Layer Altitude Research Articles

On the long-term change of ionospheric parameters

Independent of the possible sources (solar activity, geomagnetic activity, greenhouse effect, etc.) of a global change in the upper atmosphere, it is the sign of a long-term trend of temperature that might reveal the cause of a global change. Long-term change of temperature in the F region of the ionosphere has been studied and is assumed to be expressed in terms of thickness of the bottomside F2 layer characterized by the difference between height of the maximum electron density of the F2 layer hmF2 and altitude of the lower boundary of the F region represented by h′F. Using the difference of two ionospheric parameters has the advantage that it reduces the effect of changes resulting from alteration of equipment and scaling personnel. In this study, in summer only night values of the difference hmF2−h′F and in winter both day and night values have been taken into account considering that h′F might indicate the lower boundary of the F region in these periods. The study of the behaviour of hmF2−h′F taking separately the stations and determining yearly the mean measure (trend) of the variation of hmF2−h′F with solar and geomagnetic activities found that this difference increases significantly with enhanced solar activity, but trends of the solar activity effect exerted on this difference themselves do not practically change with increasing sunspot number. Further, hmF2−h′F decreases only insignificantly with growing geomagnetic activity. Trends of the geomagnetic activity effect related to hmF2−h′F change only insignificantly with increasing Ap; however, trends of the geomagnetic activity effect decreased with increasing latitude. As a result of this investigation it has been found that hmF2−h′F regarded as thickness of the bottomside F2 layer shows an effect of the change of solar activity during the last three solar cycles, indicating temperature change in the upper atmosphere to be expected on the basis of changing solar activity. Furthermore, though a long-term variation of solar activity considering only years around solar activity minima is relatively small, the difference hmF2−h′F indicates a trend opposing the change of solar activity; that is, it decreases slightly during the first three 20, 21, 22 solar cycle minima (1964–1986), but decreases more abruptly according to the change of solar activity towards the minimum of solar cycle 23 (1986–1996), thus also indicating variation of temperature in the F region. However, this variation cannot be explained by the change of solar and geomagnetic activities alone, but assumes some other source (e.g. greenhouse gases) too.

Comparison of simultaneous Na lidar and mesospheric nightglow temperature measurements and the effects of tides on the emission layer heights

A detailed comparative study of two new mesospheric temperature data sets, measured by different remote‐sensing techniques, has been performed as part of a long‐term investigation of low‐latitude mesospheric dynamics. Coincident observations using the University of Illinois Na wind/temperature lidar and the Utah State University CEDAR Mesospheric Temperature Mapper (MTM) were conducted from the summit of Haleakala Crater, Maui, Hawaii (20.8°N, 156.2°W, ∼3000 m) as part of the Maui‐MALT program. High‐quality joint measurements were obtained during four lidar campaign periods, and 16 nights of data, spanning the interval January 2002 to October 2003, are presented here as example observations during each season. The Na lidar was coupled to the Air Force 3.7 m diameter steerable telescope providing exceptional quality temperature (and wind) data spanning the altitude range ∼80–105 km. At the same time the MTM sequentially sampled the NIR OH (6,2) Meinel band and the O2 (0,1) Atmospheric band nightglow emissions to determine the height‐weighted mesospheric temperature at two nominal altitudes within this region. Comparison of these two nocturnal data sets shows exceptionally good agreement on a point‐to‐point, as well as a nightly mean basis, especially when allowances were made for physically reasonable changes in height during the course of the night for each of the nightglow layers. This analysis yields mean nocturnal altitudes of 88.6 km with a nocturnal variability of ±3.0 km for the OH M (6,2) band emission layer and 94.4 km for the O2 (0,1) Atmospheric band mean altitude with a nocturnal variability of ±4.2 km. These results are in excellent accord with previous rocket, satellite and ground‐based observations and further establish the validity of these two complementary measurement techniques. Furthermore, analysis of the computed height changes inferred from this study indicates a systematic decrease in altitude of both emission layers by up to several kilometers, whenever the lidar data showed evidence of strong diurnal or semidiurnal tidal forcing. The apparent downward trend in altitude was found to track the phase of the prevailing tidal motion providing new evidence for the effects of tides (or long‐period gravity waves) on the height variability of the nightglow layers.

