ON THE POSSIBILITY OF WEATHER MODIFICATION BY AIRCRAFT CONTRAILS

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· WALLACE B. MURCRAY

ABSTRACT

The possible effect of contrails in modifying the weather is reconsidered in the light of information obtained from ground-level contrails in Alaska. It appears likely that inadvertent cloud seeding by jet aircraft may be of the same order of magnitude as that attained in commercial cloud seeding operations. Further investigation is needed; but in the meantime, the possibility of contrail contamination should be kept in mind when evaluating the results of seeding operations.

Journal of Applied Meteorology

Article: pp. 496–508 | Abstract | PDF (1.01M)

Midwestern Cloud, Sunshine and Temperature Trends since 1901: Possible Evidence of Jet Contrail Effects

Stanley A. Changnon

Illinois State Water Survey, Champaign 61820

(Manuscript received July 18, 1980, in final form January 27, 1981)

DOI: 10.1175/1520-0450(1981)020<0496:MCSATT>2.0.CO;2

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ABSTRACT

Records of monthly sky cover, sunshine and temperature for 1901–77 in a 10-state midwestern area were analyzed on a temporal and spatial basis to discern long-term trends and indications of shifts potentially due to added cirrus generated by jet aircraft since about 1960. The skycover data show generally long-term increasing frequencies of cloudy days and decreases in clear days since 1901. Percent of possible sunshine also shows a decrease but to a lesser extent than clear day frequencies. Changes have been greatest since the 1930's. The greatest shifts to cloudier, less sunny conditions occurred since 1960 in an east-west zone across southern Iowa-northern Missouri, northern two-thirds of Illinois and Indiana, and extreme southern sections of Wisconsin and lower Michigan, the area where commercial jet traffic has been greatest. The long-term trends give evidence of natural climate changes, whereas the localized shifts to more cloudiness in the central area since 1960 suggest anomalous changes related to jet-induced cirrus. Months with moderated temperatures (below average maximum and above average minimum) have increased since 1960 in the central east-west zone and largely in summer and fall, the seasons with the major shifts to cloudiness.

NATURAL AEROSOLS AND AIRCRAFT AEROSOL WX ENGINEERING

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Title:		A possible change in cloud radiative forcing due to aircraft exhaust
Authors:		Wyser, K.; Ström, J.
Publication:		Geophysical Research Letters, Volume 25, Issue 10, p. 1673-1676 (GeoRL Homepage)
Publication Date:		00/1998
Origin:		AGU
AGU Keywords:		Atmospheric Composition and Structure: Cloud physics and chemistry, Atmospheric Composition and Structure: Pollution-urban and regional, Meteorology and Atmospheric Dynamics: Radiative processes
Abstract Copyright:		(c) 1998: American Geophysical Union
DOI:		10.1029/98GL51091
Bibliographic Code:		1998GeoRL..25.1673W

Abstract

Aircraft exhaust may reduce the crystal size in natural cirrus. This work investigates the change in cloud radiative forcing from such a size reduction by assuming a constant ice water content. A 1-dim model with radiative properties that depend on the mean crystal size is used to compute the radiative transfer for an atmospheric column. The results show that the negative shortwave cloud forcing is enhanced with smaller crystals as they mainly increase the reflectivity of clouds. The change in the longwave cloud forcing is always positive although its magnitude depends strongly on the ice water path. The weighted sum of SW and LW cloud forcings depends on the mean crystal size, surface albedo and ice water content. It appears that there is a range of diameters between 15 and 25 μm where the response to a reduction in crystal size is fairly insensitive. Below and above this range the change is negative or positive, respectively. In regions of dense airtraffic the magnitude of the change in cloud forcing could be on the order of 0.3 Wm^-2 under the assumption of a 20% decrease of the mean crystal size from about 30 μm to 24 μm. Aircraft exhaust thus has the potential to affect the climate but the results should be taken with caution as they are based on parameterized optical properties for cirrus clouds.

Bulletin of the American Meteorological Society

Article: pp. 301–309 | Abstract | PDF (1.24M)

Jet Contrails and Cirrus Cloud: A Feasibility Study Employing High-Resolution Satellite Imagery

Andrew M. Carleton^a and Peter J. Lamb^b

a. Department of Geography, Indiana University, Bloomington
b. Climate and Meteorology Section, Illinois State Water Survey, Champaign, IL 61820.

