Edward (Ward) Hindman

Air pollution transport in the Himalayas of Nepal and Tibet during the 1995–1996 dry season

Abstract To investigate if air pollution generated in the Himalayan foothills reached higher elevations, a sequence of surface meteorological and condensation nucleus (CN) measurements were made between October 1995 and May 1996. Measurements were made in the Kathmandu valley of the foothills, in the Dudh Kosi valley of the eastern Himalayas and at the base of Mt. Everest in Nepal and Tibet. The Kathmandu valley measurements revealed a semi-diurnal variation of CN and moisture in the mountain-valley wind system and a reduction of both in strong afternoon convection we call the “Kathmandu chimney”. The air was polluted at all times in the valley. The Dudh Kosi measurements revealed a diurnal variation in CN and moisture; both were drawn into the valley in the strong afternoon valley wind and cleaner and drier air flowed into the valley in the nighttime mountain wind. The air was unpolluted in the mornings and frequently polluted in the afternoon and evenings; some of the evening pollution was from local sources. The CN concentrations in Tibet were smaller than in Nepal at the same elevation due dilution in the deep afternoon convective boundary layer in Tibet; there also may be a “Tibetan chimney”. Evidence is presented for trans-Himalayan pollution transport: a 7-h pollution episode originating in Nepal was advected into Tibet and a 18-h episode originating in Tibet was advected into Nepal.

Ship-produced cloud lines of 13 July 1991

Abstract On 13 July 1991, a well-defined cloud line produced by an unidentified steaming ship was detected in satellite imagery and was simultaneously photographed from the R/V EGABRAG III . The EGABRAG produced a much less well-defined cloud line. Measurements made from the EGABRAG revealed that the cloud lines formed in a shallow boundary layer which was nearly saturated, unstable, drizzling and nearly free of cloud condensation nuclei (CCN). The EGABRAG passed through the plume of the ship as indicated by elevated CCN concentrations coincident with the cloud line. Thereafter, both ships passed under a shallow stratus layer where background CCN concentrations increased significantly. Only the cloud line produced by the ship extended into the stratus layer, the EGABRAG did not affect the layer. The CCN and updraft from the ship were involved in the formation of the cloud line. In contrast, the CCN and updraft from the EGABRAG were insufficient to produce a well-defined cloud line. Production of the cloud lines appeared dependent on a combination of environmental conditions and ship-produced CCN and updrafts.

Collecting Supercooled Cloud Droplets as a Function of Droplet Size

Abstract Supercooled cloud droplets were inertially impacted onto “cloud-sieves” at a mountaintop location. The large cross-sectional areas of the sieve meshes permitted grams of cloud water to be passively collected in minutes. Each sieve was constructed from specific diameter cylindrical strands and collected all cloud droplets larger than a critical size. Procedures are developed to produce liquid water content (LWC) and chemical composition values as a function of droplet-size interval. The sieve LWC measurements were compared with simultaneous LWC measurements obtained from a standard cloud droplet spectrometer. The sieve and spectrometer values were consistent for droplets between approximately 4 and 13 µm in diameter. The sieves overestimated the water contents of larger and smaller droplets in low LWC clouds (<0.1 gm−3). In high LWC clouds, the sieve LWC values for all droplet sizes closely approximated the spectrometer values. Sources of error were investigated. Rime “feathers” and frost grew on ...

A ten-winter record of cloud-droplet physical and chemical properties at a mountaintop site in Colorado

Abstract Cloud-droplet spectra and coincident cloud water pH measurements have been made for a portion of ten consecutive winters (1983/84x961992/93) from clouds that enveloped Storm Peak Laboratory in northwestern Colorado; cloud water ion measurements were made for eight of the winters. To determine if the physical and chemical properties are related, the data were stratified into three populations: pH ≤3.6, 3.6 < pH < 4.6, pH ≥4.6. It was found that clouds with the smallest pH values (3.4) had the largest droplet concentrations (N 329 cm−3), smallest mean droplet diameters (Dbar = 6.4 µm), and largest ion concentrations (e.g., SO44 = 5.7 mg L−1), while clouds with the largest pH values (5.1) had the smallest N values (189 cm−3), largest Dbar values (8.0 µm), and smallest ion concentrations (SO44 = 3.9 mg L−1). Nevertheless, all three populations had similar liquid water contents (LWC ≅ 0.070 g m−3). The equation LWC = π/66Dbar3Nρ where ρ is the density of water, closely describes the relationship between...

