precipitation systems in midlatitude

Question 1

Precipitation may be classified as

Answer 1

convective and stratiform

Question 2

Precipitation characterized by

Answer 2

turbulent vertical fluxes of heat and momentum

Question 3

Precipitation characterized by turbulent vertical fluxes of heat and momentum such as

Answer 3

showers and thunderstorms are convective.

Question 4

Convective precipitation regions are relatively …………….. and precipitation from them tend to be

Answer 4

Narrow intermittent and intense

Question 5

Convective precipitation systems may be

Answer 5

hydrostatic (e.g., as in extratropical cyclones and frontal zones) or non-hydrostatic (e.g., showers and thunderstorms)

Question 6

Stratiform Precipitation Systems these systems are characterized by

Answer 6

relatively gentle vertical fluxes of heat and momentum

Question 7

Stratiform Precipitation Systems This type of precipitation is often found

Answer 7

poleward of warm fronts in a broad region of warm advection.

Question 8

Stratiform precipitation systems are always

Answer 8

hydrostatic

Question 9

Stratiform precipitation regions are relatively

Answer 9

wide, and precipitation from them tends to be steady.

Question 10

Cumulus Convection:

Answer 10

Convection that results in the formation of cumulus clouds (or sometimes thunderstorms) with a flat base and rounded puffy top.

Question 11

Convection refers primarily to atmospheric motions that

Answer 11

transfer heat, moisture and momentum in the vertical direction.

Question 12

As the surface warms, it

Answer 12

heats the overlying air, which gradually becomes less dense than the surrounding air and begins to rise.

Question 13

thermal

Answer 13

The bubble of relatively warm air that rises upward from the surface

Question 14

Convective clouds (such as ………………..) are usually referred as

Answer 14

cumulonimbus deep, if their depth is a substantial fraction of the depth of the troposphere.

Question 15

Deep cumulus convection may be “based” either in

Answer 15

the boundary layer or aloft.

Question 16

A parcel of air that is warmer than its environment will

Answer 16

A parcel of air that is warmer than its environment will

Question 17

As an unsaturated air parcel located near the surface rises, its temperature will

Answer 17

follow a dry adiabat

Question 18

lifted condensation level (LCL)

Answer 18

Where the dry adiabat crosses the saturation mixing ratio line, the air becomes saturated and condensation commences.

Question 19

when does level of free convection LFC occure

Answer 19

If there is no convective inhibition blocking the ascent of the rising air parcel, the lifted condensation level becomes the level of free convection, or LFC.

Question 20

Level of Free Convection (LFC):

Answer 20

The height at which a lifted parcel of air would first become warmer (less dense) than the surrounding air.

Question 21

As the parcel continues to rise, it follows a

Answer 21

moist adiabat

Question 22

As the parcel continues to rise, it follows a moist adiabat. Once the parcel reaches the ……… and becomes …………………………………

Answer 22

LFC and becomes less dense than the surrounding air

Question 23

Once the parcel reaches the LFC and becomes less dense than the surrounding air, it continues to

Answer 23

rise freely until it becomes as cool (as dense) as the surrounding air.

Question 24

Once the parcel reaches the LFC and becomes less dense than the surrounding air, it continues to rise freely until it becomes as cool (as dense) as the surrounding air. This upper level is the

Answer 24

Equilibrium Level (EL).

Question 25

CAPE stands for

Answer 25

Convective Available Potential Energy

Question 26

An estimate of buoyant energy can be computed by

Answer 26

determining the temperature difference between the ascent path and the environment at all levels from the LFC up through the equilibrium level.

Question 27

the positive area between two curves equals

Answer 27

When we sum up all of these temperature differences, we arrive at a number equal to

Question 28

…………………………………………. is CAPE, which is given by:

Answer 28

The quantitative measure of this positive area

Question 29

CAPE is measured in units of

Answer 29

J/kg

Question 30

The environmental CAPE for convective storms is often in the range of

Answer 30

1000-2000 J/kg

Question 31

The environmental CAPE for convective storms is often in the range of 1000-2000 J/kg. However, values higher than ……… sometimes occure

Answer 31

5000 J/kg

Question 32

Wmax

Answer 32

Maximum Potential Speed of the Updraft

Question 33

The maximum potential speed of the updraft (………………….), or Wmax, can be directly obtained from ………….. as shown by this equation:

Answer 33

maximum vertical velocity

CAPE

Question 34

the wmax equation is derived from

Answer 34

from a simplification of the vertical momentum equation by ignoring mixing, water loading, and pressure effects

Question 35

In reality, these simplifications mean that Wmax often

Answer 35

overestimates the actual updraft value by a factor of 2.

