# Presentation: 704121

## Cross Equatorial Systems Northern and Southern Hemisphere Intrusions

- Mike Davison
- HPC International Desks

## Slide 2

**Notes:**
Tropical meteorologist, in addition to having to deal with tropical waves and cyclones, also have to deal with the upper level systems and how they interact with low level features.

## Characteristics of Northern Hemisphere Ridges and Troughs

- Ridge
- Warm Core
- Anticyclonic (negative/clockwise) relative vorticity increases with height
- High tropopause heights

- Trough
- Cold Core
- Cyclonic (Positive/
-     counterclockwise) relative vorticity increases with height
- Low tropopause heights

## Northern Hemisphere Upper Ridge/Trough Pattern

**Notes:**
This figure highlights the clockwise rotation in the ridge, and the counterclockwise rotation in the trough.  Areas of upper divergence are normally found on the backside of a ridge, and on the forward side of a trough, while upper convergence is normally found on the backside of a trough and on the forward side of a ridge.  However, this is a subjective representation of where the maximum areas of divergence/convergence are located.  Depending on the vertical structure of the ridge/trough, the best divergence or convergence could be closer to the axis.

## Northern Hemisphere RidgeWinds and Temperature

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots and isotherms in degrees C at an interval of three degrees.  The chart shows a high amplitude tropospheric ridge with mean axis between 85W/87W.  The image shows the warm core characteristics of the ridge, with temperature increasing horizontally towards the ridge axis.

## Northern Hemisphere RidgeWinds and Potential Temperature

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots and isotherms of potential temperature in degrees K at an interval of three degrees.  The chart shows a high amplitude tropospheric ridge with mean axis between 85W/87W.  The image shows the warm core characteristics of the ridge, with temperature increasing horizontally towards the ridge axis.

## Northern Hemisphere RidgeWinds and Relative Vorticity

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots, anticyclonic relative vorticity contoured blue and the cyclonic relative vorticity contoured red. The chart shows a high amplitude tropospheric ridge with mean axis between 85W/87W.  As characteristic of a warm core/tropospheric ridge, the anticyclonic vorticity is increasing with height. 

## Northern Hemisphere TroughWinds and Temperature

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots and isotherms in degrees C at an interval of three degrees.  The chart shows a high amplitude tropospheric trough with mean axis between 106W/108W.  The image shows the cold core characteristics of the trough, with temperature decreasing horizontally towards the trough axis.

## Northern Hemisphere TroughWinds and Potential Temperature

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots and isotherms of potential temperature in degrees K at an interval of three degrees.  The chart shows a high amplitude tropospheric trough with mean axis between 106W/108W.  The image shows the cold core characteristics of the trough, with temperature decreasing horizontally towards the trough axis.

## Northern Hemisphere TroughWinds and Relative Vorticity

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots, anticyclonic relative vorticity contoured blue and the cyclonic relative vorticity contoured red. The chart shows a high amplitude tropospheric trough with mean axis between 106W/108W.  As characteristic of a cold core/tropospheric trough, the cyclonic vorticity is increasing with height.

## Characteristics of Southern Hemisphere Ridges and Troughs

- Ridge
- Warm Core
- Anticyclonic (Positive/
-     counterclockwise) relative vorticity increases with height
- High tropopause heights

- Trough
- Cold Core
- Cyclonic (negative/clockwise) relative vorticity increases with height
- Low tropopause heights

## Southern Hemisphere Upper Trough/Ridge Pattern

**Notes:**
This figure highlights the counterclockwise rotation in the ridge, and the clockwise rotation in the trough. Areas of upper divergence are normally found on the backside of a ridge, and on the forward side of a trough, while upper convergence is normally found on the backside of a trough and on the forward side of a ridge. However, this is a subjective representation of where the maximum areas of divergence/convergence are located.  Depending on the vertical structure of the ridge/trough, the best divergence or convergence could be closer to the axis.

## Southern Hemisphere RidgeWinds and Temperature

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots and isotherms in degrees C at an interval of three degrees.  The chart shows a high amplitude tropospheric ridge with mean axis between 92W/95W.  The image shows the warm core characteristics of the ridge, with temperature increasing horizontally towards the ridge axis.

## Southern Hemisphere RidgeWinds and Potential Temperature

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots and isotherms of potential temperature in degrees K at an interval of three degrees.  The chart shows a high amplitude tropospheric ridge with mean axis between 92W/95W.  The image shows the warm core characteristics of the ridge, with temperature increasing horizontally towards the ridge axis.

## Southern Hemisphere RidgeWinds and Relative Vorticity

**Notes:**
The chart is a vertical cross section of a ridge, with wind barbs in knots, anticyclonic relative vorticity contoured blue and the cyclonic relative vorticity contoured red. The chart shows a high amplitude tropospheric ridge with mean axis between 92W/95W.  As characteristic of a warm core/tropospheric ridge, the anticyclonic vorticity is increasing with height. 

