bluuebunny/crossref_metadata_2025 huggingface dataset:
Total ozone, ozone vertical distributions, and stratospheric temperatures at South Pole, Antarctica, in 1986 and 1987
Authors: Komhyr W. D. , Grass R. D. , Reitelbach P. J. , Kuester S. E. , Franchois P. R. , Fanning M. L.
Published: February 2008

Ozone and temperatures measured in 1986 and 1987 at South Pole, Antarctica, are compared, with emphasis on observations made at the time of formation of the Antarctica ozone hole. In early October 1987, total ozone decreased at South Pole to a record low of 127 Dobson units (DU), compared with the early October 1986 value of 158 DU. Electrochemical concentration cell (ECC) ozonesonde soundings made during both years showed the ozone depletion at 11–23 km in 1987 to be greater in vertical extent and magnitude and to proceed more rapidly. As in 1986, two exponential ozone decrease rates occurred in 1987 at 17±1 km, with half‐lives of 19.5 and 4.5 days (compared with half‐lives of 35 and 12 days observed in 1986). By early October 1987, nearly all ozone was depleted from a 4‐km‐thick atmospheric layer centered at 17 km. At the time of ozone hole formation, stratospheric temperatures were colder, but tropospheric temperatures were warmer, in 1987 compared to 1986. Because polar vortex breakdown occurred 3 weeks later in 1987 than it did in 1986, stratospheric temperatures in the heart of the ozone depletion region were 10°–40°C colder in mid‐ to late November 1987.
Temperature and horizontal wind measurements on the ER‐2 aircraft during the 1987 Airborne Antarctic Ozone Experiment
Authors: Chan K. R. , Scott S. G. , Bui T. P. , Bowen S. W. , Day J.
Published: February 2008

The Meteorological Measurement System (MMS) provides accurate in situ measurements of atmospheric state variables. Since MMS data products (temperature, pressure, and wind) are extensively used by ER‐2 investigators, the accuracy of these parameters is discussed. During the 1987 Airborne Antarctic Ozone Experiment (AAOE) mission, the ER‐2 aircraft flew over Antarctica on 12 occasions between August 17 and September 22, 1987. The flight plan was to take off at about the same local time, fly southward on an isentropic surface, descend and ascend at the southern terminus over Antarctica, and return northward along the same or a different isentropic surface. MMS data are organized to provide a composite view of the polar atmosphere, which is characterized by frigid temperatures and high zonal winds. Vertical temperature profiles (during aircraft takeoff and landing and during the descent at the southern terminus) and latitudinal variations of the zonal wind are presented. On the basis of observational data, model atmospheres between 0 and 32 km at 70° and 55°S for the August‐September period are proposed. The model atmospheres, representative of the Antarctic environment of the AAOE campaign, are recommended to investigators for the analysis of the AAOE data set.
Temporal variations and sources of elements in the South Pole atmosphere: 1. Nonenriched and moderately enriched elements
Authors: Tuncel Gurdal , Aras Namik K. , Zoller William H.
Published: February 2008

High‐volume particle samples were collected from 1979 to 1983 from the south pole atmosphere and analyzed by nuclear methods. The new results are combined with similar studies at the south pole. There is no trend of concentrations during 12 years of sampling, but concentrations of elements fluctuate through seasonal cycles. Concentrations of elements associated with crustal dust and sea salt showed opposite seasonal variations. Concentrations of most crustal elements are low during winters, but double during summers. Concentration of marine elements are low in the summers and high in winters. Enrichment factors of some crustal elements, such as Ba, La, Ce, Yb, and Hf are higher in the winter than summer, indicating the presence of a second crustal component with a different chemical composition in the south pole atmosphere. A similar difference in the crustal enrichment factor of Co is due to the influence of volcanic or anthropogenic sources. Sulfate, seasalt, meteoritic particles, volatiles, and two different types of crustal particles are found to be components of the south polar aerosols. The relative contribution of each component to total aerosol mass is as follows: crustal, 4.0% in summer, 2.5% in winter; marine elements 16.6% in summer, 78.6% in winter; sulfate, 77.5% in summer, 18.0% in winter; meteoritic particles, 0.1% in summer, 0.1% in winter; volatiles, 0.9% in summer, 0.5% in winter; crustal component II, 0.8% in summer, 0.7% in winter.
The seasonal variation of light nonmethane hydrocarbons in the Antarctic troposphere
Authors: Rudolph J. , Khedim A. , Wagenbach D.
Published: February 2008

About 80 samples of antarctic air were collected between 1982 and 1985 at the “Georg von Neumayer” station (70°36′S and 8°22′W) and analyzed for ethane, ethene, acetylene, propane, and propene. Yearly average mixing ratios were 0.37, 0.36, 0.011, 0.07, and 0.21 ppb, respectively. The seasonal cycles for ethane and acetylene showed minima around the late southern hemispheric summer and maxima in late winter. The phase of the seasonal cycle in ethane and acetylene can be explained by seasonal variation of atmospheric removal rates. Seasonal variation of one of the major southern hemispheric ethane and acetylene sources, biomass burning, would cause a similar seasonal change. Propane exhibits a much higher variability and shows no clear seasonal cycle. The atmospheric mixing ratios of ethene and propene peak around early austral fall and are most probably mainly determined by seasonal variation in emissions from the oceans surrounding Antarctica.
Charging of polydispersed aerosol particles by attachment of atmospheric ions
Authors: Yair Yoav , Levin Zev
Published: February 2008