Question 36

For example, using this equation, a relatively high CAPE of 2000 J/kg would indicate a Wmax of

Answer 36

63.2 m/s

Question 37

For example, using this equation, a relatively high CAPE of 2000 J/kg would indicate a Wmax of 63.2 m/s, or, allowing for the overestimate, a more probable

Answer 37

Wmax of 31.6 m/s, or about 65 knots.

Question 38

Capping inversion acts as a

Answer 38

lid

Question 39

Capping inversion acts as a lid, which can prevent

Answer 39

near-surface parcels from reaching their level of free convection (LFC).

Question 40

CIN can prevent

Answer 40

storms from forming, even with high instability aloft.

Question 41

In the presence of a capping inversion, some additional mechanism (………………………………………………) is required to initiate convection.

Answer 41

like heating, moistening and synoptic scale lifting

Question 42

convective inhibition (CIN)

Answer 42

The work needed to lift an air parcel from rest at the surface to the LFC

Question 43

convective inhibition (CIN) it is the

Answer 43

It is the negative of the area enclosed by the environmental temperature profile and the dry and moist adiabats connecting the surface to the LFC on skew-T.

Question 44

For CIN > …………………deep convection is unlikely to occur in the absence of external forcing

Answer 44

100 J kg-1

Question 45

For CIN > 100 J kg-1, deep convection is unlikely to occur in the absence of external forcing, such as might be provided by

Answer 45

daytime heating or the approach of a strong front.

Question 46

The basic building block of the convective systems is the

Answer 46

thunderstorm cell (or deep convection)

Question 47

Deep convection takes in to various forms of convective systems:

Answer 47

a. single convective cells (some thunderstorms) consisting of a single updraft and downdraft – form under conditions of weak vertical wind shear.
b. multi cell storms (e.g., squall lines) made up of organized groups or sequences of convective cells – that develop under conditions of strong vertical wind shear and
c. supercells with rotating updrafts formed from the multicell storms mesoscale convective systems (MCS) - bands or zones of clouds and precipitation on a scale of 100 km or larger in at least one direction that are generated by interacting convective cells.

Question 48

Both multi- and supercell storms are capable of producing

Answer 48

hail and strong winds

Question 49

Most damaging tornadoes are associated with

Answer 49

supercell storms

Question 50

The necessary conditions for the occurrence of deep convection are:

Answer 50

• the existence of a conditionally unstable lapse rate Γ_w < Γ ≤ Γ_d
• substantial boundary-layer moisture, and
• low level convergence (or lifting) sufficient to release the instability.

Question 51

Convection feeds on

Answer 51

the potential energy inherent in the temperature and moisture stratification.

Question 52

The so-called convective available potential energy (CAPE), (in J kg-1) of a reference air parcel is given by:

Answer 52

Question 53

T^’_v and T_v​ stand for

Answer 53

virtual temp of the parcel and environment

Question 54

The reference air parcel used in computing the CAPE may be an air parcel at

Answer 54

the Earth’s surface

Question 55

The reference air parcel used in computing the CAPE may be an air parcel at the Earth’s surface or it may be chosen to be representative of the

Answer 55

mean temperature and humidity of the air within the boundary layer.

Question 56

The reference air parcel used in computing the CAPE may be

Answer 56

an air parcel at the Earth’s surface or it may be chosen to be representative of the mean temperature and humidity of the air within the boundary layer.

Question 57

Convective storms often form in an environment in which

Answer 57

the vertical wind shear vector (do V/do z) is dominated by the increase in scalar wind speed V with height.

Question 58

The strength of the shear affects the ……………………………… within the storm

Answer 58

vertical tilt of the updrafts and downdrafts

Question 59

The strength of the shear affects the vertical tilt of the updrafts and downdrafts within the storm:

Answer 59

• weak shear favors a structure in which the downdraft ultimately isolates the updraft from its supply of low level moisture leading to the storm’s demise,
• strong shear favors a tilted structure with a relationship between updraft and downdraft, resulting in more intense, longer lived storms capable of producing hail and strong winds

Question 60

Changes in wind direction with height also play an important role in the

Answer 60

dynamics of convective storms

Question 61

In the presence of vertical wind shear

Answer 61

air possesses vorticity that can be visualized as a rolling motion about a horizontal axis.

