  
A. Beyersdorf ◽  
L. Thornhill ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Metropolitan Area ◽  
Scattering Coefficient ◽  
Data Set ◽  
Ambient Relative Humidity ◽  
Microphysical Properties ◽  
The Us ◽  
Dry Conditions ◽  
The Impact

Abstract. During the NASA DISCOVER-AQ campaign over the US Baltimore, MD–Washington, D.C., metropolitan area in July 2011, the NASA P-3B aircraft performed extensive profiling of aerosol optical, chemical, and microphysical properties. These in situ profiles were coincident with ground-based remote sensing (AERONET) and in situ (PM2.5) measurements. Here, we use this data set to study the correlation between the PM2.5 observations at the surface and the column integrated measurements. Aerosol optical depth (AOD550 nm) calculated with the extinction (550 nm) measured during the in situ profiles was found to be strongly correlated with the volume of aerosols present in the boundary layer (BL). Despite the strong correlation, some variability remains, and we find that the presence of aerosol layers above the BL (in the buffer layer – BuL) introduces significant uncertainties in PM2.5 estimates based on column-integrated measurements (overestimation of PM2.5 by a factor of 5). This suggests that the use of active remote sensing techniques would dramatically improve air quality retrievals. Indeed, the relationship between the AOD550 nm and the PM2.5 is strongly improved by accounting for the aerosol present in and above the BL (i.e., integrating the aerosol loading from the surface to the top of the BuL). Since more than 15% of the AOD values observed during DISCOVER-AQ are dominated by aerosol water uptake, the f(RH)amb (ratio of scattering coefficient at ambient relative humidity (RH) to scattering coefficient at low RH; see Sect. 3.2) is used to study the impact of the aerosol hygroscopicity on the PM2.5 retrievals. The results indicate that PM2.5 can be predicted within a factor up to 2 even when the vertical variability of the f(RH)amb is assumed to be negligible. Moreover, f(RH = 80%) and RH measurements performed at the ground may be used to estimate the f(RH)amb during dry conditions (RHBL < 55%).

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2016 ◽  
Vol 16 (1) ◽  
pp. 35-46 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved.With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, a low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INCs.

scholarly journals Effect of gravity wave temperature fluctuations on homogeneous ice nucleation in the tropical tropopause layer

2015 ◽  
Vol 15 (6) ◽  
pp. 8771-8799 ◽  
Author(s):  
T. Dinh ◽  
A. Podglajen ◽  
A. Hertzog ◽  
B. Legras ◽  
R. Plougonven
Keyword(s):  
Cooling Rate ◽  
Gravity Wave ◽  
High Frequency ◽  
Full Range ◽  
Temperature Fluctuations ◽  
Ice Nucleation ◽  
Microphysics Scheme ◽  
Tropical Tropopause ◽  
The Absolute ◽  
The Impact

Abstract. The impact of high-frequency fluctuations of temperature on homogeneous nucleation of ice crystals in the vicinity of the tropical tropopause is investigated using a bin microphysics scheme for air parcels. The imposed temperature fluctuations come from measurements during isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency, guaranteeing that gravity wave signals are well resolved. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentration (INC) as previously observed in the tropical upper troposphere. In particular, low INC may be obtained if the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This work suggests that homogeneous ice nucleation is not necessarily inconsistent with observations of low INC.

scholarly journals Cloud-scale ice supersaturated regions spatially correlate with high water vapor heterogeneities

2013 ◽  
Vol 13 (8) ◽  
pp. 22249-22296
Author(s):  
M. Diao ◽  
M. A. Zondlo ◽  
A. J. Heymsfield ◽  
L. M. Avallone ◽  
M. E. Paige ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Small Scale ◽  
Cirrus Cloud ◽  
Median Length ◽  
Upper Troposphere ◽  
Earth’S Climate

Abstract. Cirrus clouds have large yet uncertain impacts on the Earth's climate. Ice supersaturation (ISS) – where the relative humidity with respect to ice (RHi) is greater than 100% – is the prerequisite condition of ice nucleation. Here we use 1 Hz (~230 m) in situ aircraft-based observations from 87° N–67° S to analyze the spatial characteristics of ice supersaturated regions (ISSRs). The median length of 1-D horizontal ISSR segments is found to be very small (~1 km), which is two orders of magnitude smaller than previously reported. To understand the conditions of these small scale ISSRs, we compare individual ISSRs with their horizontally adjacent subsaturated surroundings and show that 99% and 73% of the ISSRs are moister and colder, respectively. When quantifying the contributions of water vapor (H2O) and temperature (T) individually, the magnitudes of the differences between the maximum RHi values inside ISSRs (RHimax) and the RHi in subsaturated surroundings are largely derived from the H2O spatial variabilities (by 88%) than from those of T (by 9%). These features hold for both ISSRs with and without ice crystals present. Similar analyses for all RHi horizontal variabilities (including ISS and non-ISS) show strong contributions from H2O variabilities at various T, H2O, pressure (P) and various horizontal scales (~1–100 km). Our results provide a new observational constraint on ISSRs on the microscale (~100 m) and point to the importance of understanding how these fine scale features originate and impact cirrus cloud formation and the RHi field in the upper troposphere (UT).