The charge distribution on polydispersed aerosol particles was obtained by a simultaneous solution of the ion‐aerosol balance equations for a finite range of aerosol sizes. All aerosols were assumed to be uncharged initially, and external electric fields, particle transport, coagulation and turbulence were ignored. The effects of varying the aerosol size distribution, aerosol concentration, and initial positive space charge on the charging process were considered for particles between 0.01‐ and 0.5‐μm radius. Results show that a larger depletion in the free negative ion concentration occurred early in the charging process due to the larger values of the attachment coefficients of negative ions to aerosols. It was found that for small aerosol concentrations, particles were charged mostly negatively, but that an increase in aerosol concentrations lead to differential charging, resulting in opposite charging of the small (mostly negative) and the large (mostly positive) particles. This effect was enhanced for size distributions which had a significant component of large particles. The time needed for a polydispersed aerosol to reach steady state is long and grows with particle concentration.
Ground coronae and lightning
Authors: Chauzy Serge , Soula Serge , Despiau Serge
Published: February 2008

The influence of corona emission during and immediately after a lightning flash is studied experimentally as well as by numerical modeling. Simultaneous electric field measurements made at ground level, 30 m above ground level, and over water (zero level) show that corona ions generated during the flash can strongly modify not only the field recovery that follows, but also the brief field signature during the flash. The higher the field intensity reached during the flash, the stronger this influence. As a matter of fact, under strong field conditions, the initial recovery rate appears to be higher at ground level than aloft, and the overall surface field change produced by a lightning flash can be considerably reduced owing to the creation of ions. A numerical model computes the modification, by this phenomenon, of the field evolution at various levels.
Statistics on fine structure of cloud‐to‐ground lightning field waveforms
Authors: Ishii Masaru , Hojo Jun‐Ichi
Published: February 2008

Electric and magnetic field changes associated with lightning return strokes have been observed by waveform recording systems and a magnetic direction‐finding system on the coast of the Sea of Japan. Parameters characterizing the fine structure of a return‐stroke field waveform are statistically investigated. The 10‐bit resolution of the recording system revealed long duration of the slow front, resulting in the 0–100% risetime of 8.6‐μs mean for negative and 13.2 μs for positive return strokes in summer. These values are about 1.5–2 times those previously reported. The risetime for positive return‐stroke waveforms shows seasonal variation, and the mean in winter is 21.2 μs, which is consistent with the previous report of the authors. Fast transition in the wave front was measured with a fast antenna of 24‐ns overall risetime. The 10–90% risetime of the fast transition for positive return‐stroke waveforms propagated over seawater shows a similar distribution to that for negative return strokes obtained in Florida. The mean and standard deviation are 0.11 μs and 62 ns, respectively. The zero‐crossing time for radiation waveforms from return strokes shows seasonal variation in both polarities and becomes shorter in winter. Dependence on polarity also exists. The mean values for negative return strokes are 79 and 40 μs in summer and winter, and those for positive return strokes are 151 and 93 μs, respectively. The zero‐crossing time for negative return strokes in summer is about 1.5 times longer than the value measured in North America, but the difference might come from the characteristics of the measuring device, as is the case for the 0–100% risetime. The depth of the dip after the peak of return‐stroke waveforms also has seasonal variation and dependence on the polarity of return strokes. The mean of 42% for negative return strokes in summer increases to 78% in winter and, similarly, increases from 24% to 40% for positive return strokes.
Dynamics, radiation, and photochemistry in the mesosphere: Implications for the formation of noctilucent clouds
Authors: Garcia Rolando R.
Published: February 2008

The nature of noctilucent clouds, which occur at very great heights and high latitudes during summer, has remained something of a mystery for over 100 years. The realization that the summer mesopause is the coldest region of the Earth's atmosphere, together with the possibility that transport by atmospheric motions could maintain a substantial mixing ratio of water vapor against very rapid chemical destruction, has led to the present consensus that noctilucent clouds are formed of water ice. A number of recently developed microphysical models have been successful in simulating cloud particle distributions whose characteristics are consistent with satellite radiance observations. However, because of the scarcity of data on temperature, dynamics, and water vapor abundances, these models have had to rely on a number of assumptions about the behavior of these quantities. This paper attempts to illustrate by means of model calculations how various dynamical and photochemical processes interact to produce the unique environment that makes possible the existence of noctilucent clouds. In particular, it focuses on how thermal relaxation influences the altitude and strength of gravity wave breaking and on the effects of such wave breaking on the circulation, temperature distribution, and transport of water vapor near the summer mesopause. It is also shown that, if present understanding of hydrogen chemistry in the mesosphere is even approximately correct, variations in Lyman α radiation should have a significant effect on water vapor abundances near the summer mesopause and, therefore, on the occurrence of noctilucent clouds.
Intercomparison of daily values of atmospheric variables, including diabatic heating rates, from the ECMWF, GFDL, and Goddard Laboratory for Atmospheres FGGE level IIIb analyses
Authors: Mizzi Arthur P. , Kasahara Akira
Published: February 2008

