Implications of the VEGA balloon results from Venus atmospheric dynamics

The VEGA Venus Balloon Mission returned data on the themodynamic state of the atmosphere together with wind and cloud information. In this invited paper we review possible explanations for three aspects of the data: 1) the large amplitude atmospheric vertical winds encountered by the VEGA balloons; 2) the observed 6.5 K temperature difference consistently measured between the two VEGA balloons; and 3) the apparent influence of surface topography on atmospheric motions seen by the VEGA-2 balloon as it flew over the mountainous terrain known as Aphrodite.     

Preliminary evidence for drizzle in the middle cloud layer of Venus

Vertical trajectory data from the VEGA 1 and 2 balloon flights in the atmosphere of Venus is re-analyzed. A previously employed helium leak rate profile invoked to entirely account for the decrease in equilibrium float altitude of VEGA 2 is questioned and deemed ad hoc. As an alternative, it is proposed that both VEGA 1 and 2 experienced in-flight mass increases due to the deposition of cloud particles onto their envelopes, as well as losing helium at a reduced rate consistent with the pre-flight prediction. Particle deposition rates are estimated and found to be compatible with this alternative scenario. Possible evidence for drizzle is also presented. Preliminary experiments to derive aerosol deposition rate on a flat plate and the maximum feasible liquid mass that may be accumulated on a near-spherical envelope are briefly described. Further experimental work is recommended to constrain the deposition efficiency values involved and the maximum feasible drizzle fluxes that could have been encountered by both VEGA 1 and 2.     

Meteorological variations in the middle clouds of Venus from VEGA balloon in situ measurements

Instruments aboard the gondolas of the two VEGA balloons obtained in situ measurements of pressure, temperature, vertical velocity relative to the balloon, cloud particle backscatter, lightning and the ambient light level. Atmospheric motions at the balloon float altitudes were also determined from Earth-based tracking results. To illustrate the history of the balloon flights and to facilitate comparisons between some of the different observed quantities, measurements of pressure, temperature and backscatter are presented as time series for the entire lifetime of each balloon. Both long and short period variations have been detected. In addition, the environmental entropy encountered by each balloon will be discussed.     

Estimates of convective heat fluxes and gravity wave amplitudes in the Venus middle cloud layer from VEGA balloon measurements

Atmospheric temperatures and vertical velocities obtained from the VEGA balloon measurements indicate that the dynamical heat flux is upward and has an amplitude that ranges from 0 to 360 W m⁻² in the middle cloud region. The static stability is positive and ranges from 0 to 2.0 K km⁻¹. Time series analysis of these results indicates that convection is the principal mechanism for generating the large vertical motions. Gravity waves were also detected at these levels and account for about 15% of the covariance between temperature and vertical velocity.     

Initial estimates of Venus winds from ground-based radio tracking of the VEGA balloons

A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere by the VEGA spacecraft. Initial analysis of only radial velocities indicates that each balloon was blown westward about 11,500 kilometers (8000 kilometers on the night side) by zonal winds with a mean speed of about 70 meters per second. Excursions of the data from a model of constant zonal velocity are generally less than 3 meters per second; however, a much larger variation is evident near the end of the flight of the second balloon. Consistent systematic trends in the residuals for both balloons indicate the possibility of a solar-fixed atmospheric feature.     

The VEGA Venus balloon experiment

In June 1985, two instrumented balloons were placed in the atmosphere of Venus as part of the VEGA mission. Each balloon traveled about 30 percent of the way around the planet at a float altitude near 54 kilometers. In situsensors measured pressure, temperature, vertical wind velocity, cloud particle backscatter, ambient light level, and frequency of lightning. A ground-based network of 20 radio antennas tracked the balloons by very long baseline interferometry (VLBI) techniques to monitor the Venus winds. The history, organization, and principal characteristics of this international balloon experiment are described.     

Radio occultation experiments with Comet Halley

Previous radio occultation investigations on cometary comae and tails have included refraction measurements and intensity scintillations of natural radio sources used to derive the density and structure of the cometary plasma. Significant improvements in the coverage and sensitivity of these measurements will be achieved during the present apparition of Comet Halley. The comet missions GIOTTO and VEGA will also feature passive radio science expeirments designed to measure comet-induced Doppler shifts of the dual-frequency spacecraft signals during Halley flyby. A brief survey of these radio occultation measurement techniques and their application in the specific case of Comet Halley are presented.     

