Occlusion cyclogenesis II Upper level influences on cyclogenesis Vorticity Advection (CVA) and the 4-quadrant jet streak model (Uccellini) Potential Vorticity (PV) (Hoskins Theory) Rapid cyclogenesis
14 July 2016/18 UTC WCB occlusion Cyan: Orange/Black: zeroline of relative vorticity 300 hpa Red/blue: relative vorticity 04 February 2016/12 UTC CCB occlusion Orange/ Black: zeroline of relative vorticity 300 hpa Red/blue : relative vorticity
14 July 2016/18 UTC WCB occlusion Cyan: Height contours 300 hpa Yellow: isotachs 300 hpa Orange/Black: Red (left, right): relative vorticity advection CVA 300 hpa 04 February 2016/12 UTC CCB occlusion Cyan: Height contours 300 hpa Yellow: isotachs 300 hpa Orange/Black: Red (left, right): relative vorticity advection CVA 300 hpa
Reflectance of occlusion process / cyclogenesis in derived upper level parameters For Cold and Warm Fronts Temperature Advection is a dominating parameter For Cyclogenesis also Vorticity and Vorticity Advection are dominating parameters Vorticity = rot z v 2 = v/ x - u/ y = + f f = 2 sin cyclonic: 0 (NH) < 0 (SH) anticyclonic: < 0 (NH), 0 (SH) Vorticity is a quality of the stream field Vorticity describes rotation movements Vorticity is one of the parameters that are involved in the configuration of cloudiness Vorticity Advection VA = - v. Advection of rel. vorticity VA = - v. Advection of abs. vorticity VA > 0 positive Vorticity advection: PVA/CVA VA < 0 negative Vorticity advection: NVA/AVA PVA/CVA: it becomes more cyclonic or less anticyclonic (NH) NVA/AVA: it becomes more antiyclonic or less cyclonic (NH) The Advection of Vorticity is one of the parameters that are involved in the development of cloudiness
Omega equation in a quasi geostrophic system Assumptions for a Quasi-geostrophic Systems: 1.) there is hydrostatic equilibrium in the vertical 2.) Pressure- and vorticity fields are in a geostrophic equilibrium 1.) 2.) 3.) The right side in this representation of the omega equation consists of three terms: 1.) the vertical change of the vorticity advection 2.) the Laplacian of the temperature advection(the change of the horizontal gradient of the temperature advection) 3.) the Laplacian of diabatic heat transfer (the change of the gradient of diabatic heat transfer)
Some basic considerations for vorticity and vorticity advection the vertical change of the vorticity advection / p. (- v p. ) Upward motion is connected with The increase of PVA (CVA) with height The decrease of NVA (AVA) with height In the method of analysing satellite images together with numerical model a simplification is applied: Instead of the vertical change of Vorticity Advection only the pronounced maxima of Vorticity Advection in upper levels (500, 400, 300, 250 hpa) are taken into account This needs the assumption of: Increase of wind speed with height This is reasonable but every time fulfilled
The significance of processes in the upper troposphere for cyclogenesis Vorticity (rotation) Vorticity Advection Vorticity consists of two contributions: curvature and shear vorticity Typical areas for Positive (Cyclonic) Vorticity values are (on the NH): lows, troughs and jet streaks If a weather system with high cyclonic values of vorticity is moving: Downstream from Vorticity maxima becomes the troposphere more cyclonic Areas of Positive/Cyclonic Vorticity Advection (PVA(CVA)
14 July 2016/18 UTC WCB occlusion Orange: Zeroline of relative vorticity 300 hpa Cyan: Height contours 300 hpa Red : CVA 300 hpa 4 February 2016/12 UTC CCB occlusion Orange: Zeroline of relative vorticity 300 hpa Yellow: Isotachs 300 hpa Red (left): CVA 300 hpa
Jet streaks 4-quadrant Model (Uccellini) Consideration 1: Jet streaks: Distribution of vorticity and vorticity advection in jet level N-Pole cold N-Pole cold Equator warm Equator warm Vorticitymaximum on the cyclonic side of a jet streak maximum (increased shear) Vorticityminimum on the anticyclonic side
14 July 2016/18 UTC WCB occlusion Black: zeroline of rel. Vorticity 300 hpa Red/blue: rel. vorticity (cycl/anticycl.) 300 hpa Yellow: isotachs 300 hpa Red (left): CVA 300 hpa 4 February 2016/12 UTC CCB occlusion Black: zeroline of rel. Vorticity 300 hpa Red/blue: rel. vorticity (cycl/anticycl.) 300 hpa Yellow: isotachs 300 hpa Red (left): CVA 300 hpa
Interpretation of small scale features and separation of noise from meteorologically useful signals In a numerical model with a small grid distance (new ECMWF model as basis for eport Pro) much more small scale phenomena are analysed Many of these small scale structures represent noise and do not contain a meteorologically significant content Partly they can be mathematically filtered/smoothed but very strong values remain Meteorologically important structures have to be separated from meteorologically not so indicative ones. Jet streaks and vorticity advection are a typical example: Often small bands of very high CVA values appear at the jet axis They are dependant on very high relative vorticity gradients and fast system movement 4 February 2016/12 UTC
