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Flatau, PJ.  1997.  Improvements in the discrete-dipole approximation method of computing scattering and absorption. Optics Letters. 22:1205-1207.   10.1364/ol.22.001205   AbstractWebsite

Improvements in complex-conjugate gradient algorithms applied to the discrete-dipole approximation are reported. It is shown that computational time is reduced by use of the stabilized version of the biconjugate gratings algorithm, with diagonal left preconditioning. (C) 1997 Optical Society of America.

Markowicz, KM, Flatau PJ, Quinn PK, Carrico CM, Flatau MK, Vogelmann AM, Bates D, Liu M, Rood MJ.  2003.  Influence of relative humidity on aerosol radiative forcing: An ACE-Asia experiment perspective. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003066   AbstractWebsite

We present direct radiometric observations of aerosol radiative forcing during the ACE-Asia experiment (March and April of 2001). The observational analysis is based on radiometer data obtained from the NOAA ship Ronald H. Brown, and shipboard measurements of the aerosol chemical and scattering properties are used to construct a model of the aerosol optical properties for use in radiative transfer calculations. The model is validated against the radiometric observations and is used to diagnose the aerosol and environmental factors that contribute to the observed forcings. The mean value of aerosol optical thickness observed during the ACE-Asia cruise over the Sea of Japan was 0.43 (+/-0.25) at 500 nm, while the single-scattering albedo was 0.95 (+/-0.03) at ambient relative humidity. We find a large correlation (r(2) = 0.69) between single-scattering albedo and relative humidity. Aerosols caused a mean decrease in the diurnally averaged solar radiation of 26.1 W m(-2) at the surface, while increasing the atmospheric solar absorption and top of atmosphere reflected solar radiation by 13.4 W m(-2) and 12.7 W m(-2), respectively. The mean surface aerosol forcing efficiency (forcing per unit optical depth) over the Sea of Japan was -60 W m(-2) and is influenced by high values of relative humidity. We show that decreasing the relative humidity to 55% enhances the aerosol forcing efficiency by as much as 6-10 W m(-2). This dependency on relative humidity has implications for comparisons of aerosol forcing efficiencies between different geographical locations.

Flatau, PJ.  1978.  Kinetics of Intraband Absorption and Magnetoabsorption Coefficients in Mixed Semiconductors with Composition Fluctuations. Physica Status Solidi B-Basic Research. 90:251-260.   10.1002/pssb.2220900127   AbstractWebsite

The influence of short-range ordering in a mixed semiconductor on the intraband absorption and magnetoabsorption coefficients is determined. The coefficients are shown to be temperature-dependent. Their time-evolution after changing the temperature is calculated. An experiment, permitting measurements of the degree of ordering (non-ideality) in alloys is proposed, and a numerical example for HgTe–CdTe is given.

Flatau, PJ, Draine BT.  2014.  Light scattering by hexagonal columns in the discrete dipole approximation. Optics Express. 22:21834-21846.   10.1364/oe.22.021834   AbstractWebsite

Scattering by infinite hexagonal ice prisms is calculated using Maxwell's equations in the discrete dipole approximation for size parameters x = pi D/lambda up to x = 400 (D = prism diameter). Birefringence is included in the calculations. Applicability of the geometric optics approximation is investigated. Excellent agreement between wave optics and geometric optics is observed for large size parameter in the outer part of the 22 degree halo feature. For smaller ice crystals halo broadening is predicted, and there is appreciable "spillover" of the halo into shadow scattering angles < 22 degrees. Ways to retrieve ice crystal sizes are suggested based on the full width at half-maximum of the halo, the power at < 22deg, and the halo polarization. (C) 2014 Optical Society of America

Flatau, PJ, Stephens GL, Draine BT.  1990.  Light-Scattering by Rectangular Solids in the Discrete-Dipole Approximation - a New Algorithm Exploiting the Block-Toeplitz Structure. Journal of the Optical Society of America a-Optics Image Science and Vision. 7:593-600.   10.1364/josaa.7.000593   AbstractWebsite

