scholarly journals Evaluation of radar reflectivity factor simulations of ice crystal populations from in situ observations for the retrieval of condensed water content in tropical mesoscale convective systems

2017 ◽  
Vol 10 (6) ◽  
pp. 2239-2252 ◽  
Author(s):  
Emmanuel Fontaine ◽  
Delphine Leroy ◽  
Alfons Schwarzenboeck ◽  
Julien Delanoë ◽  
Alain Protat ◽  
...  
Keyword(s):  
Water Content ◽  
Relative Error ◽  
Number Concentration ◽  
Radar Reflectivity ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Condensed Water ◽  
Relative Errors ◽  
Reflectivity Factor

Abstract. This study presents the evaluation of a technique to estimate cloud condensed water content (CWC) in tropical convection from airborne cloud radar reflectivity factors at 94 GHz and in situ measurements of particle size distributions (PSDs) and aspect ratios of ice crystal populations. The approach is to calculate from each 5 s mean PSD and flight-level reflectivity the variability of all possible solutions of m(D) relationships fulfilling the condition that the simulated radar reflectivity factor (T-matrix method) matches the measured radar reflectivity factor. For the reflectivity simulations, ice crystals were approximated as oblate spheroids, without using a priori assumptions on the mass–size relationship of ice crystals. The CWC calculations demonstrate that individual CWC values are in the range ±32 % of the retrieved average CWC value over all CWC solutions for the chosen 5 s time intervals. In addition, during the airborne field campaign performed out of Darwin in 2014, as part of the international High Altitude Ice Crystals/High Ice Water Content (HAIC/HIWC) projects, CWCs were measured independently with the new IKP-2 (isokinetic evaporator probe) instrument along with simultaneous particle imagery and radar reflectivity. Retrieved CWCs from the T-matrix radar reflectivity simulations are on average 16 % higher than the direct CWCIKP measurements. The differences between the CWCIKP and averaged retrieved CWCs are found to be primarily a function of the total number concentration of ice crystals. Consequently, a correction term is applied (as a function of total number concentration) that significantly improves the retrieved CWC. After correction, the retrieved CWCs have a median relative error with respect to measured values of only −1 %. Uncertainties in the measurements of total concentration of hydrometeors are investigated in order to calculate their contribution to the relative error of calculated CWC with respect to measured CWCIKP. It is shown that an overestimation of the concentration by about +50 % increases the relative errors of retrieved CWCs by only +29 %, while possible shattering, which impacts only the concentration of small hydrometeors, increases the relative error by about +4 %. Moreover, all cloud events with encountered graupel particles were studied and compared to events without observed graupel particles. Overall, graupel particles seem to have the largest impact on high crystal number-concentration conditions and show relative errors in retrieved CWCs that are higher than for events without graupel particles.

scholarly journals Radar Reflectivity Factors Simulations of Ice Crystal Populations from In-Situ Observations for the Retrieval of Condensed Water Content in Tropical Mesoscale Convective Systems

2016 ◽  
Author(s):  
Emmanuel Fontaine ◽  
Delphine Leroy ◽  
Alfons Schwarzenboeck ◽  
Julien Delanoë ◽  
Alain Protat ◽  
...  
Keyword(s):  
Water Content ◽  
Number Concentration ◽  
Radar Reflectivity ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Aspect Ratios ◽  
Median Error ◽  
Condensed Water ◽  
T Matrix