气球卫星1990—81B和1990－81C的轨道变化和高层大气密度的测定

本文测定给出我国首次发射的专用于高层大气探测的两颗气球卫星DQ-1A(1990-81B)和DQ-1B(1990-81C)整个寿命期间的轨道变化,以及利用轨道衰变率,采用适合气球卫星近国轨道反测密度的一种方法,获得500-900km高度范围内太阳峰年期间的高层大气密度及其变化。结果表明,同时发射的两颗面积质量比不同的气球卫星所测定的高层大气密度及其变化非常一致,且明显地显示密度随太阳活动逐日的和27天周期性的变化。本文将密度测定结果与高层大气模型进行了比较和分析。      

A balloon tracking system that uses the VHF omidirectional range (VOR) network

The VHF Omnidirectional Range (VOR) system is a primary navigational aid to aircraft in the United States. Although the quantity of stations in the United States exceeds that of other areas, VOR stations are found all over the world. An inexpensive balloon navigational package that uses the existing VOR system has been developed. It employs the principle of triangulation between stations to yield position information. The station selection can be changed by telemetry command during the balloon flight in order to maximize triangulation accuracy and to minimize effects of weak signals. The VOR radials are part of the telemetry transmitted from the balloon package. Preliminary results from several flights in Palestine, Texas indicate that this system may be a viable backup or substitute for the OMEGA system commonly used. Typical accuracy of the down point prediction has been ± 1 mile.     

Variation of monthly mean foF2 and hmF2 over a mid latitude station during the period 1997–2006

Ionosonde data of a mid latitude station Novosibirsk (Geog. Lat. 54.6°N, Geog. Long. 83.2°E) has been analyzed for the years 1997–2006 that covers the major part of solar cycle 23. Our results show the presence of winter anomaly in the daytime F2 layer critical frequency during different phases of solar activity. Results also reveal a semiannual variation of foF₂ with two maxima and a minimum that always appears in summer. While the first maximum is in the spring equinox, the second one is found to shift from autumn to winter with the increase of solar activity. The maximum height of F2 layer during the daytime shows variation with the solar activity. It is higher during the higher activity periods and lower during the periods of low activity. Results of ionosonde observations have been compared with those obtained from IRI-2007 model and it is found that model reproduces gross features of foF₂ variation. However, the modeled hmF₂ variations during equinoxes are significantly different from the ones derived using the ionosonde data. The model also underestimates the hmF₂ values.     

Infrared observation of the nucleus of comet Halley with the IKS instrument from the VEGA 1 probe

The Infrared thermal emission of the nucleus has been observed by the imaging channel of the infrared spectrometer IKS during the fly-by of Comet Halley by the VEGA 1 probe. An emissive region with a temperature in excess of 300 K has been detected. The results are compatible with a simplified model assuming a spherical nucleus covered by an insulating black material.     

Application of BDS-GEO for studying TEC variability in equatorial ionosphere on different time scales

The Earth's ionosphere and especially its equatorial part is a highly dynamical medium. Geostationary satellites are known to be a powerful tool for ionospheric studies. Recent developments in BDS-GEO satellites allow such studies on the new level due to the best noise pattern in TEC estimations, which corresponds to those of GPS/GLONASS systems. Here we used BDS-GEO satellites to demonstrate their capability for studying equatorial ionosphere variability on different time scales. Analyzing data from the equatorial SIN1 IGS station we present seasonal variations in geostationary slant TEC for the periods of high (October 2013 - October 2014) and low (January 2017 - January 2018) solar activity, which show semi-annual periodicity with amplitudes about 10 TECU during solar maximum and about 5 TECU during the solar minimum. The 27-day variations are also prominent in geostationary slant TEC variations, which correlates quite well with the variations in solar extreme UV radiation. We found semi-annual pattern in small scale ionospheric disturbances evaluated based on geostationary ROTI index: maximal values correspond to spring and fall equinoxes and minimum values correspond to summer and winter solstices. The seasonal asymmetry in ROTI values was observed: spring equinox values were almost twice as higher than fall equinox ones. We also present results on the 2017 May 28–29 G3 geomagnetic storm, when ～30 TECU positive anomaly was recorded, minor and final major sudden stratospheric warmings in February and March 2016, with positive daytime TEC anomalies up to 15–20 TECU, as well as the 2017 September 6 X9.3 solar flare with 2 TECU/min TEC rate. Our results show the large potential of geostationary TEC estimations with BDS-GEO signals for continuous monitoring of space weather effects in low-latitude and equatorial ionosphere.     

