- Email: [email protected]
Synopsis of troposphere and lower stratosphere
Adv. Space Res. Vol.1, pp.5—Il.
0273—11]7/81/0401—0005$05.OO/O
©COSPAR, 1981. Printed in Great Britain.
SYNOPSIS OF TROPOSPHERE AND LOWER STRATOSPHERE Daniel Cadet Laboratoire de Météorologie Dynamique du C.N.R.S., Ecole Polytechnique, 91128 Palaiseau Ceder, France
ABSTRACT The use of different types of balloons for the investigation of the troposphere and lower stratosphere is reviewed with a special emphasis on the application for the next 10 years. The instrumentation currently flown aboard balloons or under development is described. Some possible scientific objectives of such balloon experiments are presented. The specific applications of the different types of bal— loons available within the next few years for scientific flights are discussed.
INTRODUCTION During the last decade, balloons have been used for atmospheric studies essentially to investigate the large scale dynamics of the atmosphere on a global scale in the upper troposphere or lower stratosphere [1], [2], or on a regional scale in the boundary layer [3]. These balloons were constant—level balloons of relatively small diameter (up to 6 m), which are able to fly small payloads at the same level in the atmosphere during very long periods. Important scientific results were deduced from these experiments. During these experiments, different types of location and data collection systems from space were experimented. Using these balloons as instrumented platforms, some experiments were also performed essentially at stratospheric levels to investigate the dynamics of turbulence and gravity waves. For these experiments, specific instrumentation were designed, developed and tested in flight conditions. New developments have been or are made in balloon technology and extension of constant—level flights at higher levels than previously is now possible. New instrumentation is also currently developed. In this paper, the possibilities offered by these recent developments for the investigation of the troposphere and lower stratosphere are discussed.
THE PLATFORMS
The balloons usually used for the investigation of the atmosphere are superpres— sure constant—level balloons which fly at a level where the mass of the displaced air equals the mass of the balloon and its instrument package. Such balloons have been manufactured in different shapes but the sphere is the most efficient one because it provides uniform stress distribution over the entire surface [L+]. 5
6
D. Cadet Long balloon lifetime is one of the keys to a successful experiment. As long as a balloon is overpressurized, it keeps floating at a constant density level. Theoretical lifetime is determined by the rate of diffusion through the balloon envelope. However, actual flight durations are often shorter than expected from theoretical considerations. Lifetime can be reduced by the loss of gas through pinholes, film degradation by UV radiation, ice and frost deposit on the balloon skin which can prevent free lifting and force the balloon downward [5] or modif i— cation of the radiative fluxes received by the balloon, which can destroy its thermal equilibrium [6]. Despite these limitations long duration flights were succeeded at different levels (200 mb, 150 mb, 100 mb and 50 mb). We can say that for flights up to the 100 tnb level and with balloon having diameter less than 6 m the technology is now well overcome. However a need for balloons flying higher in the stratosphere and carrying heavier payloads, appeared a few years ago. This need was correlated with the interest in the stratosphere following the studies on the impact of supersonic transportation on the layer of the atmosphere. Now, a new interest exists with the future imple— inentation of the Middle Atmospheric Program (MAP). There is also an interest from the non—atmospheric community to conduct balloon experiments with long duration vehicles, including recovery of payloads. Attempts have been made to increase altitude and payloads (i.e. the diameter of the balloons) using classical polyester films, but the limits of the films have became apparent and new envelope materials or new balloon shapes were proposed. C.N.E.S. (Centre National d’Etudes Spatiales) developed the “pumpkin shape” balloon made with conventional unreinforced films. The key of this approach is the use of a net consisting of high strength, high modulus (Keviar) meridian straps, inside which the envelope is placed. The straps are attached at both ends to steel apex pieces which, together with the straps, take up most of the forces of pressurization. The envelope thus budges out between the straps to form lobes with a small radius of curvature in the crosswise direction (Figure 1). Such “pumpkin” balloons (8 m diameter) have been successfully tested at 100 mb during fall 1978.
1-
_~ Fig. I
View of the “pumpkin shape” balloon developed by C.N.E.S. to fly above 20 km.