Abstract. This study presents the evaluation of a technique to estimate cloud condensed water content (CWC) in tropical convection from airborne cloud radar reflectivity factors at 94 GHz and in-situ measurements of particle size distributions (PSDs) and aspect ratios of ice crystal populations. The approach is to calculate the variability of 5 second average PSD CWCs and all possible solutions of corresponding m(D) relationships fulfilling the condition that the simulated radar reflectivity factors (T-matrix method) matches the measured reflectivity. For the reflectivity simulations, ice crystals were approximated as oblate spheroids, without using a priori assumptions on the mass-size relationship of ice crystals. The CWC calculations demonstrate that measured CWC values are in the range ±32 % of the average CWC value: averaged over all CWC solutions for the chosen 5s time intervals. In addition, during the airborne field campaign performed out of Darwin in 2014, as part of the international High Altitude Ice Crystals (HAIC) – High Ice Water Content (HIWC) projects, CWCs were measured directly with the new IKP-2 (isokinetic evaporator probe) instrument along with simultaneous particle imagery and radar reflectivity. Averaged CWC retrieved from the radar reflectivity simulations are roughly 16 % higher than the IKP-2 CWC measurements. The differences between the IKP-2 and PSD derived CWCs from the entire set of realistic m(D) solutions for T-matrix retrievals is found to be a function of the total number concentration of ice crystals. Consequently, a correction term is applied (as a function of total number concentration) that significantly improves the retrieved CWC. After correction, the retrieved CWC have a median error relative to measured values of only −1 %.

scholarly journals A Comparison of Airborne In Situ Cloud Microphysical Measurement with Ground-Based C-Band Radar Observations in Deep Stratiform Regions of African Squall Lines

2015 ◽  
Vol 54 (12) ◽  
pp. 2461-2477 ◽  
Author(s):  
E. Drigeard ◽  
E. Fontaine ◽  
W. Wobrock ◽  
A. Schwarzenböck ◽  
C. Duroure ◽  
...  
Keyword(s):  
Water Content ◽  
Ice Crystals ◽  
Southwestern Part ◽  
Radar Observations ◽  
Squall Lines ◽  
Ice Water Content ◽  
Ice Water ◽  
Reflectivity Factor

AbstractThis study addresses clouds with significant ice water content (IWC) in the stratiform regions downwind of the convective cores of African squall lines in the framework of the French–Indian satellite Megha-Tropiques project, observed in August 2010 next to Niamey (13.5°N, 2°E) in the southwestern part of Niger. The objectives included comparing the IWC–Z reflectivity relationship for precipitation radars in deep stratiform anvils, collocating reflectivity observed from ground radar with the calculated reflectivity from in situ microphysics for all aircraft locations inside the radar range, and interpreting the role of large ice crystals in the reflectivity of centimeter radars through analysis of their microphysical characteristics as ice crystals larger than 5 mm frequently occurred. It was found that, in the range of 20–30 dBZ, IWC and C-band reflectivity are not really correlated. Cloud regions with high IWC caused by important crystal number concentrations can lead to the same reflectivity factor as cloud regions with low IWC formed by a few millimeter-sized ice crystals.

scholarly journals Cirrus Cloud Properties as Seen by the CALIPSO Satellite and ECHAM-HAM Global Climate Model

2018 ◽  
Vol 31 (5) ◽  
pp. 1983-2003 ◽  
Author(s):  
B. Gasparini ◽  
A. Meyer ◽  
D. Neubauer ◽  
S. Münch ◽  
U. Lohmann
Keyword(s):  
Water Content ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Water Vapor Transport ◽  
Formation Mechanisms ◽  
Ice Crystal ◽  
Extinction Coefficients ◽  
Ice Water Content ◽  
Ice Water

Cirrus clouds impact the planetary energy balance and upper-tropospheric water vapor transport and are therefore relevant for climate. In this study cirrus clouds at temperatures colder than −40°C simulated by the ECHAM–Hamburg Aerosol Module (ECHAM-HAM) general circulation model are compared to Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO) satellite data. The model captures the general cloud cover pattern and reproduces the observed median ice water content within a factor of 2, while extinction is overestimated by about a factor of 3 as revealed by temperature-dependent frequency histograms. Two distinct types of cirrus clouds are found: in situ–formed cirrus dominating at temperatures colder than −55°C and liquid-origin cirrus dominating at temperatures warmer than −55°C. The latter cirrus form in anvils of deep convective clouds or by glaciation of mixed-phase clouds, leading to high ice crystal number concentrations. They are associated with extinction coefficients and ice water content of up to 1 km−1 and 0.1 g m−3, respectively, while the in situ–formed cirrus are associated with smaller extinction coefficients and ice water content. In situ–formed cirrus are nucleated either heterogeneously or homogeneously. The simulated homogeneous ice crystals are similar to liquid-origin cirrus, which are associated with high ice crystal number concentrations. On the contrary, heterogeneously nucleated ice crystals appear in smaller number concentrations. However, ice crystal aggregation and depositional growth smooth the differences between several formation mechanisms, making the attribution to a specific ice nucleation mechanism challenging.

