can someone explain the difference..........................

[weatherwindow]

between the monsoon troughs of the pacific and the ICTZ in the atlantic and what, if any, difference in their functions in tropical cyclogenesis....thanks in advance

[MWatkins]

between the monsoon troughs of the pacific and the ICTZ in the atlantic and what, if any, difference in their functions in tropical cyclogenesis....thanks in advance

I believe the equatorial trough, the ITCZ and monsoon trough are all different words for the same thing...the trough does take on different characteristics from basin to basin but I don't believe that's your question.

MW

[Derek Ortt]

ITCZ is more convergence driven while the monsoon is much more complicated than simple convergence. Monsoon starts with a surface heat flux, and due to the idea gas law, the warmer air expands upward, causing the pressure gradient to increase with height, which due to the hydrostatic equation, causes vertical motion. The SLP is lowered by the upper high, which is caused by the upward transport of heat (this is all accelerated once latest heat is released from precip). The uppwer high and relative lows aaway from the UH, causes UL divergence, which takes air mass form the atmospheric column, causing SLP to fall. This is the basic principles, but of course, it is much mroe complicated than this

[Aslkahuna]

No, the ITCZ and the Monsoon Trough are NOT the same entity. The ITCZ is the convergence zone between the opposing Trade wind regimes of the Northern and Southern Hemisphere thus has SE winds on one side and NE winds on the other side. The ITCZ does not wander as far poleward in the Summer Hemisphere as the Monsoon trough does which in Asia can move upwards of 30 degrees poleward of the equator in the Summer. The Monsoon trough is a distinct trough of low pressure with discrete centers of circulation with the Summer Hemisphere Trades on the poleward side and Monsoonal westerlies on the equatorward side. In all cases, the monsoonal flow originates in the Winter Hemisphere and crosses the equator as a westerly flow (as opposed to an easterly flow with the ITCZ.
Because of the presence of cyclonic horizontal shear and the vorticity it generates and the discrete centers of circulation, Tropical Cyclone development tends to occur more frequently and easier within a monsoon trough. In the case of the ITCZ, we need to impose a preexisting disturbance upon it to develop a storm. The Primary Monsoon Troughs are found during the Northern Summer extending from an area SE of Guam NW into China across the areas north of India into Africa and then a short distance off the West Coast of Africa near the Cape Verde Islands.
The EPAC Monsoon Trough extends from well west of Central America into Mexico with an extension late in the monsoon into the western Caribbean. The Southern Monsoon trough extends from Africa across northen Australia into the SWPAC. The Asian trough moves over land in regions north of the Bay of Bengal and the Arabian Sea during the Summer-consequently this is the reason why there are no storms that form there during July and August. Because of the horizontal shear within the monsoon trough, storms can form at lower latitudes when they form
within them which is why we often see storm formation below 10 degrees latitude (N/S) and even 4-5 degrees latitude (N/S) including that renowned storm Vamei which was a typhoon at 1.5N.

Steve

[MWatkins]

No, the ITCZ and the Monsoon Trough are NOT the same entity. The ITCZ is the convergence zone between the opposing Trade wind regimes of the Northern and Southern Hemisphere thus has SE winds on one side and NE winds on the other side. The ITCZ does not wander as far poleward in the Summer Hemisphere as the Monsoon trough does which in Asia can move upwards of 30 degrees poleward of the equator in the Summer. The Monsoon trough is a distinct trough of low pressure with discrete centers of circulation with the Summer Hemisphere Trades on the poleward side and Monsoonal westerlies on the equatorward side. In all cases, the monsoonal flow originates in the Winter Hemisphere and crosses the equator as a westerly flow (as opposed to an easterly flow with the ITCZ.
Because of the presence of cyclonic horizontal shear and the vorticity it generates and the discrete centers of circulation, Tropical Cyclone development tends to occur more frequently and easier within a monsoon trough. In the case of the ITCZ, we need to impose a preexisting disturbance upon it to develop a storm. The Primary Monsoon Troughs are found during the Northern Summer extending from an area SE of Guam NW into China across the areas north of India into Africa and then a short distance off the West Coast of Africa near the Cape Verde Islands.
The EPAC Monsoon Trough extends from well west of Central America into Mexico with an extension late in the monsoon into the western Caribbean. The Southern Monsoon trough extends from Africa across northen Australia into the SWPAC. The Asian trough moves over land in regions north of the Bay of Bengal and the Arabian Sea during the Summer-consequently this is the reason why there are no storms that form there during July and August. Because of the horizontal shear within the monsoon trough, storms can form at lower latitudes when they form
within them which is why we often see storm formation below 10 degrees latitude (N/S) and even 4-5 degrees latitude (N/S) including that renowned storm Vamei which was a typhoon at 1.5N.

