R. H. Holzworth

Auroral boundary variations and the interplanetary magnetic field

Abstract This paper describes a DMSP data set of 150 auroral images during magnetically quiet times which have been analyzed in corrected geomagnetic local time and latitudinal coordinates and fit to offset circles. The fit parameters R (circle radius) and ( X , Y ) (center location) have been compared to the hourly interplanetary magnetic field (IMF) prior to the time of the satellite scan of the aurora. The results for variation of R with B z , agree with previous works and generally show about a 1° increase of R with increase of southward B z by 1 nT. The location of the circle center also has a clear statistical shift in the Southern Hemisphere with IMF B y such that the southern polar cap moves towards dusk (dawn) with B y > ( B y

Thunderstorm and lightning characteristics associated with sprites in Brazil

[1] Astudy ofthe thunderstorm andcloud-ground lightning characteristics associated with sprite events observed in Brazil is presented. The study is based on ground and aircraft sprite observations with high sensitivity intensified CCD cameras of six different thunderstorms, GOES satellite infrared images, radar and lightning network data. A total of eighteen transient optical events were recorded at three different days in 2002 and 2003, sixteen of which exhibited vertical structures typically associated with sprites. Four thunderstorms were associated with two different cold fronts, one with a Mesoscale Convective System, and one was a local isolated thunderstorm. The sprites occurred during time periods when the percentage of positive flashes was higher than the average percentage for the storm lifetime. The lightning associated with the sprite events was all positive flashes with a mean peak current higher than the mean value for all flashes in the storms. INDEX TERMS: 3304 Meteorology and Atmospheric Dynamics: Atmospheric electricity; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 3324 Meteorology and Atmospheric Dynamics: Lightning; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342). Citation: Pinto, O., Jr., M. M. F. Saba, I. R. C. A. Pinto, F. S. S. Tavares, K. P. Naccarato, N. N. Solorzano, M. J. Taylor, P. D. Pautet, and R. H. Holzworth (2004), Thunderstorm and lightning characteristics associated with sprites in Brazil, Geophys. Res. Lett., 31, L13103, doi:10.1029/2004GL020264.

The Plasma Wave Instrument on Board the AMPTE IRM Satellite

The AMPTE IRM plasma wave instrumentation is designed to provide basic information on the plasma wave activity in the magnetosphere/solar-wind environment and inside the artificial plasma clouds which will be created in space. The instruments use one long electric dipole antenna and two magnetic search coil sensors in order to cover frequency ranges from dc to 5.6 MHz for the electric measurements and from about 30 Hz to 1.5 MHz for the magnetic measurements. A set of spectrum analyzers along with a fast memory and an analog wide-band system are used to determine wave intensities and to identify wave modes.

Strong electric fields from positive lightning strokes in the stratosphere

[1] A balloon payload launched in Brazil has measured vector electric fields from lightning at least an order of magnitude larger than previously reported above 30 km in the stratosphere. During the flight hundreds of lightning events were recorded, including several positive cloud to ground lightning strokes. A two stroke flash, with small (15 kA peak current) and moderate (53 kA) positive strokes at a horizontal range of 34 km, produced field changes over 140 V/m at 34 km altitude. On-board optical lightning detection, recorded with GPS timing, coupled with ground based lightning location gives high time resolution for study of the electric field transient propagation. These measurements imply that lightning electric fields in the mesosphere over large thunderstorms may be much larger than previously measured. Citation: Holzworth, R. H., M. P. McCarthy, J. N. Thomas, J. Chin, T. M. Chinowsky, M. J. Taylor, and O. Pinto Jr. (2005), Strong electric fields from positive lightning strokes in the stratosphere, Geophys. Res. Lett., 32, L04809, doi:10.1029/2004GL021554.

Conductivity and electric field variations with altitude in the stratosphere

Electric field and conductivity measurements were made in the altitude range from 10 to 27 km during the Electrodynamics of the Middle Atmosphere superpressure balloon experiment in 1983 and 1984. These balloons primarily floated at a constant altitude of 26 km, but due to the eventual loss of superpressure near the end of each flight, daily altutide variations at sunset and sunrise occurred. This paper presents electric field, conductivity and derived current density data from the two EMA flights which underwent the longest periods of this daily altitude variation. This includes data from 18 days in late 1983 and early 1984 when the balloons were between longitudes of 50° and 100°E and between magnetic L values of 4.3 and 9.5 in the southern hemisphere. The average conductivity for all the data is well represented by the fit to the EMA6 flight where = (1.8±0.2)×10−13 exp(z/7.5) S/m and Z is the altitude in kilometers. The vertical electric field is also shown to be well fit in this altitude range by a similar single term exponential with a scale height of the opposite sign but similar magnitude. No convincing evidence for variation of the current density with altitude was found. While the average scale height was about 7.5 km, it is also shown that data from individual days are also well fit by an exponential, but with values which can be significantly different (up to +8.9 km in one case). The paper also presents evidence for a small (25% maximum) perturbation in the conductivity caused by the balloon wake. The paper concludes with a comparison of these data to other measurements and to various models of the stratospheric conductivity. It is found that the EMA conductivity measurements are quite similar to other previous measurements, yet significantly different from some model predictions.