DOI: 10.1175/1520-0477(1986)067<0301:JCACCA>2.0.CO;2

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· Andrew M. Carleton

· Peter J. Lamb

ABSTRACT

The results of a pilot study to assess the feasibility of documenting the occurrence of jet contrails over the United States from high-resolution Defense Meteorological Satellite Program (DMSP) imagery are presented. They are strongly positive, suggesting that 1) contrails can be distinguished from natural cirrus on the imagery; 2) contrails are consistently identifiable; 3) contrails often occur in association with the natural cirrus and frequently spread, and 4) this spreading could extend the accompanying natural cirrus shield. The analyses also indicate that contrails tend to occur relatively frequently, that they more often cluster in groups than appear singly, and that they seem to show a preference for developing in (near) upper-tropospheric cold troughs (ridgelines). It is accordingly suggested that DMSP imagery can provide a basis for research into a contrail-cirrus-climate relationship.

FEBRUARY 2002

AMERICAN METEOROLOGICAL SOCIETY

| CONTROLLING THE

GLOBAL WEATHER

OSS

N. H

OFFMAN

AFFILIATION:

OFFMAN

—Atmospheric and Environmental

Research, Inc., Lexington, Massachusetts

CORRESPONDING AUTHOR:

Ross N. Hoffman, Atmospheric and

Environmental Research, Inc., 131 Hartwell Avenue, Lexington, MA

02421-3126

E-mail: rhoffman@aer.com

In final form 25 September 2001

It had not been easy to persuade the surviving superpowers to relinquish their orbital for-

tresses and to hand them over to the Global Weather Authority, in what was—if the meta-

phor could be stretched that far—the last and most dramatic example of beating swords into

plowshares. Now the lasers that had once threatened mankind directed their beams into care-

fully selected portions of the atmosphere, or onto heat-absorbing target areas in remote re-

gions of the earth. The energy they contained was trifling compared with that of the smallest

storm; but so is the energy of the falling stone that triggers an avalanche, or the single neu-

tron that starts a chain reaction.—A

RTHUR

C. C

LARKE

, Fountains of Paradise, 1978

Technological advances over the next 30–50 years may make it possible to control the

weather. If we can, should we? Are “weather wars” inevitable?

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FEBRUARY 2002

The earth’s atmosphere has been hypothesized to be chaotic. Chaos implies that there is a finite predictability time limit no matter how well the atmosphere is observed and modelled. It is generally accepted that this limit is typically 2 weeks for large-scale weather systems (Lorenz 1982), although some situations may be more or less predictable, and smaller scales are certainly less predictable. Chaos also implies sensitivity to small perturbations. The most realistic numerical weather prediction (NWP) models are very sensitive to initial conditions. It is therefore very likely that the atmosphere is also extremely sensitive to small perturbations.

A series of such perturbations to the atmosphere might be devised to effectively control the evolution of the atmosphere, if the atmosphere is observed and modelled sufficiently well. We present system architecture to control the global weather that might be implemented within a few decades.

It is a dream of mankind to control the weather—not to make every day the same, but to protect lives and property. We believe that this dream is in fact a possibility. Just imagine: no droughts, no tornadoes, no snowstorms during rush hour, etc.

We probably cannot eliminate hurricanes, but we might be able to control the paths of hurricanes, and essentially prevent hurricanes from striking population centres. Our goal is not to change the climate, but to control the precise timing and paths of weather systems. For ex-ample, eliminating hurricanes and the associated mix-

ing of the upper layers of the ocean would presumably change the climate in many indirect ways. Because of the intensive coupling of the weather over different regions of the globe, nothing short of control of the global weather should be considered.

The nation that controls its own weather will necessarily control the weather of other nations. If there are several nations, each attempting to control the

weather over its territory, then each may operate at odds with the others and “weather wars” are conceivable.

An international weather control treaty may be prudent now. In the future, an international agency may be required so that weather control is used “for the good of all.” Perhaps for the good of all is unattainable. Any change to weather will have both positive and negative effects. How can the interests of both the “winners and losers” be accommodated?