A comparative study of ozone production in five U.S. metropolitan areas

We present observations of O3 and O3 precursors measured at mid boundary layer altitude during field campaigns in Nashville, Tennessee (1995), New York City, New York (1996), Phoenix, Arizona (1998), Philadelphia, Pennsylvania (1999), and Houston, Texas (2000). Ozone production rates P(O3) and their sensitivity to NOx and volatile organic carbons (VOCs) are calculated using observed concentrations as inputs to a steady state box model. City to city comparisons are made to illustrate common features of urban photochemistry and features that are unique to specific cities. Ozone production rates vary from nearly zero to 155 ppb h−1. Differences in P(O3) depend on precursor concentrations, namely, radical sources, NOx and VOCs. Under conditions where P(O3) is greater than 25 ppb h−1, there is a potential to produce enough same‐day O3 to transform a typical regional background into a severe O3 episode. Six such cases were observed, in Nashville, Philadelphia, and Houston, with elevated O3 concentrations in the afternoon (130–211 ppb) following a morning in which P(O3) was 25–140 ppb h−1. High P(O3) occurs when NOx concentrations are 5–25 ppb and OH‐VOC reactivity is above 5 s−1. These conditions are infrequent, and aside from a common dependence on calm winds, reasons vary from city to city. In Nashville, high P(O3) was observed during a stagnation event over downtown and under the circumstance that an air mass with a high concentration of isoprene encountered a NOx source. In Houston, NOx and light olefins are coemitted from petrochemical facilities leading to the highest P(O3)s of the five cities studied. High values of P(O3) did not occur in Phoenix because of low radical production, caused mainly by a dry atmosphere, and a low VOC to NOx ratio. The sensitivity of P(O3) to its precursors varied from NOx limited in rural samples to VOC limited near emission sources. In Philadelphia, and especially Phoenix, the highest O3 production rates occurred under VOC‐limited conditions. In Nashville, New York City, and Houston the high‐P(O3) samples were near the ridge line where P(O3) responds somewhat to VOC reductions but is insensitive to NOx changes.

Temperature lidar measurements from 1 to 105 km altitude using resonance, Rayleigh, and Rotational Raman scattering

Abstract. For the first time, three different temperature lidar methods are combined to obtain time-resolved complete temperature profiles with high altitude resolution over an altitude range from the planetary boundary layer up to the lower thermosphere (about 1–105 km). The Leibniz-Institute of Atmospheric Physics (IAP) at Kühlungsborn, Germany (54° N, 12° E) operates two lidar instruments, using three different temperature measurement methods, optimized for three altitude ranges: (1) Probing the spectral Doppler broadening of the potassium D1 resonance lines with a tunable narrow-band laser allows atmospheric temperature profiles to be determined at metal layer altitudes (80–105 km). (2) Between about 20 and 90 km, temperatures were calculated from Rayleigh backscattering by air molecules, where the upper start values for the calculation algorithm were taken from the potassium lidar results. Correction methods have been applied to account for, e.g. Rayleigh extinction or Mie scattering of aerosols below about 32 km. (3) At altitudes below about 25 km, backscattering in the Rotational Raman lines is strong enough to obtain temperatures by measuring the temperature dependent spectral shape of the Rotational Raman spectrum. This method works well down to about 1 km. The instrumental configurations of the IAP lidars were optimized for a 3–6 km overlap of the temperature profiles at the method transition altitudes. We present two night-long measurements with clear wave structures propagating from the lower stratosphere up to the lower thermosphere.

