Past and future changes in Sahel precipitation: Possible systems Kerry H. Cook Department of Earth and Atmospheric Sciences Cornell University Ithaca NYSlide 2
Present a portion of the dynamical procedures that are in charge of variability in the Sahel on unsurpassed scales paleoclimate – the African Humid Period decadal (Samson Hagos) interannual intraseasonalSlide 3
The African Humid Period with Christina PatricolaSlide 4
African Humid Period AHP Present Day Vegetation for (a) present day (b) and African Humid Period as indicated by Hoelzmann et al. (1998) with meadow - 7, shrubland - 8, savanna - 10, evergreen broadleaf backwoods - 13, and desert - 19.Slide 6
Enhancement of the westerly low-level plane is an essential dampness source. Note that the southerly low-level southerly stream is unaltered.Slide 7
The African easterly stream is not a part of the AHP atmosphereSlide 8
The Monsoon Jump with Samson HagosSlide 9
Smoothed precipitation in mm/day from TRMM (top) and FEWS (base) 2004 Coastal SahelSlide 12
Daily precipitation in mm/day from TRMM 2002, 2003, 2005, 2006Slide 13
Precipitation contrast: "Sahel" – "Coast"Slide 14
Precipitation distinction: "Sahel" – "Coast" storm onset 2002: July 14 2003: June 24 2004: June 16 2005: July 8 2006: July 10Slide 15
The territorial model catches the rainstorm hopSlide 17
Pre-rainstorm onset A changeless sensible warming most extreme exists from around 10N-12N: relatively low albedo => shortwave radiation greatest and net all out radiative warming greatest This sensible warming drives a shallow meridional course (Zhang et al. 2006) low-level dampness union moisture transport into the center layer (825 - 525 hPa), difference The radiative constraining increments through the spring and, close to the center of May, the bit by bit expanding dampness supply from the limit layer starts gathering in the center layer => buildup and precipitation increments in the mainland interiorSlide 19
Monsoon Onset The condensational warming in the 825 - 525 hPa layer presents a meridional weight slope in this layer which brings about an inertial shakiness => beach front area gets to be unfavorable for joining => most extreme precipitation unexpectedly moves from the coast into the SahelSlide 20
Eastern Sahel: Another "Monsoon Jump" Two-Stage Monsoon Onset over Ethiopia with Emily RiddleSlide 23
Low-level 910 mb winds Pre-onset Mar 1 – Mar 31 Transitional Apr 20 – May 15 Post-onset Jun 1 – Jun 30Slide 24
The precipitation dipole reaction to SSTAs in the Gulf of Guinea with Edward VizySlide 25
Surface Temperature Anomalies An unmistakable method of interannual variability : ~ 25% of the years 1950 – 2000 are distinguished as dipole years (12 years) Extremely high relationship with warm SSTAs in the Gulf of Guinea amid dipole years 1984 Precipitation AnomaliesSlide 26
A north/south cross-segment along the Greenwich meridian Streamlines (v, w x 10 - 2) and meridional speed (m/s)Slide 27
A north/south cross-segment along the Greenwich meridian Vertically-restricted rainstorm inflow A north/south cross-segment along the Greenwich meridian Streamlines (v, w x 10 - 2) and meridional speed (m/s)Slide 28
2 nd determination rule: Reasonable storm dissemination Subsidence over the Gulf of Guinea Streamlines (v, w x 10 - 2) and meridional speed (m/s)Slide 29
Southward mid-tropospheric stream (African easterly fly) Saharan high warm low Streamlines (v, w x 10 - 2) and meridional speed (m/s)Slide 30
Top: Climatological flow From a territorial atmosphere model. Base: Circulation irregularities connected with warming in the Gulf of Guinea and the dipole precipitation mode. Bizarrely high precipitation along the Guinean coast happens in relationship with an expansion in the dampness substance of the storm inflow. Subsidence over the Gulf of Guinea stifles the precipitation inconsistency over the sea.Slide 31
With warm SSTAs in the Gulf of Guinea, the southward outpouring from the Saharan high has a bigger meridional degree, and is found nearer to the surface. These distinctions in the outpouring create subsidence and drying over the Sahel because of contracting of both planetary and relative vorticity.Slide 32
Cold Air Surges and Monsoon Breaks with Edward (Ned) VizySlide 33
What is an icy surge? Mid-tropospheric edge/trough design Shallow arch of cool air with a sharp temperature angle along it\'s driving edge Typically moves along geography, e.g., east of the Rockies and Andes Fig 2. from Garreaud (2001): Conceptual model of an icy surge moving from mid-scopesSlide 34
The climatology summer mid-tropospheric geopotential tallness field has the edge/trough design Topography (m) and June-August climatological 500 hPa geopotential statures (m) and winds (m/s) from the NCEP2 reanalysisSlide 35