OF course, weather always has both positive and negative effects, and there are winners and losers now. In what follows we present the underlying concepts for our approach and then outline the system architecture of a controller for the global atmosphere, describing the components of such a controller. Legal and ethical questions are only touched on, and the issues of feasibility and cost–benefit trade-offs are only briefly considered. Our proposed controller is similar in general to feedback control systems common in many industrial processes; however, it is greatly complicated by the number of degrees of freedom required to represent the atmosphere adequately, the nonlinear nature of the governing equations, the paucity of observations of the atmosphere, the difficulty of effecting control, and the requirements that control be effected at significant time lags. However, the existence of the technology to implement the weather controller is plausible at the time range of 30–50 yr.

CHAOS, THE LIMITS OF PREDICTABILITY,

AND IMPLICATIONS FOR CONTROL.

Theoretical and model studies have established that the dynamics governing the atmosphere can be extremely sensitive to small changes in initial conditions (e.g., Rabier et al. 1996). Current operational practice at NWP centres illustrate this daily. Examples summarized in what follows include data assimilation, generation of ensembles, and targeted observations.

The key factor enabling control of the weather is that

the atmosphere is sensitive to small perturbations.

That is, it is the very instability of the atmosphere’s dy-

namics that makes global weather control a possibility.

Chaos causes extreme sensitivity to initial condi-

tions. Although the atmosphere, and indeed realistic

models of the atmosphere, have not been proven to

be chaotic, the theory of dynamical systems and chaos

provide a useful background for this discussion. In a

realistic NWP model, since small differences in ini-

tial conditions can grow exponentially, small but cor-

rectly chosen perturbations induce large changes in

the evolution of the simulated weather. Therefore we

hypothesize that as we observe and predict the atmo-

sphere with more and more accuracy, we will become

able to effect control of the atmosphere with se-

quences of smaller and smaller perturbations. Note

the basic difference between predictability and con-

trol theory: Predictability theory states that small dif-

ferences grow; control theory states that a sequence

of small perturbations can be used to track a desired

solution. By tracking (i.e., following) a desired solu-

tion, our control method may overcome differences

between model and reality. We will expand and ex-

plain these basic ideas in the following paragraphs.

The phase space description of dynamical systems. The

evolution of dynamical systems is conveniently dis-

cussed using the phase space description of Poincaré

(Lorenz 1963). The state of the system is specified by

n variables. For continuous systems, such as the at-

mosphere, we may first approximate the continuous

system by discretization and thereby obtain a large

number of coupled nonlinear ordinary differential

equations. For a physically realizable system, the col-

lection of feasible points in the n-dimensional phase

space will be bounded.

For a single time, the state of the system is repre-

sented by a single point. As the system evolves, the

point representing the system will in general describe

a curved line. This is termed the trajectory. If the sys-

tem is in a stable state, the trajectory is just the single

point. Small perturbations about the point decay in

time toward the stable point. A stable point is an

attractor. A stable point is also a fixed point of the

system. There can be unstable fixed points. Some tra-

jectories form closed curves—these represent peri-

odic solutions.

For a realistic model of the atmosphere with fixed

boundary conditions, periodic solutions probably ex-

ist but are unstable. There are many unstable periodic

solutions close to chaotic attractors. Chaotic systems

are aperiodic, but given enough time, return arbi-

trarily close to points in the attractor. For the atmo-

sphere, the lack of success for analog forecast tech-

niques suggests that this return time is very long.

Chaotic systems.The strict definition of chaos describes

it as a behavior of purely deterministic systems with

as few as three components for a continuous phase

space flow (e.g., Lorenz 1963), or as few as a single

component for an iterated mapping (e.g., Lorenz

1964). Chaotic systems can appear to be random when

sampled at timescales that are large compared to the

dynamical timescale. The key characteristics associ-

ated with chaos are that the system be bounded and

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AMERICAN METEOROLOGICAL SOCIETY

possess at least one positive Lyapunov exponent

(Lorenz 1965). A positive Lyapunov exponent implies

average growth in the associated direction that is ex-

ponential. Typically in the phase space of such sys-

tems, a small initial sphere of radiusε will over a short

time deform into an ellipsoid. The axes of the ellip-

soid might be called the finite time or local Lyapunov

directions, and the ratio of these axes to ε might be

called the finite time or local Lyapunov factors. As the

ellipsoid evolves it tends to flatten parallel to the

attractor of the system. Chaotic attractors are also

called strange attractors. A characteristic of these

attractors is that perturbations perpendicular to the

attractor collapse exponentially, while perturbations

parallel to the attractor grow exponentially.