Optical and radio measurements of a 630‐nm airglow enhancement over Japan on 9 September 1999

Using a comprehensive data set from optical and radio instruments, we investigate a midnight brightness wave that appeared in 630‐nm airglow images over Japan on the night of 9 September 1999. This may be the first such observation of the brightness wave with an all‐sky imager in the East‐Asian longitudinal sector. The imager at Shigaraki (35.6°N, 136.1°E) tracked a north‐northeastward propagation of the wave with an apparent velocity of 500 m s−1 after midnight. Ionosonde observations at five stations in Japan showed that rapid descent of the F2 layer propagated northward beyond 35°N with decreasing amplitude. Incoherent scatter observations with the MU radar at Shigaraki also revealed that the F2 peak altitude decreased from 360 to 280 km during the event. During the F2 layer descent the altitude profile of the electron density became sharp, enhancing the F2 peak electron density. After the F2 layer altitude reached 280 km, electron density in the F2 layer rapidly decreased because of increased neutral density at low altitude. A Fabry‐Perot interferometer (FPI) at Shigaraki observed northward neutral winds of 10–70 m s−1 during the event. A model calculation demonstrates that the meridional winds estimated from the MU radar electron density profiles are fairly consistent with those observed with the FPI. From these results we conclude that the observed northward wind enhancements, probably caused by the midnight temperature maximum, pushed down the plasma in the F2 layer to lower altitudes along the geomagnetic field to cause the 630‐nm airglow intensity enhancement.

Distribution of organochlorine pesticides in pine needles of an oceanic island: The case of Tenerife (Canary Islands, Spain)

The distribution of persistent organochlorine pesticides (HCB, HCH, DDT and its metabolites) was studied by analyzing pine needles in the oceanic island of Tenerife (Canary Islands, Spain). Tenerife is a subtropical oceanic island, characterized by the presence of a high mountain (Pico de Teide, 3,718 m a.s.l.) and by a peculiar climatic condition. The southern side is warm and sometimes during the year influenced by dry winds coming from Africa, while the northern side is cool and wet, with an almost persistent cloudiness (called `mar de nubes'), due to winds coming from the northern Atlantic. Furthermore a developed agricultural area is present at sea level. Pine needle samples were collected on both sides of the island, from the sea level up to the upper level of pine distribution (2,100 m a.s.l.). The distribution patterns of organochlorine pesticides seem to be affected mainly by local emissions. Up to the considered altitude layer, the influence of global circulation of persistent organic pollutants seems to play a negligible role. The behavior of chemicals is consistent with their physical-chemical properties, with some influence due to climatic conditions.

Multiple field of view layer-oriented adaptive optics

In layer-oriented adaptive optics, multiconjugation is performed in a much more efficient way than conventional wavefront sensing. This improved efficiency is impressive for high altitude layers and moderate for ground ones. On the other hand, high altitude layers can be covered with only a limited field of view (where one can search for natural guide stars) while for ground layers the usable field of view is limited essentially by practical reasons. We introduce the further concept of multiple field of view layer-oriented adaptive optics where a combination of sampling and covered field leads easily to sky coverages for 8 m class telescopes that nearly approach the whole sky with the usage solely of natural guide stars. The extension of the concept to much larger apertures is also discussed.

ELF propagation parameters for uniform models of the Earth–ionosphere waveguide

Uniform models for the Earth–ionosphere cavity are considered with particular attention to the physical properties of the ionosphere for the extremely low frequency (ELF) range. Two consistent features have long been recognized for the range: the presence of two distinct altitude layers of maximum energy dissipation within the lower ionosphere, and a “knee”-like change in the vertical conductivity profile representing a transition in dominance from ion-dominated to electron-dominated conductivity. A simplified two-exponential version of the Greifinger and Greifinger (1978) technique widely used in ELF work identifies two slopes in the conductivity profile and, providing accurate results in the ELF communication band (45– 75 Hz ), simulates too flat a frequency dependence of the quality factor within the Schumann resonance frequency range (5– 40 Hz ). The problem is traced to the upward migration, with frequency increasing, of the lower dissipation layer through the “knee” region resulting in a pronounced decrease of the effective scale height for conductivity. To overcome this shortcoming of the two-exponential approximation and still retain valuable model analyticity, a more general approach (but still based on the Greifinger and Greifinger formalism) is presented in the form of a “knee” model whose predictions for the modal frequencies, the wave phase velocities and the quality factors reasonably represent observations in the Schumann resonance frequency range.