Application of HF Doppler measurements for the investigation of internal atmospheric waves in the ionosphere

We present results of the spectral analysis of data series of Doppler frequency shifted signals reflected from the ionosphere, using experimental data received at Kazan University, Russia. Spectra of variations with periods from 1 min to 60 days have been calculated and analyzed for different scales of periods. The power spectral density for spring and winter differs by a factor of 3–4. Local maxima of variation amplitude are detected, which are statistically significant. The periods of these amplitude increases range from 6 to 12 min for winter, and from 24 to 48 min for autumn. Properties of spectra for variations with the periods of 1–72 h have been analyzed. The maximum of variation intensity for all seasons and frequencies corresponds to the period of 24 h. Spectra of variations with periods from 3 to 60 days have been calculated. The maxima periods of power spectral density have been detected by the MUSIC method for the high spectral resolution. The detected periods correspond to planetary wave periods. Analysis of spectra for days with different level of geomagnetic activity shows that the intensity of variations for days with a high level of geomagnetic activity is higher.     

Charging effects in the cometary environment of Halley

Electrostatic charging of the GIOTTO spacecraft in different impact induced charged particle environments was studied with 3D numerical particle-in-cell models. The simulation results are assessed according to first experimental results of GIOTTO and VEGA instruments. Decreasing and even negative spacecraft potentials measured on VEGA near closest approach to the comet suggest the influence of the cometary plasma, which is also confirmed by corresponding numerical simulations.     

Numerical study of forced convective heat transfer around a spherical aerostat

Forced convective heat transfer is one of the major factors that dominate the thermal behaviors of aerostats. Due to the large physical size, the convection around an aerostat has high Reynolds numbers. The existing forced convective heat transfer correlations are limited to the Reynolds number lower than 10⁵, which are not appropriate for aerostat applications. Therefore, it is necessary to obtain a convective heat transfer correlation applicable to spherical aerostats at high Reynolds numbers. In this paper, steady convective heat transfer from an isothermal spherical aerostat is numerically investigated. The numerical simulation is carried out by commercial computational fluid dynamic software with the Reynolds number from 20 to 10⁸. The average Nusselt numbers are obtained and compared with those of available in literature. Based on regression and optimization with software, a new piecewise correlation of Nusselt number is proposed. The verification shows that the new correlation is reliable.     

Solar signals in the minimum extreme temperature records in the southern region of the Gulf of Mexico

Minimum extreme temperature series from several meteorological stations of the Gulf of Mexico are spectrally analyzed using the Maximum Entropy Method.We obtained significant periodicities similar to those found in meteorological and solar activity phenomena. This indicates that probably the solar activity signals are present in the minimum extreme temperature records of this Mexican region.     

Solar UV and ozone balloon measurements

Absolute solar UV spectra were obtained with a $\text{1}\text{4}$m spectrometer on a balloon flight from Palestine, Texas on September 23, 1981. This balloon reached a float altitude of 39 km at solar noon. The ozone density profiles derived from these spectra are discussed. The measurements are compared with data obtained from the same calibrated instrument flown in 1976 at solar minimum.     

Investigation on the MLT tidal variability during September 2019 minor sudden stratospheric warming

Tidal variability in the mesosphere and lower thermosphere (MLT) during September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing ground-based meteor radar wind observations from the equatorial, extratropical, middle, and high latitude stations and global reanalysis dataset. The polar warming is found to move from the mesosphere to the stratosphere until the peak warming day (PWD) of the SSW. The diurnal and semidiurnal tides at individual observational sites do not exhibit any consistent response during the observational interval, but a notable and consistent variability in some specific zonal wavenumber components, i. e., DW1 (migrating diurnal tide), DE3 (nonmigrating eastward wavenumber 3 diurnal tide), and SW2 (migrating semidiurnal tide) is found in the global reanalysis dataset. Incidentally, the warming event occurs during Spring equinox when a dominant seasonal change in the tidal activities generally takes place and hence seasonal variability is also looked into while identifying the SSW impact during the observational interval. It is found that the seasonal broad changes in the DW1, DE3, and SW2 amplitudes can be explained by the variability in the tidal sources, i.e., water vapor, convective activity, ozone, etc during the observational period. However, the extracted short-term variability in the global tidal modes on removing seasonal trend reveals noticeable response in connection with the warming event. The deseasoned amplitude of the DW1 significantly enhances around the PWD at most of the present latitudes. The deseasoned DE3 amplitude responds significantly in the middle atmosphere at low latitudes during the warming phase. The deseasoned SW2 exhibit clear enhancement around the PWD at all the latitudes. However, the deseasoned tidal features do not seem to correlate well with that of the source species unlike the seasonal ones that imply involvement of complex processes during the warming event, seeking further future investigations in this regard.