The discrete-dipole approximation is used to study the problem of light scattering by homogeneous rectangular particles. The structure of the discrete-dipole approximation is investigated, and the matrix formed by this approximation is identified to be a symmetric, block-Toeplitz matrix. Special properties of block-Toeplitz arrays are explored, and an efficient algorithm to solve the dipole scattering problem is provided. Timings for conjugate gradient, Linpack, and block-Toeplitz solvers are given; the results indicate the advantages of the block-Toeplitz algorithm. A practical test of the algorithm was performed on a system of 1400 dipoles, which corresponds to direct inversion of an 8400 × 8400 real matrix. A short discussion of the limitations of the discrete-dipole approximation is provided, and some results for cubes and parallelepipeds are given. We briefly consider how the algorithm may be improved further.

Welton, EJ, Voss KJ, Quinn PK, Flatau PJ, Markowicz K, Campbell JR, Spinhirne JD, Gordon HR, Johnson JE.  2002.  Measurements of aerosol vertical profiles and optical properties during INDOEX 1999 using micropulse lidars. Journal of Geophysical Research-Atmospheres. 107   10.1029/2000jd000038   AbstractWebsite

[1] Micropulse lidar (MPL) systems were used to measure aerosol properties during the Indian Ocean Experiment (INDOEX) 1999 field phase. Measurements were made from two platforms: the NOAA ship R/V Ronald H. Brown, and the Kaashidhoo Climate Observatory (KCO) in the Maldives. Sun photometers were used to provide aerosol optical depths (AOD) needed to calibrate the MPL. This study focuses on the height distribution and optical properties (at 523 nm) of aerosols observed during the campaign. The height of the highest aerosols (top height) was calculated and found to be below 4 km for most of the cruise. The marine boundary layer (MBL) top was calculated and found to be less than 1 km. MPL results were combined with air mass trajectories, radiosonde profiles of temperature and humidity, and aerosol concentration and optical measurements. Humidity varied from approximately 80% near the surface to 50% near the top height during the entire cruise. The average value and standard deviation of aerosol optical parameters were determined for characteristic air mass regimes. Marine aerosols in the absence of any continental influence were found to have an AOD of 0.05+/-0.03, an extinction-to-backscatter ratio (S ratio) of 33+/-6 sr, and peak extinction values around 0.05 km(-1) (near the MBL top). The marine results are shown to be in agreement with previously measured and expected values. Polluted marine areas over the Indian Ocean, influenced by continental aerosols, had AOD values in excess of 0.2, S ratios well above 40 sr, and peak extinction values approximately 0.20 km(-1) (near the MBL top). The polluted marine results are shown to be similar to previously published values for continental aerosols. Comparisons between MPL derived extinction near the ship (75 m) and extinction calculated at ship level using scattering measured by a nephelometer and absorption using a particle soot absorption photometer were conducted. The comparisons indicated that the MPL algorithm (using a constant S ratio throughout the lower troposphere) calculates extinction near the surface in agreement with the ship-level measurements only when the MBL aerosols are well mixed with aerosols above. Finally, a review of the MPL extinction profiles showed that the model of aerosol vertical extinction developed during an earlier INDOEX field campaign (at the Maldives) did not correctly describe the true vertical distribution over the greater Indian Ocean region. Using the average extinction profile and AOD obtained during marine conditions, a new model of aerosol vertical extinction was determined for marine atmospheres over the Indian Ocean. A new model of aerosol vertical extinction for polluted marine atmospheres was also developed using the average extinction profile and AOD obtained during marine conditions influenced by continental aerosols.

