Dr. Eddy GrahamUHI Research Conference Presentation
Thursday 8 November 2012
SASKA: Search for an Astronomical Site in Kenya
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Why study Astronomy?
1. Aesthetic beauty!
2. Unanswered questions
about “dark matter”
(83% of universe) and
“dark energy” (73% of
mass-energy universe)
3. “Are we alone?” .. Last
count on exoplanet.eu =
843
4. Humans want to “explore
and extend beyond…”
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Why Astronomy, Weather and Climate?
• Clear skies (not even partial
cloudiness)
• Little atmospheric water vapour
• Minimal turbulence…
• Other variables: Gentle and consistent
winds; few aerosols / dust; no extreme
weather (snow, hail, lightning, etc..); low
night-time relative humidity; low seismic
risk; nearness to infrastructure.
Weather and climate are vital for successful
astronomical observations:
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Twinkling stars and refraction of light
Parallel wave front of
stellar image gets
distorted by
atmosphereAtmosphere
Space
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Where is Kenya?
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Kenya: Topography
metres
R I F
T V
A L
L E
Y
Semi-Arid / Desert
More Humid Mt. Kenya
Mt. Kilimanjaro
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Kenya: Identification of candidate sitesMount Kulal (2293m)
Warges (2688m)
Mount Kenya (~4400m)
Google Earth followed by site visits
Data Provenance:
ECMWF ERA-interim 1979-2012 “reanalysis”• 0.5 deg lat/lon resolution (~50km), ~ 50 levels• 24 years of data, 6-hourly temporal resolution• Easy to use, small file sizes (kb to mb)
United Kingdom Met Office Africa Limited Area Model (“Africa-LAM”) output• Very high 12km resolution, 70 levels, night-time hourly
resolution• run daily in real-time- archive 2010-2012- large file sizes (2 GB per day!)
Analyses and Results: Cloud cover & variability
(Integrated)
Analyses and Results: Integrated water vapour
Vertical velocity and height of turbulent layers
-> need to go as high as possible -> surface turbulent layer is deep (2,500 to 3,000m, or more)
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Interim decision soon, South Africa (Dec 2012):
Mount Kulal (2293m)
Warges (2688m)
Mount Kenya (~4400m)
Monitoring
conditions for two
years.
~2017: begin
construction of 1.5
to 2-metre telescope
Not quite ESO Paranal (Chile)…
But a worthy project nonetheless: - Will provide a much-needed economic boost to Kenyan economy - Provide a dedicated research and training facility for African physics and astronomy students at home
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Thank you to sponsors!
Spiral Galaxy, NGC 1232 21 Sep 1998, VLT Paranal (ESO)
Hurricane Epsilon, 3 Dec 2005, NASA
But 1017 times difference in scale!!
Appendix 1: Seismic Risk
Appendix 2: TOMS 20-year aerosol index
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Appendix 3: What are “Reanalyses” ?
Reanalysis
Re-analyses are reconstructed weather analyses (maps) for the
past (~1950s onwards) using all available weather data for the
past, but using a fixed numerical meteorological model of
today (avoids inhomogenities)
ERA40 mid-to-upper tropospheric (775 to 200 hPa) vertical velocities in range 2.5 < > 5.0 cm /sec (i.e. gently subsiding air, turbulence less likely)
H H
H H
H H
H H
Appendix 4: Vertical velocities
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Appendix 5: Prevailing windspeeds
Appendix 6: Global mean annual IWV
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Kenya: Identification of candidate sitesMount Kulal (2293m)
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Kenya: Identification of candidate sites
OlDonyoNyiro (2752m)
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Kenya: Identification of candidate sites
Mount Kenya (~4400m)
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Identification of candidate sites
OlDonyoLenkiyo (2550m)
Mount Kenya (~4400m)
Loita Hills (2642m)
ERA: cloud cover data and variability
Mt_Kulal
OlDonyoNyiro
Mt_Marsabit
Kapcholio Ndoto
Warges Loita_Hills Mtelo
CC 160.90 168.82 180.02 461.55 182.58 171.27 365.34 421.25St.dev 110.42 110.97 120.81
1212.98 119.83 112.66 164.57 170.18
Mt_Furroli
OlDonyoLenkyo Sololo
Mt_Kenya
Cherangany
3350m_ODY
CC 331.08 174.53 244.34 141.10 237.18 145.41St.dev 171.02 114.47 139.18 93.94 138.29 96.08More or less same results with UK Met Office African-LAM
Analyses and Results: Cloud cover & variability
Analyses and Results: Integrated water vapour (IWV)
IWV is extremely height dependent
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