scholarly journals Development and characterization of an ice-selecting pumped counterflow virtual impactor (IS-PCVI) to study ice crystal residuals

2016 ◽  
Vol 9 (8) ◽  
pp. 3817-3836 ◽  
Author(s):  
Naruki Hiranuma ◽  
Ottmar Möhler ◽  
Gourihar Kulkarni ◽  
Martin Schnaiter ◽  
Steffen Vogt ◽  
...  
Keyword(s):  
Transmission Efficiency ◽  
Number Concentration ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Cloud Droplets ◽  
Virtual Impactor ◽  
Wide Range ◽  
Aerosol Cloud Interactions ◽  
Cloud Activation ◽  
Dynamics Simulations

Abstract. Separation of particles that play a role in cloud activation and ice nucleation from interstitial aerosols has become necessary to further understand aerosol-cloud interactions. The pumped counterflow virtual impactor (PCVI), which uses a vacuum pump to accelerate the particles and increase their momentum, provides an accessible option for dynamic and inertial separation of cloud elements. However, the use of a traditional PCVI to extract large cloud hydrometeors is difficult mainly due to its small cut-size diameters (< 5 µm). Here, for the first time we describe a development of an ice-selecting PCVI (IS-PCVI) to separate ice in controlled mixed-phase cloud system based on the particle inertia with the cut-off diameter  ≥  10 µm. We also present its laboratory application demonstrating the use of the impactor under a wide range of temperature and humidity conditions. The computational fluid dynamics simulations were initially carried out to guide the design of the IS-PCVI. After fabrication, a series of validation laboratory experiments were performed coupled with the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) expansion cloud simulation chamber. In the AIDA chamber, test aerosol particles were exposed to the ice supersaturation conditions (i.e., RHice > 100 %), where a mixture of droplets and ice crystals was formed during the expansion experiment. In parallel, the flow conditions of the IS-PCVI were actively controlled, such that it separated ice crystals from a mixture of ice crystals and cloud droplets, which were of diameter  ≥  10 µm. These large ice crystals were passed through the heated evaporation section to remove the water content. Afterwards, the residuals were characterized with a suite of online and offline instruments downstream of the IS-PCVI. These results were used to assess the optimized operating parameters of the device in terms of (1) the critical cut-size diameter, (2) the transmission efficiency and (3) the counterflow-to-input flow ratio. Particle losses were characterized by comparing the residual number concentration to the rejected interstitial particle number concentration. Overall results suggest that the IS-PCVI enables inertial separation of particles with a volume-equivalent particle size in the range of  ~ 10–30 µm in diameter with small inadvertent intrusion (~  5 %) of unwanted particles.

scholarly journals Ice crystal number concentration estimates from lidar-radar satellite retrievals. Part 2: Controls on the ice crystal number concentration

2018 ◽  
Author(s):  
Edward Gryspeerdt ◽  
Odran Sourdeval ◽  
Johannes Quaas ◽  
Julien Delanoë ◽  
Philipp Kühne
Keyword(s):  
Global Scale ◽  
Number Concentration ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Radar Satellite ◽  
Mixed Phase Clouds

Abstract. The ice crystal number concentration (Ni) is a key property of ice clouds, both radiatively and microphysically. However, due to sparse in-situ measurements of ice cloud properties, the controls on the Ni have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved. This work uses the DARDAR-LIM Ni retrieval described in part one to investigate the controls of the Ni at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraught and aerosol concentrations are investigated. Variations in the cloud top Ni (Ni(top)) consistent with both homogeneous and heterogeneous nucleation are observed and along with a possible role of aerosol both increasing and decreasing the Ni(top) depending on the prevailing meteorological situation. Away from the cloud top, the Ni displays a different sensitivity to these controlling factors, providing a possible explanation to the low Ni sensitivity to temperature and INP observed in previous in-situ studies. This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds.