Conant, WC, Seinfeld JH, Wang J, Carmichael GR, Tang YH, Uno I, Flatau PJ, Markowicz KM, Quinn PK.  2003.  A model for the radiative forcing during ACE-Asia derived from CIRPAS Twin Otter and R/V Ronald H. Brown data and comparison with observations. Journal of Geophysical Research-Atmospheres. 108   10.1029/2002jd003260   AbstractWebsite

Vertical profiles of aerosol size, composition, and hygroscopic behavior from Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter and National Oceanic and Atmospheric Administration R/V Ronald H. Brown observations are used to construct a generic optical model of the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) aerosol. The model accounts for sulfate, black carbon, organic carbon, sea salt, and mineral dust. The effects of relative humidity and mixing assumptions (internal versus external, coating of dust by pollutants) are explicitly accounted for. The aerosol model is integrated with a Monte Carlo radiative transfer model to compute direct radiative forcing in the solar spectrum. The predicted regional average surface aerosol forcing efficiency (change in clear-sky radiative flux per unit aerosol optical depth at 500 nm) during the ACE-Asia intensive period is -65 Wm(-2) for pure dust and -60 Wm(-2) for pure pollution aerosol (clear skies). A three-dimensional atmospheric chemical transport model (Chemical Weather Forecast System (CFORS)) is used with the radiative transfer model to derive regional radiative forcing during ACE-Asia in clear and cloudy skies. Net regional solar direct radiative forcing during the 5-15 April 2001 dust storm period is -3 Wm(-2) at the top of the atmosphere and -17 Wm(-2) at the surface for the region from 20degreesN to 50degreesN and 100degreesE to 150degreesE when the effects of clouds on the direct forcing are included. The model fluxes and forcing efficiencies are found to be in good agreement with surface radiometric observations made aboard the R. H. Brown. Mean cloud conditions are found to moderate the top of atmosphere (TOA) radiative forcing by a factor of similar to3 compared to clear-sky calculations, but atmospheric absorption by aerosol is not strongly affected by clouds in this study. The regional aerosol effect at the TOA ("climate forcing") of -3 Wm(-2) is comparable in magnitude, but of opposite sign, to present-day anthropogenic greenhouse gas forcing. The forcing observed during ACE-Asia is similar in character to that seen during other major field experiments downwind of industrial and biomass black carbon sources (e.g., the Indian Ocean Experiment (INDOEX)), insofar as the primary effect of aerosol is to redistribute solar heating from the surface to the atmosphere.

Remiszewska, J, Flatau PJ, Markowicz KM, Reid EA, Reid JS, Witek ML.  2007.  Modulation of the aerosol absorption and single-scattering albedo due to synoptic scale and sea breeze circulations: United Arab Emirates experiment perspective. Journal of Geophysical Research-Atmospheres. 112   10.1029/2006jd007139   AbstractWebsite

The spectral aerosol absorption properties in the Arabian Gulf region were observed during the United Arab Emirates Unified Aerosol Experiment (UAE(2)). Measurements were taken at a coastal region of the Arabian Gulf located 60 km northeast of Abu Dhabi, the capital of the United Arab Emirates, allowing characterization of pollution and dust absorption properties in a highly heterogeneous environment. A large observed change of the diurnal signal during the period under study ( 27 August through 30 September 2004) was due to ( 1) strong sea and land breeze and ( 2) changes in prevailing synoptic-scale flow. During the night, stagnating air resulted in gradual accumulation of pollution with maximum absorption in the early morning hours. The rising sun increased both the depth of the boundary layer and the temperature of the interior desert, resulting in strong and sudden sea breeze onset which ventilated the polluted air accumulated during the night. Our observations show that the onshore winds brought cleaner air resulting in decreasing values of the absorption coefficient and increasing values of the single-scattering albedo (SSA). The mean value of the absorption coefficient at 550 nm measured during the sea breeze was 10.2 +/- 0.9 Mm(-1), while during the land breeze it was 13.8 +/- 1.2 Mm(-1). Synoptic- scale transport also strongly influenced particle fine/ coarse partition with "northern'' flow bringing pollution particles and "southern'' flow bringing more dust.