Synopsis of Troposphere and Lower Stratosphere
7
Larger balloons (20 m diameter) which are able to carry payloads weighting up to 50 kg at 22 km will be flown before the end of 1980. Superpressure balloon flights can be extended down to the tropical boundary layer : successful long—duration trajectories over the Indian Ocean were succeeded in 1975 [3] and 1979 [7]. The key of the success of these flights was the design of a payload inside the envelope of the balloons. The ambient transducers and the antenna for transmitting the data are put outside (Figure 2). With such a design, if the balloon is washed down to the sea when encountering a tropical shower, it can recover its nominal flight level without any destruction when drying up. Flight duration is only limited by land or the existence of intense convective activity where balloons encounter very severe conditions.
pf...W. trai~.d.c., HyVijetOf
Ak ISMS,.tUf,
O..,p,.s.u,.
! Fig. 2
Schematic view of the balloon and internal payload used for low—level flights in the tropical boundary layer.
Another type of balloons for long scientific flights is also being developed in France by C.N.E.S. This balloon which is the hot air balloon combines two capacities : long duration and ability to perform reversible vertical excursions [81. The IR Montgolfière is a hot air balloon heated by the telluric and atmospheric IR radiation. Vertical excursions by day and by night can be obtained in making the thermal lift to vary, that is the temperature inside the balloon, by means of a valve placed at the upper part of the balloon. When the valve is opened, the hot air released is replaced by cold air inhaled through the lower hole, the diameter of which is greater than the valve diameter. The balloon volume remains constant ; closing the valve makes the balloon climb. The feasibility of the3) IR Montgolfière was demonstrated in December 1977 : a successful flight (5600 m was performed from France and lasted 66 hours. To explore the concept of the vertical sounding, a larger Montgolfière was designed (12 000 m3) but due to technological problems, the flight was not successful. Present work is made on the material technology. To study the composition of the atmosphere classical stratospheric balloons are used to carry sophisticated payloads but their application at low stratospheric levels is very limited.
8
D. Cadet THE INSTRUMENTATION Another technical problem is that of designing light electronic equipment and power supplies capable of operating at very low ambient temperatures for a long time and capable of transmitting the data. Moreover, aboard the superpressure balloons the equipment must be packaged in a way that would be safe in case of collision with an aircraft (below 100 mb). The balloon package is a radio beacon generally consisting of four main elements power supply, data encoding logic, sensors and associated electronics and radio transmitter. The package is often solar powered, but batteries have also been used, since batteries with good efficiency at very low temperatures are available. All these problems are now well mastered. In the near future, more sophisticated experiments will certainly be performed using microprocessors aboard balloons for on—board data managements and for compacting the raw data in order to telemeter processed information. To transmit the data, different systems have been tested in flights, the early ones being based on very simple and cost—efficient telemetry system as that one developed for the GHOST program. These systems are being replaced, specially for superpressure balloon flights, by satellite data collection as the operational ARGOS system. The bit transmission rate of the ARGOS seems to be limited (256 bits every 6 hours), but using sub commutation of the messages, this rate can be considerably increased. Higher bit rates for transmission can be obtained using a geosynchronous satellite relay but power consumption for the emission of the information is very important compared to the other systems. For location of the platforms, the ARGOS system and the OMEGA system are currently used [9]. The design of transducers to achieve the scientific objectives is also very important. Light sensors having very low power consumptions have been designed specially for dynamical studies. Thus, very good sensors have been designed to measure the air temperature [10], the pressure [11], the altitude of the balloon [12], the wind [13], [iLl],radiative fluxes [15]. For moisture measurements, no satisfactory sensors have been designed to fly at stratospheric altitudes despite some attempts [16]. With the new developments of constant—level balloons or hot air balloons capable to carry heavier payloads (up to 50 kg) at an altitude of 22 km, the constraints on the weight and consequently on the power consumption is going to be relaxed. Thus, new instrumentation specially to investigate the composition of the atmosphere will be able to fly during a very long time in the stratosphere. SCIENTIFIC OBJECTIVES It is very difficult to present the scientific problems which are going to be tackled during the next 10 years. However some ideas cam be given, which, of course, reflect the views of the author of the paper. Due to the existence of adequate platforms, it seems quite clear that two regions of the atmosphere can be studied with long duration balloons. The first one is the stratosphere where there is an interest from the atmospheric dynami— clans and chemists. Furthermore, MAP is going to be implemented during the first part of the coming decade. Between 15 and 25 kin, the dynamics of gravity waves (transport of wave momentum and wave energy, absorption, etc.) seems to be am interesting scientific objective.