Question 62

explain the rotation of the convective systems

Answer 62

When boundary layer air is drawn into the updraft of a convective storm, the vorticity about a horizontal axis may be tilted so that it is transformed into vorticity about a vertical axis

Question 63

When boundary layer air is drawn into the updraft of a convective storm, the vorticity about a horizontal axis may be tilted so that it is transformed into vorticity about a vertical axis

Note how

Answer 63

ounterclockwise vorticity about the x axis (as viewed looking in the positive direction along the axis) is tilted into counterclockwise vorticity about the z axis, as viewed from above.

Question 64

In the presence of vertical wind shear, air possesses vorticity that can be visualized as a rolling motion about a horizontal axis.

This is a powerful mechanism for

Answer 64

imparting rotation to convective storms

Question 65

When the environmental vertical shear is relatively weak and only the CAPE is dynamically significant, ………….. occure

Answer 65

ordinary cells

Question 66

When the low level vertical shear is larger and the CAPE is not too small a …………………….. storm can form

Answer 66

multicell (succession of ordinary cells)

Question 67

If CAPE is high and the vertical shear is strong,

Answer 67

a supercell forms

Question 68

Since storm behavior is a function of

Answer 68

both shear and updraft strength

Question 69

Since storm behavior is a function of both shear and updraft strength, and maximum updraft strength is a function of

Answer 69

CAPE

Question 71

Since storm behavior is a function of both shear and updraft strength, and maximum updraft strength is a function of CAPE, it is useful to consider an

Answer 71

empirical quantity, the bulk Richardson’s number (R).

Question 72

The bulk Richardson’s number is

Answer 72

ratio of CAPE to a quantity proportional to the square of the mean vertical shear integrated over height (S2) as an indicator of storm type

Question 73

what is (R)’s formula

Answer 73

Question 74

u₆₀₀₀ and u₅₀₀​ are

Answer 74

the pressure-weighted mean-vector wind speeds in the

lowest 6 km and 500 m, respectively.

Question 75

Observational and numerical work suggests that ordinary cells form exclusively when R is

Answer 75

greater than 30-40

Question 76

When R is …………………….., supercells or long-lived multicell storms develop.

Answer 76

smaller (<40)

Question 77

If R is ………………, while both ………………………………, less severe long-lived cells are possible.

Answer 77

less than 30-40

the CAPE and the vertical shear are small

Question 78

Thunderstorms (single cell storms)

These are

Answer 78

the small isolated cumulonimbus clouds produced by local convection in an unstable airmass rather than by fronts or instability lines.

Question 79

Thunderstorms (single cell storms)

These systems generally develop

Answer 79

just one main precipitation shower (a single cell storm), and the pressure field is entirely determined by buoyancy of the warm updraft.

Question 80

Thunderstorms (single cell storms)

Only about ………of the water vapor ………………….in the updraft actually reaches the ground in the form of precipitation.

Answer 80

20%

condensed

Question 81

Thunderstorms (single cell storms)

Only about 20% of the water vapor condensed in the updraft actually reaches the ground in the form of precipitation.

The remainder

Answer 81

evaporates either in the downdraft or into the ambient air.

Question 82

self-destruct mechanism:

Answer 82

The single-cell thunderstorm is short lived and rarely produces destructive winds or hail because it contains a built in self-destruct mechanism namely, the downdraft circulation.

Question 83

In the absence of vertical wind shear, the precipitation produced in

Answer 83

the downdraft destroys the buoyant updrafts that feed it.

Question 84

Multicell storms are characterized by

Answer 84

a succession of cells, each evolving through its own cycle as in a single cell storm and promoting the development of new cells.

Question 85

A prominent feature of many convective storms is the gust front, where

Answer 85

warm, moist boundary-layer air is lifted by the leading edge of the evaporatively cooled air diverging from the base of the downdraft.

Question 86

New cells tend to form along the

Answer 86

advancing gust front

Question 87

New cells tend to form along the advancing gust front, sustaining​ ………………. while

Answer 87

the multicell storm

older cells die out as they fall behind the gust front and become surrounded by cooler, denser downdraft air.

Question 88

From the perspective of a ground-based observer, the passage of this storm would be marked by

Answer 88

thickening high overcast, followed by the approach of a much lower, darker cloud base, followed by an abrupt wind shift and temperature drop that marks the arrival of the gust front.

Question 89

Multicell storms

Heavy precipitation would not begin until

Answer 89

a few minutes after the passage of the gust front and might include hail.