Steve

Excellent explaination...thanks...I should have looked that one up

MW

[MWatkins]

Actually...I think I have to revert back to my first answer and clairify some...I looked up the definition...at least in the AMS glossary...and found that my initial idea is not as far off as I thought:

equatorial trough—1. The quasi-continuous belt of low pressure lying between the subtropical high pressure belts of the Northern and Southern Hemispheres.
This entire region is one of very homogeneous air, probably the most ideally barotropic region of the atmosphere. Yet humidity is so high that slight variations in stability cause major variations in weather. The position of the equatorial trough is fairly constant in the eastern portions of the Atlantic and Pacific, but it varies greatly with season in the western portions of those oceans and in southern Asia and the Indian Ocean. It moves into or toward the summer hemisphere. It has been suggested that this name be adopted as the one general term for this region of the atmosphere. Thus, the equatorial trough would be said to contain regions of doldrums; portions of it could be described as intertropical convergence zones; and within it there might be detected intertropical fronts. However, one weakness of this nomenclature is that it alludes specifically and only to the existence of a trough of low pressure. Perhaps an even more general term might be preferable, for example, atmospheric equator. 2. Same as meteorological equator.
Riehl, H., 1954: Tropical Meteorology, p. 238.
Berry, F. A., E. Bollay and N. R. Beers, Eds., 1945: Handbook of Meteorology, 776–777.

So the ITCZ could be used to describe a portion of the belt of trade winds surrounding the earth...which covers the part about the ITCZ and the equatorial trough (an ITCZ is a subset of the ET)...but Aslkahuna's explaination shows the distinct difference between these and the monsoonal torugh...although I am 100% positive that the ITCZ is sometimes (and apparetly incorrectly) referred to as the monsoonal trough by meteorologists from time to time.

MW

[weatherwindow]

thanks steve, mw et al.....only one more question, why dont monsoon troughs form in the atlantic rather than the ICTZ and, conversely, is does the ICTZ exist in the pacific?....insatiable curiosity.

[cycloneye]

thanks steve, mw et al.....only one more question, why dont monsoon troughs form in the atlantic rather than the ICTZ and, conversely, is does the ICTZ exist in the pacific?....insatiable curiosity.

Yes ITCZ exists in pacific and is the same as in the atlantic.

...ITCZ...

ITCZ AXIS ALONG 5N77W 7N101W 6N115W 9N129W 10N140W. SCATTERED
MODERATE TO STRONG WITHIN 60 NM EITHER SIDE OF AXIS FROM 103W TO
107W AND ALSO FROM 111W TO 114W. SCATTERED MODERATE WITHIN 90 NM
OF AXIS FROM 79W TO 81W. SCATTERED MODERATE FROM 97W TO 99W
WITHIN 60 NM EITHER SIDE OF AXIS.

[Stormsfury]

So the ITCZ could be used to describe a portion of the belt of trade winds surrounding the earth...which covers the part about the ITCZ and the equatorial trough (an ITCZ is a subset of the ET)...but Aslkahuna's explaination shows the distinct difference between these and the monsoonal torugh...although I am 100% positive that the ITCZ is sometimes (and apparently incorrectly) referred to as the monsoonal trough by meteorologists from time to time.

MW

Yes .. it's all too common ... I see the misuse of it all the time around here in Charleston.

[Aslkahuna]

The term ITCZ has also been incorrectly applied to the monsoon trough as well. There is a defined ITCZ in the Pacific as well mainly in the eastern sections when the EPAC Monsoon Trough is not present (like now). Unlike the western sections of the Pacific and extending across the Indian Ocean, there is NO Monsoon Trough in SEPAC. It has to do with the absence of a monsoon in that area which relates directly to the fact that unlike the Northern Hemisphere, The two Continents of South America and Africa narrow with increasing latitude rather than become wider while Australia is totally in the Tropical and Subtropical latitudes for the most part.

Steve

[weatherwindow]

referring to my earlier question, does a monsoon trough, in the true sense of the word, exist in the atlantic and if so where and when....thanks again, rich

[Derek Ortt]

in the east atlantic, near the cape verde islands