Piskozub, J, Flatau PJ, Zaneveld JVR.  2001.  Monte Carlo study of the scattering error of a quartz reflective absorption tube. Journal of Atmospheric and Oceanic Technology. 18:438-445.   10.1175/1520-0426(2001)018<0438:mcsots>;2   AbstractWebsite

A Monte Carlo model was used to study the scattering error of an absorption meter with a divergent light beam and a limited acceptance angle of the receiver. Reflections at both ends of the tube were taken into account. Calculations of the effect of varying optical properties of water as well as the receiver geometry were performed. A weighting function showing the scattering error quantitatively as a function of angle was introduced. Some cases of practical interest are discussed.

Baranowski, DB, Flatau MK, Flatau PJ, Schmidt JM.  2017.  Multiple and spin off initiation of atmospheric convectively coupled Kelvin waves. Climate Dynamics. 49:2991-3009.   10.1007/s00382-016-3487-7   AbstractWebsite

A novel atmospheric convectively coupled Kelvin wave trajectories database, derived from Tropical Rainfall Measuring Mission precipitation data, is used to investigate initiation of sequential Kelvin wave events. Based on the analysis of beginnings of trajectories from years 1998-2012 it is shown that sequential event initiations can be divided into two distinct categories: multiple initiations and spin off initiations, both of which involve interactions with ocean surface and upper ocean temperature variability. The results of composite analysis of the 83 multiple Kelvin wave initiations show that the local thermodynamic forcing related to the diurnal sea surface temperature variability is responsible for sequential Kelvin wave development. The composite analysis of 91 spin off Kelvin wave initiations shows that the dynamic forcing is a dominant effect and the local thermodynamic forcing is secondary. Detail case studies of both multiple and spin off initiations confirm statistical analysis. A multiple initiation occurs in the presence of the high upper ocean diurnal cycle and a spin off initiation results from both dynamic and local thermodynamic processes. The dynamic forcing is related to increased wind speed and latent heat flux likely associated with an off equatorial circulation. In addition a theoretical study of the sequential Kelvin waves is performed using a shallow water model. Finally, conceptual models of these two types of initiations are proposed.

Flatau, MK, Talley L, Niiler PP.  2003.  The North Atlantic Oscillation, surface current velocities, and SST changes in the subpolar North Atlantic. Journal of Climate. 16:2355-2369.   10.1175/2787.1   AbstractWebsite

Changes in surface circulation in the subpolar North Atlantic are documented for the recent interannual switch in the North Atlantic Oscillation (NAO) index from positive values in the early 1990s to negative values in 1995/96. Data from Lagrangian drifters, which were deployed in the North Atlantic from 1992 to 1998, were used to compute the mean and varying surface currents. NCEP winds were used to calculate the Ekman component, allowing isolation of the geostrophic currents. The mean Ekman velocities are considerably smaller than the mean total velocities that resemble historical analyses. The northeastward flow of the North Atlantic Current is organized into three strong cores associated with topography: along the eastern boundary in Rockall Trough, in the Iceland Basin ( the subpolar front), and on the western flank of the Reykjanes Ridge (Irminger Current). The last is isolated in this Eulerian mean from the rest of the North Atlantic Current by a region of weak velocities on the east side of the Reykjanes Ridge. The drifter results during the two different NAO periods are compared with geostrophic flow changes calculated from the NASA/Pathfinder monthly gridded sea surface height (SSH) variability products and the Advanced Very High Resolution Radiometer (AVHRR) SST data. During the positive NAO years the northeastward flow in the North Atlantic Current appeared stronger and the circulation in the cyclonic gyre in the Irminger Basin became more intense. This was consistent with the geostrophic velocities calculated from altimetry data and surface temperature changes from AVHRR SST data, which show that during the positive NAO years, with stronger westerlies, the subpolar front was sharper and located farther east. SST gradients intensified in the North Atlantic Current, Irminger Basin, and east of the Shetland Islands during the positive NAO phase, associated with stronger currents. SST differences between positive and negative NAO years were consistent with changes in air-sea heat flux and the eastward shift of the subpolar front. SST advection, as diagnosed from the drifters, likely acted to reduce the SST differences.