Synopsis of Troposphere and Lower Stratosphere
9
Very fruitful results using the TWERIE balloons were obtained to determine vertical motions in the stratosphere [2] (Figure 3) and it has been demonstrated that estimations of the flux of momentum and energy can be given from superpressure constant—level balloons. The flights could be made at different latitudes to study also the tropical regions. For that purpose, the constant—level balloons are really adequate platform and some proposals in that direction have been made by French groups. Some flights are expected to be performed before the end of 1981. With the hot air balloons, the vertical structure of the waves could be studied : the vertical dimension gives a different information than the horizontal one. The hot air balloon seems to be an adequate platform to tackle the problem of stratospheric turbulence because it allows reversible vertical excursions (generation, relation to synoptic fields, etc.)
.05
w
LEE WAVES (7.5~6’)
GRAVITY WAVES .04 -4. (38’)
4.
~E A\1~P~
~j~O(41)
0.0
0.1
0.2
0.3
0.4
0.5
FREQ.(CYCLES/MIN) Fig. 3
Frequency spectrum of a pressure trace for a TWERLE flight launched from Christchurch (New—Zealand) on 8 December 1975. The maximum of 4 mm represents the neutral buoyancy oscil— lation (NBO) and the peaks at 6 and 7.6 mm are caused by stationary lee waves. The peak at 38 mm is related to a propagating internal gravity wave.
If constant—level balloons can be flown at very high altitudes i.e. between 25 and 30 km, which seems to be possible before the end of the eighties, the climatology of the dynamics of the middle layers of the stratosphere could be studied. The horizontal motion of the balloon together with accurate measurements of altitude, pressure and local vertical gradient of temperature, will permit the study of the rate of conversion of potential energy into kinetic energy which is vital to the energy budget of the stratosphere. At these high altitudes, it seems
JASR 1:11 - B
10
D. Cadet
interesting to study the extent to which fluctuations of the radiative flux are coupled to other stratospheric phenomena such as variations in ozone and aerosol density and to improve our understanding of the radiative coupling between the troposphere and the stratosphere. This last study could be tackled with presently available balloons. The transport of trace species across the tropopause and their redistribution within the stratosphere is also another interesting problem for which the contribution from balloon experiments could be important. The main constituent in that field is the water vapor : there are some proposals aboard superpressure balloons at stratospheric levels to determine the water vapor content and give some ideas about the origin of stratospheric water vapour. This idea could be applied to other constituents if specific instrument can be designed. The advantages of constant—level balloons or hot air balloons is obvious compared to zero—pressure balloons : due to the duration of the flights, time and space variations can be separated (latitude, seasonal, altitude dependance). The second level at which balloon flights can be very helpful is the boundary layer, specially over oceanic tropical areas. Two French experiments, the last one during MONEX-79, have already been performed over the Indian Ocean to study the modification of the boundary layer over the Arabian Sea [7]. The GARP climatic program recommends joint studies of the oceanic and atmospheric circulations in the meso and large scale range. The interactions between the two circulations takes place at the interface between the two medium and the exchanges between the free atmosphere and the ocean takes place through the planetary boundary layer. The turbulent vertical heat and moisture fluxes at certain levels in the tropical boundary layer can be measured with the sensors presently available and the help of microprocessors to reduce the volume of information. Such an experiment over the tropical Atlantic Ocean has been proposed by a French group.
CONCLUSION Since the last years, new developments have been made in balloon technology new superpressure balloons to fly higher with heavier payloads, hot air balloons capable to make reversible vertical excursions. With the implementation of the Middle Atmospheric Program, these platforms will be largely used specially to study the dynamics of the lower stratosphere essentially gravity waves and turbulence. It is hopeful that specific experiments to study the composition of the lower stratosphere will be flown aboard the balloons. It seems also that there is a need for larger balloons to fly higher in the stratosphere (around 30 kin). As the technology of flights in the boundary layer is now well overcome, some experiments will be made to investigate this particular and very important layer of the atmosphere directly in contact with the ocean or the land.