In order to assess the agreement among three First GARP Global Experiment (FGGE) Level IIIb analysis data sets produced by the European Centre for Medium Range Weather Forecasts, the Geophysical Fluid Dynamics Laboratory, and the Goddard Laboratory for Atmospheres, the intercomparisons of daily values of large‐scale vorticity ζ, divergence δ, temperature T, static stability Γ, vertical motion ω, and diabatic heating rate Q/Cp are performed during the period January 26 to February 11, 1979. The ζ, δ, and ω fields are calculated from the velocity components u and v after interpolation of Level IIIb analyses onto the National Center for Atmospheric Research Community Climate Model, version 0B (NCAR CCM0B) grid. The Q/Cp is obtained as a residual of the thermodynamic energy balance. Using standard descriptive and comparative statistics, we intercompare the three analyses in three geographic regions: NH (60°N–30°N), TR (30°N–30°S) and SH (30°S–60°S). The agreement among the ζ analyses is excellent, though a slight disagreement is found in the lower troposphere of the TR and SH. However, the agreement among the δ analyses is generally weaker, except for the lower troposphere of the NH. Intercomparison of the T analyses shows significant systematic differences, though the agreement in their geographical distributions is generally good. This influences the Γ analyses, which show weak agreement particularly in the lower troposphere. The intercomparison of kinematic and thermodynamic fields for the different analyses gives an indication of the degree of agreement among the Q/Cp analyses whose calculations involve many highly sensitive quantities. The intercomparison statistics provide us with a quantitative assessment of the systematic differences, spatial coherence, and quantitative agreement between the different analyses for each meteorological field, but they do not provide a measure of the relative accuracy. To provide such a measure, we compare the heating rates and vertical motion with equivalent blackbody emission temperatures observed by TIROS‐N in the TR. Through this technique, we infer the relative accuracy of the three FGGE Level IIIb analyses. It is clear that the method of objective analysis for meteorological observations must be refined to improve the quality of the divergent wind analysis and the temperature analysis in the tropics.
The electrification of New Mexico thunderstorms: 2. Electric field growth during initial electrification
Authors: Breed Daniel W. , Dye James E.
Published: February 2008

Electric field measurements were made by a sailplane inside thunderstorms near Langmuir Laboratory and the Magdalena Mountains in central New Mexico. The continuity of these measurements in‐cloud allows us to deduce electric field growth rates in six cases ranging from initial electrification through the production of lightning. The electric field data are combined with radar reflectivity data to estimate charge locations and magnitudes. In each case, the dominant charge was negative, associated with a local reflectivity core, and demonstrated a cellular structure centered at altitudes ranging from 5.5 to 7.3 km mean sea level (−3 to −15° C). Three distinct phases characterize the electric field measurements during initial electrification: an early stage of slowly increasing fields that largely could be explained by the sailplane motion toward the estimated charges, followed by a rapid exponential growth period, and then a plateau in electric field growth rate (at about 300 V m−1 s−1) after the rapid growth period. These six cases extend earlier studies to further establish the character and magnitude of electric field growth during the early stages of thunderstorm electrification.
Direct measurements of the photolysis rate coefficients and Henry's law constants of several alkyl nitrates
Authors: Luke Winston T. , Dickerson Russell R. , Nunnermacker Linda J.
Published: February 2008

We report the direct measurement of the photolysis rate coefficients of ethyl, n‐propyl, n‐butyl, and 2‐butyl nitrate to NO2 and the alkoxy radical, RONO2 + hν → RO + NO2, using a luminol chemiluminescence NO2 detector. The photolysis of primary and secondary alkyl nitrates is slow: at a temperature of 288 K, a zenith angle of 60°, and an ozone column abundance of 0.295 atm cm, jRONO2 ≈ 0.40 × 10−6 s−1 for the primary alkyl nitrates, and 0.65 × 10−6 s−1 for 2‐butyl nitrate. This implies a photolytic lifetime of 15 to 30 days in the planetary boundary layer. The photolysis frequency is very temperature dependent, with an effective activation energy of 11.2 kJ mol−1 for 2‐butyl nitrate and 10.1 kJ mol−1 for ethyl nitrate. Observed photolysis rate coefficients agree, within experimental uncertainty, with coefficients calculated using recently measured absorption cross sections and an assumed quantum yield of unity. The photolysis rate coefficients of ethyl, n‐propyl, and 2‐butyl nitrate for an overhead Sun, a temperature of 298 K, and an ozone column abundance of 0.295 atm cm are estimated to be 1.45, 1.33, and 2.54 × 10−6 s−1, respectively. Henry's law constants (H) at a temperature of ∼295 K are 1.26±0.12 M atm−1 and 0.74±0.04 M atm−1 for n‐butyl and 2‐butyl nitrate, respectively. At a temperature of ∼279 K, H increases to 3.94±0.59 M atm−1 for n‐butyl nitrate and 2.27±0.23 M atm−1 for 2‐butyl nitrate. Wet deposition is concluded to be an unimportant sink for alkyl nitrates in the absence of aqueous phase reactions.
Flux divergence of thermal radiation within stratiform clouds
Authors: Davies Roger , Alves Adil R.
Published: February 2008