It is for these reasons that we say the small pertur-

bations can grow exponentially. A randomly chosen

perturbation may be decomposed into contributions

from the finite time Lyapunov directions. Some, per-

haps most, will decay, but the others will grow. The

perturbation may therefore first decrease in size, be-

fore growing explosively. A perturbation may also be

constructed which projects only onto a particular

growing mode. Such a perturbation will initially grow

exponentially.

The limits to predictability. Since small differences grow

rapidly in chaotic systems, chaotic systems are diffi-

cult to predict. Inevitably small errors will exist in our

specification of the initial conditions. Further, errors

in model formulation induce errors in the model state

at every model time step. Although the magnitude of

the error may initially decay with time, eventually

small errors will begin to grow exponentially and

continue to do so until they become large. It is gen-

erally accepted that useful forecasts of the instanta-

neous weather beyond 2–3 weeks are impossible

(Lorenz 1982; Simmons et al. 1995).

For the atmosphere, motions occur over a huge

spectrum of scales. Smaller spatial scales have shorter

timescales. Errors in the smallest scales will com-

pletely contaminate those scales on the characteristic

timescale associated with that spatial scale. These er-

rors will then induce errors in the next larger scale

and so on (Lorenz 1969). In fluids, advection implies

that tiny errors on the large scales will in turn cause

large errors on the shortest scales. These interactions

lead to a finite predictability time limit.

Control of chaotic systems. Since chaos may appear to

be random, control of chaos might seem impossible.

But sensitivity to initial conditions also implies sen-

sitivity to small perturbations. As we have mentioned,

small perturbations in some directions decay quickly,

but properly chosen perturbations grow quickly.

Therefore a sequence of very small amplitude but pre-

cisely chosen perturbations will steer the chaotic sys-

tem within its attractor. There have been many stud-

ies reported in the literature that support this view

(Kapitaniak 1996). We note two examples of the con-

trol of chaotic systems.

The first is the phenomena of resonance (Pecora and

Carroll 1990). Suppose that there are two copies of

an evolving dynamical system. Initially the two sys-

tem states are arbitrarily different. One system evolves

freely but is observed. In particular, one variable of

that system is accurately observed. The correspond-

ing variable in the second system is constantly reset

to the value observed in the first system. Over time

all variables of the second system approach the values

of the corresponding variables in the first system. We

say that the second system has become entrained by

the first system.

Second, within the attractor of a chaotic system,

there are a multitude of unstable periodic orbits.

Techniques to compute these orbits are available.

Once the system is close to one of these orbits, it is

possible to continually follow the orbit by regularly

applying small perturbations (Ott et al. 1990).

Control of realistic atmospheric models. To control the

weather we must effect changes on timescales shorter

than those of the examples of the previous section, and

to a system of huge complexity. The numerical meth-

ods used must be computationally feasible. The NWP

community has already taken the first steps to con-

trol large dynamical systems. One current NWP data

assimilation practice, called 4DVAR, finds the small-

est perturbation at the start of each data assimilation

period, which grows to best fit all the available data,

thereby demonstrating the practical control of large-

scale realistic systems. Current 4DVAR practice finds

the smallest global perturbation, as measured by the

a priori or background error covariances, but it should

be possible to modify 4DVAR to find the smallest lo-

cal perturbation or the smallest perturbation of a par-

ticular type. This method is described further in the

section about data assimilation systems. Further, some

other current NWP technology may be adapted to de-

termine the optimal perturbations to effect control.

These techniques are described in what follows.

