Note: since the figures on this web page were created the value range used for dewpoint depression was reduced from 0-50C, to 0-20C, to enable the user to see moist environments in more detail.
In Cycle 45r1, released 5 June 2018, a Vertical Profiles Window was added to the ecCharts Views Menu to supplement the tools already available (Probe, Time-series, Cities, EPSgram). The Vertical Profiles window provides information about the vertical structure of the forecast model atmosphere for any location, as selected by the Probe Tool, and any time, as selected by the Time Navigator (6-hourly, up to T+120 - various constraints currently preclude the inclusion of more validity times). The values given at the selected location and time by each ENS member, plus the Control, HRES and ENS median, are combined into a single display comprising the following elements:
Temperature, Dewpoint and Dewpoint Depression on (most) Model levels
Fig8.1.12.1A: An example of ecCharts vertical profile output.
Fig8.1.12.1B: Magnified portion of Fig 8.1.12.1A showing the possible overlap between temperatures and dewpoints among the ENS members. At some levels (here 910hPa taken for illustration) some ENS members forecast dewpoints higher than the temperature forecast by other ENS members.
In order to save disk space and reduce plotting time, whilst at the same time retaining the information most pertinent for forecasting tasks, we elected to used every model level in the lower troposphere up to about 700mb, and every other level higher up than that. Before the spread metrics (e.g. 25th and 75th percentiles) are computed the model levels from each ENS member are all set to correspond the same (ensemble mean) pressure values. For typical mean sea level pressure variations seen up to T+120 this is not problematic.
Horizontal Winds on Pressure levels
Fig 8.1.12.2: An example of ENS and HRES winds plotted as hodographs. Depending on the case, these can be very informative (e.g. the consistency of significant shear among ENS members).
CAPE and CIN
Fig8.1.12.3: An example of box and whisker plot of the distribution among ENS members of CIN and CAPE. These diagrams indicate the variation among ENS members of the inensity of convection that may occur (CAPE) together with the likelihood of attaining the release of convection (i.e overcoming CIN). The numbers of ENS members within each CIN category are given at the top of each column and the number of members without CAPE is shown in the top right hand corner (e.g. CAPE=0:6 meaning 6 ENS members failed to identify any CAPE in the forecast ENS ascent).
CAPE release:
Where less than five ENS members are allocated to a CIN category the CAPE values are shown as dots rather than in box and whisker format.
The number (n) of ENS members NOT indicating any CAPE is given in the top right hand corner of the diagram in the form "(CAPE=0: n)".
Scaling for CAPE varies according to the full range of CAPE values present. Certain CAPE values are highlighted with coloured horizontal lines, namely 200, 500, 1000, 2000 and 5000 J/kg.
It should be remembered that the CIN and CAPE values indicated are diagnostic. They show the state of the model atmosphere as forecast for that time. They do not indicate whether convective instability will be released, but rather provide a measure of the potential for that release. It is up to the user to assess the likelihood of CIN values being overcome during the following hours, either by diurnal heating, by dynamically induced uplift of the airmass, or by mechanical uplift caused by flow over mountains etc.
CIN, the convective inhibition, is always zero or a positive value. Where the parcel curve (from any of the levels tested) never even reaches the environment curve (i.e. it lies always to the left of the environment curve) then CIN is in effect infinite. In practice a missing value is stored or indicated when the minimum CIN encountered exceeds a pre-defined very large threshold - CIN cannot be stored or indicated as zero, because that would have a completely opposite meaning! CIN can be computed, in principal, from any model level and the temperature structure of the forecast atmosphere is scanned in the vertical, working out what CIN from each level is, and then the minimum of those values is stored in MARS.
CAPE is different in that that is bounded between 0 and some large value dependant on atmospheric structure. It can never be infinity. So that is stored in a different manner that does not include missing values.
Fig8.1.12.4: A forecast vertical profile for a location in SW Calabria, Italy, T+12hr valid at 12UTC 9 July 2018, base time 00UTC 9 July 2018. The map shows HRES forecast convective precipitation during the previous 6hr. The spread of temperatures is small at this short lead time but there are noticeable differences in the detail of the inversion below 900hPa. There are larger differences among ENS members regarding forecast dewpoints, especially between 700hPa and 600hPa, and this is also reflected in the spread of the dewpoint depression trace. Most ENS members (32) suggest that fairly high CIN (owing to the relative dryness of the near-surface air) would need to be overcome for instability release, and even then with relatively small CAPE, convection is unlikely and would not be that vigorous. Meanwhile 11 ENS members suggest that only moderate CIN needs to be overcome for release of more active (greater CAPE) convection, and these include HRES (blue dot, see also HRES precipitation on map) and CNTL (red dot). So for these convection is possible but would only be moderately vigorous. 4 ENS members (black dots) suggest that only small CIN would need to be overcome, with release of vigorous convection (high CAPE) resulting - convection is probable for these ENS members. Finally note that 3 ENS members have zero CAPE, suggesting no convective activity. Although this case does not definitively highlight active convection the hodograph shows well marked shear (notably in speed) through the model atmosphere which would be favourable for organised deep moist convection if large CAPE were available.
