1. ISDC Data Centre for Astrophysics, Geneva
Atmospheric Monitoring
Andrii Neronov
ISDC Data Centre for Astrophysics, Geneva

2. Atmospheric Monitoring
IR camera: overall morphology of distribution of optically-thick clouds,
measurement of altitude of the tops of optically thick clouds
LIDAR: detection of optically thick and thin (down to τ~0.15) cloud and aerosol layers
Global meteorological data: temperature, pressure profiles from GMMO or ECMWF
The slow mode data: maps of reflected airglow from the clouds / ground /sea

3. IR camera Temperature variation over the troposphere
Determines the precision of the measurement ofthe cloud-top altitude
Required for the stereo method of determination of the cloud-top altitude

4. LIDAR To allow several measurements for each EAS trigger
Structures with optical depths 0.15
Should be detectable
1 GTU corresponds to
375 m in nadir direction

5. Slow Mode Data
Could be used for atmospheric monitoring provided that cloud patterns could be recognized in UV in the night time.
Qualitatively, clouds should reflect and scatter the airglow, differently from the ground/sea.
The case for UV emission from the clouds and its usefulness for AM has to be investigated;
One of the possible science topics for EUSO-balloon?

6. Global atmospheric models
The most complete information on the state of the atmosphere is contained in the global atmospheric models used for weather forecast and climate analysis.
This information should be routinely taken into account in EAS reconstruciton.
Specifications of the necessary data and requirements on the global atmospheric model data
in JEM-EUSO reconstruction should be worked out.

7. Timeline of AM system

8. The main challenge
Only ~30% of UHECR events will happen in the "clear sky" conditions.
We need to learn how to use most of the remaining 70% of events, if we want to keep the duty cycle close to 0.2, rather than 0.2×0.3=0.06.
* We know that this is possible, but for the moment only on a qualitative level
* Quantitative level of understanding could be reached only through simulations of EAS in realistic atmospheric "scenes" and reconstruction of UHECR parameters using the information on the atmospheric "scene" provided by the AM data in the foreseen configuration. This was not done up to now.

9. The main challenge
... from debriefing of the NASA proposal
"The duty cycle and detection volume are strongly dependent on the atmospheric transparency to ultraviolet light, the density of clouds within the field-of-view of the instrument, and the reduction of available dark-time by the moon, anthropogenic, or other background light sources. The proposers estimate that the combination of these effects will reduce the duty cycle of the science observations to about 13%. However, the Auger Observatory Fluorescence Detector (FD), situated in a high-desert, dark site, has a 5-year measured average duty cycle of 12%, after accounting for the same factors. Thus, the proposers' estimate appears unrealistic. The effect of average global cloud cover is likely to be significantly worse than the best ground-based sites, and no justification or reference for the proposers’ 13% value is given."
The proposal does not provide an adequate statistical description of the expected aperture, including effects of weather, cities, aurora, and solar activity on optical transmission and background light levels. The proposal does not provide adequate information of the seasonal averages and statistical fluctuations of these effects. The variations of cloud cover and atmospheric humidity have strong impact on the size of the detection volume, and may adverseley affect the number of observable hours and the energy threshold. A statistical approach is needed to model the cumulative effects of these factors, including cross-correlations.
Simulations / reconstruction of EAS in realistic atmospheric "scenes", continuously variable in time /space, is required to answer the comments.

10. Simulations /reconstruction with real atmosphere
For any real atmospheric scene
Derive the AM system data which will be taken into account in EAS reconstruction
– global atmospheric model data → temperature/density profile, clouds
– IR camera → cloud top altitudes
–LIDAR → optical depth profile toward EAS
Input this information in ESAF
Generate a sample of UHECR events
What fraction of reconstructed events could be retained / rejected in spectral/angular analysis?
What are the selection criteria for "good" events?
Reconstruct UHECR parameters for the simulated sample
How to calculate the aperture and exposure with account of atmospheric conditions?

