A Statistical Analysis of the Influence of Deep Convection on Water Vapor Variability in the Tropical Upper Troposphere

The factors that control the influence of deep convective detrainment on water vapor in the tropical upper troposphere are examined using observations from multiple satellites in conjunction with a trajectory model. Deep convection is confirmed to act primarily as a moisture source to the upper troposphere, modulated by the ambient relative humidity (RH). Convective detrainment provides strong moistening at low RH and offsets drying due to subsidence across a wide range of RH. Strong day-to-day moistening and drying takes place most frequently in relatively dry transition zones, where between 0.01% and 0.1% of Tropical Rainfall Measuring Mission Precipitation Radar observations indicate active convection. Many of these strong moistening events in the tropics can be directly attributed to detrainment from recent tropical convection, while others in the subtropics appear to be related to stratosphere-troposphere exchange. The temporal and spatial limits of the convective source are estimated to be about 36-48 h and 600-1500 km, respectively, consistent with the lifetimes of detrainment cirrus clouds. Larger amounts of detrained ice are associated with enhanced upper tropospheric moistening in both absolute and relative terms. In particular, an increase in ice water content of approximately 400% corresponds to a 10-90% increase in the likelihood of moistening and a 30-50% increase in the magnitude of moistening.NASA Global Energy and Water Cycle programNASA Earth System Science researchTerraACRIMSAT NNG04GK90GGeological Science

Flight-based chemical characterization of biomass burning aerosols within two prescribed burn smoke plumes

Biomass burning represents a major global source of aerosols impacting direct radiative forcing and cloud properties. Thus, the goal of a number of current studies involves developing a better understanding of how the chemical composition and mixing state of biomass burning aerosols evolve during atmospheric aging processes. During the Ice in Clouds Experiment-Layer Clouds (ICE-L) in the fall of 2007, smoke plumes from two small Wyoming Bureau of Land Management prescribed burns were measured by on-line aerosol instrumentation aboard a C-130 aircraft, providing a detailed chemical characterization of the particles. After ~2–4 min of aging, submicron smoke particles, produced primarily from sagebrush combustion, consisted predominantly of organics by mass, but were comprised primarily of internal mixtures of organic carbon, elemental carbon, potassium chloride, and potassium sulfate. Significantly, the fresh biomass burning particles contained minor mass fractions of nitrate and sulfate, suggesting that hygroscopic material is incorporated very near or at the point of emission. The mass fractions of ammonium, sulfate, and nitrate increased with aging up to ~81–88 min and resulted in acidic particles. Decreasing black carbon mass concentrations occurred due to dilution of the plume. Increases in the fraction of oxygenated organic carbon and the presence of dicarboxylic acids, in particular, were observed with aging. Cloud condensation nuclei measurements suggested all particles >100 nm were active at 0.5% water supersaturation in the smoke plumes, confirming the relatively high hygroscopicity of the freshly emitted particles. For immersion/condensation freezing, ice nuclei measurements at −32 °C suggested activation of ~0.03–0.07% of the particles with diameters greater than 500 nm

A comparison of small and larger mesoscale latent heat and radiative fluxes: December 6 case study

Because of the small amounts of water vapor, the potential for rapid changes, and the very cold temperatures in the upper troposphere, moisture measuring instruments face several problems related to calibration and response. Calculations of eddy moisture fluxes are, therefore, subject to significant uncertainty. The purpose of this study is to examine the importance of latent heat (moisture) fluxes due to small and larger mesoscale circulations in comparison to radiative fluxes within cirrus. Scale separation is made at about 1 km because of significant changes in the structures within cirrus. Only observations at warmer than -40 C are used in this study. The EG&G hygrometer that is used for measuring dewpoint temperature (Td) is believed to be fairly accurate down to -40 C. On the other hand, Lyman-Alpha (L-alpha) hygrometer measurements of moisture may include large drift errors. In order to compensate for these drift errors, the L-alpha hygrometer is often calibrated against the EG&G hygrometer. However, large errors ensue for Td measurements at temperatures less than -40 C. The cryogenic hygrometer frost point measurements may be used to calibrate L-alpha measurements at temperatures less than -40 C. In this study, however, measurements obtained by EG&G hygrometer and L-alpha measurements are used for the flux calculations

Ice hydrometeor profile retrieval algorithm for high-frequency microwave radiometers: application to the CoSSIR instrument during TC4