References I.
P. Morel and W. Bandeen,
Bull. Amer. Met. Soc., 54, 298 (1973).
2.
The TWERLE Team,
3.
D. Cadet and H. Ovarlez,
4.
R. Regipa, Scientific Ballooning COSPAR Advances in Space Exploration Volume 5, 39 (1979).
5.
P. Morel et al.,
Bull. Amer. Met. Soc., 58, 936 (1977). Quart. J. Roy. Met. Soc., 102, 805 (1976).
J. Appi. Met., 7, 626 (1968).
Synopsis of Troposphere and Lower Stratosphere
11
6.
J.P. Pommereau and A. Hauchecorne. Scientific Ballooning in Space Exploratiqp, volume 5, 21 (1979).
COSPAR Advances
7.
D. Cadet et al.
8.
J.P. Pommereau and A. Hauchecorne, Scientific Ballooning in Space Exploration, volume 5, 55 (1979).
9.
E.W. Lichfield and M.L. Olson, Scientific Ballooning. COSPAR Advances in Space Exploration, volume 5, p. 59 (1979).
10.
P. Morel et al., J. Appi. Meteor., 7, 626 (1968).
II.
J. Ovarlez et al., J. Appl. Meteor., 17, 796 (1978).
12.
N. Levanon,
13.
D. Cadet, Quart. J. Roy. Met. Soc., 101, 485 (1975).
14.
J. Ovarlez et al. Preprints Symposium on Meteorological Observations and Instrumentation, AIlS, Boston, 65 (1978).
15.
V.E. Suomi and P.M. Kuhn,
Tellus,
16.
M. Roulleau and M.M. Poc,
J. AppI. Meteor., 17, 803 (1978).
Submitted to Bull. Amer. Meteor. Soc., 1980. COSPAR Advances
IEEE Trans. Geosci. Electron., 8, 19 (1970).
10, 160 (1958).
0273—11]7/81/0401—0005$05.OO/O
©COSPAR, 1981. Printed in Great Britain.
SYNOPSIS OF TROPOSPHERE AND LOWER STRATOSPHERE Daniel Cadet Laboratoire de Météorologie Dynamique du C.N.R.S., Ecole Polytechnique, 91128 Palaiseau Ceder, France
ABSTRACT The use of different types of balloons for the investigation of the troposphere and lower stratosphere is reviewed with a special emphasis on the application for the next 10 years. The instrumentation currently flown aboard balloons or under development is described. Some possible scientific objectives of such balloon experiments are presented. The specific applications of the different types of bal— loons available within the next few years for scientific flights are discussed.
INTRODUCTION During the last decade, balloons have been used for atmospheric studies essentially to investigate the large scale dynamics of the atmosphere on a global scale in the upper troposphere or lower stratosphere [1], [2], or on a regional scale in the boundary layer [3]. These balloons were constant—level balloons of relatively small diameter (up to 6 m), which are able to fly small payloads at the same level in the atmosphere during very long periods. Important scientific results were deduced from these experiments. During these experiments, different types of location and data collection systems from space were experimented. Using these balloons as instrumented platforms, some experiments were also performed essentially at stratospheric levels to investigate the dynamics of turbulence and gravity waves. For these experiments, specific instrumentation were designed, developed and tested in flight conditions. New developments have been or are made in balloon technology and extension of constant—level flights at higher levels than previously is now possible. New instrumentation is also currently developed. In this paper, the possibilities offered by these recent developments for the investigation of the troposphere and lower stratosphere are discussed.