A longwave radiative transfer model based on the narrow‐band transmission functions of Lowtran 6 has been developed to investigate the profile of radiative flux divergence at the tops of stratiform clouds. The model has a vertical resolution of 1 m and a spectral resolution of 20 cm−1. These features are shown to permit modeling of broadband radiative transfer in the presence of a cloud top inversion and finite liquid water gradient. Radiative cooling rates in excess of 40 K hr−1 are shown to be possible for extreme conditions, with values of 10 K hr−1 being representative of more typical conditions. The values obtained are shown to be strongly influenced by the magnitude of liquid water concentration, by the gradient of liquid water in the top 50 m, and by the strength of the temperature inversion.
Measurements of stratospheric hydrogen cyanide at McMurdo Station, Antarctica: Further evidence of winter stratospheric subsidence?
Authors: Jaramillo M. , de Zafra R. L. , Barrett J. , Emmons L. K. , Solomon P. M. , Parrish A.
Published: February 2008

We have made measurements of hydrogen cyanide (HCN) in the springtime Antarctic stratosphere using ground‐based millimeter wave spectroscopy. We find a steeper decrease in volume mixing ratio with altitude than that found at tropical latitudes, from an assumed value of ∼160 pptv in the troposphere to a value of 65±30 pptv at 40 km, which may be further evidence of substantial vertical subsidence of the Antarctic winter stratosphere.
Analysis of sources and sinks of atmospheric nitrous oxide (N2O)
Authors: Cicerone Ralph J.
Published: February 2008

There are major unanswered questions about the sources of atmospheric nitrous oxide. Recent assessments of N2O sources are diverging rather than converging. Here I use a simple model to place constraints on the relative sizes of N2O sources in the northern and southern hemispheres (NH and SH). Using measurements of the rate of temporal increase of atmospheric nitrous oxide (N2O) concentrations and observations of their cross‐equator differences, I calculate the total sources of N2O for the (NH and SH). The NH source ΦN must exceed the SH source ΦS; their ratio R (= ΦN/ΦS) is between 1.7 and 2.4 for the case where the NH concentration is 1 ppb higher than that in the SH. When the NH concentration is 0.75 ppb higher, R is between 1.5 and 1.9. These values of R increase by about 50% when more rapid loss to the NH stratosphere is introduced. Slightly wider ranges of R are calculated for certain choices of parameters. For these calculations I have used a two‐box model which permits an array of assumptions to be tested; a range of values is employed for interhemispheric exchange times and for removal times due to stratospheric destruction of N2O. In addition to the common case of no uptake of atmospheric N2O by soils, I have tested the model sensitivity to two hypothesized nonzero soil sinks. Relatively small soil sinks would decrease the atmospheric residence time of N2O to values below those that are calculated from stratospheric removal alone.
Trends of atmospheric methane during the 1960s and 1970s
Authors: Khalil M. A. K. , Rasmussen R. A. , Shearer M. J.
Published: February 2008

Sporadic measurements of atmospheric methane, using gas chromatography, have been taken since the early 1960s. We found 188 measurements between 1962 and 1979 reported in various publications with data in 70 of the 216 months. We have analyzed these measurements to estimate the trends of methane between 1960 and 1980. The data were adjusted for differences of absolute calibration and for latitudinal variations, and analyzed by ordinary regression analysis, weighted regression analysis, and nonparametric methods. Our best estimate of the increasing trend during this period is 13±3 ppbv/yr which is similar to, but somewhat less than, the trend of about 17 ppbv/yr over the last decade.
The Sharav Cyclone: Observations and some theoretical considerations
Authors: Alpert P. , Ziv B.
Published: February 2008

A special study of the Sharav Cyclones indicates that they are the result of large‐scale weak baroclinicity, enhanced by vigorous boundary‐layer baroclinicity between the North African coast and the Mediterranean. It is illustrated how the jet stream plays a major role in the vertical circulation in producing a complex cyclonic circulation dominated by at least three mechanisms: large‐scale interior baroclinicity, boundary‐layer baroclinicity, and jet stream related circulations. The main characteristics of the Sharav Cyclone (also called the Saharan Depression or Khamsin Depression) in the Mediterranean are reviewed. Unlike the cold winter cyclone, the Sharav Cyclone is a spring cyclone. Its tracks lie mainly along the North African coast and turn to the north near the southeastern Mediterranean. Its warm front is active and is sometimes associated with extremely high surface temperatures. Its cold front is shallow. The Sharav Cyclone moves eastward relatively fast, typically faster than 10 m s−1, and with a small speed variability. In general, there is an upper level trough to the west of the surface low and the surface horizontal scale is of the order of 500–1000 km. Finally, it is frequently associated with heavy dust/sand storms and low visibilities. Some of these features are illustrated in a case study of the April 28–30, 1986, cyclone. Vertical cross sections indicate a deep circulation associated with the exit region of an upper level jet. In addition to presenting evidence that the Sharav Cyclone is a deep tropospheric circulation, it is shown that the transverse indirect circulation at the exit region of the jet is a major component of its circulation. The classic two‐level baroclinic model (Phillips, 1954) is applied. The effects of the major diabatic heating due to the sensible heat flux above the North African desert and the large north to south temperature gradients are incorporated through the thermal wind of the basic state. The model predicts the fast eastward motion, the relatively smaller horizontal scale and the fast growth rate. Furthermore, the model predicts an annual maximum growth rate in April and a secondary peak in October, which agrees with the frequency of occurrences of the Sharav Cyclones.
Parameter estimation and sensitivity analysis for the modified Bartlett‐Lewis rectangular pulses model of rainfall
Authors: Islam S. , Entekhabi D. , Bras R. L. , Rodriguez‐Iturbe I.
Published: February 2008