The climatological summer mid-tropospheric stature field has the edge/trough design eastern Mediterranean Saharan high Topography (m) and June-August climatological 500 hPa geopotential statures (m) and winds (m/s) from the NCEP2 reanalysisSlide 36
A B C D E F Local rate of progress of temperature (unimportant) Mean diabatic warming and cooling term (ascertained as a lingering from the NCEP2) Mean vertical shift in weather conditions of potential temperature term Mean flat shift in weather conditions of temperature term (Zonal + Meridional segments) Vertical transient term Horizontal transient termSlide 37
A B C D E F 850 hPa JJA Thermodynamical Budget Analysis B C E+F DSlide 38
Strong mid-tropospheric subsidence over the eastern Mediterranean Sea June-August Climatological Vertical-p speed along 35N NW Africa E. Med SeaSlide 39
Daily TRMM precipitation rates (mm/day) and 850 hPa wind meeting (formed) for a JULY 2005 cool air surge occasionSlide 40
Precipitation climatology in the ebb and flow era of atmosphere models 1949 – 2000 JJASSlide 44
Daily precipitation in mm/day from TRMM (top) and FEWS (base) 2004 Coastal SahelSlide 47
Smoothed precipitation in mm/day from TRMM (top) and FEWS (base) 2004 Coastal SahelSlide 48
Daily precipitation in mm/day from TRMM 2002, 2003, 2005, 2006Slide 49
Daily precipitation in mm/day from FEWS 2002, 2003, 2005, 2006Slide 50
Precipitation distinction: "Sahel" – "Coast" storm onset 2002: July 14 2003: June 24 2004: June 16 2005: July 8 2006: July 10Slide 51
The provincial model catches the rainstorm hopSlide 53
Cold Surges A sort of rainstorm breakSlide 55
Long term objective: Predicting rainstorm onset (storm hop) Why does the hop happen? What controls the planning of the storm onset? Does the planning of the onset correspond with regular precipitation sums? Is there an association with interannual variability? … . and so forthSlide 56
Long term objective: Predicting rainstorm onset (storm bounce) Why does the hop happen? What controls the planning of the rainstorm onset? Does the planning of the onset connect with occasional precipitation sums? Is there an association with interannual variability? … . and so onSlide 57
The West Frican storm bounce is an outcome of inertial shakiness that creates in the beach front district over the limit layer (825 - 525 hPa layer) Hagos and Cook 2007: Dynamics of the West African Monsoon Jump. J .Climate)Slide 58
The West Frican rainstorm bounce is a result of inertial insecurity that creates in the seaside area over the limit layer (825 - 525 hPa layer) Hagos and Cook 2007: Dynamics of the West African Monsoon Jump. J .Climate) An update about inertial shakiness …Slide 59
Consider a geostrophic, zonal essential state stream in the Northern Hemisphere.Slide 60
Perturb the package toward the north …Slide 61
If the bundle will return southward (stable). In the event that the package will proceed with northward (unsteady).Slide 62
So inertial unsteadiness is brought on by an irregularity between weight angle strengths and inertial powers:Slide 64
X For instance, in accordance with the possibility of inertial flimsiness, consider a package of air situated at point X on the zero shape of speeding up (Fig. 10a). At first its quickening is zero. Any northward uprooting would move the bundle into a locale of positive net compel and make it quicken further into the landmass. Similarly, a package uprooted southward is additionally quickened facilitate southward. Hence, in light of inertial unsteadiness the seaside area (the district encompassed by the shape of zero increasing speed) gets to be unfavorable for meridional union toward the end of May and the meridional wind union hops into the mainland inside where meeting is feasible. Looking at Fig. 10b, which demonstrates the aggregate of the initial two right hand side terms of Eq. (5), with Fig. 10a demonstrates that the adjustment in indication of the meridional increasing speed is identified with an adjustment to be decided between the Coriolis and weight inclination powers, while contact postpones the procedure by around three days. Subsequently, the condition for northward increasing speed and the related movement in meridional union is an adjustment in indication of - fu-dphi/dy For a geostrophic, zonally uniform stream, this condition can be improved to the adjustment in indication of total vorticity as examined previously. The noteworthy meridional speeding up over both the sea and the landmass all through the time of recreation, nonetheless, makes presumption of simply zonal stream amid the pre-storm period sketchy.Slide 65
So inertial in
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