Wind‐shear‐driven, closed‐current dynamos in midlatitude sporadic E

Rocket and radar experiments have found anomalously large electric fields associated with midlatitude sporadic E (Es). In Cosgrove and Tsunoda [2001], a neutral wind source mechanism for the electric fields was proposed, by way of a simple model involving two idealized Es patch dynamos closing current with one another. Below, we show that this source mechanism can operate in generic distortions or fragmentations of an Es layer. The result is a closed‐current dynamo phenomenon that occurs whenever a Es layer is distorted against a wind shear background. Either modulation of the Es layer altitude by a gravity wave, or Kelvin‐Helmholtz billows, could produce large electric fields.

50 MHz radar observations of mid‐latitude E‐region irregularities at Camp Santiago, Puerto Rico

A 50 MHz radar interferometer was used near Salinas, Puerto Rico, to probe the meter‐scale E‐region plasma density irregularities during two campaigns conducted in 1998. During the February–April period E‐region echoing layers were primarily observed between 90 and 100 km heights. The layers were typically thin (∼1 km) and unstructured, although in several cases short period (∼90 s) layer oscillations were observed. During the June–July period E‐region echoes showed more varied characteristics. In addition to low altitude layers, quasi‐periodic structures with descending echoing layers were observed at altitudes above 100 km. Zonal motions detected during descending layer events were at times variable and oscillated between westward and eastward directions while the layer descent rates remained fixed.

Diagnostics of the Jovian Aurora Deduced from Ultraviolet Spectroscopy: Model and HST/GHRS Observations

A model coupling an electron energy degradation code with a detailed synthetic spectrum of the H 2 Lyman and Werner band system is used to calculate the emerging auroral ultraviolet spectra from Jupiter's atmosphere excited by electrons with different initial energy distributions. The atmospheric model is adapted from the vertical P-T profile measured by the Galileo probe and mid-latitude model hydrocarbon photochemistry. Each altitude layer, with its own gas temperature, contributes to the emergent ultraviolet spectrum and the absorbers are vertically distributed within the source region of the auroral emissions. Examples of the calculated spectra are shown to validate the synthetic spectrum and to illustrate the importance of the electron energy distribution and the vertical structure. The model is then applied to the analysis of seven HST/GHRS spectra of the 1200–1700 Å region obtained with 5-Å resolution at various locations in the north and south Jovian aurora. These spectra have different color ratios which characterize the energy of the precipitated electrons, although they do not have a high enough spectral resolution to permit a determination of the H 2 temperature. We find that the characteristic energy of the assumed initial Maxwellian distribution ranges between 17 and 40 keV. A clear signature of acetylene absorption is observed near 1520, 1480, and 1440 Å where the C 2H 2 cross section shows strong absorption peaks. The acetylene column abundance overlying the emission peak varies from 0.02 to 0.2 of the methane column. A better fit is obtained for some spectra when ethane absorption is added. The C 2H 6 column abundance varies from 0 to 0.5 of the methane column. These changes relative to methane are presumably the result of perturbations by heat released by the fast electron thermalization and/or perturbations to the hydrocarbon chemistry resulting from the production of H atoms by the aurora. A spectrum of the Io flux tube footprint and its trailing tail shows an ultraviolet color and hydrocarbon absorption quite similar to some of the main oval spectra. This observation suggests that the electrons of the Io flux tube are energized to a few tens of keV, similar to the electron precipitated in the main ovals and polar caps. Echelle spectra between 1216 and 1220 Å at 0.07 Å resolution are also compared with the model fitting best the mid-resolution spectra. It is found that the effective H 2 rovibrational temperature associated with the echelle spectra are significantly higher than predicted by the mid-latitude model. A large vertical temperature gradient just above the methane homopause due to large heating by auroral precipitation is a plausible explanation for this difference.