Light absorption by aerosol particles: First International Workshop

The First International Workshop on light absorption by aerosol particles is introduced, and its goal-to separate the two sources of variability in light absorption measurements by establishing instrumentation errors-is reviewed.

Observations of ship tracks from ship-based platforms

Abstract Ship-based measurements in June 1994 provided information about ship-track clouds and associated atmospheric environment observed from below cloud levels that provide a perspective different from satellite and aircraft measurements. Surface measurements of latent and sensible heat fluxes, sea surface temperatures, and meteorological profiles with free and tethered balloons provided necessary input conditions for models of ship-track formation and maintenance. Remote sensing measurements showed a coupling of ship plume dynamics and entrainment into overlaying clouds. Morphological and dynamic effects were observed on clouds unique to the ship tracks. These morphological changes included lower cloud bases early in the ship-track formation, evidence of raised cloud bases in more mature tracks, sometimes higher cloud tops, thin cloud-free regions paralleling the tracks, and often stronger radar returns. The ship-based lidar aerosol measurements revealed that ship plumes often interacted with the over...

Optical properties of continental haze and cumulus and orographic clouds based on Space Shuttle polarimetric observations

Digitized Space Shuttle imagery in the red, green, and blue spectral regions (0.600, 0.540, and 0.435 µm, respectively) is used to characterize the mean radius and the index of refraction of droplets in cumulus and orographic clouds. The clouds are shown to consist concurrently of submicrometer and supermicrometer droplets, with the percent polarization indicative of the dominant sizes. Cloud development from haze as well as inhomogeneities in the cloud decks can be traced remotely. The absorption properties of clouds can also be determined remotely. An optical depth of continental haze in the same three spectral regions as the clouds is computed from the polarimetric and photometric contributions. Both Mie and Rayleigh scattering are included in the model.

An Undergraduate Field Course in Meteorology and Atmospheric Chemistry

A field course for undergraduate science students at The City College of New York (CCNY) is described. The students, who have completed an introductory meteorology course, conduct experiments at Storm Peak Laboratory (SPL) in the northern Colorado Rockies during winter breaks. The students apply their classroom learning to understand actual meteorological conditions. Prior to the field work, the students learn the necessary measurement and observation skills in a series of laboratories at CCNY and SPL. Experiments are conducted in both cloudy and clear conditions. From the clouds that envelop SPL, the students collect cloud droplets and snow crystals for physical and chemical analyses and for more detailed analyses at CCNY. For example, the students measure the pH of droplets as a function of droplet size and, in clear conditions, measure the diurnal behavior of valley temperature inversions. Following the winter field experiments, the students reduce and analyze their data during the spring semester. At ...

A Marine Stratus Layer Modified by Nuclei from a Ship Plume

Abstract On 13 July 1991, a steaming ship produced a long, linear feature in a marine stratus layer offshore Baja California, detected in a 2207 UTC NOAA-11 3.7-µ m satellite image. Droplet sizes were inferred from the satellite image: small droplets existed in the linear feature, and larger droplets existed in the adjacent ambient region. A one-dimensional cloud formation model was used to investigate the contributions of measured cloud condensation nuclei (CCN) and assumed updrafts to the formation of droplets in the ambient cloud and embedded linear feature. The results indicate that 1) the ambient CCN and ambient updraft could explain the large droplets detected in the ambient stratus, 2) the elevated CCN measured in the ship plume and the assumed ambient updraft could explain small droplets detected in the linear feature, and 3) the ambient CCN and assumed ship-enhanced updraft could not explain the small droplets in the linear feature. The measured ship-produced nuclei appear to have caused the obse...

Field comparison of optical particle counters

Abstract Particle size distribution measurements were obtained simultaneously at a coastal field site with six different commercial optical particle counters (OPCs) in clear-air and in fog. Systematic differences between the measurements from the various instruments were documented. The differences were smallest (factor of 1.5–2.5) for sub-micron particles and largest (factor of 8–15) for super-micron particles. These discrepancies were due to inaccuracies in the instruments and to sampling errors. The high size resolution of one OPC enabled the sub- and super-micron droplet populations in fog to be measured. Significant differences occurred between the concentrations of equivalent size particles in clear-air and in fog demonstrating the sensitivity of the measurements to the free-air relative humidity.