Witek, ML, Flatau PJ, Teixeira J, Markowicz KM.  2011.  Numerical Investigation of Sea Salt Aerosol Size Bin Partitioning in Global Transport Models: Implications for Mass Budget and Optical Depth. Aerosol Science and Technology. 45:401-414.   10.1080/02786826.2010.541957   AbstractWebsite

In this study the importance of sea salt aerosol (SSA) size representation in a global transport model is investigated. For this purpose the Navy Aerosol Analysis and Prediction System (NAAPS) model is employed in a number of SSA simulations. A new dry deposition velocity parameterization is implemented into NAAPS in order to more physically represent deposition processes in the model. SSA size distribution is divided into size bins using two different partition procedures: the previously used iso-log method and the iso-gradient method, which relies on size-dependence of deposition processes. The global SSA simulations are analyzed in terms of the total sea salt mass and the average SSA optical thickness. The results indicate that there is a large dependence of the total mass and average aerosol optical depth on the number of size bins used to represent the aerosol size distribution. The total SSA mass is underestimated by 20% if 2 instead of 15 (reference) size intervals are used. The average aerosol optical depth underestimation is even higher and reaches over 35%. Such large differences can have substantial implications on the accuracy of SSA radiative forcing simulations in climate models. A comparison of the two division procedures shows that the simulations with the iso-gradient intervals are more accurate than the iso-log ones if at least 6 size bins are used. This result indicates that the more physically based division scheme can offer better performance and reduce computational cost of global aerosol transport models.

Augustynowicz, M, Flatau PJ.  1981.  Numerical study of the sea breeze phenomena. Acta Geophysica Polonica, Warsaw. 29:117-122. AbstractWebsite

A two-dimensional, nonhydrostatic model of the sea breeze phenomena is proposed. The integration is done for 30 hr, starting from the atmosphere at rest. The preliminary results of the model include the temperature and wind fields and characteristics of the sea breeze front.

Markowicz, KM, Flatau PJ, Remiszewska J, Witek M, Reid EA, Reid JS, Bucholtz A, Holben B.  2008.  Observations and modeling of the surface aerosol radiative forcing during UAE(2). Journal of the Atmospheric Sciences. 65:2877-2891.   10.1175/2007jas2555.1   AbstractWebsite

Aerosol radiative forcing in the Persian Gulf region is derived from data collected during the United Arab Emirates (UAE) Unified Aerosol Experiment (UAE(2)). This campaign took place in August and September of 2004. The land -sea-breeze circulation modulates the diurnal variability of the aerosol properties and aerosol radiative forcing at the surface. Larger aerosol radiative forcing is observed during the land breeze in comparison to the sea breeze. The aerosol optical properties change as the onshore wind brings slightly cleaner air. The mean diurnal value of the surface aerosol forcing during the UAE2 campaign is about -20 W m(-2), which corresponds to large aerosol optical thickness (0.45 at 500 nm). The aerosol forcing efficiency [i. e., broadband shortwave forcing per unit optical depth at 550 nm, W m(-2) (tau(500))(-1)] is -53 W m(-2) (tau(500))(-1) and the average single scattering albedo is 0.93 at 550 nm.

Vogelmann, AM, Flatau PJ, Szczodrak M, Markowicz KM, Minnett PJ.  2003.  Observations of large aerosol infrared forcing at the surface. Geophysical Research Letters. 30   10.1029/2002gl016829   AbstractWebsite

Studies of aerosol effects on the Earth's energy budget usually consider only the cooling effects at short (solar) wavelengths, but we demonstrate that they also have important warming effects at thermal infrared (IR) wavelengths that have rarely been observed and are commonly ignored in climate models. We use high-resolution spectra to obtain the IR radiative forcing at the surface for aerosols encountered in the outflow from northeastern Asia. The spectra were measured by the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) from the NOAA Ship Ronald H. Brown during the Aerosol Characterization Experiment-Asia (ACE-Asia). We show that the daytime surface IR forcing are often a few Wm(-2) and can reach almost 10 Wm(-2) for large aerosol loadings. Thus, even the smaller aerosol IR forcing observed here are comparable to or greater than the 1 to 2 Wm(-2) IR surface enhancement from increases in greenhouse gases. These results highlight the importance of aerosol IR forcing which should be included in climate model simulations.