THE PLATFORMS
The balloons usually used for the investigation of the atmosphere are superpres— sure constant—level balloons which fly at a level where the mass of the displaced air equals the mass of the balloon and its instrument package. Such balloons have been manufactured in different shapes but the sphere is the most efficient one because it provides uniform stress distribution over the entire surface [L+]. 5
6
D. Cadet Long balloon lifetime is one of the keys to a successful experiment. As long as a balloon is overpressurized, it keeps floating at a constant density level. Theoretical lifetime is determined by the rate of diffusion through the balloon envelope. However, actual flight durations are often shorter than expected from theoretical considerations. Lifetime can be reduced by the loss of gas through pinholes, film degradation by UV radiation, ice and frost deposit on the balloon skin which can prevent free lifting and force the balloon downward [5] or modif i— cation of the radiative fluxes received by the balloon, which can destroy its thermal equilibrium [6]. Despite these limitations long duration flights were succeeded at different levels (200 mb, 150 mb, 100 mb and 50 mb). We can say that for flights up to the 100 tnb level and with balloon having diameter less than 6 m the technology is now well overcome. However a need for balloons flying higher in the stratosphere and carrying heavier payloads, appeared a few years ago. This need was correlated with the interest in the stratosphere following the studies on the impact of supersonic transportation on the layer of the atmosphere. Now, a new interest exists with the future imple— inentation of the Middle Atmospheric Program (MAP). There is also an interest from the non—atmospheric community to conduct balloon experiments with long duration vehicles, including recovery of payloads. Attempts have been made to increase altitude and payloads (i.e. the diameter of the balloons) using classical polyester films, but the limits of the films have became apparent and new envelope materials or new balloon shapes were proposed. C.N.E.S. (Centre National d’Etudes Spatiales) developed the “pumpkin shape” balloon made with conventional unreinforced films. The key of this approach is the use of a net consisting of high strength, high modulus (Keviar) meridian straps, inside which the envelope is placed. The straps are attached at both ends to steel apex pieces which, together with the straps, take up most of the forces of pressurization. The envelope thus budges out between the straps to form lobes with a small radius of curvature in the crosswise direction (Figure 1). Such “pumpkin” balloons (8 m diameter) have been successfully tested at 100 mb during fall 1978.
1-
_~ Fig. I
View of the “pumpkin shape” balloon developed by C.N.E.S. to fly above 20 km.
Synopsis of Troposphere and Lower Stratosphere
7
Larger balloons (20 m diameter) which are able to carry payloads weighting up to 50 kg at 22 km will be flown before the end of 1980. Superpressure balloon flights can be extended down to the tropical boundary layer : successful long—duration trajectories over the Indian Ocean were succeeded in 1975 [3] and 1979 [7]. The key of the success of these flights was the design of a payload inside the envelope of the balloons. The ambient transducers and the antenna for transmitting the data are put outside (Figure 2). With such a design, if the balloon is washed down to the sea when encountering a tropical shower, it can recover its nominal flight level without any destruction when drying up. Flight duration is only limited by land or the existence of intense convective activity where balloons encounter very severe conditions.
pf...W. trai~.d.c., HyVijetOf
Ak ISMS,.tUf,
O..,p,.s.u,.
! Fig. 2
Schematic view of the balloon and internal payload used for low—level flights in the tropical boundary layer.
Another type of balloons for long scientific flights is also being developed in France by C.N.E.S. This balloon which is the hot air balloon combines two capacities : long duration and ability to perform reversible vertical excursions [81. The IR Montgolfière is a hot air balloon heated by the telluric and atmospheric IR radiation. Vertical excursions by day and by night can be obtained in making the thermal lift to vary, that is the temperature inside the balloon, by means of a valve placed at the upper part of the balloon. When the valve is opened, the hot air released is replaced by cold air inhaled through the lower hole, the diameter of which is greater than the valve diameter. The balloon volume remains constant ; closing the valve makes the balloon climb. The feasibility of the3) IR Montgolfière was demonstrated in December 1977 : a successful flight (5600 m was performed from France and lasted 66 hours. To explore the concept of the vertical sounding, a larger Montgolfière was designed (12 000 m3) but due to technological problems, the flight was not successful. Present work is made on the material technology. To study the composition of the atmosphere classical stratospheric balloons are used to carry sophisticated payloads but their application at low stratospheric levels is very limited.
