Rambler's Top100



Глоссарий

Это описание того, что такое глоссарий. Еще пара слов про то, как он работает.

CL

Ар

C

CAPE assumes Parcel Theory, in that 1) a rising parcel exhibits no environmental entrainment, 2) the parcel rises (moist) adiabatically, 3) all precipitation falls out of the parcel (no water loading), and 4) the parcel pressure is equal to the environmental pressure at each level. Parcel Theory can have significant errors, especially for large parcel displacements, at cloud edges, and for significant water loading. However, the method often works quite well in the undiluted core of a thunderstorm updraft.

CAPE represents the amount of buoyant energy available to accelerate a parcel vertically, or the amount of work a parcel does on the environment. CAPE is the positive area on a sounding between the parcel's assumed ascent along a moist adiabat and the environmental temperature curve from the level of free convection (LFC) to the equilibrium level (EL). The greater the temperature difference between the warmer parcel and the cooler environment, the greater the CAPE and updraft acceleration to produce strong convection.

                 EL
CAPE = g  {  [(Tparcel - Tenvir) / Tenvir] dz
                 LFC

in Joules/kg. The "{" symbol here represents a vertical integration between the LFC (level of free convection, above which the parcel is warmer than the environment, i.e., the parcel is positively buoyant and will rise) and the EL (equilibrium level, below which the parcel is warmer than the environment).

 CAPE below 0: Stable.
 CAPE = 0 to 1000: Marginally unstable.
 CAPE = 1000 to 2500: Moderately unstable.
 CAPE = 2500 to 3500:  Very unstable.
 CAPE above 3500-4000:  Extremely unstable.

The above values are based on a parcel lifted with the average temperature and moisture of the lowest 50 to 100 mb layer (i.e., the boundary layer). The value of CAPE is dependent on the level from which a parcel is lifted. Parcels lifted from the surface usually exhibit a higher (sometimes significantly higher) CAPE value than for those lifted using mean boundary layer characteristics.

While CAPE is sensitive to the properties utilized to initialize a parcel, CAPE often is a much better indicator of instability than indices which depend on level data (e.g. lifted index, total totals index, etc). CAPE involves an integration over a depth of the atmosphere and is not as sensitive to specific sounding details.

Using CAPE, the maximum updraft speed in a thunderstorm (w-max) at the equilibrium level can be calculated. In general, w-max = square root of [2(CAPE)] . For example, a range of CAPE of 1500-2500 J/kg gives a w-max range of about 50-70 m/s (100-140 kts). However, due to water loading, mixing, entrainment, and evaporative cooling, the actual w-max is approximately one-half that calculated above.

Finally, the profile or shape of the positive area is important, besides the actual CAPE value. Two soundings could have the same CAPE value, but lead to different convective characteristics due to differences in the shape of the area between the LFC and EL. For example, given the same CAPE value in each, a longer, narrower profile represents the potential for a slower updraft acceleration but taller thunderstorms which is best for high precipitation efficiency. However, a shorter, fatter profile would lead to a more rapid vertical acceleration which would be important for potential development of updraft rotation within the storm.

CIN represents the amount of negative buoyant energy available to inhibit or suppress upward vertical acceleration, or the amount of work the environment must do on the parcel to raise the parcel to its LFC. CIN basically is the opposite of CAPE, and represents the negative energy area (B-) on the sounding where the parcel temperature is cooler than that of the environment. The smaller (larger) the CIN is, the weaker (stronger) must be the amount of synoptic and especially mesoscale forced lift to bring the parcel to its LFC. High CIN values in the presence of little or no lift can cap or suppress convective development, despite possibly high CAPE values. Remember, CAPE is the «available potential» energy. That energy must be released to become «kinetic» energy to produce thunderstorms.

L

Lifted Index (LI)

The LI is a commonly utilized measure of stability which measures the difference between a lifted parcel’s temperature at 500 mb and the environmental temperature at 500 mb. It incorporates moisture and lapse rate (static stability) into one number, which is less vulnerable to observations at individual pressure levels. However, LI values do depend on the level from which a parcel is lifted, and rally cannot account for details in th environmental temperature curve above the LCL and below 500 mb. LI was originally intended to utilize average moisture and temperature properties within the planetary boundary layer.

LI = T(500 mb envir) — T(500 mb parcel)

in degrees C, where T (500 mb envir) represents the 500 mb environmental temperature and T (500 mb parcel) is the rising air parcel’s 500 mb temperature.

These LI values are based on lifted parcels using the average lowest 50 to 100 mb moisture and temperature values (i.e., the boundary layer). Variations exist on how LI values are calculated, as discussed below.

Surfaced-based LI: Surface-based LIs can be calculated hourly, and assume a parcel is lifted from the surface using surface-based moisture and temperature values, as well as assigned environmental temperatures at 500 mb. This method is valid for a well—mixed nearly dry adiabatic afternoon boundary layer where surface characteristics are similar to those in the lowest 50 to 100 mb layer. However, these values would not be representative of the ambient elevated instability if a nocturnal inversion or shallow cool air to the north of a frontal boundary is present. In these cases, more instability resides above the surface, and parcels may be lifted to form thunderstorms from the top of the inversion.

Best LI: The Best LI represents the lowest (most unstable) LI computed from a series of levels from the surface to about 850 mb. This index is most useful during cases when shallow cool air exists north of a frontal boundary resulting in surface conditions and boundary layer-based LI values that are relatively stable. However, the airmass at the top of the inversion, from which lifting may occur, is potentially unstable. An example of this would be elevated («overrunning») convection (possibly a nocturnal MCS).

  • LI over 0: Stable but weak convection possible for LI = 1—3 if strong lifting is present.
  • LI = 0 to −3: Marginally unstable.
  • LI = −3 to −6: Moderately unstable.
  • LI = −6 to −9: Very unstable.
  • LI below −9: Extremely unstable.

А

В метеорологических подразделениях по данным радиозондирования составляют специальные графики — аэрологические диаграммы. С их помощью анализируют состояние атмосферы на различных высотах. Особенно они нужны для прогноза развития конвекции и конвективной облачности. Такой график представляет поэтому большой интерес для оценки метеорологических условий полетов.

р

радиозондирование

В метеорологических подразделениях по данным радиозондирования составляют специальные графики — аэрологические диаграммы. С их помощью анализируют состояние атмосферы на различных высотах. Особенно они нужны для прогноза развития конвекции и конвективной облачности. Такой график представляет поэтому большой интерес для оценки метеорологических условий полетов.