Witek, ML, Teixeira J, Flatau PJ.  2008.  On stable and explicit numerical methods for the advection-diffusion equation. Mathematics and Computers in Simulation. 79:561-570.   10.1016/j.matcom.2008.03.001   AbstractWebsite

In this paper two stable and explicit numerical methods to integrate the one-dimensional (1D) advection-diffusion equation are presented. These schemes are stable by design and follow the main general concept behind the semi-Lagrangian method by constructing a virtual grid where the explicit method becomes stable. It is shown that the new schemes compare well with analytic solutions and are often more accurate than implicit schemes. In particular, the diffusion-only case is explored in some detail. The error produced by the stable and explicit method is a function of the ratio between the standard deviation an of the initial Gaussian state and the characteristic virtual grid distance AS. Larger values of this ratio lead to very accurate results when compared to implicit methods, while lower values lead to less accuracy. It is shown that the sigma(0)/Delta S ratio is also significant in the advection-diffusion problem: it determines the maximum error generated by new methods, obtained with a certain combination of the advection and diffusion values. In addition, the error becomes smaller when the problem becomes more advective or more diffusive. (C) 2008 IMACS. Published by Elsevier B.V. All rights reserved.

Flatau, PJ, Stephens GL.  1988.  On the Fundamental Solution of the Radiative-Transfer Equation. Journal of Geophysical Research-Atmospheres. 93:11037-11050.   10.1029/JD093iD09p11037   AbstractWebsite

This paper outlines the general solution of the one-dimensional, azimuthally averaged radiative transfer equation in terms of a matrix exponential. The link between this fundamental solution and those more commonly used in radiative transfer is established. The formulation is developed for a general vertically inhomogeneous atmosphere with sources. Several new concepts, based on properties of the matrix exponentials, are described in the context of radiative transfer, including the use of the commutator and product integrals. It is also demonstrated how the matrix exponential formulation provides for new insights, not only into improvements of the numerical efficiency and stability of the solution, but also into the understanding of radiative transfer through a layered atmosphere. The various concepts introduced in this paper are illustrated throughout by the two-stream simplification of the general radiative transfer equation.

Maslowska, A, Flatau PJ, Stephens GL.  1994.  On the Validity of the Anomalous Diffraction Theory to Light-Scattering by Cubes. Optics Communications. 107:35-40.   10.1016/0030-4018(94)90099-x   AbstractWebsite

The extinction and absorption efficiencies of a cube at light incidence normal to its four-fold symmetry axis are calculated using the anomalous diffraction theory (ADT). The results are compared with those based on the discrete dipole approximation (DDA). It is shown that for certain cases of the orientation of a cube relative to the direction of the incident light the extinction efficiency calculated using DDA and ADT do not agree. However, the ADT-based absorption efficiencies for the cases studied are dependent on a particle volume and exhibit smaller errors. Hence the validity of the ADT for cubes is not as good as for spheres.

Stramski, D, Wozniak SB, Flatau PJ.  2004.  Optical properties of Asian mineral dust suspended in seawater. Limnology and Oceanography. 49:749-755. AbstractWebsite

The spectral optical properties of Asian mineral dust suspended in seawater exhibit significant variability associated with the origin (and, hence, the chemistry and mineralogy) and particle size distribution of the samples. The measurements of dust samples from different locations show that the mass-specific absorption coefficient of particles, a(p)*, at a wavelength of light lambda = 440 nm, varies from about 0.028 m(2) g(-1) for the soil dust from Chinese desert Pnear Dunhuang to 0.15 m(2) g(-1) for the soil dust of volcanic origin in Cheju Island (South Korea). At lambda = 400 nm, this range is 0.05-0.23 m(2) g(-1). The aerosol sample collected in the Sea of Japan during a massive dust storm in East Asia shows a(p)*(lambda) > 0.1 m(2) g(-1) for lambda < 425 nm. The mass-specific scattering coefficient, b(p)*(lambda), ranges from about 0.8 to 1.5 m(2) g(-1) at blue and green wavelengths for the samples examined. The single scattering albedo, omega(0) increases with wavelength. For lambda > 400 nm, omega(0) was > 0.78 for the sample from Cheju Island and > 0.9 for other samples. In the near-infrared region (750-850 nm), where absorption by dust particles is small or undetectable, omega(0), was close to 1.