8
D. Cadet THE INSTRUMENTATION Another technical problem is that of designing light electronic equipment and power supplies capable of operating at very low ambient temperatures for a long time and capable of transmitting the data. Moreover, aboard the superpressure balloons the equipment must be packaged in a way that would be safe in case of collision with an aircraft (below 100 mb). The balloon package is a radio beacon generally consisting of four main elements power supply, data encoding logic, sensors and associated electronics and radio transmitter. The package is often solar powered, but batteries have also been used, since batteries with good efficiency at very low temperatures are available. All these problems are now well mastered. In the near future, more sophisticated experiments will certainly be performed using microprocessors aboard balloons for on—board data managements and for compacting the raw data in order to telemeter processed information. To transmit the data, different systems have been tested in flights, the early ones being based on very simple and cost—efficient telemetry system as that one developed for the GHOST program. These systems are being replaced, specially for superpressure balloon flights, by satellite data collection as the operational ARGOS system. The bit transmission rate of the ARGOS seems to be limited (256 bits every 6 hours), but using sub commutation of the messages, this rate can be considerably increased. Higher bit rates for transmission can be obtained using a geosynchronous satellite relay but power consumption for the emission of the information is very important compared to the other systems. For location of the platforms, the ARGOS system and the OMEGA system are currently used [9]. The design of transducers to achieve the scientific objectives is also very important. Light sensors having very low power consumptions have been designed specially for dynamical studies. Thus, very good sensors have been designed to measure the air temperature [10], the pressure [11], the altitude of the balloon [12], the wind [13], [iLl],radiative fluxes [15]. For moisture measurements, no satisfactory sensors have been designed to fly at stratospheric altitudes despite some attempts [16]. With the new developments of constant—level balloons or hot air balloons capable to carry heavier payloads (up to 50 kg) at an altitude of 22 km, the constraints on the weight and consequently on the power consumption is going to be relaxed. Thus, new instrumentation specially to investigate the composition of the atmosphere will be able to fly during a very long time in the stratosphere. SCIENTIFIC OBJECTIVES It is very difficult to present the scientific problems which are going to be tackled during the next 10 years. However some ideas cam be given, which, of course, reflect the views of the author of the paper. Due to the existence of adequate platforms, it seems quite clear that two regions of the atmosphere can be studied with long duration balloons. The first one is the stratosphere where there is an interest from the atmospheric dynami— clans and chemists. Furthermore, MAP is going to be implemented during the first part of the coming decade. Between 15 and 25 kin, the dynamics of gravity waves (transport of wave momentum and wave energy, absorption, etc.) seems to be am interesting scientific objective.
Synopsis of Troposphere and Lower Stratosphere
9
Very fruitful results using the TWERIE balloons were obtained to determine vertical motions in the stratosphere [2] (Figure 3) and it has been demonstrated that estimations of the flux of momentum and energy can be given from superpressure constant—level balloons. The flights could be made at different latitudes to study also the tropical regions. For that purpose, the constant—level balloons are really adequate platform and some proposals in that direction have been made by French groups. Some flights are expected to be performed before the end of 1981. With the hot air balloons, the vertical structure of the waves could be studied : the vertical dimension gives a different information than the horizontal one. The hot air balloon seems to be an adequate platform to tackle the problem of stratospheric turbulence because it allows reversible vertical excursions (generation, relation to synoptic fields, etc.)
.05
w
LEE WAVES (7.5~6’)
GRAVITY WAVES .04 -4. (38’)
4.
~E A\1~P~
~j~O(41)
0.0
0.1
0.2
0.3
0.4
0.5
FREQ.(CYCLES/MIN) Fig. 3
Frequency spectrum of a pressure trace for a TWERLE flight launched from Christchurch (New—Zealand) on 8 December 1975. The maximum of 4 mm represents the neutral buoyancy oscil— lation (NBO) and the peaks at 6 and 7.6 mm are caused by stationary lee waves. The peak at 38 mm is related to a propagating internal gravity wave.
