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