This paper investigates the dependence of parameters of a stationary point process model on seasonal and spatial variability of rainfall. Twenty‐four years of hourly rainfall data for two stations from the Arno River basin in central Italy have been used to estimate parameters for each month, assuming local stationarity within the month. The estimated model parameters are physically reasonable, vouching for the model's ability to capture the general temporal and spatial structure of rainfall events. Parameter sensitivity analysis provide useful guidelines for understanding the model structure and devising effective parameter estimation strategies.
The estimation of convective rainfall by area integrals: 1. The theoretical and empirical basis
Authors: Atlas David , Rosenfeld Daniel , Short David A.
Published: February 2008

This work develops a unified theory for the estimation of both total rainfall from an individual convective storm over its lifetime and the areawide instantaneous rainfall from a multiplicity of such storms by use of measurements of the areal coverage of the storms within a threshold rain intensity isopleth or the equivalent threshold radar reflectivity. The method is based upon the existence of a well‐behaved probability density function (pdf) of rain rate either from the many storms at one instant or from a single storm during its life. In the first method, the lifetime storm rainfall volume is V = [〈A(τ)〉T]S(τ), where 〈A(τ)〉 is the average storm area over the life of the storm of duration, T, in which R > τ and the bracketed term is the area time integral. In the second method, the instantaneous areawide rain rate, 〈R〉 = F(τ)S(τ), where F(τ) is the fractional observed area with R > τ. In both methods, S(τ) is the climatological rain rate for the regime divided by the relative frequency with which R > τ. For thresholds exceeding some minimum value, S(τ) is essentially linear with τ for the kind of lognormal pdf which characterizes convective rain, and is a constant for specified τ. Thus both the lifetime V of the individual storm and the instantaneous 〈R〉 for a multiplicity of storms are linear functions of A(τ) and F(τ), respectively. This is in accord with the observations of Doneaud et al. (1984) and Chiu (1988a, b). Because the autocorrelation time of the areawide rain rate of convective storms in areas in excess of 104 km2 is about 5–6 hours, the snapshot 〈R〉 is representative of the rain for a few hours. This enhances the accuracy of snapshot measurements for climate purposes and also extends their utility to smaller time/space problems such as hydrology and numerical weather prediction. We also discuss ways of obtaining climatologically valid and unbiased values of S(τ) and means of establishing its values from aircraft and space.
A comparison of Solar Mesosphere Explorer and Stratosphere Aerosol and Gas Experiment II ozone densities near the stratopause
Authors: Rusch D. W. , Clancy R. T. , Mccormick M. P. , Zawodny J. M.
Published: February 2008

Ozone measurements made by the Ultraviolet Spectrometer on the Solar Mesosphere Explorer and those from the Stratosphere Aerosol and Gas Experiment II are compared at 1.0 mbar for the time period from October 1984, to December 1986. A model of the diurnal variation of ozone is used to correct for the difference in local times of the two measurements. The two instruments agree to within 5% at all latitudes considered in the comparison. Further, no significant divergence is found between the data sets for the time period of overlap. The results support the accuracy and precision of each instrument and the accuracy of ozone trends derived over the 1982–1986 period from Solar Mesosphere Explorer data.
Direct determination of the helium 3 content of atmospheric air by mass spectrometry
Authors: Davidson Thomas A. , Emerson David E.
Published: February 2008

The Bureau of Mines, Helium Field Operations, in Amarillo, Texas, has developed a method for direct measurement of the helium 3 content of air by mass spectrometry. The helium is preconcentrated by passing samples of air through a charcoal trap at liquid nitrogen temperature. Sample measurements are compared with identically made measurements of gravimetrically prepared standards. The helium 3 content of near‐surface atmospheric air is determined to be 7.27±0.20 parts per trillion by volume (pptv). The accuracy of 0.20 pptv is at the 68% confidence level. The helium 4 content of near‐surface atmospheric air has recently been determined at this facility to be 5.2204±0.0041 parts per million by volume (ppmv). The helium 3/helium 4 ratio for atmospheric helium, RA, is established as 1.393×10−6 by independent measurements of the separate components.
Multistroke cloud‐to‐ground strike to the NASA F‐106B airplane
Authors: Mazur Vladislav , Fisher Bruce D. , Brown Philip W.
Published: February 2008

