Period: September-November; 1 degree fieldsPeriod: September-November; 1 degree fields

Collaborators: Joe Terry, Juan Carlos Collaborators: Joe Terry, Juan Carlos JusemJusem

Preliminary synoptic-dynamic evaluation Preliminary synoptic-dynamic evaluation of the ECMWF Nature Run: the African of the ECMWF Nature Run: the African

Monsoon region and the tropical AtlanticMonsoon region and the tropical Atlantic

Part IIPart II

Oreste RealeOreste Reale

Searching for realistic tropical weather Searching for realistic tropical weather systems in the Tropical Atlantic region systems in the Tropical Atlantic region

• Statistical properties of midlatitude cyclone activity Statistical properties of midlatitude cyclone activity have been proved very satisfactory (Joe Terry)have been proved very satisfactory (Joe Terry)

• Precipitation in the tropics is still far from being Precipitation in the tropics is still far from being realistic (Jusem) which is somewhat to be expected realistic (Jusem) which is somewhat to be expected from a global model, but does represent an from a global model, but does represent an improvement with respect to previous Nature Runsimprovement with respect to previous Nature Runs

• In this presentation we are trying to understand if In this presentation we are trying to understand if fundamental dynamical fundamental dynamical features features associated to the associated to the climate-weather interface generally present in the climate-weather interface generally present in the tropical atmosphere, are reproduced in the Nature Run. tropical atmosphere, are reproduced in the Nature Run. Focus is the AMMA region and the tropical AtlanticFocus is the AMMA region and the tropical Atlantic

• Until few years ago, to search for evidence of Until few years ago, to search for evidence of tropical tropical weather weather in a global model was quite pointless and only in a global model was quite pointless and only large-scale, diluted large-scale features could be large-scale, diluted large-scale features could be detecteddetected

The African Easterly Jet (AEJ) in The African Easterly Jet (AEJ) in SeptemberSeptember

• Improved AEJ depition with Improved AEJ depition with respect to July and August: the respect to July and August: the AEJ appears at the `perfect’ AEJ appears at the `perfect’ climatological elevation climatological elevation (650hPa) but is still slightly (650hPa) but is still slightly more to the north with respect more to the north with respect to climatology and analyses, to climatology and analyses, as pointed out for the as pointed out for the operational model (e.g. operational model (e.g. Tompkins et al., 2005). Tompkins et al., 2005).

• Intensity (11m/s) compares Intensity (11m/s) compares well with observed climatology well with observed climatology (e.g Burpee 1972 and (e.g Burpee 1972 and operational analyses for the operational analyses for the period)period)

• Realistic clear separation Realistic clear separation between AEJ and low-level between AEJ and low-level Harmatthan flow at 20EHarmatthan flow at 20E

• Weaker than climatology low-Weaker than climatology low-level westerly monsoonal flowlevel westerly monsoonal flow

• Reduced vertical easterly shear Reduced vertical easterly shear due to reduction of the TEJ at due to reduction of the TEJ at 150 hPa with respect to Jul-Aug150 hPa with respect to Jul-Aug

• Strong horizontal cyclonic Strong horizontal cyclonic shear on the southern flank of shear on the southern flank of the AEJ, leads to condition the AEJ, leads to condition much more favorable to much more favorable to tropical developmenttropical development

The AEJ in OctoberThe AEJ in October

• October shows a October shows a realistic receding of realistic receding of the African monsoonthe African monsoon

• A realistic weakening A realistic weakening of the AEJ, but also of of the AEJ, but also of the easterly vertical the easterly vertical shear is evidentshear is evident

• Tropical Easterly Jet at Tropical Easterly Jet at 200-150 hPa follows 200-150 hPa follows climatology, reducing climatology, reducing vertical shear and vertical shear and allowing several AEWs allowing several AEWs to become vortices in to become vortices in spite of reduced spite of reduced horizontal shear in the horizontal shear in the southern flank of the southern flank of the AEJAEJ

AEJ (cont.)AEJ (cont.)

The AEJ has a perfectly realistic maximum of 11 m/s at 600 hPa in September and gradually weakens in October following climatology.