Nonmethane hydrocarbon mixing ratios in continental outflow air from eastern North America: Export of ozone precursors to Bermuda

High surface ozone levels at Bermuda during springtime are associated with the transport of large scale frontal systems from the U.S. east coast over the North Atlantic. An objective of the AEROCE III study was to adopt a meteorologically informed sampling strategy of the chemical characteristics of air masses both in advance and behind eastward progressing cold fronts in order to differentiate between vertical sources of these elevated tropospheric ozone signals. Concentrations of hydrocarbons in air sampled over the eastern US and in offshore flights varied in a complex manner with sample altitude and prevailing meteorological situation. In several aircraft flights, the presence at altitude of distinct layers of air of elevated concentrations of NMHC's attested to the dynamic mixing of lower and upper air masses associated with springtime frontal activity. Layers of mid‐tropospheric air of high O3 (140 ppbv) and low background NMHC mixing ratios (1.44 ppbv ethane, 0.034 ppbv propene, 0.247 ppbv propane, 0.034 ppbv isobutene, 0.041 ppbv n‐butane, 0.063 ppbv benzene, 0.038 ppbv toluene) mixing ratios were indicative of descending, stratospherically influenced air on a flight to the east of Norfolk, VA on April 24 (alt 4600 m). Layers of high O3 (60–70 ppbv) and elevated NMHC concentrations (1.88 ppbv ethane, 0.092 ppbv propene, 0.398 ppbv propane, 0.063 ppbv isobutene, 0.075 ppbv n‐butane, 0.106 ppbv benzene, 0.102 ppbv toluene) observed on a flight to the west of Bermuda on April 28 (alt. 4100 m) indicated upwardly lifting convective activity of continentally sourced air masses. A meteorologically informed sampling strategy employed in the study was valuable in providing a framework with which to both optimize NMHC sampling decisions and to provide a context with which to interpret their observed mixing ratios.

On optimal cooperative conflict resolution for air traffic management systems

We consider optimal resolution of air traffic (AT) conflicts. Aircraft are assumed to cruise within a given altitude layer and are modeled as a kinematic system with constant velocity and curvature bounds. Aircraft cannot get closer to each other than a predefined safety distance. For such a system of multiple aircraft, we consider the problem of planning optimal paths among given waypoints. Necessary conditions for optimality of solutions are derived and used to devise a parametrization of possible trajectories that turns into efficient numerical solutions to the problem. Simulation results for a realistic aircraft conflict scenario are provided. A decentralized implementation of the optimal conflict resolution scheme is introduced that may allow free-flight coordination in a cooperative airspace management scheme. Impact of decentralization on performance and safety is finally discussed with the help of extensive simulations.

A taste of Fabry and Perot's discoveries

One century ago, Fabry and Perot invented the interferometer which bears their name. The instrument was the culmination of two centuries of related work on light and its interaction with both matter and itself. Today, hundreds of scientists throughout the world use this interferometer daily, perhaps without giving any thought to its ingenious inventors. Fabry and Perot built the instrument, produced theoretical studies and developed methods of analysis; but it was in using it for major scientific discoveries that the instrument would definitively remain synonymous with their names. They studied physics, astronomy and geophysics and strongly contributed to narrowing the gap between physics and astronomy so giving meaning to a new science emerging at the beginning of the century, i.e. astrophysics. Their major works remain the determination of the temperature and kinematics of the Orion nebula, the measurement of the gravitational redshift of light and a contribution to the standard metric system. Other discoveries of theirs are less known: the determination of the altitude and thicknesses of the atmospheric ozone layers; the calibration of the flux of the Moon, the Sun, stars and the Milky Way; the improvement of stellar spectro-photometry; the development of electrometers to measure weak potentials; the elaboration of an atlas of emission lines; the laboratory verification of the Doppler-Fizeau principle and much more.

