1. River proximity bias in Amazon rainfall data: a decade of observations near Santarém David Fitzjarrald, Ricardo Sakai, Osvaldo Moraes, Raimundo Cosme de Oliveira, Otávio Acevedo, Rodrigo da Silva, Matthew Czikowsky, and Troy Beldini Jungle Research Group & many other folks too…

2. Do the influences of river breezes or other mesoscale effects lead to a systematic river proximity bias in Amazon region climate data? (Emphasize rainfall data today.)

3. Leibman and Allured (BAMS 2005). Daily gridded data made from this station data base. How processed do you want your “data”?

4. Does it matter that the climate stations are all along the rivers?

5. Dry season average CMORPH rainfall top: day; bottom: night

6. Wet season average CMORPH rainfall top: day; bottom: night

7. Large land use change boundaries sharp, but ‘vegetation breeze’ is subordinate to the river breeze.

8. Average GOES low cloudiness May 2001 Known bias in clouds from the river breeze effect. Molion (≈1980’s) Detected breeze at Manaus back in 1985, 1987 (ABLE-2). Oliveira & Fitzjarrald (1990 ab); (LBA, CIRSAN, Santarem) Silva Dias et al. (2001) Lu et al. (2005) Confluence of the Amazon and Tapajós rivers. 15-20 km wide

9. Step 1: go out into the field

10. Original Belterra LBA station km117 station Installed July 1998 LBA-ECO weather stations

12. The Tapajós river breeze can overpower a weak easterly…

14. Wet season Max Mean Min Near river Inland

15. Dry season Max Mean Min Near river Inland

16. Now focus on precipitation near the rivers’ confluence

17. Molion and Dallarosa (1988)--river breeze suppresses rain at a, b, g, e, f ….

18. Measuring convective precipitation in the Amazon is still a challenge. Data sources: Conventional rain gauge network: daily totals, some stations with hourly data (Hidro, INMET) LBA-ECO special observations CMORPH remotely sensed rainfall (Joyce et al.) Passive microwave, ‘CMORPH uses IR only as a transport vehicle, i.e. IR data are NOT used to make estimates of rainfall when passive microwave data are not available.

21. Daily totals Monthly totals Belterra station as the intercomparison point: TB & conventional measurements Find the daily averaged rainfall and then scale up to months, seasons.

22. FLONA Tapajós wedge gauges--substantial overestimation relative to tipping buckets…

23. Need to know what kind of rainfall is occurring. Astronauts are useful! Which station is ‘representative’?

24. More extreme events very near the Amazon channel…

25. Gradients in mean total annual rainfall

26. Evaporation contrast deforested/forested depends on soil moisture to rooting depth --> natural ‘irrigation’ interval is important Forest/cleared area thermal contrast depends on interval…

27. Gridded rainfall data looks like that seen along the river, but there is less rainfall inland--where is the ‘breeze suppression’?

28. Strong gradients in the interval between rainfall events “Natural irrigation”

29. 00-03 UTC 06-09 UTC 12-15 UTC 18-21 UTC (From Kousky et al. 2006, CMORPH analyses) Influence of large scale ‘instability lines’ on precipitation at STM provides a nocturnal rainfall maximum… Time of ‘maximum precipitation rate’

30. convectivesynoptic Rain Dial (UT) Afternoon precipitation: local convective activity Nocturnal rainfall: instability line rainfall

33. CMORPH wet season averages. Gross pattern observed, but ….

34. Conclusions Near-river stations do indeed miss the afternoon convective rain as would be expected if a river breeze influence dominates. This deficiency is more than compensated by additional nocturnal rainfall. This effect is local; for areas only a few kilometers inland from the rivers, nocturnal squall lines contribute less than half of total precipitation. Breeze circulations associated with the Amazon River (with a wind component approximately normal to the mean flow) affect rainfall more than does the Tapajós breeze (which approximately opposes the prevailing wind). Describing the proper mixture of types of precipitation should be a concern for those assessing model sensitivity, especially since the reanalysis rainfall data are currently flawed

35. Continuing work: rain producing events Are mesoscale circulations, perhaps related to the large lake- like expanse of water at the confluence responsible for the nocturnal precipitation preference? As squall lines approach this region, does enhanced moist inflow augmented by southerly channeling up the Tapajós channel water vapor into the storm as it approaches? Are larger rainfall totals west of the confluence the result of convergence promoted by air following the narrowing channel? This issue can be addressed using mesoscale modeling case studies of well-documented individual squall line passages. Júlia Cohen (next presentation) shows the first such results.