Interpretation of small scale features and separation of noise from applicable signals 4 February 2016/12 UTC
Jet streaks 4-quadrant Model (Uccellini) Consideration 2: Jet streaks: Stream components in jet level entrance exit acceleration retardation Acceleration vector Ageostrophic Wind vector Resulting vector
Jet streaks 4-quadrant Model (Uccellini) Consideration 3: Jet streaks: Vertical cross section in entrance ad exit region left right frontogenetic frontolytic Entrance Region: 1. Frontogenetic in low levels 2. Frontolytic in middle levels 3. Upward motion in right entrance region 4. Preferred area for wave developments Exit Region: 1. Frontolytic in low levels 2. Frontogenetic in middle levels 3. Upward motion in left exit region 4. Preferred area for rapid developments
2 January 2016/ 18UTC Exit region Yellow: Red (left): Red(right): Black: Green: VCS: black: Brown: Orange: isotachs cyclonic rel. Vorticity CVA maxima zeroline of rel. Vorticity (jet axis) VCS line in exit region moist isentropes isotachs jetcore
2 January 2016/ 18UTC Exit region VCS: black: Red/blue(above): Red/blue(below): moist isentropes VA (CVA/NVA) omega (rising/sinking) Brown: Orange: isotachs jetcore
2 January 2016/ 18UTC Entrance region Yellow: Red (left): Red(right): Black: Green: VCS: black: Brown: Orange: isotachs cyclonic rel. Vorticity CVA maxima zeroline of rel. Vorticity (jet axis) VCS line in entrance region moist isentropes isotachs jetcore
2 January 2016/ 18UTC Entrance region VCS: black: Red/blue(above): Red/blue(below): moist isentropes VA (CVA/NVA) omega (rising/sinking) Brown: Orange: isotachs jetcore
14 July 2016/ 18UTC Exit region Yellow: Red (left): Red(right): Black: Green: VCS: black: Brown: Orange: isotachs cyclonic rel. Vorticity CVA maxima zeroline of rel. Vorticity (jet axis) VCS line in exit region moist isentropes isotachs jetcore
14 July 2016/ 18UTC Exit region VCS: black: Red/blue(above): Red/blue(below): moist isentropes VA (CVA/NVA) omega (rising/sinking) Brown: Orange: isotachs jetcore
4 February 2016/ 12UTC Exit region Yellow: Red (left): Red(right): Black: Green: VCS: black: Brown: Orange: isotachs cyclonic rel. Vorticity CVA maxima zeroline of rel. Vorticity (jet axis) VCS line in exit region moist isentropes isotachs jetcore
4 February 2016/ 182UTC Exit region Yellow: Red (left): Red(right): Black: Green: VCS: black: Brown: Orange: isotachs cyclonic rel. Vorticity CVA maxima zeroline of rel. Vorticity (jet axis) VCS line in exit region moist isentropes isotachs jetcore
Rapid Cyclogenesis Intensive deepening of surface low within 12 hours the rate of deepening of the central sea-level pressure greater than or equal to 1 mb or 1 hpa per hour, generally over a period of time 12 hours or longer Cannot be explained with the classical polar front theory alone They are connected with very dangerous weather events especially in wind and precipitation; damaging events Very typical structure in satellite images which show involvement of processes in upper levels
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage Cloud Head Cloud Head 8-9 January 2015: Rapid Cyclogenesis: IR 8 January 2015/ 18 UTC: advanced stage 9 January 2015/ 06 UTC: mature stage
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage Cloud Head Cloud Head 8-9 January 2015: Rapid Cyclogenesis: WV 8 January 2015/ 18 UTC: advanced stage 9 January 2015/ 06 UTC: mature stage
Cloud Head Cloud Head 8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage 8-9 January 2015: Rapid Cyclogenesis: Air Mass 8 January 2015/ 18 UTC: advanced stage 9 January 2015/ 06 UTC: mature stage
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage Magenta: Height contours 1000 hpa (close surface Low) 8 January 2015/ 18 UTC: advanced stage Deepening of height at 1000 hpa from -8 gpm to -28 gpm within 12 hours
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage Rapid Cyclogenesis PVA max In LEX Of intensive jet streak Why such A rapid cyclogenesis!? 8 January 2015/ 18 UTC: advanced stage
The significance of processes in the upper troposphere for cyclogenesis: Potential Vorticity (PV) PV = - g ( f + ) / p = const PV (IPV) is constant for adiabatic processes; that means constant on isentropic surfaces Product of vorticity and stability is constant on isentropic surfaces PV has very high values in stratosphere >= 2 units (NH); <= -2 units (SH) If stratospheric air with the inherent PV protrudes downward from stratosphere into troposphere - static stability decreases and (because of conservation) cyclonic vorticity has to increase there This is a motor for enhancing cyclogenesis