scholarly journals Observing cirrus halos to constrain in-situ measurements of ice crystal size

2007 ◽  
Vol 7 (1) ◽  
pp. 1295-1325 ◽  
Author(s):  
T. J. Garrett ◽  
M. B. Kimball ◽  
G. G. Mace ◽  
D. G. Baumgardner
Keyword(s):  
Crystal Size ◽  
In Situ Measurements ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Optical Extinction ◽  
Airborne Measurements ◽  
Ice Cloud ◽  
Ice Crystal Size ◽  
High Concentrations

Abstract. In this study, characteristic optical sizes of ice crystals in synoptic cirrus are determined using airborne measurements of ice crystal size distributions, optical extinction and water content. The measurements are compared with coincident visual observations of ice cloud optical phenomena, in particular the 22° and 46° halos. In general, the scattering profiles derived from the in-situ cloud probe measurements are consistent with the observed halo characteristics. It is argued that this implies that the measured ice crystals were small, probably with characteristic optical radii between 10 and 20 μm. There is a current contention that in-situ measurements of high concentrations of small ice crystals reflect artifacts from the shattering of large ice crystals on instrument inlets. Significant shattering cannot be entirely excluded using this approximate technique, but it is not indicated. On the basis of the in-situ measurements, a parameterization is provided that relates the optical effective radius of ice crystals to the temperature in mid-latitude synoptic cirrus.

scholarly journals In-situ aircraft observations of ice concentrations within clouds over the Antarctic Peninsula and Larsen Ice Shelf

2012 ◽  
Vol 12 (7) ◽  
pp. 17295-17345
Author(s):  
D. P. Grosvenor ◽  
T. W. Choularton ◽  
T. Lachlan-Cope ◽  
M. W. Gallagher ◽  
J. Crosier ◽  
...  
Keyword(s):  
Antarctic Peninsula ◽  
Particle Production ◽  
Supercooled Liquid ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Ice Shelf ◽  
Aircraft Observations ◽  
The Antarctic ◽  
Larsen Ice Shelf

Abstract. In-situ aircraft observations of ice crystal concentrations in Antarctic clouds are presented for the first time. Orographic, layer and wave clouds around the Antarctic Peninsula and Larsen Ice shelf regions were penetrated by the British Antarctic Survey's Twin Otter Aircraft, which was equipped with modern cloud physics probes. The clouds studied were mostly in the free troposphere and hence ice crystals blown from the surface are unlikely to have been a major source for the ice phase. The temperature range covered by the experiments was 0 to −21°C. The clouds were found to contain supercooled liquid water in most regions and at heterogeneous ice formation temperatures ice crystal concentrations (60 s averages) were often less than 0.07 l−1, although values up to 0.22 l−1 were observed. Estimates of observed aerosol concentrations were used as input into the DeMott et al., 2010 ice nuclei (IN) parameterisation. The observed ice crystal number concentrations were generally in broad agreement with the IN predictions, although on the whole the predicted values were higher. Possible reasons for this are discussed and include the lack of IN observations in this region with which to characterise the parameterisation, and/or problems in relating ice concentration measurements to IN concentrations. Other IN parameterisations significantly overestimated the number of ice particles. Generally ice particle concentrations were much lower than found in clouds in middle latitudes for a given temperature. Higher ice crystal concentrations were sometimes observed at temperatures warmer than −9 °C, with values of several per litre reached. These were attributable to secondary ice particle production by the Hallett Mossop process. Even in this temperature range it was observed that there were regions with little or no ice that were dominated by supercooled liquid water. It is likely that in some cases this was due to a lack of seeding ice crystals to act as rimers to initiate secondary ice particle production. This highlights the complicated nature of this process and indicates that the accurate representation of it in global models is likely to represent a challenge. However, the contrast between Hallett Mossop zone ice concentrations and the fairly low concentrations of heterogeneously nucleated ice suggests that the Hallet Mossop process has the potential to be very important in remote, pristine regions such as around the Antarctic coast.

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