Baranowski, DB, Flatau MK, Flatau PJ, Matthews AJ.  2016.  Phase locking between atmospheric convectively coupled equatorial Kelvin waves and the diurnal cycle of precipitation over the Maritime Continent. Geophysical Research Letters. 43:8269-8276.   10.1002/2016gl069602   AbstractWebsite

Convectively coupled Kelvin waves (CCKWs) are a major component of the tropical atmospheric circulation, propagating eastward around the equatorial belt. Here we show that there are scale interactions between CCKWs and the diurnal cycle over the Maritime Continent. In particular, CCKW packets that pass a base point in the eastern Indian Ocean at 90 degrees E between 0600 and 0900UTC subsequently arrive over Sumatra in phase with the diurnal cycle of convection. As the distance between Sumatra and Borneo is equal to the distance traveled by a CCKW in 1day, these waves are then also in phase with the diurnal cycle over Borneo. Consequently, this subset of CCKWs has a precipitation signal up to a factor of 3 larger than CCKWs that arrive at other times of the day and a 40% greater chance of successfully traversing the Maritime Continent.

Flatau, PJ, Walko RL, Cotton WR.  1992.  Polynomial Fits to Saturation Vapor-Pressure. Journal of Applied Meteorology. 31:1507-1513.   10.1175/1520-0450(1992)031<1507:pftsvp>;2   AbstractWebsite

The authors describe eighth- and sixth-order polynomial fits to Wexler's and Hyland-Wexler's saturation-vapor-pressure expressions. Fits are provided in both least-squares and relative-error norms. Error analysis is presented. The authors show that their method is faster in comparison with the reference expressions when implemented on a CRAY-YMP.

Schmidt, JM, Flatau PJ, Harasti PR, Yates RD, Littleton R, Pritchard MS, Fischer JM, Fischer EJ, Kohri WJ, Vetter JR, Richman S, Baranowski DB, Anderson MJ, Fletcher E, Lando DW.  2012.  Radar observations of individual rain drops in the free atmosphere. Proceedings of the National Academy of Sciences of the United States of America. 109:9293-9298.   10.1073/pnas.1117776109   AbstractWebsite

Atmospheric remote sensing has played a pivotal role in the increasingly sophisticated representation of clouds in the numerical models used to assess global and regional climate change. This has been accomplished because the underlying bulk cloud properties can be derived from a statistical analysis of the returned microwave signals scattered by a diverse ensemble comprised of numerous cloud hydrometeors. A new Doppler radar, previously used to track small debris particles shed from the NASA space shuttle during launch, is shown to also have the capacity to detect individual cloud hydrometeors in the free atmosphere. Similar to the traces left behind on film by subatomic particles, larger cloud particles were observed to leave a well-defined radar signature (or streak), which could be analyzed to infer the underlying particle properties. We examine the unique radar and environmental conditions leading to the formation of the radar streaks and develop a theoretical framework which reveals the regulating role of the background radar reflectivity on their observed characteristics. This main expectation from theory is examined through an analysis of the drop properties inferred from radar and in situ aircraft measurements obtained in two contrasting regions of an observed multicellular storm system. The observations are placed in context of the parent storm circulation through the use of the radar's unique high-resolution waveforms, which allow the bulk and individual hydrometeor properties to be inferred at the same time.