Tethered balloon measurements of biogenic VOCs in the atmospheric boundary layer

Biogenic volatile organic compounds (BVOCs) were measured on tethered balloon platforms in 11 deployments between 1985 and 1996. A series of balloon sampling packages have been used to describe boundary layer dynamics, BVOC distribution, chemical transformations of BVOCs, and to estimate BVOC emission rates from terrestrial vegetation. Measurements indicated a slow decrease of concentration for BVOCs with altitude in the mixed layer when sampling times were greater than average convective turnover time; surface layer concentrations were more variable because of proximity to various emission sources in the smaller surface layer footprint. Mixed layer concentrations of isoprene remained fairly constant in the middle of the day, in contrast to canopy-level isoprene concentrations, which continued to increase until early evening. Daytime emissions, which increase with temperature and light, appear to be balanced by changes in entrainment and oxidation. Daytime measurements of methacrolein and methyl vinyl ketone, reaction products of the atmospheric oxidation of isoprene, showed fairly constant ratio to each other with altitude throughout the mixed layer. BVOC emission flux estimates using balloon measurements and from the extrapolation of leaf level emissions to the landscape scale were in good agreement.

Measurement of optical seeing on the high antarctic plateau

Results from the 1995 season of site-testing experiments at the South Pole are presented, in which the seeing was measured using balloon-borne microthermal probes. Our analysis shows a marked division of the atmosphere into two characteristic regions: (i) a highly turbulent boundary layer (0-220 m) associated with a strong temperature inversion and wind shear, and (ii) a very stable free atmosphere. The mean seeing, averaged over 15 balloon flights, was measured to be 1.86″, of which the free atmosphere component was only 0.37″. The seeing from ~200 m upward is superior to the leading mid-latitude sites (e.g. Fuchs 1995; Roddier et al. 1990) by almost a factor of two. The results are in good agreement with optical seeing data obtained by a differential image motion monitor on three of the five occasions when the two measurements were performed simultaneously. The boundary layer winds are of katabatic origin, and so we may consider the possibility of exceptional seeing conditions from surface level at other locations on the plateau such as Domes A and C, where there is little or no katabatic wind. In addition, the proximity of the optical turbulence to the focus of a telescope situated at ground level is a highly favourable situation for the use of adaptive optics, since the wavefront spatial coherence scale is related to the altitude of the turbulent layers producing the image distortion. Some comparisons are made between the relevant adaptive optics parameters measured at the South Pole and Cerro Paranal, one of the best mid-latitude sites.

A comparative study of in-situ and remote intermediate layer measurements against wind model predictions of vertical ion drift

Abstract Measurements from a sequence of rockets launched from Wallops Island (37.95°N, 75.47°W) on a single night in 1968 still provide the only in-situ data on the midlatitude intermediate layer phenomenon. TMA vapor trail observations made during this sequence of rocket flights were the first to experimentally examine the wind shear theory for the formation and slow downward motion of the layers. Using these rocket data from solar maximum, as well as several intermediate layer data sets from the Arecibo Observatory (18.35°N, 66.75°W) at solar minimum, we compare the location and motion of the layer observations to the predictions of two widely used thermospheric wind models: the HWM-93 thermospheric wind model and the TIEGCM. HWM-93 is an empirical model derived largely from measurements that had limited capabilities for determining night-time winds at lower thermospheric altitudes, and TIEGCM is a self consistent first principles model. Like an earlier study by Szuszczewicz et al., 1995 , we find that some of our intermediate layer data agree quite well with the location of a convergent null in the meridional wind predicted by TIEGCM, but the correlation between layer altitude and the null in the vertical ion drift is in general poor. This finding contradicts theoretical expectations based on the two fluid plasma equations. We also demonstrate that uncertainties in the ion neutral collision frequency do not improve the agreement between the model vertical drifts and the observed layer behavior. Furthermore, we find some evidence that the HWM-93 model may overemphasize diurnal tidal effects in the winter, post-midnight period. The discrepancies found in this study demonstrate that our present understanding of midlatitude lower thermospheric wind systems is inadequate for predicting intermediate layer dynamics in the post-sunset period.