INGULAR VECTORS

.Singular vectors are the fastest grow-

ing perturbations about a given model forecast over

a finite time interval, say 24 or 72 h, with respect to a

particular measure of difference. (For example, the

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FEBRUARY 2002

size of the perturbation might be taken to be its en-

ergy.) Singular vectors are currently calculated opera-

tionally at the European Centre for Medium-Range

Weather Forecasts (ECMWF) for the purpose of en-

semble forecasting (Molteni et al. 1996). In principle,

ensemble forecasting introduces equally likely small

perturbations in the initial conditions of each en-

semble member. In practice, because each of the fore-

casts within the ensemble is computationally expen-

sive, only perturbations that are rapidly growing are

included. The growth rates of these perturbations are

explosive—24-h amplification factors of 10–20 are

reported for large-scale calculations with limited

physics, and much larger amplification factors are

expected when smaller scales and moist physics are

included. A basic version of control can be effected

by calculating the leading singular vectors, determin-

ing if a positive or negative perturbation along one of

these modes would produce a desired result, and then

introducing that perturbation, if it was feasible.

ARGETED OBSERVATIONS

. During the last decade there

has been considerable research on targeted observa-

tions (Lorenz and Emanuel 1998; Bergot et al. 1999;

Bishop and Toth 1999). Given a current forecast of

some storm of interest, we can backtrack from the

forecast to find that region of the initial state that, if

better observed, would improve the forecast of that

storm. The theory and methodology of this approach

have advanced sufficiently so that actual trials were

undertaken for several field experiments including the

Fronts and Atlantic Storm-Track Experiment

(FASTEX; Joly et al. 1997), the North Pacific Experi-

ment (NORPEX; Langland et al. 1999), and the 1999

Winter Storms Reconnaissance Program (WSRP 99;

Bergot et al. 1999).

This technology can be adapted to calculate the

optimal perturbation. Determining where to target

observations is related to the problem of determin-

ing where to introduce perturbations to effect a cer-

tain change in the forecast. In both cases we are opti-

mizing a figure of merit or objective function that is

calculated in terms of the forecast with respect to

some change in the initial conditions. Note that the

figure of merit can include both costs and benefits.

THE GLOBAL WEATHER CONTROL SYS-

TEM. The global weather control (GWC) system we

envision is a feedback control system, made complicated

by a number of factors. These include the following:

• The number of degrees of freedom required to

represent the atmosphere adequately.

• The nonlinear nature of the governing equations.

The atmosphere is nonlinear and sometimes dis-

continuous. For example, clouds have sharp edges.

• The paucity and inaccuracy of observations of the

atmosphere. Satellites provide a huge volume of

information. However this information is not al-

ways in the right place, accurate enough, or of the

right type.

• The control must be effected at significant time lags

to minimize the size of the perturbations, yet the

system is inherently unpredictable at long lead times.

• The difficulty of effecting control. The control

mechanisms do not yet exist. The ideal perturba-

tions, while small in amplitude, may be large in

scale.

• The ambiguous nature of the figure of merit. For

inhabitants of New Orleans, eliminating a hurri-

cane threat to that city may take precedence over

all else. But in general attempting to satisfy mul-

tiple objectives may result in conflicts.

The GWC system is sketched in Fig. 1. The “con-

troller” and “random effects” perturb the system state.

The controller must therefore compete with random

effects. However the controller perturbations are de-

signed to grow, while the random effects perturba-

tions tend to decay. The “governing equations” ad-

vance the system from time t

to time t

n+1

. If we

eliminate the “observations” and controller elements

in this figure we have a sketch showing how a NWP

model approximates the atmosphere. On the other

hand, if we remove only the random effects element,

we have a sketch of a system that must be simulated

within the controller element in order to estimate the

system state and then the optimal perturbations. Note

the various noise sources: The observations are inex-

act, the perturbations are effected with some inaccura-

cies, the model introduces further errors. The statistics

of these errors are also inexact and must be estimated

empirically (from the time history of the differences

between short-term forecasts and observations).