Collins, WD, Valero FPJ, Flatau PJ, Lubin D, Grassl H, Pilewskie P.  1996.  Radiative effects of convection in the tropical Pacific. Journal of Geophysical Research-Atmospheres. 101:14999-15012.   10.1029/95jd02534   AbstractWebsite

The radiative effects of tropical clouds at the tropopause and the ocean surface have been estimated by using in situ measurements from the Central Equatorial Pacific Experiment (CEPEX). The effect of clouds is distinguished from the radiative effects of the surrounding atmosphere by calculating the shortwave and longwave cloud forcing. These terms give the reduction in insolation and the increase in absorption of terrestrial thermal emission associated with clouds. At the tropopause the shortwave and longwave cloud forcing are nearly equal and opposite, even on daily timescales. Therefore the net effect of an ensemble of convective clouds is small compared to other radiative terms in the surface-tropospheric heat budget. This confirms the statistical cancellation of cloud forcing observed in Earth radiation budget measurements from satellites. At the surface the net effect of clouds is to reduce the radiant energy absorbed by the ocean. Under deep convective clouds the diurnally averaged reduction exceeds 150 W m(-2). The divergence of flux in the cloudy atmosphere can be estimated from the difference in cloud forcing at the surface and tropopause. The CEPEX observations show that the atmospheric cloud forcing is nearly equal and opposite to the surface forcing. Based upon the frequency of convection, the atmospheric forcing approaches 100 W m(-2) when the surface temperature is 303 K. The cloud forcing is closely related to the frequency of convective cloud systems. This relation is used in conjunction with cloud population statistics derived from satellite to calculate the change in surface cloud forcing with sea surface temperature. The net radiative cooling of the surface by clouds increases at a rate of 20 W m(-2)K(-1)during the CEPEX observing period.

Stephens, GL, Tsay SC, Stackhouse PW, Flatau PJ.  1990.  The Relevance of the Microphysical and Radiative Properties of Cirrus Clouds to Climate and Climatic Feedback. Journal of the Atmospheric Sciences. 47:1742-1753.   10.1175/1520-0469(1990)047<1742:trotma>;2   AbstractWebsite

This paper examines the effects of the relationship between cirrus cloud ice water content and cloud temperature on climate change. A simple mechanistic climate model is used to study the feedback between ice water content and temperature. The central question studied in this paper concerns the extent to which both the radiative and microphysical properties of cirrus cloud influence such a feedback. To address this question, a parameterization of the albedo and emissivity of clouds is introduced. Observations that relate the ice water content to cloud temperature are incorporated in the parameterization to introduce a temperature dependence to both albedo and emittance. The cloud properties relevant to the cloud feedback are expressed as functions of particles size re, asymmetry parameter g and cloud temperature and analyses of aircraft measurements, lidar and ground based radiometer data are used to select re and g. It was shown that scattering calculations assuming spherical particles with a distribution described by re = 16 μm reasonably matched the lidar and radiometer data. However, comparison of cloud radiation properties measured from aircraft to those parameterized in this study required values of g significantly smaller than those derived for spheres but consistent with our understanding of nonspherical particle scattering.The climate simulations revealed that the influence of cirrus cloud on climate was strongly affected by the choice of re and g: parameters that are both poorly known for cirrus. It was further shown that the effect of ice water feedback on a CO2 warming simulation could be either positive or negative depending on the value of re assumed. Based on these results, it was concluded that prediction of cirrus cloud feedback on climate is both premature and limited by our lack of understanding of the relationship between size and shape of ice crystals and the gross radiative properties of cirrus.

Flatau, PJ, Flatau M, Zaneveld JRV, Mobley CD.  2000.  Remote sensing of bubble clouds in sea water. Quarterly Journal of the Royal Meteorological Society. 126:2511-2523.   10.1256/smsqj.56807   AbstractWebsite

We report on the influence of submerged bubble clouds on the remote-sensing properties of water. We show that the optical effect of bubbles on radiative transfer and on the estimate of the ocean colour is significant. We present a global map of the volume fraction of air in water derived from daily wind speed data. This map. together with the parametrization of the microphysical properties, shows the possible significance of bubble clouds on the albedo to incoming solar energy.