Fig8.1.12.5: A forecast vertical profile for Mostar, Bosnia and Herzegovina, T+48hr valid 12UTC 6 July 2018, base time 12UTC 4 July 2018. The corresponding map shows a forecast probability for convective precipitation (same model runs). In this case many ENS members suggest CIN can be overcome, and where CIN is small quite vigorous convection is possible (large CAPE values). One of the 4 ENS members with CIN<50J/kg shows CAPE~2000J/kg. The probability of precipitation chart shows that most ENS members are not producing rain but the CIN/CAPE diagram suggests that quite active convection with heavier showers is nevertheless possible.
Fig8.1.12.6: Sequence of forecast vertical profiles for Ražanj, Federation of Bosnia and Herzegovina illustrating the variation in CIN and consequent availability of CAPE through a full 24h diurnal cycle in which the structure of the atmosphere above the lowest layers remains largely unchanged.
At 00UTC 12 July CIN is large at the lowest layers although some ENS members show warm air very near the surface requiring only moderate energy input to release convection. If sufficient energy were available then fairly active deep convetion could be released (including by HRES), though most ENS members suggest weaker convection and 5 ENS members have zero CAPE.
At 06UTC 12 July CIN in the lowest layers seems to be similar overall, but with overnight cooling CAPE values have reduced. The low-level inversion looks more substantial. However, 4 ENS members suggest probable CAPE release with minimal CIN.
At 12UTC 12 July remnants of the inversion remain, and a high surface temperature is still required to release free active convection. CAPE values remain low overall; this is probably due, in large part, to relatively suppressed near-surface dewpoints. Only 2 ENS members have zero CAPE, these appear to be associated with temperatures at the leftmost extremity of the pink zone seen at lower levels on the tephigram.
At 18UTC 12 July CIN has reduced considerably after diurnal heating and the majority of ENS members show that CAPE release would require only moderate or low CIN to be overcome. Now there are no members with zero CAPE. As well as being influenced by diurnal heating these changes seem to relate also to an increase in near-surface dewpoint, and a cooling of the "warm nose" near 800hPa.
At 00UTC 13 July CIN values overall have reduced further (18 members are now in the lowest category). This looks to be mainly due to further erosion of the warm nose near 800hPa. On the other hand median CAPE values have reduced slightly, probably because it is night-time.
Fig8.1.12.7: An example of a forecast vertical profile in the vicinity of a mobile cold front at the location of the pin shown on the chart, T+108hr valid 12UTC 1 July 2018, base time 00UTC 27 June 2018. The chart shows the HRES forecast precipitation but there are a range of forecast locations among the ENS solutions. These are illustrated by the broad spread of temperatures, and more especially of dewpoints. A classic cold front tephigram is shown by HRES (thick solid trace) and by the HRES vertical wind structure - specifically backing with height (shown on the dewpoint depression chart). The temperature spread within the inter-quartile range of ENS members is fairly narrow, though some members show continued presence of pre-frontal warm air (implying slower advance of the front) and others the intrusion of post-frontal cold air (implying faster advance of a cold front). The colder temperatures are not necessarily associated with the lower dewpoints, but the spread on the dewpoint depression diagram gives an indication of the likelihood of intrusion of post-frontal drier air. The hodograph illustrates a wide variation amongst ENS members in the vertical wind structure. Apparently this relates not only to the near-surface front, but also to uncertainties in the upper level pattern. By comparing with a standard ECMWF front spaghetti plot (lower diagram) from the same runs one can confirm, firstly, a clear-cut cold front in HRES (thick green line, strictly at 1km altitude) northeast of Iceland, and secondly a large spread in ENS cold front positions in the same region. Examining also a fixed-time animation of synoptic charts from the cyclone database products (not shown) one sees that a few members have a rather different synoptic pattern. So the user may find it helpful, at times, to examine tephigram and cyclone database products alongside one another.
(Note: In older material there may be references to issues that have subsequently been addressed)
Read more information on “Using ECMWF's new ensemble vertical profiles”.
See a summer 2018 ECMWF Newsletter article (P39-44).