An analysis of electromagnetic waveform records and video images of a multistroke cloud‐to‐ground (CG) strike to the NASA F‐106B instrumented airplane is presented. The CG flash started as a lightning strike triggered by the airplane and later produced multiple return strokes to the ground (the ground strike network registered six return strokes). Although there are some uncertainties in data interpretation resulting from lack of independent measurements with other than the airborne instruments, recoil streamers and eight sequences of dart leaders followed by return strokes (two more than were indicated by the ground network) were identified in the airborne data. At least three of the subsequent return strokes were attached to the airplane. The analysis provides evidence that formation of recoil streamers and dart leaders is accompanied by a surge in continuous current. This feature is similar to that observed in the bidirectional leader development during lightning initiation on the airplane.
In situ measurements of the fine‐scale structure and turbulence in the mesosphere and lower thermosphere by means of electrostatic positive ion probes
Authors: Blix T. A. , Thrane E. V. , Andreassen Ø.
Published: February 2008

The paper presents and discusses a large set of in situ measurements of fine‐scale structure in the mesosphere and lower thermosphere at high latitudes. The experimental technique used is a rocket‐borne electrostatic positive ion probe with linear amplification and high precision and time resolution. This type of probe has proved to be very efficient. The accuracy and limitations of the experiment are discussed. The measured ion density fluctuations are used as passive tracers for motions in the nonionized air. Quantitative estimates of the characteristics of turbulence have been derived. The method of analysis is carefully discussed and related to previous work, and a revision of earlier methods is proposed. The results show a characteristic minimum in turbulent intensity at or below the mesopause region.
Characterization and error analysis of profiles retrieved from remote sounding measurements
Authors: Rodgers Clive D.
Published: February 2008

The characterization and error analysis of profiles retrieved from remote measurements present conceptual problems, particularly concerning interlevel correlations between errors, the smoothing effect of remote sounding and the contribution of a priori information to profile. A formal analysis for profile retrieval is developed which is independent of the nature of the retrieval method, provided that the measurement process can be characterized adequately. The relationship between the retrieved and true profiles is expressed in terms of a smoothing function which can be straightforwardly calculated. The retrieval error separates naturally into three components, (1) random error due to measurement noise, (2) systematic error due to uncertain model parameters and inverse model bias, and (3) null‐space error due to the inherent finite vertical resolution of the observing system. A recipe is given for evaluating each of the components in any particular case. Most of the error terms appear as covariance matrices, rather than simple error variances. These matrices can be interpreted in terms of “error patterns”, which are statistically independent contributions to the total error. They are the multidimensional equivalent of “error bars”. An approach is described which clarifies the relation of a priori data to the retrieved profile, and identifies a priori in cases where it is not an explicit part of the retrieval.
Seasonal ozone variations in the upper mesosphere
Authors: Thomas Ronald J.
Published: February 2008

The global daytime ozone was measured by the Solar Mesosphere Explorer satellite (SME) for 5 years. The measurements extend through the mesosphere, covering from 50 km to over 90 km. The ozone in the upper mesosphere varies annually by up to a factor of 3. The observed seasonal variations may be summarized in several different ways. From year to year there is a great deal of repeatability of these variations. This repeatability occurs in most of the upper mesosphere outside the tropics. Near 0.01 mbar (80 km) the mid‐ and high‐latitude mixing ratio peaks each year in mid‐April. A secondary maximum in the altitude profile of ozone density usually occurs near 85 km. Changes in this structure are directly related to the April maximum and other seasonal changes seen at 0.01 mbar. The changing seasonal structure produces a “bump” at the ozone mixing ratio minimum that is largest just after spring equinox. This perturbation to the mixing ratio profile seems to move upward during the first half of the year. The seasonal changes of ozone were analyzed in terms of annual and semiannual structure. The variations generally have both an annual and semiannual component depending on altitude and latitude. The phases of the variations change quickly with both altitude and latitude. The semiannual component peaks in April, over most of the upper mesosphere.
Effect of solar proton events on the middle atmosphere during the past two solar cycles as computed using a two‐dimensional model
Authors: Jackman Charles H. , Douglass Anne R. , Rood Richard B. , McPeters Richard D. , Meade Paul E.
Published: February 2008

Daily average solar proton flux data for the years 1963–1984 (two solar cycles) have been used in a proton energy degradation scheme to derive ion pair production rates and, subsequently, HOx (H, OH, HO2) and NOx (N, NO, NO2) production rates. These HOx and NOx production rates are computed in a form suitable for inclusion in an atmospheric two‐dimensional time‐dependent photochemical model. The HOx increases, although large for certain solar proton events (SPEs), are relatively short‐lived because the HOx species have lifetimes of only hours in the middle atmosphere. For longer‐lived NOx species, increases are important for 2–4 months past the more intense SPEs but are generally negligible 6 months after the SPE. The only exception to this scenario was the gigantic August 1972 SPE, whose stratospheric effects lasted about a year past the event. Comparisons of model results with the ozone data from the Nimbus 4 backscattered ultraviolet (BUV) instrument indicate relatively good agreement in the time dependence and magnitude of the ozone depletion for the middle stratosphere between the model and measurements for the August 1972 SPE and for 2 months past the event. The model predictions for the August 1972 SPE indicate at most a 1% decrease in total ozone at the highest latitudes with a significant interhemispheric difference. The model predicts a larger middle latitude stratospheric ozone change in the southern than the northern hemisphere caused by the difference in seasons between the two hemispheres. The computed ozone decreases associated with the HOx and NOx increases are substantial in the upper stratosphere at high latitudes for only a few SPEs in the 22 years studied. A mechanism is presented for transport of NOy from the stratosphere to the ground, which may be involved in the enhancements in nitrate fluxes noticed in Antarctic deposition data. Our computations, however, indicate that the SPE contributions to these nitrate fluxes (even for the August 1972 SPE) are probably small.
Upwelling diffusion climate models: Analytical solutions for radiative and upwelling forcing
Authors: Morantine Michael , Watts Robert G.
Published: February 2008

