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Where on Earth...? MISR Mystery Quizzes
Where on Earth...? MISR Mystery Image Quiz #21
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(See quiz questions or a list of previous quizzes.)

Where on Earth...? MISR Mystery Image Quiz #21

Here's another chance to play geographical detective! This mystery concerns a particular type of cloud, one example of which was imaged by the Multi-angle Imaging SpectroRadiometer (MISR) in November, 2001. Usually, clouds take their names - cirrus, cumulus, and stratus - from Latin terms that describe the way they appear to someone standing on the ground. But clouds look very different when viewed from space, because satellites can detect, much more easily than a single observer on the ground, "cells" of cloudiness that form on scales ranging from tens to hundreds of kilometers. This image covers an area of 380 kilometers x 325 kilometers over the eastern tropical Pacific. Use any reference material you like and answer the following seven questions about the type of cloud shown in the image. The letters in parentheses associated with the correct answers, when put together, will spell out a relevant word. Submit this seven-letter word as your quiz solution.


These cloud features are referred to as "actinoform" (sometimes spelled "actiniform"), and they derive their name from their appearance. Actinoform clouds are marine convective clouds having a radial pattern or structure. The base "actino-" comes from the Greek word for "ray". Such features are referred to as "actinoform patterns" or "radial groups", and the radial arms possessed by such clouds are called "actinae".

Note: Playing with the letters and looking for real words, at least three 7-letter words can be formed. For example, if you came up with TYPHOON or FUNNELS, you would still have to examine the picture carefully. Without an eye, or the strong convective bands associated with inflow and outflow regions, these clouds do not recall typhoons or cyclones. Nor do these clouds look like the thick cumulus (lumpy) thunderstorm clouds associated with funnels and tornadoes (vortices of water and air spinning at high velocities). Although the statements whose corresponding letters create the words TYPHOON and FUNNELS are correct for those cloud types, typhoon and funnel clouds do not correspond with what appears in this picture.

1. Two of these statements are false. Which one is true?
(A) The individual convective cells that collectively make up this cloud structure are quite shallow, with heights generally less than 2 km.
(T) These cloud systems only occur when the ocean temperature is above 80 degrees F (26.5 degrees C).
(F) These clouds are usually associated with violent storm systems.

Answer: A is True. These clouds are associated with cellular (or shallow) convection, and are restricted to the bottom 2 km of the atmosphere.

2. Two of these statements are false. Which one is true?
(U) These clouds are often detected using ground-based radar.
(C) This type of cloud was first imaged from space in the early 1960's, soon after the launch of the TIROS V satellite.
(Y) These clouds are commonly tracked using propeller-driven research aircraft.

Answer: C is True. The weather satellite, TIROS V, was the first to image these clouds. The first example image was published in January 1963, in the Monthly Weather Review, Picture of the Month Series.

3. Two of these statements are false. Which one is true?
(N) These clouds persist only for a short time when severe weather is occurring.
(P) Clouds of this type occasionally produce heavy precipitation.
(T) The organization of these clouds resembles Rayleigh-Bénard convection.

Answer: T is True. The cloud organization (with clouds forming where air has risen, and clearing where the air descends) does indeed resemble Rayleigh-BĂ©nard convection, which is easily produced in the laboratory by heating a shallow layer of fluid from below and cooling it from above.

4. Two of these statements are false. Which one is true?
(H) When these clouds make landfall, they often spawn tornadoes.
(I) These clouds are often observed to form off the western coasts of continents.
(N) These clouds form when the atmospheric pressure drops very rapidly, causing condensation.

Answer: I is True. Actinoform clouds have been most commonly observed over the Pacific Ocean to the west of South America, and have also been found over the oceans to the west of Africa and Australia, in areas associated with extensive low cloud.

5. Two of these statements are false. Which one is true?
(N) These clouds were originally thought to be a transitional form between open and closed cells.
(E) This type of cloud system plays a major role in the 1939 movie adaptation of a book published in 1900.
(O) Cloud systems of this type are often given names contributed by Asian-Pacific countries.

Answer: N is True. Although the verdict is still out on exactly how open and closed cell patterns develop, and why one type of pattern develops versus the other, actinoform clouds can no longer be classed as a transitional form between open and closed cells.

6. Two of these statements are false. Which one is true?
(L) Hail often occurs when these clouds are seen.
(A) Cloud systems like these are associated with cold ocean currents.
(O) These cloud systems rarely form near the equator.

Answer: A is True. The cellular patterns associated with actinae generally occur over cool ocean currents, although it has been suggested that they can also can occur over warm currents.

7. Two of these statements are false. Which one is true?
(N) The Coriolis force strongly influences the morphology of these cloud patterns.
(E) The name describing these cloud forms is also used in conjunction with certain sea creatures.
(S) The vorticity associated with such clouds can be very dangerous, and when they are seen, you should take cover.

Answer: E is True. The word "actinae" refers to radial symmetry. Radial symmetry is present in animals such as starfish, sea urchins, and sea anemones.

190 people from all over the world sent in responses before the deadline. Individuals who answered all seven questions correctly are listed below in the order in which responses were received. The prize winners are indicated by an asterisk.

  1. John Parenteau, Littleton, CO, USA*
  2. Orion Lyau, Albany, Canada*
  3. Matthew Ciampa, Fuquay-Varina, NC, USA*
  4. Steve Kluge, North Salem, NY, USA
  5. Michael J. Smith, Newark, DE, USA
  6. Gustavo Torres, Caracas, Venezuela
  7. Tim Ehlenbeck, York, PA, USA
  8. Evan Ratner, Palm Harbor, FL, USA
  9. Yu Wei, Xiamen, China
10. Alexander Tsiprianovich, Tuapse, Russia
11. Neki Frasheri, Tirana, Albania
12. Monika Draga, Bad Kissingen, Germany
13. Joy Turlo, Redondo Beach, CA, USA
14. C. Dougherty, Denver, CO, USA
15. Ivan P. Anderson, Kent, England
16. Pam Mitchel, Gardiner, ME, USA
17. Alex Reinecke, Seattle WA, USA
18. Julian Charles Brimelow, Edmonton, Alberta, Canada
19. Rosy Hunt, York, UK
20. Sean Hattersley, Wolverhampton, UK
21. LHC, Hampton, VA, USA
22. Debbie Gill-Fox, Christchurch, New Zealand
23.Chandra Bales, Albuquerque, NM, USA
24. Doug Jackson, Arlington, VA, USA
25. BB, Reston, VA, USA
26. Geoff Kempter, Sellersville, PA, USA
27. Dave Evans, Glendale, CA, USA
28. Louise Williams, Anchorage, AK, USA
29. R.A. Bileti, Kampala, Uganda
30. Heim, Zurich, Switzerland
31. B. Kabat, La Crosse, WI, USA
32. JMc, Great Falls, MN, USA
33. Fred Igo, Cambridge, MA, USA

MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.

Credit: Image credit: NASA/GSFC/LaRC/JPL, MISR Team.
Text acknowledgment: Mike Garay (Jet Propulsion Laboratory), Clare Averill (Raytheon ITSS/ Jet Propulsion Laboratory) and David Diner (Jet Propulsion Laboratory).