African Easterly Waves (AEWs)African Easterly Waves (AEWs)

AEWs in Sep/Oct show again a realistic propagation speed of about 5-9 deg/dayMoreover, unlike July and August, there is a period of about six weeks in which the majority of waves present signs of development. This is similar to what happensin very active seasons. The disappearance from the Hovm relates to changes in latitude.

AEWs (continue)AEWs (continue)

The appearance of pulses of westerly flow in the Hovm is an evident sign of closed circulations and increasing latitudes (only the southern part of the circulation remains in thelatitude band). Strong development of some systems in late September and October can be seen.

700hPa u,v wind

The Tropical Easterly Jet (TEJ)The Tropical Easterly Jet (TEJ)

• The TEJ at about 200-100 hPa is a planetary scale flow, related to the The TEJ at about 200-100 hPa is a planetary scale flow, related to the Indian MonsoonIndian Monsoon

• It is the main responsible of the vertical easterly shear which is one of the It is the main responsible of the vertical easterly shear which is one of the factors controlling suppression or development at the factors controlling suppression or development at the earlyearly stages of stages of development development

• Fluctuations on interannual scale are known (Chen and van Loon, 1987) but Fluctuations on interannual scale are known (Chen and van Loon, 1987) but intraseasonal variations, despite their importance, are still little knownintraseasonal variations, despite their importance, are still little known

• Only certain fact is the eastward retreat of strong easterly speed Only certain fact is the eastward retreat of strong easterly speed throughout the monsoon season, produces decreased easterly shear over throughout the monsoon season, produces decreased easterly shear over the Atlantic and an increasingly favorable environment for developmentthe Atlantic and an increasingly favorable environment for development

• The presence of strong vertical easterly shear could be perhaps related to The presence of strong vertical easterly shear could be perhaps related to early recurving systems, since only the systems that recurve immediately early recurving systems, since only the systems that recurve immediately can survive the vertical shearcan survive the vertical shear

• The NR shows a stronger than climatology TEJ, but a very credible and The NR shows a stronger than climatology TEJ, but a very credible and realistic decrease of easterly speed with the progress of the monsoon realistic decrease of easterly speed with the progress of the monsoon season. As a consequence, the environment becomes conducive to more season. As a consequence, the environment becomes conducive to more developmentdevelopment

Tropical Easterly Jet (TEJ)Tropical Easterly Jet (TEJ)

Diurnal Cycle of the TEJDiurnal Cycle of the TEJ

In the NR, in addition to the realistic changes on a monthly scale, the TEJ displays oscillations (intensity and latitude of the core) on a 3-6day scale (possibly realistic) and already discussed strong diurnal cycle.Diurnal cycle (DC) at single points is much stronger than when it is latitudinally averaged (cfr. Previous discussion). DC is stronger at some distance from the Jet core and is very evident on one flank of the TEJ whenever the jet core experiences a trend. No observational evidence so far to either confute or confirm these fluctuations

Longitude bands in which recurving of Longitude bands in which recurving of disturbances out of AEWs occur: Septemberdisturbances out of AEWs occur: September

In both months (Sep and Oct) the model manifests a tendency to create severalearly recurvers (around or east of 45W) or system that remain in the Eastern Atlantic

LatitudeUpward,Time horizontal

700hPa u,v wind

Longitude bands in which recurving of Longitude bands in which recurving of disturbances occur: Octoberdisturbances occur: October

However, the most intense systems occur in the western Atlantic. The number of early recurversis higher than climatology (about 50% against observed less than 20%).

LatitudeUpward,Time horizontal

700hPa u,v wind

However, early recurvers However, early recurvers dodo occur in packs occur in packs

Example of a number of early recurving systems in an active season, 2004.

At least 9 `major’ tropical cyclone-like At least 9 `major’ tropical cyclone-like systemssystems

Only TCLs having a center pressure of less than 1000 hPa in the 1x1 fields and900 hPa vorticity greater than 3x10-4 s-1 are considered

More HL vortices: horizontal structureMore HL vortices: horizontal structure

As observed in July and August, the 1 degree fields do not allow a full evaluation of HL vortices structure, since little evidence of bands is seen. However, pressure center and 850hPa wind are very realistic (970 hPa and 50 m/s) in the major 20 October 2005 Gulf of Mexico `Hurricane’

`Major’ hurricane over the Gulf: vertical `Major’ hurricane over the Gulf: vertical structurestructure