Cost–benefit trade-offs. Controlling small-scale phe-

nomena will not be cost effective. Certainly we want

to control destructive tornadoes, but the time- and

space scales are so fine that this may be impossible on

an individual basis. It may be more effective to elimi-

nate the large-scale conditions leading to the forma-

tion of tornadoes. In general, theoretical predictabil-

ity studies (Lorenz 1969) suggest that doubling the

resolution of the observations will only increase pre-

dictability by an amount similar in magnitude to the

timescale of the motions of the smallest resolved phe-

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AMERICAN METEOROLOGICAL SOCIETY

nomena. For example, since the timescale for the evo-

lution of a thunderstorm is smaller than 1 h, observ-

ing details of individual thunderstorms will improve

predictability by no more than 1 h. Effecting control

at very large scales may not be cost effective either.

The largest spatial scales have the largest “inertia.”

These scales have the longest associated timescales and

the greatest part of the energy (Nastrom et al. 1984).

The GWC system will be subject to optimization

itself. Our control of the weather will increase as we

increase the skill of the NWP models, the accuracy of

the observations, and the size of the controlling per-

turbations. All three facets of the problem require re-

sources. A cost–benefit analysis will balance resources

devoted to remote sensing, computer power, and per-

turbations. As advances in the supporting disciplines

accumulate, the optimal point will shift, become fea-

sible, and eventually become economically sensible.

Enabling technology.Implementation of the overall sys-

tem architecture will require major advances in many

disciplines. Here we discuss the required discoveries

and refinements. Although it is difficult to predict the

pace of technological advance, the control of the

weather is a plausible outcome of advances in various

fields over the time span of a few decades.

UMERICAL WEATHER PREDICTION

. NWP is now a mature

science (Kalnay et al. 1998). Advances in computer

power will enable the refinement of NWP. Current

high-resolution mesoscale models point the way for

advances in global models. In early NWP models,

many physical processes were either removed by

filtering approximations or modeled by parameteri-

zations. As NWP models evolve, more and more of

the physics of the atmosphere are resolved explicitly.

A recent report (ECMWF 1999) makes estimates

of the spatial resolving power of NWP models over

the next decade. In summary, this report predicts

horizontal resolution increasing from the current 60

to 15 km by 2008. Extrapolating for another 30 yr sug-

gests global resolution of approximately 250 m.

(Currently vertical resolution is much finer than hori-

zontal resolution, but at the much higher future hori-

zontal resolution, the same scale will be appropriate

for both horizontal and vertical resolution in the tro-

posphere. This would allow even higher resolution

than our simple extrapolation would suggest.)

ATA ASSIMILATION SYSTEMS

. Data assimilation systems

estimate the state of the atmosphere given limited

observations and an imperfect model of the evolution

of the atmosphere. This problem is complicated by the

paucity of observations, the huge number of degrees

of freedom needed to specify the atmosphere, and

the extreme nonlinearity of the governing equa-

tions. The data assimilation system is a key part of

the controller of Fig. 1—the data assimilation pro-

vides estimates of the current state of the atmo-

sphere.

The current state of the art is 4DVAR or four-

dimensional variational data assimilation. Opera-

tional 4DVAR assumes a perfect model over short

time periods (6 or 24 h) and finds the initial condi-

tion at the start of the period that best fits all avail-

able observations during the period (e.g., Thépaut

et al. 1993). [This optimization is made efficient by

the adjoint technique. In practical implementations,

the adjoint model performs a backward in time in-

tegration of the sensitivity of the objective function

to the model state (Courtier 1997).] Because the

NWP model is used to extrapolate the initial condi-

tions, the 4DVAR solution is necessarily dynamically

consistent. The end point of the solution from the

previous period is called the background and is used

as a special type of observation. The error structure

of the background is necessarily complex but has a

greatly simplified representation in current versions

of 4DVAR. In the near future we expect to see

higher resolution used in 4DVAR in line with in-

creases in resolution in NWP models, better esti-

mates of the background error statistics, and a con-

vergence to the Kalman filter methodology (Todling

and Cohn 1994; Houtekamer and Mitchell 1998).

ATELLITE REMOTE SENSING

. Satellites observe the at-

mosphere and the earth’s surface with global cover-

age, rapid refresh, and high horizontal resolution in vis-

.1. Schematic global weather controller flow chart.

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FEBRUARY 2002

ible, infrared, and microwave spectral domains.