A Bayesian algorithm to retrieve profiles of cloud ice water content (IWC), ice particle size (<i>D</i><sub>me</sub>), and relative humidity from millimeter-wave/submillimeter-wave radiometers is presented. The first part of the algorithm prepares an a priori file with cumulative distribution functions (CDFs) and empirical orthogonal functions (EOFs) of profiles of temperature, relative humidity, three ice particle parameters (IWC, <i>D</i><sub>me</sub>, distribution width), and two liquid cloud parameters. The a priori CDFs and EOFs are derived from CloudSat radar reflectivity profiles and associated ECMWF temperature and relative humidity profiles combined with three cloud microphysical probability distributions obtained from in situ cloud probes. The second part of the algorithm uses the CDF/EOF file to perform a Bayesian retrieval with a hybrid technique that uses Monte Carlo integration (MCI) or, when too few MCI cases match the observations, uses optimization to maximize the posterior probability function. The very computationally intensive Markov chain Monte Carlo (MCMC) method also may be chosen as a solution method. The radiative transfer model assumes mixtures of several shapes of randomly oriented ice particles, and here random aggregates of spheres, dendrites, and hexagonal plates are used for tropical convection. A new physical model of stochastic dendritic snowflake aggregation is developed. The retrieval algorithm is applied to data from the Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) flown on the ER-2 aircraft during the Tropical Composition, Cloud and Climate Coupling (TC4) experiment in 2007. Example retrievals with error bars are shown for nadir profiles of IWC, <i>D</i><sub>me</sub>, and relative humidity, and nadir and conical scan swath retrievals of ice water path and average <i>D</i><sub>me</sub>. The ice cloud retrievals are evaluated by retrieving integrated 94 GHz backscattering from CoSSIR for comparison with the Cloud Radar System (CRS) flown on the same aircraft. The rms difference in integrated backscattering is around 3 dB over a 30 dB range. A comparison of CoSSIR retrieved and CRS measured reflectivity shows that CoSSIR has the ability to retrieve low-resolution ice cloud profiles in the upper troposphere

Cirrus microphysics and radiative transfer: A case study

During the Cirrus Intensive Field Operations of FIRE, data collected by the NCAR King Air in the vicinity of Wausau, WI on October 28 were selected to study the influence of cirrus cloud microphysics on radiative transfer and the role of microphysical approximations in radiative transfer models. The instrumentation of the King Air provided, aside from temperature and wind data, up-and downwelling broadband solar and infrared fluxes as well as detailed microphysical data. The aircraft data, supplied every second, are averaged over the 7 legs to represent the properties for that altitude. The resulting vertical profiles, however, suffer from the fact that each leg represents a different cloud column path. Based on the measured microphysical data particle size distributions of equivalent spheres for each cloud level are developed. Accurate radiative transfer calculations are performed, incorporating atmospheric and radiative data from the ground and the stratosphere. Comparing calculated to the measured up- and downwelling fluxes at the seven cloud levels for both the averaged and the three crossover data will help to assess the validity of particle size and shape approximation as they are frequently used to model cirrus clouds. Once agreement is achieved the model results may be applied to determine, in comparison to a cloudfree case, the influence of this particular cirrus on the radiation budget of the earth atmosphere system

Factors influencing ice formation and growth in simulations of a mixed-phase wave cloud

In this paper, numerical simulations of an orographically induced wave cloud sampled in-situ during the ICE-L (Ice in Clouds Experiment - Layer clouds) field campaign are performed and compared directly against the available observations along various straight and level flight paths. The simulations are based on a detailed mixed-phase bin microphysics model embedded within a 1-D column framework with the latest parameterizations for heterogeneous ice nucleation and an adaptive treatment of ice crystal growth based on the evolution of crystal habit. The study focuses on the second of two clouds sampled on 16th November 2007, the in-situ data from which exhibits some interesting and more complex microphysics than other flights from the campaign. The model is used to demonstrate the importance of both heterogeneous and homogeneous nucleation in explaining the in-situ observations of ice crystal concentration and habit, and how the ability to isolate the influence of both nucleation mechanisms helps when quantifying active IN concentrations. The aspect ratio and density of the simulated ice crystals is shown to evolve in a manner consistent with the in-situ observations along the flight track, particularly during the transition from the mixed-phase region of the cloud to the ice tail dominated by homogeneous nucleation. Some additional model runs are also performed to explore how changes in IN concentration and the value of the deposition coefficient for ice affect the competition between heterogeneous and homogeneous ice formation in the wave cloud, where the Factorial Method is used to isolate and quantify the effect of such non-linear interactions. The findings from this analysis show that the effect on homogeneous freezing rates is small, suggesting that any competition between the microphysical variables is largely overshadowed by the strong dynamical forcing of the cloud in the early stages of ice formation