The significance of processes in the upper troposphere for cyclogenesis: Potential Vorticity (PV) PV Anomalies - Hoskins theory Interaction and mutual intensification of cyclonic circulation: Rapid cyclogenesis 8 January13/ 00
Importance of PV and PV anomaly The height of PV >= 2 units (-2 on SH) shows how far the air from stratosphere has protruded downward In case of classical cyclogenesis the typical height is 400 500 hpa In case of a rapid cyclogenesis it is down to 600 700 hpa and at same time the intensification of the lower tropospheric PV values takes place Consequently rapidly a tunnel of high PV values from tropopause down to surface develops Vertical cross sections can show the downward protrusion below the frontal surface
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage Magenta: Height of PV >=2 units 8 January 2015/ 18 UTC: advanced stage
8 January 2015: Top: 06 UTC, initial stage Middle: 12 UTC, development stage Bottom: 18 UTC, advanced stage Left row: Magenta: height contours 1000 hpa Blue: shear vorticity 300 hpa Black: zeroline odf shear vorticity 300 hpa Right row: Magenta: Height of PV>=2 units
Black: moist isentropes Red: PV Rapid Cylogenesis: Downward Protrusion of stratospheric Air tropopause folding
Parameter Precipitation Description Intense precipitation associated with the Warm Conveyor Belt. Thunderstorms are possible within the inner edge of the cloud head at the western side of the surface low as well as within the dry slot Temperature Strong rise in surface temperature within the area of Warm Conveyor Belt. Wind (incl. gusts) Strong winds within the area of the cloud head. In extreme cases winds reaching hurricane force. Very strong gusts in the transition zone between dark and white as can be seen in the WV channels near the cold front and the cloud head Possibility of the development of a sting jet in the Advanced and Mature stage in the southern semicircle of the low centre and S of the decaying cloud spiral. (See below) In case of a sting jet hurricane force winds with gusts up to 200 km/h are possible. Other relevant information Very strong pressure falls and rises. In the initial stage, falls ahead exceed the rises behind.
9 January 2015/ 06 UTC: mature stage
8 January 2015/ 18 UTC NWCSAF products u.l.: cloud type u.r.: Precipitating Cloud l.l.: Cloud top Pressure l.r.: Convective rainfall rate
8 January 2015/18 UTC 9 January 2015/00 UTC 9 January 2015/06 UTC 8 9 January 2016 Cloud Type (NWCSAF)
8 January 2015/18 UTC 9 January 2015/00 UTC 9 January 2015/06 UTC 8 9 January 2016 Cloud Top Pressure (NWCSAF)
8 January 2015/18 UTC 9 January 2015/00 UTC 9 January 2015/06 UTC 8 9 January 2016 Precipitation Clouds (NWCSAF)
8 January 2015/18 UTC 9 January 2015/00 UTC 9 January 2015/06 UTC 8 9 January 2016 Convective Rainfall Rate (NWCSAF)
8 January 2015/ 06 UTC: Initial stage 8 January 2015/ 12 UTC: development stage 10 m winds 8 January 2015/ 18 UTC: advanced stage 9 January 2015/ 06 UTC: mature stage
Rapid Cyclogenesis Cases There are cases from the last years in the course page 2016 no intensive rapid cyclogenesis could be observed but some developments which have many features of a rapid cyclogenesis: 6 May 2016/ 06-18
6 May 2016/06 UTC/IR 6 May 2016/12 UTC/IR Blue: Height contours 1000 hpa (close surface Low) 6 May 2016/18 UTC/IR Deepening of height at 1000 hpa from 7 gpm to -3 gpm within 12 hours (-8 within 18 hours) 7 May 2016/00 UTC/IR
6 May 2016/06 UTC/airmass RGB 6 May 2016/12 UTC/air mass RGB 6 May 2016/18 UTC/air mass RGB 7 May 2016/00 UTC/air mass RGB
6 May 2016/06 UTC/IR 6 May 2016/12 UTC/IR Magenta: Height of PV >2 units 6 May 2016/18 UTC/IR 7 May 2016/00 UTC/IR
Enough for today!
Outlook:Other developments of occlusion spirals from mesoscale features Cold Air development Instant Occlusion We will come back to all this on 8 November: Comma clouds Mesoscale features in Cold Air
Detect elements of the 4-quandrant jet streak model in a real case: 7 May 2016/00 UTC 7 May 2016/ 00 UTC Yellow: Isentropes 300 hpa Which elements of the 4-quandrat jet streak model can you detect in the jet streak above; choose VCSs similar to the one indicated Make slides similar to numbers 15,16 in the presentation of Occlusion Cyclogenesis II
Detect and locate PV Anomalies in Vertical Cross Sections 6 May 2016/06 UTC/IR 6 May 2016/12 UTC/IR 6 May 2016/18 UTC/IR 6 May 2016/06 UTC/IR 6 May 2016/18 UTC/IR Make the process of sinking tropospheric air visible 6 May 2016/18 UTC/IR Compute the relevant VCS (use VCS line similar to the indicated ones) Indicate height of PV=2 units directly in the VCS frontal surface and determine how far downward tropospheric air has protruded Make a slide similar to 34 in this presentation.
Enough for today! Any Questions already now? The Students Forum is open for all questions coming up later! Thank you for your attention! Meet you in the Students Forum, in November and in Langen!