Observations and parameterization of the stratospheric electrical conductivity

Simultaneous in situ measurements of the stratospheric electrical conductivity, made from multiple balloon platforms during the 1992–1993 Extended Life Balloon-Borne Observatories (ELBBO) experiment, have yielded the most comprehensive data set on the stratospheric electrical conductivity. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, beginning November 10, 1992, and lasting through March 18, 1993. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the South Pole to 28°S, and circled around the southern hemisphere several times. On average, the positive polar conductivity (conductivity of positive ions alone) was about 15% higher than that of the negative conductivity, suggesting that differences may exist between the mobilities of positive and negative ions. Data from each polarity of polar conductivity also indicate persistent, apparently organized, short-term and localized variations, with amplitude within 30% of the mean value. In corrected geomagnetic (CGM) coordinates the conductivity variations were found to be a function of latitude but not of longitude. The total conductivity can increase 150% from low latitude to high latitude, and does remain nearly constant at latitudes above 55° (namely, the cosmic ray knee latitude). Calculations based on ionization theory demonstrate that the latitudinal variations in the conductivity measurements were mainly due to the latitudinal variations in incident galactic cosmic ray intensity, with only little effect from the air temperature variations. The calculations shown here also suggest that small ions (as opposed to large ions) provide the main contribution to the stratospheric conductivity. The comparisons between conductivity measurements and models show that commonly used models can underestimate the latitudinal variation by a factor of 2. In this paper the stratospheric conductivity is parameterized based on the measurements, and a simple empirical model is presented in geographic coordinates.

Characteristics of an African Easterly Wave Observed during NAMMA

Abstract The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006. Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and...

Global electrodynamics from superpressure balloons

Electric field and conductivity measurements in the stratosphere between November 1992 and March 1993 have been made using superpressure balloons in the southern hemisphere. Over 400 payload-days of data have been made during a record setting experiment called ELBBO (Extended Life Balloon Borne Observatories). This experiment resulted in 4 flights aloft simultaneously for over 2 months including one flight which lasted over 4 months. Electrodynamical coupling between the atmosphere and ionosphere is studied using the measured electric fields, and a simple empirical model of the stratospheric conductivity. Altitude profiles of conductivity have been obtained from several superpressure balloon flights using the large end-of-flight altitude swings on the last few days of each flight (as the balloon begins to loose superpressure). Coupling between the fields and atmospheric inertial waves has been observed. Effects and dynamics of the global circuit suggest that standard models are missing significant phenomena. Large scale ionospheric convection activity has been studied from the polar cap to the middle latitudes. Cusp latitude fields have been continuously measured for many days in a row.

Daily and intraseasonal relationships between lightning and NO2 over the Maritime Continent

[1] The relationship between lightning and NO2 over Indonesia is examined on daily and intraseasonal time scales based on lightning observations from the World Wide Lightning Location Network (WWLLN) and tropospheric NO2 column densities from the Global Ozone Monitoring Experiment (GOME‐2) satellite mission. Composites of the daily NO2 observations regressed onto lightning frequency reveal a plume of enhanced NO2 following a day of enhanced lightning. Lightning and NO2 also vary coherently with the intraseasonal Madden‐Julian Oscillation (MJO) in a manner distinct from the cloudiness signature, with variations of up to ∼50% of the annual mean. Citation: Virts, K. S., J. A. Thornton, J. M. Wallace, M. L. Hutchins, R. H. Holzworth, and A. R. Jacobson (2011), Daily and intraseasonal relationships between lightning and NO2 over the Maritime Continent, Geophys. Res. Lett., 38, L19803, doi:10.1029/2011GL048578.

An inertial wave‐driven stratospheric horizontal electric field: New evidence

We report our recent measurements of horizontal electric fields from multiple stratospheric balloon platforms during the Extended Life Balloon-Borne Observatories (ELBBO) experiment. The ELBBO project involved launches of five superpressure balloons into the stratosphere from Dunedin, New Zealand, during November and December 1992. Most of the balloons floated at a constant altitude of 26 km for over 3 months, covered a wide range of latitudes from the south pole to 281°S, and circled around the southern hemisphere several times. The electric field measurements from the ELBBO experiment have confirmed the earlier discovery of a new source of stratospheric horizontal electric fields [Holzworth, 1989], with wider latitude coverages than the original finding. This newly found horizontal electric field has an average magnitude of 10 to 20 mV/m at night and 100 to 150 mV/m in the daytime. Its field vector has a unique characteristic of counterclockwise rotation in the southern hemisphere, with the rotation period near the atmospheric inertial wave period. The horizontal scale size of this new-source E field was found to be near 500 km, of the order of the horizontal wavelength of the inertial wave in the stratosphere. This new-source E field is a steady background feature of the stratosphere, with local disturbance from underlying thunderstorms or other sources. At high latitude, a dawn-to-dusk electric field mapped down from the magnetosphere was observed at the local midnight, with a larger amplitude than that of the new-source E field. One of the implications of the new-source E field is that the neutral dynamic processes are strongly coupled into the electrodynamic processes in the stratosphere, making this region electrically active and not passive as previously thought by many.