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gatorcane wrote:Waters off Africa in the Indian Ocean are still relatively cool (top graphic) but look how they are starting to warm up (bottom graphic) when you look at the 5-day SST change. Maybe this will allow more waves and disturbances to generate over Africa?
Notice also SSTs across the Caribbean are still warming:
http://img823.imageshack.us/img823/5260/8m2.gif
TropicalAnalystwx13 wrote:Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.
'CaneFreak wrote:Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.TropicalAnalystwx13 wrote:Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.
'CaneFreak wrote:Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.TropicalAnalystwx13 wrote:Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.
TropicalAnalystwx13 wrote:Tropical waves form over East Africa as a result of instability created by the Sahara Desert and the Guinean Forest. The potency of the waves depend on the amount of instability, which depends on the difference in moisture and temperature between the two aforementioned locations. That's why a cool Gulf of Guinea is favorable as well...it creates a higher difference in temperature => higher instability. During a positive IOD, we get enhanced convection over the Indian Ocean. Rising air here means it's sinking over Africa. Sinking air over Africa => less waves => more dry air in the East Atlantic.
Ntxw wrote:TropicalAnalystwx13 wrote:Tropical waves form over East Africa as a result of instability created by the Sahara Desert and the Guinean Forest. The potency of the waves depend on the amount of instability, which depends on the difference in moisture and temperature between the two aforementioned locations. That's why a cool Gulf of Guinea is favorable as well...it creates a higher difference in temperature => higher instability. During a positive IOD, we get enhanced convection over the Indian Ocean. Rising air here means it's sinking over Africa. Sinking air over Africa => less waves => more dry air in the East Atlantic.
This is interesting. I wonder why it conflicts with the research that states there is a strong correlation between convection firing in the IO (MJO related phases 2-3) and significantly increasing Atlantic activity. The IO monsoon plays an important role in feeding the ITCZ through Africa thus increasing moisture downstream over the Atlantic (rise in Instability). Sinking air over Africa itself is better correlated with convection near the Maritimes and definitely the WPAC, I'm not familiar with the IOD though so I'm uncertain if it's a whole different ballgame but it just seems to conflict.
'CaneFreak wrote:Yes but don't you need tropical waves to go over warmer than normal waters in order for them to grow BEFORE going over the African continent? It sure seems that if they went over cooler than normal waters, they would be less potent tropical waves and they might die before they could even get to the AEJ. I think I know what you are saying in an overall sense though.TropicalAnalystwx13 wrote:Warming waters in the Indian Ocean are a bad sign. The Indian Ocean Dipole is currently negative, meaning cooler waters. This enhances the African monsoon and puts the atmosphere in a La Nina-like state. During a positive IOD, when the waters are warm, the monsoon is weakened. The upper-level axis of the subtropical ridge is shunted farther south than normal as well, creating a lid for convective activity => less vertical instability. This was the problem in 2007 and 2011.
TropicalAnalystwx13 wrote:The MJO still has a profound positive influence over Africa during octants 2/3. It's not really until 4-5 when it starts to become unfavorable.
There's a difference. When the MJO is in phases 2 and 3, you still have rising air over the African continent. When the IOD is positive (or just the Indian ocean is warm as a whole), you favor less convection over the African continent.Ntxw wrote:TropicalAnalystwx13 wrote:The MJO still has a profound positive influence over Africa during octants 2/3. It's not really until 4-5 when it starts to become unfavorable.
Correct, which is why in my post I stated Maritime Continent is when Africa starts getting dry (phases 4-5) not the Indian Ocean phases (2+3) conflicting with the idea of IO convection (rising air) creating subsidence in Africa that you mentioned in the previous post.
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