Tidal variations of noctilucent clouds measured at 69°N latitude by groundbased lidar

During June/July 1997 we observed with a groundbased lidar noctilucent clouds (NLCs) overhead the ALOMAR observatory in Northern Norway (69°N, 16°E). These daylight observations of NLC were made possible by use of a very small field‐of‐view for the lidar receiving telescope in combination with a narrowband double‐etalon Fabry‐Perot interferometer in front of the photon counting detectors. During 148 hours of lidar measurements, NLCs were observed for 69 hours. Thus, the mean occurrence frequency of NLC was 46%. The observed NLCs exhibited marked variations of the layer altitude and backscatter ratio with local time (LT). The temporal behaviour of both the NLC altitude and NLC backscatter ratio are dominated by a semidiurnal variation. The NLC altitude attains maxima near 13 LT and 01 LT and minima near 07 LT and 19 LT. The backscatter ratio clearly maximizes at times of minimum NLC layer altitude. These observations point to a strong control of variations in NLC altitude and backscatter ratio by a stable semidiurnal tide. The mean centroid NLC altitude is 82.7 km.

Appleton anomaly increase following sunset: Its observed relation to equatorial F layer E × B drift velocity

The upward E × B drift velocity of the postsunset F layer at the dip equator, in response to the prereversal electric field, and the resulting enhancement of the fountain effect plasma at the Appleton anomaly are observed nearly simultaneously near the same geomagnetic meridian. Measurements, the first under such controlled conditions, are by a chain of ionospheric sounders recording ionograms at intervals of 5–15 min on two consecutive days during equinox at solar maximum, both having quiet magnetic conditions and high solar fluxes. Measured is the following sequence of cause and effect: the equatorial F layer electron density that persists through sunset; the solar E layer electron density conjugate to this F layer that decays rapidly through sunset; the bottomside equatorial F layer altitude, h′F, as it drifts upward in response to the F region dynamo electric field; and the anomaly F layer electron density that increases with the arrival of the resulting enhanced fountain effect plasma at 16.0° and at 20.3° dip latitude. At the equator the maximum drift velocity measured by dh′F/dt is 70 m s−1 on the first day and 50 m s−1 on the second. The differences in drift velocity are reflected in the anomaly in latitudinal distributions of F layer maximum electron density between 0° and 30° dip latitude that show the anomaly crest to increase in magnitude and in latitude: rapidly on the first day, reaching a maximum of 55 × 105 el cm−3 18° dip latitude at 2100 LT, and more slowly on the second day, reaching ≥38 × 105 el cm−3 at ≤16° dip latitude, also at 2100 LT. In addition to the qualitative relationship, maximum drift velocity and anomaly crest maximum electron density and its maximum rate of increase are all reduced by about the same factor on the second day relative to the first.

Airborne scanning lidar observations of aircraft contrails and cirrus clouds during SUCCESS

An angular scanning backscatter lidar was deployed on the NASA DC‐8 research aircraft as part of SUCCESS. The lidar viewing direction could be continuously scanned from vertically upward to forward to vertically downward. Real‐time pictorial displays generated from lidar signatures were used to locate clouds and contrails above, ahead of, and below the DC‐8; to depict their spatial structure; and to help select DC‐8 altitudes for achieving optimum sampling by onboard in situ sensors. The lidar data are being analyzed to establish their value in the interpretation and extension of the in situ sensor databases. Data examples are presented that illustrate (1) correlation with particulate, gas, and radiometric measurements made by onboard sensors, (2) discrimination and identification between contrails observed by the onboard sensors, (3) a 13.1 km altitude layer that exhibits greatly enhanced vertical backscatter relative to off‐vertical backscatter, and (4) mapping of vertical distributions of individual precipitating ice crystals and their capture by cloud layers.