11. Common AM – Simulations tasks
Task 1: ESAF simulations with one optically thick cloud at different altitudes. Study the quality of reconstruction in the presence of cloud, find the maximal altitude of the cloud at which the quality of reconstruction becomes insufficient. Explore different optical depths and scattering-to-absorption ratios. ✔
Task 2: Implement the possibility of account of the atmospheric optical depth profiles in the ESAF simulation.
a) investigate inside ESAF what are the available options to insert cloud parameters: geometrical thickness,
optical depth, scattering ratio etc.
b) Make an interface to CALIPSO database, to feed realistic atmospheric conditions in ESAF.
Task 3: Study EAS developing in realistic atmospheric conditions: with account of the optical depth profiles and cloud / aerosol masks. the effects of complicated OD profiles on the reconstruction of the UHECR parameters.
Task 4: Implement lidar data analysis in the ESAF: simulation of laser backscatter signal, lidar trigger, analysis of the backscatter profile, derivation of the list of cloud/aerosol features and their parameters (top/bottom altitude, optical depth, backscatter-to-absorption ratio). Analyze the dependence of precision of measurement of tau on the laser characteristics. ✔
Task 4. Investigate the precision of reconstruction of the cloud top altitude with the IR camera (both for stereo and radiative method). How could the IR camera information be taken into account in ESAF? ✔
Task 5. Investigate UV emission from clouds at nighttime with Tatyana, Meris, DMSP/OLS (Operational Linescan System) REIMEI(INDEX)/MAC data. What information could be obtained using the slow-mode data? How could it be taken into account in ESAF?

12. Common AM – Simulations tasks
Task 1: ESAF simulations with one optically thick cloud at different altitudes. Study the quality of reconstruction in the presence of cloud, find the maximal altitude of the cloud at which the quality of reconstruction becomes insufficient. Explore different optical depths and scattering-to-absorption ratios.
G.Saez, K.Shinozaki
Impact of the presence of the cloud on trigger efficiency is understood
Next step: work out the "quality cuts" which would reject events not suitable for UHECR analysis
We need to know
(a) the direction of events (not affected by atmospheric conditions) for angular anisotropy analysis
(b) energy of events to take into account in the angular anisotropy analysis
(c) energy of events to take into account in the spectral analysis
(d) effective area ("efficacy") as a function of energy to take into account in the spectral analysis
all events
How could we judge, based on the available data, that the energy reconstruction worked Ok?
How could we judge, based on available data, what fraction of EAS was lost due to the cloud / aerosol cover?

13. Common AM – Simulations tasks
Task 2: Implement the possibility of account of the atmospheric optical depth profiles in the ESAF simulation.
a) investigate inside ESAF what are the available options to insert cloud parameters: geometrical thickness,
optical depth, scattering ratio etc.
b) Make an interface to CALIPSO database, to feed realistic atmospheric conditions in ESAF.
G.Medina-Tanco, A.Guzman
R.Cremonini
First progress on simulations of EAS in real atmospheric scenes, using a stand-alone code (not within ESAF).

14. Common AM – Simulations tasks
Task 4: Implement lidar data analysis in the ESAF: simulation of laser backscatter signal, lidar trigger, analysis of the backscatter profile, derivation of the list of cloud/aerosol features and their parameters (top/bottom altitude, optical depth, backscatter-to-absorption ratio). Analyze the dependence of precision of measurement of tau on the laser characteristics.
L.Valore
First progress on implementation of the laser signal propagation / backscatter in the atmosphere within ESAF.

15. Common AM – Simulations tasks
Task 4. Investigate the precision of reconstruction of the cloud top altitude with the IR camera (both for stereo and radiative method). How could the IR camera information be taken into account in ESAF?
A.Anzalone, S.Briz
Clouds do not thermalize when their optical depth is τ<5. In this case the radiative method gives an error on the cloud top height which exceeds the required 500 m.
Stereo reconstruction method could provide the required precision of the cloud-top altitude determination for clouds with τ<5, provided that sufficiently long and sharp cloud boundary could be recognized in the images of the IR camera.

16. Common AM – Simulations tasks
Task 5. Investigate UV emission from clouds at nighttime with Tatyana, Meris, DMSP/OLS (Operational Linescan System) REIMEI(INDEX)/MAC data. What information could be obtained using the slow-mode data? How could it be taken into account in ESAF?
P.Bobik
Possibly a good task for the EUSO balloon: intentionally fly the balloon over the clouds in moonless night, to study the properties of UV emission from the clouds?

17. Summary 70% of UHECR events appear in cloudy sky conditions.
Simulations with EAS reconstruction with account of AM data in realistic meteorological conditions are needed to support the back-of-the-envelope calculations and give a realistic estimate of the instrument duty cycle, work out event selection criteria etc.
Possibility to account of realistic atmospheric conditions has to be implemented in ESAF.