FIRE Cirrus on October 28, 1986: LANDSAT; ER-2; King Air; theory

A simultaneous examination was conducted of cirrus clouds in the FIRE Cirrus IFO-I on 10/28/86 using a multitude of remote sensing and in-situ measurements. The focus is cirrus cloud radiative properties and their relationship to cloud microphysics. A key element is the comparison of radiative transfer model calculations and varying measured cirrus radiative properties (emissivity, reflectance vs. wavelength, reflectance vs. viewing angle). As the number of simultaneously measured cloud radiative properties and physical properties increases, more sharply focused tests of theoretical models are possible

Relationships of Biomass-Burning Aerosols to Ice in Orographic Wave Clouds

Ice concentrations in orographic wave clouds at temperatures between −24° and −29°C were shown to be related to aerosol characteristics in nearby clear air during five research flights over the Rocky Mountains. When clouds with influence from colder temperatures were excluded from the dataset, mean ice nuclei and cloud ice number concentrations were very low, on the order of 1–5 L^(−1). In this environment, ice number concentrations were found to be significantly correlated with the number concentration of larger particles, those larger than both 0.1- and 0.5-μm diameter. A variety of complementary techniques was used to measure aerosol size distributions and chemical composition. Strong correlations were also observed between ice concentrations and the number concentrations of soot and biomass-burning aerosols. Ice nuclei concentrations directly measured in biomass-burning plumes were the highest detected during the project. Taken together, this evidence indicates a potential role for biomass-burning aerosols in ice formation, particularly in regions with relatively low concentrations of other ice nucleating aerosols

Ice Initiation by Aerosol Particles: Measured and Predicted Ice Nuclei Concentrations versus Measured Ice Crystal Concentrations in an Orographic Wave Cloud

The initiation of ice in an isolated orographic wave cloud was compared with expectations based on ice nucleating aerosol concentrations and with predictions from new ice nucleation parameterizations applied in a cloud parcel model. Measurements of ice crystal number concentrations were found to be in good agreement both with measured number concentrations of ice nuclei feeding the clouds and with ice nuclei number concentrations determined from the residual nuclei of cloud particles collected by a counterflow virtual impactor. Using lognormal distributions fitted to measured aerosol size distributions and measured aerosol chemical compositions, ice nuclei and ice crystal concentrations in the wave cloud were reasonably well predicted in a 1D parcel model framework. Two different empirical parameterizations were used in the parcel model: a parameterization based on aerosol chemical type and surface area and a parameterization that links ice nuclei number concentrations to the number concentrations of particles with diameters larger than 0.5 μm. This study shows that aerosol size distribution and composition measurements can be used to constrain ice initiation by primary nucleation in models. The data and model results also suggest the likelihood that the dust particle mode of the aerosol size distribution controls the number concentrations of the heterogeneous ice nuclei, at least for the lower temperatures examined in this case

On the Importance of Small Ice Crystals in Tropical Anvil Cirrus

In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small ]crystals could be artifacts of large ]crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2 ] Dimensional Stereo (2D ]S) probe, which detects particles as small as 10 m. The 2D ]S has detector "arms" instead of an inlet tube. Since the 2D ]S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D ]S will be less susceptible to shattering artifacts. In addition, particle inter ]arrival times are used to identify and remove shattering artifacts that occur even with the 2D ]S probe. The number of shattering artifacts identified by the 2D ]S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small ]crystal concentration. The 2D ]S measurements in tropical anvil cirrus suggest that natural small ]crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D ]S ratio of small ]crystal concentrations and large ]crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D ]S large ]crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large ]crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D ]S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D ]S ice concentrations in fresh anvil cirrus may often exceed 1 cm.3, and are observed to exceed 10 cm.3 in turrets, they are typically ~0.1 cm.3 and rarely exceed 1 cm.3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small ]scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC ]4