A globally averaged energy balance climate model with a deep ocean reduced to the one‐dimensional case is used to study the transient thermal response characteristics of the system. Analytical solutions are presented for the upwelling diffusion and the box diffusion models for a general radiation forcing function in terms of a convolution integral. An exact solution for a step change in upwelling rate is presented, and an approximate solution for small variations in upwelling rate about some initial value is presented. Comparison between the exact and the approximate solutions indicates that the approximate transient response due to a time‐dependent upwelling fluctuation is accurate for |Δw/w0| < 0.02. The transient thermal response of surface temperature due to radiation forcing of an upwelling diffusion model is found to be significantly more rapid than that of the box diffusion model.
Outgoing long‐wave radiation computed from HIRS2/MSU soundings
Authors: Wu Man‐Li C. , Susskind J.
Published: February 2008

Fields of outgoing long‐wave radiation (OLR) have been computed using geophysical parameters retrieved from analysis of HIRS2/MSU sounding data as input to a modified version of the Wu‐Kaplan radiation code used in the Goddard Laboratory for Atmospheres fourth‐order general circulation model. Monthly mean results for 1979 agree with monthly mean OLR fields measured by the Nimbus 7 Earth radiation budget (ERB) broadband narrow field of view instrument within standard deviations of 6.3 W m−2 but with a global mean bias of 8.0 W m−2. Results are shown for July 1979. The areas of disagreement between high‐resolution infrared radiation sounder OLR and ERB OLR are small but spatially coherent with patterns which may be related to sampling differences. The difference patterns are much less extensive than those between OLR derived from advanced very high resolution radiometer 11‐μm observations and ERB OLR. The ability to compute OLR from geophysical parameters is complementary to direct measurement of OLR because it enables one to attribute changes in OLR in space and time to changes in other geophysical parameters. In addition, it allows one to compute fields not directly measurable from satellite, such as the difference of the upward long‐wave flux between the surface and the top of the atmosphere and the long‐wave cloud radiative forcing.
Discrete angle radiative transfer: 2. Renormalization approach for homogeneous and fractal clouds
Authors: Gabriel Philip , Lovejoy Shaun , Davis Anthony , Schertzer Daniel , Austin Geoffrey L.
Published: February 2008

The discrete angle radiative transfer systems discussed in part 1 readily lend themselves to approximation schemes in which simple scaling systems with known radiative transfer properties can be doubled in size yielding analytic expressions relating the transfer coefficients corresponding to the initial and doubled scale. This “real space renormalization” method can be viewed as a generalization of conventional invariant imbedding techniques to scaling systems. Analytic nonlinear doubling mappings are obtained for homogeneous square, cubic and triangular systems, as well as for a simple fractal system with both open and cyclic horizontal boundary conditions. The doubling mappings have both thick and thin cloud fixed points; to which the transmission and albedoes are respectively algebraically attracted and repelled, with universal (phase function independent) exponents we estimate analytically. The method is approximate since it systematically neglects small‐scale intensity gradients; however, the results are qualitatively correct, arid it therefore establishes the connection between the scaling of the cloud optical density field and the scaling of the corresponding transfer coefficients. We also discuss the limitations of the method; in part 3 we compare it with a numerical approach.
Discrete angle radiative transfer: 3. Numerical results and meteorological applications
Authors: Davis Anthony , Gabriel Philip , Lovejoy Shaun , Schertzer Daniel , Austin Geoffrey L.
Published: February 2008