If constant—level balloons can be flown at very high altitudes i.e. between 25 and 30 km, which seems to be possible before the end of the eighties, the climatology of the dynamics of the middle layers of the stratosphere could be studied. The horizontal motion of the balloon together with accurate measurements of altitude, pressure and local vertical gradient of temperature, will permit the study of the rate of conversion of potential energy into kinetic energy which is vital to the energy budget of the stratosphere. At these high altitudes, it seems
JASR 1:11 - B
10
D. Cadet
interesting to study the extent to which fluctuations of the radiative flux are coupled to other stratospheric phenomena such as variations in ozone and aerosol density and to improve our understanding of the radiative coupling between the troposphere and the stratosphere. This last study could be tackled with presently available balloons. The transport of trace species across the tropopause and their redistribution within the stratosphere is also another interesting problem for which the contribution from balloon experiments could be important. The main constituent in that field is the water vapor : there are some proposals aboard superpressure balloons at stratospheric levels to determine the water vapor content and give some ideas about the origin of stratospheric water vapour. This idea could be applied to other constituents if specific instrument can be designed. The advantages of constant—level balloons or hot air balloons is obvious compared to zero—pressure balloons : due to the duration of the flights, time and space variations can be separated (latitude, seasonal, altitude dependance). The second level at which balloon flights can be very helpful is the boundary layer, specially over oceanic tropical areas. Two French experiments, the last one during MONEX-79, have already been performed over the Indian Ocean to study the modification of the boundary layer over the Arabian Sea [7]. The GARP climatic program recommends joint studies of the oceanic and atmospheric circulations in the meso and large scale range. The interactions between the two circulations takes place at the interface between the two medium and the exchanges between the free atmosphere and the ocean takes place through the planetary boundary layer. The turbulent vertical heat and moisture fluxes at certain levels in the tropical boundary layer can be measured with the sensors presently available and the help of microprocessors to reduce the volume of information. Such an experiment over the tropical Atlantic Ocean has been proposed by a French group.
CONCLUSION Since the last years, new developments have been made in balloon technology new superpressure balloons to fly higher with heavier payloads, hot air balloons capable to make reversible vertical excursions. With the implementation of the Middle Atmospheric Program, these platforms will be largely used specially to study the dynamics of the lower stratosphere essentially gravity waves and turbulence. It is hopeful that specific experiments to study the composition of the lower stratosphere will be flown aboard the balloons. It seems also that there is a need for larger balloons to fly higher in the stratosphere (around 30 kin). As the technology of flights in the boundary layer is now well overcome, some experiments will be made to investigate this particular and very important layer of the atmosphere directly in contact with the ocean or the land.
References I.
P. Morel and W. Bandeen,
Bull. Amer. Met. Soc., 54, 298 (1973).
2.
The TWERLE Team,
3.
D. Cadet and H. Ovarlez,
4.
R. Regipa, Scientific Ballooning COSPAR Advances in Space Exploration Volume 5, 39 (1979).
5.
P. Morel et al.,
Bull. Amer. Met. Soc., 58, 936 (1977). Quart. J. Roy. Met. Soc., 102, 805 (1976).
J. Appi. Met., 7, 626 (1968).
Synopsis of Troposphere and Lower Stratosphere
11
6.
J.P. Pommereau and A. Hauchecorne. Scientific Ballooning in Space Exploratiqp, volume 5, 21 (1979).
COSPAR Advances
7.
D. Cadet et al.
8.
J.P. Pommereau and A. Hauchecorne, Scientific Ballooning in Space Exploration, volume 5, 55 (1979).
9.
E.W. Lichfield and M.L. Olson, Scientific Ballooning. COSPAR Advances in Space Exploration, volume 5, p. 59 (1979).
10.
P. Morel et al., J. Appi. Meteor., 7, 626 (1968).
II.
J. Ovarlez et al., J. Appl. Meteor., 17, 796 (1978).
12.
N. Levanon,
13.
D. Cadet, Quart. J. Roy. Met. Soc., 101, 485 (1975).
14.
J. Ovarlez et al. Preprints Symposium on Meteorological Observations and Instrumentation, AIlS, Boston, 65 (1978).
15.
V.E. Suomi and P.M. Kuhn,
Tellus,
16.
M. Roulleau and M.M. Poc,
J. AppI. Meteor., 17, 803 (1978).
Submitted to Bull. Amer. Meteor. Soc., 1980. COSPAR Advances
IEEE Trans. Geosci. Electron., 8, 19 (1970).
10, 160 (1958).