Vertical structure of a HL vortex shows, even at the degraded resolution of 1 deg, a distinct eye-like feature and a very prominent warm core. Structure even more impressive than the system observed in August. Low-level wind speed exceeds 55 m/s

Wind speed (m/s)Temp (oC)

Realistic Variability of TCL system tracks in the Realistic Variability of TCL system tracks in the AtlanticAtlantic

Looping andBinary vortex interaction

4 systems:Looping,Binary vortex Interaction,ExtratropicalTransitionsand Extra-tropicalRe-intensification

Singuarities, binary vortexInteractions, Intensity fluctuationsDue to large-scale forcing fluctuations

Multiple simultaneous tropical cyclones in the Multiple simultaneous tropical cyclones in the AtlanticAtlantic

500 hPa geop (m) and 900 hPa rel vort (s-1)

Remarkable days in which almost all possible Remarkable days in which almost all possible processes related to Tropical Cyclones happen processes related to Tropical Cyclones happen

together:together:21-24 September21-24 September

Although weaker systems than atother times, the period 21-24Sep isextremely interesting.

Multiple tropical cyclogenesis, cyclolysis, subtropical cyclogenesisextratropical transition, looping,binary vortex interaction, center jump, rejuvenation, extratropical reintensification.

Up to four tropical or at least partially tropical systems simultaneously present.

Tropical-Extratropical interaction is very evident

Given the resolution limitations,this is an extraordinary realistic representation of a very active period

500 hPa geop (m) and 900 hPa rel vort (s-1)

Preliminary concluding remarks on Preliminary concluding remarks on the African Monson region and the African Monson region and

tropical Atlantictropical Atlantic• A synoptic assessment of the NR over the AM region and the A synoptic assessment of the NR over the AM region and the

tropical Atlantic shows an overall very realistic African tropical Atlantic shows an overall very realistic African Monsoon, AEJ and wave activityMonsoon, AEJ and wave activity

• In addition to the 2 `major’ systems with a full hurricane-like In addition to the 2 `major’ systems with a full hurricane-like development up to Aug 31development up to Aug 31st ,st , at least other 9 `strong’ systems at least other 9 `strong’ systems (for 1x1 res.) develop during September and October (for 1x1 res.) develop during September and October

• Several weaker tropical and sub-tropical systems are also Several weaker tropical and sub-tropical systems are also presentpresent

• In spite of a tendency of creating several early recurvers, it In spite of a tendency of creating several early recurvers, it can be stated that the NR, given the resolution limitation, does can be stated that the NR, given the resolution limitation, does have a good representativeness of tropical cyclone track have a good representativeness of tropical cyclone track variability in the Atlantic, as it would occur in an active seasonvariability in the Atlantic, as it would occur in an active season

• This Nature Run seems to represent a very promising tool to This Nature Run seems to represent a very promising tool to perform OSSEs over the tropical Atlanticperform OSSEs over the tropical Atlantic

CURRENT and FUTURE WORK at NASA CURRENT and FUTURE WORK at NASA GSFC (GLA and SIVO) on the NR GSFC (GLA and SIVO) on the NR

validationvalidation

• Comprehensive statistics on midlatitude cyclone activity have Comprehensive statistics on midlatitude cyclone activity have been performed (J. Terry)been performed (J. Terry)

• Comprehensive statistics on precipitation (J.C. Jusem) are in Comprehensive statistics on precipitation (J.C. Jusem) are in progress and will be presented in the next meeting together progress and will be presented in the next meeting together with an assessment of the South American monsoonwith an assessment of the South American monsoon

• Analysis of tropical weather over Indian Ocean and Asian Analysis of tropical weather over Indian Ocean and Asian Monsoon regions with emphasis on the Somali Jet, monsoon Monsoon regions with emphasis on the Somali Jet, monsoon onset and breaks, tropical depressions, is being completedonset and breaks, tropical depressions, is being completed

• An assessment of the Eastern Pacific tropical cyclone season An assessment of the Eastern Pacific tropical cyclone season is also being completedis also being completed

• Southern Hemisphere and Western Pacific tropical weather Southern Hemisphere and Western Pacific tropical weather systems will be investigated in the near futuresystems will be investigated in the near future