Site Testing at Sierra Negra

1. Site Testing at Sierra Negra Esperanza Carrasco Licea Instituto Nacional de Astrofísica, Optica y Electrónica Tucson, June - 2002

2. Sierra Negra • Large Millimeter Telescope (LMT) site • Latitute: 18°59´ • Longitude: 97°18´W • 4600m above sea level • Low water vapour content: Median opacity at 225 GHz lower than 0.1 (dry season)

3. Large Millimeter Telescope • 50 m antenna to work between 0.8 - 3mm • Bi-national project: Mexico – USA • INAOE - University of Massachusettsat Amherst

4. 100 km from the Gulf of Mexico 300 km from the closest Pacific Coast

6. Site ownership • Sierra Negra is within Pico de Orizaba National Park (275 km² ) • INAOE owns 0.1 km² at the summit LMT office is working with the community to stablish a Management Plan (Plan de Manejo) for the National Park.

7. High mountains in the region Sierra Negra 4600 m Citlaltepetl 5740 m, 7.3 km (n-east) Popocatepetl* 5400 m, 140 km (west) Iztaccihuatl 5110 m, 141 km (west) La Malinche 4400 m, 80 km (west) Cofre de Perote 4200 m, 60 km (n-east) * Activity period started in December 1995. Ash.

8. Cofre de Perote La Malinche Sierra Negra & Citlaltepetl Popo & Izta

9. 100 km Mexico City Sierra Negra Puebla Orizaba Córdoba

10. Cities Inhabitants Altitude (m) Distance (km) Mexico City 200 17000000 2233 Puebla 94 1000000 2162 Orizaba 27 54000 1284 Córdoba 42 132000 924 Cd. Serdán 14 34000 2540 Source: INEGI. Instituto Nacional de Estadística, Geografía e Informática

11. Towns in the vicinity Atzitzintla: 2700 inhab. 2680 m altitude 9 km distance LMT office LMT Texmalaquilla: 1000 inhab. 3100m altitude 5.3 km distance Cd. Serdán Atzitzintla

12. 100 km motorway from Puebla City + 13 km of access road 2 hrs journey from INAOE´s headquarters

13. Summit view

14. Site Layout

15. 1st quart: 0.614” Median: 0.782” 3rd quart: 1.042” Minimum: 0.229” 83 nights Instrument: DIMM Seeing distribution (Vernin & Muñoz-Tuñón, 1995)

16. Seeing-daily

17. Global statistics Date Nn/Nh N Mean s Min q1 Median q3 Global 83/258.9 49567 0.897  0.443 0.229 0.614 0.783 1.042 Feb00 1/0.2 31 0.773 0.093 0.606 0.704 0.768 0.830 Mar00 2/2.7 227 0.541 0.077 0.397 0.488 0.531 0.586 Apr00 1/1.2 194 0.655 0.133 0.482 0.585 0.634 0.700 Oct00 2/2.3 399 1.022 0.349 0.454 0.737 0.949 1.257 Nov00 1/0.5 748 0.669 0.216 0.274 0.500 0.669 0.819 Dec00 7/16.7 2317 0.657 0.348 0.238 0.401 0.503 0.892 May01 2/1.5 302 0.887 0.204 0.552 0.722 0.854 1.021 Jun01 3/6 1178 0.910 0.468 0.466 0.749 0.848 0.965 Jul01 4/9.6 1926 0.736 0.374 0.229 0.488 0.670 0.870 Ago01 8/20.2 4451 1.587 0.602 0.476 1.169 1.487 1.891 Sep01 2/5 1015 0.797 0.307 0.404 0.586 0.686 0.870 Oct01 3/9.4 2009 0.811 0.258 0.376 0.616 0.789 0.962 Nov01 9/35.6 7363 0.826 0.312 0.290 0.622 0.777 0.960 Dec01 7/31 6391 0.834 0.326 0.343 0.613 0.754 0.962 Jan02 4/21.7 3621 0.797 0.345 0.332 0.587 0.693 0.855 Feb02 5/20.7 3706 0.847 0.411 0.272 0.595 0.741 0.970 Mar02 8/22.7 3807 0.945 0.493 0.293 0.643 0.808 1.147 Apr02 10/35.8 7004 0.796 0.290 0.274 0.591 0.748 0.927 May02 4/16.3 3202 0.972 0.447 0.347 0.675 0.834 1.100

18. Seeing seasonal variation Dry season: November - April; Wet season: May - October dry wet wet_ago01 1st quartile 0.567 0.694 0.634 Median 0.728 0.924 0.787 3rd quartile 0.941 1.341 0.996 Minimum 0.238 0.229 0.229

19. Cloud cover estimates From October 2001 to Apr 2002 • Photometric nights: 64% • Useful nights: 74% Comparable to Chajnantor: 80% useful time, (visual records, Giovanelli, 2001)

20. Opacity LMT project 225 GHz radiometers Global median < 0.2 Winter median < 0.1 http://www.lmtgtm.com Carrasco, L. et al. 2000

21. Meteorological data From October 2000 to May 2002 Data points: 240479 (522751 minutes, 69% coverage) • Temperature • Wind • Relative humidity • Pressure (64% coverage)

22. Temperature distribution • 1st quartile: -0.7 °C • Median: 0.9 ± 2.4 °C • 3rd quartile: 2.3° C

23. Temperature diurnal variation • day (°C) night all • 1st quartile 0.2 -1.2 -0.7 • Median 2.0 0.3 0.9 • 3rd quartile 3.4 1.4 2.3 Nigttime T at Mauna Kea: 2 ± 4 °C (ESPAS Report, 2002) day: 8:am - 6:pm, night: 8:pm - 6: am

24. Wind speed (m/s) • day night all • 1st quartile 2.22 2.69 2.69 • Median 4.03 4.47 4.03 • 3rd quartile 5.81 6.69 6.69 Nighttime median at Chajnantor: ~ 4 m/s (Giovanelli, 2001)

25. Wind speed distribution • Solid line: average speed • Dashed line: maximum speed 90% time, v < 10 m/s 80% time,vmax<10m/s

26. Wind speed maximum (m/s) • day night all • 1st quartile 4.47 3.58 4.03 • Median 6.25 5.81 6.25 • 3rd quartile 9.39 8.94 8.94 No. Points: 222168 (483048 minutes)

27. Wind direction

28. Wind direction & velocity

29. Search for seasonal variations

30. Search for seasonal variations

31. Relative Humidity (%) • day night all • 1st quartile 39 22 31 • Median 68 59 64 • Mean 63 56 59 • 3rd quartile 94 93 93 Average Relative Humidity at Mauna Kea: 48% (ESPAS Report, 2002)

32. Relative Humidity seasonal • dry (%) wet all 1st quartile 15 56 31 • Median 47 86 64 • Mean 46 75 59 • 3rd quartile: 78 98 93

33. Seasonal trend • Dry season: Nov - Apr: 80% time, RH < 80% (Nov-Jan, RH 14%) • Wet season: May - Oct: 45% time, RH < 80%

34. Snow • Time: 20% • Months: June-Agust • Heavy storms: Jan - March

35. Overview...

36. Conclusions • Seeing median is: 0.78 arc sec. • Median value between 0.72” (dry time) & 0.94” (wet time). • Weather: relatively benign conditions. • Sky brightness measurements programmed for October 2002. • Further Monitoring in progress.