Ice-nucleating Macromolecules from Alpine Forests as Possible Contributors to Cloud Glaciation Processes

2020 ◽  
Author(s):  
Teresa M. Seifried ◽  
Paul Bieber ◽  
Laura Felgitsch ◽  
Hinrich Grothe
Keyword(s):  
Land Surface ◽  
Global Climate ◽  
Life Time ◽  
Ice Nucleation ◽  
Radiative Properties ◽  
Small Scale ◽  
Emission Rates ◽  
Sampling Systems ◽  
Rain Fall

&lt;p&gt;Ice nucleation in the atmosphere leads to the formation of mixed-phase as well as cirrus clouds in the upper troposphere. Cloud glaciation can either occur homogeneously at temperatures below -38&amp;#176;C or heterogeneously in the presence of ice-nucleating particles (INPs) at temperatures higher than -38&amp;#176;C. Depending on the aggregate state of a cloud, it&amp;#8217;s life time and radiative properties vary and thus affect regional and global climate. The influence of biogenic INPs on atmospheric processes as well as the transport of these particles from the land surface to the atmosphere remains elusive. Several plants from boreal and alpine forests are known to contain ice-nucleating macromolecules (INMs) to survive in extreme conditions. However, less is known about chemical characteristics and actual emission rates of such INMs.&lt;/p&gt;&lt;p&gt;We present here our investigation of surface extracts from different tree tissues (Betula pendula and Pinus sylvestris). We were able to extract INMs from nearly all samples. Furthermore, we analyzed the ability of these INMs to be released during rain fall events in-situ. To investigate possible transport mechanisms of INMs from the canopy of studied tree species to the atmosphere we sampled aerosols with two small scale drones, carrying our self-build sampling systems called DAPSI (Drone-based Aerosol Particles Sampling Impinger/Impactor). Results indicate that birches and pines outline an important source of airborne biogenic INPs.&lt;/p&gt;

scholarly journals Observations of ice multiplication in a weakly convective cell embedded in supercooled mid-level stratus

2011 ◽  
Vol 11 (1) ◽  
pp. 257-273 ◽  
Author(s):  
J. Crosier ◽  
K. N. Bower ◽  
T. W. Choularton ◽  
C. D. Westbrook ◽  
P. J. Connolly ◽  
...  
Keyword(s):  
Carbonaceous Material ◽  
Temperature Inversion ◽  
Convective Cell ◽  
Cloud Base ◽  
Stratus Cloud ◽  
Microphysical Properties ◽  
Ice Nuclei ◽  
Immersion Freezing ◽  
Ice Multiplication

Abstract. Simultaneous observations of cloud microphysical properties were obtained by in-situ aircraft measurements and ground based Radar/Lidar. Widespread mid-level stratus cloud was present below a temperature inversion (~5 °C magnitude) at 3.6 km altitude. Localised convection (peak updraft 1.5 m s−1) was observed 20 km west of the Radar station. This was associated with convergence at 2.5 km altitude. The convection was unable to penetrate the inversion capping the mid-level stratus. The mid-level stratus cloud was vertically thin (~400 m), horizontally extensive (covering 100 s of km) and persisted for more than 24 h. The cloud consisted of supercooled water droplets and small concentrations of large (~1 mm) stellar/plate like ice which slowly precipitated out. This ice was nucleated at temperatures greater than −12.2 °C and less than −10.0 °C, (cloud top and cloud base temperatures, respectively). No ice seeding from above the cloud layer was observed. This ice was formed by primary nucleation, either through the entrainment of efficient ice nuclei from above/below cloud, or by the slow stochastic activation of immersion freezing ice nuclei contained within the supercooled drops. Above cloud top significant concentrations of sub-micron aerosol were observed and consisted of a mixture of sulphate and carbonaceous material, a potential source of ice nuclei. Particle number concentrations (in the size range 0.1

scholarly journals Cloud-scale ice-supersaturated regions spatially correlate with high water vapor heterogeneities

2014 ◽  
Vol 14 (5) ◽  
pp. 2639-2656 ◽  
Author(s):  
M. Diao ◽  
M. A. Zondlo ◽  
A. J. Heymsfield ◽  
L. M. Avallone ◽  
M. E. Paige ◽  
...  
Keyword(s):  
Water Vapor ◽  
High Water ◽  
Ice Nucleation ◽  
Cloud Formation ◽  
Small Scale ◽  
Cirrus Cloud ◽  
Median Length ◽  
Upper Troposphere ◽  
Earth’S Climate

Abstract. Cirrus clouds have large yet uncertain impacts on Earth's climate. Ice supersaturation (ISS) – where the relative humidity with respect to ice (RHi) is greater than 100% – is the prerequisite condition of ice nucleation. Here we use 1 Hz (~230 m) in situ, aircraft-based observations from 87° N to 67° S to analyze the spatial characteristics of ice-supersaturated regions (ISSRs). The median length of 1-D horizontal ISSR segments is found to be very small (~1 km), which is 2 orders of magnitude smaller than previously reported. To understand the conditions of these small-scale ISSRs, we compare individual ISSRs with their horizontally adjacent subsaturated surroundings and show that 99% and 73% of the ISSRs are moister and colder, respectively. When quantifying the contributions of water vapor (H2O) and temperature (T) individually, the magnitudes of the differences between the maximum RHi values inside ISSRs (RHimax) and the RHi in subsaturated surroundings are largely derived from the H2O spatial variabilities (by 88%) than from those of T (by 9%). These features hold for both ISSRs with and without ice crystals present. Similar analyses for all RHi horizontal variabilities (including ISS and non-ISS) show strong contributions from H2O variabilities at various T, H2O, pressure (P) and various horizontal scales (~1–100 km). Our results provide a new observational constraint on ISSRs on the microscale (~100 m) and point to the importance of understanding how these fine-scale features originate and impact cirrus cloud formation and the RHi field in the upper troposphere (UT).

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