## Southern Hemisphere TroughWinds and Temperature

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots and isotherms in degrees C at an interval of three degrees.  The chart shows a high amplitude tropospheric trough with mean axis along 75W.  The image shows the cold core characteristics of the trough, with temperature decreasing horizontally towards the trough axis.

## Southern Hemisphere TroughWinds and Potential Temperature

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots and isotherms of potential temperature in degrees K at an interval of three degrees.  The chart shows a high amplitude tropospheric trough with mean axis along 75W.  The image shows the cold core characteristics of the trough, with temperature decreasing towards the center of the axis.

## Southern Hemisphere TroughWinds and Relative Vorticity

**Notes:**
The chart is a vertical cross section of a trough, with wind barbs in knots, anticyclonic relative vorticity contoured blue and the cyclonic relative vorticity contoured red. The chart shows a high amplitude tropospheric trough with mean axis between 72W/80W.  As characteristic of a cold core/tropospheric trough, the cyclonic vorticity is increasing with height. 

## What Happens When a Southern Hemisphere System Crosses the Equator?

**Northern Hemisphere**
**Southern Hemisphere**

## Does it behaves like a Nrn Hemisphere Ridge or a Srn Hemisphere Trough?

## Case Study

- 31 Oct 2001

## Evaluation of Upper Circulation over the Tropical Atlantic

**Notes:**
This is a plot of the 200 hPa winds, shown in barbs/knots.  Let’s concentrate on the circulation east of South America, and between the equator and 10N, with mean axis along 43W.  First impressions suggests that this is an anticyclonic circulation.

## Vertical Cross Section of Temperature (C) and Winds

**Notes:**
A vertical cross section along 05N is shown, depicting the winds and isotherms in degrees C at an interval of 3 degrees.  A circulation is evident aloft above 500 hPa, and along 40W/43W.  Evaluation of the horizontal temperature gradient shows minor fluctuations in temperatures towards the center of the circulation.

## Vertical Cross Section of Relative Vorticity and Winds

**Notes:**
A vertical cross section along 05N is shown, depicting the winds, negative relative vorticity contoured in red and positive relative vorticity contoured in blue.  The negative vorticity is increasing with height along the axis of circulation between 400-200 hPa.

## Vertical Cross Section of Potential Temperature (K), Winds, and Relative Vorticity

**Notes:**
A vertical cross section along 05N is shown, depicting the winds, negative relative vorticity contoured in red and positive relative vorticity contoured in blue, and isotherms of potential temperature in degrees K contoured in cyan at an interval of 2 degrees..  The negative vorticity is increasing with height along the axis of circulation between 400-200 hPa.  This is the same area where the isotherms of potential temperature suggest that the circulation might have cold core characteristics.  Thus in this case, the negative vorticity along the circulation axis might correlate with cyclonic vorticity rather than anticyclonic vorticity as one might expect from a northern hemisphere system.

## Vertical Cross Section of  Potential Temperature (K) and Winds

**Notes:**
A vertical cross section along 05N is shown, depicting the winds and isotherms of potential temperature in degrees K at an interval of 2 degrees.  A circulation is evident aloft above 500 hPa, and along 40W/43W.  Evaluation of the horizontal temperature gradient shows a gradual decrease in temperature towards the axis of the circulation as we near 42W/43W.  This suggests that the circulation has cold core characteristics. 

## 250 hPa Winds and DivergenceObjective Analysis

**Notes:**
This is an objective analysis of upper level divergence and convergence.  This figure shows the 250 hPa winds and areas of upper divergence (yellow contours) and convergence (magenta contours).  Note the areas of upper divergence along and east of the northern hemisphere trough as it extends to Suriname and French Guiana.  The southern hemisphere trough, clockwise rotation along 43W, also shows an area of divergence to the east of the axis, as expected/suggested by the subjective analysis.

## 250 hPa Winds

**Notes:**
The 250 hPa winds, centered farther south, clearly show the clockwise circulation as it extends across the equator from northeastern Brasil.  The trough axis was analyzed in the magenta dashed lines.

## 250 hPa Winds and DivergenceObjective Analysis

**Notes:**
This is an objective analysis of upper level divergence and convergence.  This figure shows the 250 hPa winds and areas of upper divergence (yellow contours) and convergence (magenta contours).  Note the areas of upper divergence along and east of the northern hemisphere trough as it extends to Suriname and French Guiana.  The southern hemisphere trough, clockwise rotation along 43W that originates on northeastern Brasil, also shows an area of divergence to the east of the axis, as expected/suggested by the subjective analysis.

## Verification

## IR Loop

**Notes:**
The IR loop confirms the objective analysis, with positive interaction of the northern/ southern hemisphere troughs with the ITCZ over the Atlantic and the Equatorial 
Trough over northern South America.

## WV Loop

**Notes:**
The water vapor imagery clearly shows the cross equatorial clockwise rotation originating over northeastern Brasil, and its positive interaction with the ITCZ over the Tropical Atlantic.