In the first two installments of this series, various cloud models were studied with angularly discretized versions of radiative transfer. This simplification allows the effects of cloud inhomogeneity to be studied in some detail. The families of scattering media investigated were those whose members are related to each other by scale changing operations that involve only ratios of their sizes (“scaling” geometries). In part 1 it was argued that, in the case of conservative scattering, the reflection and transmission coefficients of these families should vary algebraically with cloud size in the asymptotically thick regime, thus allowing us to define scaling exponents and corresponding “universality” classes. In part 2 this was further justified (by using analytical renormalization methods) for homogeneous clouds in one, two, and three spatial dimensions (i.e., slabs, squares, or triangles and cubes, respectively) as well as for a simple deterministic fractal cloud. Here the same systems are studied numerically. The results confirm (1) that renormalization is qualitatively correct (while quantitatively poor), and (2) more importantly, they support the conjecture that the universality classes of discrete and continuous angle radiative transfer are generally identical. Additional numerical results are obtained for a simple class of scale invariant (fractal) clouds that arises when modeling the concentration of cloud liquid water into ever smaller regions by advection in turbulent cascades. These so‐called random “β models” are (also) characterized by a single fractal dimension. Both open and cyclical horizontal boundary conditions are considered. These and previous results are contrasted with plane‐parallel predictions, and measures of systematic error are defined as “packing factors” which are found to diverge algebraically with average optical thickness and are significant even when the scaling behavior is very limited in range. Several meteorological consequences, especially concerning the “albedo paradox” and global climate models, are discussed, and future directions of investigation are outlined. Throughout this series it is shown that spatial variability of the optical density field (i.e., cloud geometry) determines the exponent of optical thickness (hence universality class), whereas changes in phase function can only affect the multiplicative prefactors. It is therefore argued that much more emphasis should be placed on modeling spatial inhomogeneity and investigating its radiative signature, even if this implies crude treatment of the angular aspect of the radiative transfer problem.
Correlative radar and airborne sodium lidar observations of the vertical and horizontal structure of gravity waves near the mesopause
Authors: Kwon Kang H. , Gardner Chester S. , Avery Susan K. , Avery James P.
Published: February 2008

In November 1986, joint radar and Na lidar observations were conducted in Colorado to study mesopause dynamics. The radar observations were conducted at Platteville, Colorado with a Stratosphere Troposphere (ST) radar in a meteor echo detection mode. The Na lidar observations included ground‐based observations at Broomfield and Denver, Colorado, and airbome observations during three flights over the Great Plains, Rocky Mountains, and Pacific Coast. Both radar and lidar identified a 6‐hour wave that was remarkably coherent during the November campaign. The vertical wavelength of the 6‐hour wave estimated from the radar data was 8 to 9 km, the amplitude of the zonal wind component was 10 m S−1, and the amplitude of the meridional wind component was 4 m s−1. The vertical wavelength estimated from the ground‐based and airborne lidar data was 7.3 km, and the amplitude of the scalar horizontal wind ranged from 13 to 16 m s−1. The zonal wavelength of this wave was approximately 772 km, and the intrinsic zonal phase velocity was 35 m s−1 westward. The 6‐hour wave was dominant in the height range of 80–90 km, which corresponds to the bottomside of the Na layer. An additional 2‐hour wave was observed with the Na lidar during both the ground‐based and airborne observations. The vertical wavelength of this wave was about 12 km, and the zonal wavelength was 260 km. The intrinsic zonal phase velocity was 43 m s−1 westward. This 2‐hour wave was also present only on the bottomside of the Na layer.
Particle production associated with marine clouds
Authors: Hegg Dean A. , Radke Lawrence F. , Hobbs Peter V.
Published: February 2008

Vertical profiles of Aitken nuclei, cloud condensation nuclei, sulfate, and SO2 concentrations have been measured in the marine atmosphere under relatively clean conditions. The vertical profiles of Aitken nucleus concentrations commonly showed maximum values just above cloud tops. We interpret these measurements as evidence for the nucleation of new sulfate particles in these locations. The cloud condensation nucleus profiles are consistent with this interpretation. A theoretical analysis of the measurements, utilizing a model of homogeneous, heteromolecular nucleation, predicts that the nucleation of new sulfate particles should occur primarily in the proximity of clouds. Implications of these results for the dimethyl sulfide‐cloud‐climate hypothesis are discussed.
The significance of biomass burning as a source of carbon monoxide and ozone in the southern hemisphere tropics: A satellite analysis
Authors: Watson Catherine E. , Fishman Jack , Reichle Henry G.
Published: February 2008

Carbon monoxide mixing ratios obtained by the October 1984 Measurement of Air Pollution from Satellites (MAPS) experiment are compared with the distribution of October 1984 Total Ozone Mapping Spectrometer (TOMS) ozone concentrations. The TOMS and MAPS data show coincident high values of ozone and carbon monoxide over central South America and southeastern Africa. The 1984 MAPS data are also compared with tropospheric ozone concentrations derived from 6 years of TOMS and Stratospheric Aerosol and Gas Experiment (SAGE) I and II measurements. Examination of the October climatological distribution of tropospheric ozone also reveals high concentrations over central South America and southeastern Africa. These coincident high values of CO and ozone in the rural southern tropics are most likely due to biomass burning and the subsequent transport of CO and ozone by large‐scale weather patterns. It appears that both CO and ozone are being transported thousands of kilometers from their source regions by the prevailing winds.
OH vertical column abundance: Tropical measurements
Authors: Burnett Clyde R. , Minschwaner Kenneth R. , Burnett Elizabeth B.
Published: February 2008

Measurements of the vertical column abundance of atmospheric hydroxyl (OH) have been made during the period 1987–1989 at the National Weather Service (NWS) station at Moen, Truk, Federated States of Micronesia (7°N, 152°E). A total of 384 independent data sets was obtained. Tropical OH abundance levels average about 22% above corresponding mid‐latitude values, with OH levels during late winter and early spring up to 50% above those observed at 40°N. Stratospheric wind and temperature data obtained from the daily NWS radiosonde data are examined for correlations with the OH results.