Sensors currently being prepared for launch have

very high spectral resolution, which in turn will pro-

duce higher vertical resolution for the retrieved tem-

perature and moisture profiles. Advances are ex-

pected in terms of higher resolution, greater numbers

of satellites, and higher accuracy in the future. Ac-

tive sensors, such as the Tropical Rainfall Measuring

Mission (TRMM) precipitation radar, may be used

more in the future.

The ability to collect observations from space cur-

rently outstrips our ability to use these data in global

NWP. Typically, the observations are thinned to re-

duce resolution and quantity. This will be more of a

problem with higher spectral resolution sensors.

However, advances in computing power and data as-

similation techniques will improve this situation.

PERTURBATIONS

. Everything mankind does that can be

controlled may be considered a source of perturba-

tions. Here we mention a few possibilities:

• Aircraft produce contrails. Contrails are essentially

cirrus clouds and influence both the solar and ther-

mal radiation (Poellot et al. 1999). Slight variations

in the timing, levels, and routes of aircraft would

produce perturbations (Murcray 1970).

• Solar reflectors, in low earth orbit, capable of vary-

ing orientation, would produce bright spots on the

night side, and shadows on the day side, thereby

changing the heating of the atmosphere. First

steps have already been taken. However, the lat-

est Russian experiment, named Znamya 2.5, failed

to unfurl a 25-m diameter thin sheet mirror in

space in February 1999 (Beatty 1999). In the fu-

ture inflatable structures may be used (Dornheim

1999).

• Solar-powered generators in geostationary orbit

have been suggested as a low-cost energy source.

A concern is that losses from the microwave down-

link would be a heat source (Lee et al. 1979). If the

spatial area and timing of the downlink were con-

trolled this would be a source of perturbations. In

addition, tuning of the microwave downlink fre-

quency would control the height in the atmosphere

of the energy deposition.

• An enormous grid of fans that doubled as wind

turbines might transfer atmospheric momentum

in the form of electric energy.

To be effective the individual actions must be co-

ordinated, so that the total perturbation is one that

produces a desired effect. This may be difficult.

COMPUTER TECHNOLOGY

. Computer processing capabil-

ity has been increasing exponentially. The require-

ments of GWC are truly staggering, but global NWP

models at the subkilometer scale seem attainable in the

30–50 yr time frame, if the pace of advances in com-

puter technology can be maintained. (If computer

power doubles every year, then after 30 yr it will have

increased 1 billion times.) However, current estimates

suggest that Moore’s laws governing the exponential

growth of chip functionality as well as the exponen-

tial growth of the cost of chip fabrication facilities will

encounter physical obstacles around 2012 (Birnbaum

and Williams 2000). Potential breakthroughs in nano-

technology, quantum devices, or in other areas will be

needed.

SYSTEM INTEGRATION

.The GWC system is a megasystem.

Development of tools and methodologies for

megasystems engineering is driven by recent defense

and aerospace projects, such as the space shuttle, the

strategic defense initiative (SDI), etc. In some ways

the GWC system is analogous to SDI. Both require

huge real-time data gathering, prediction, and com-

mand capabilities. For GWC the problem is more

complex, but the timescale is more relaxed and there

is no active opposing intelligence.

Concluding remarks: The next step.The next step should

involve demonstration tests in simulation. We suggest

a focus on the hurricane problem. This problem is

both important and feasible. Controlling the path of

hurricanes will be a first-order priority of GWC. A hur-

ricane track is largely determined by winds of the

large-scale environment. Reasonable forecasts of hur-

ricane tracks can be made without modeling the in-

ternal dynamics of the hurricane. Recent studies have

examined the sensitivity of such a model to changes

in initial conditions (Aberson and Franklin 1999;

Cheung and Chan 1999).

For the demonstration tests, we would be con-

cerned only with the forecasting and control of the

hurricane tracks. For this purpose our “NWP” model

could be a simple quasigeostropic model. The hurri-

cane could be modeled as a vertical tracer. A plausible

control mechanism would be localized height pertur-

bations. The goal would be to protect the Gulf and

East Coast populations centers. This setup is feasible

and capable of exploring some of the issues related to

the practicality of global weather control and to quan-

tify, albeit in a limited context, the required resources

to effect GWC. Of course application to real hurricanes

will require a model that faithfully predicts hurricane

tracks.

Page 7

247

FEBRUARY 2002

AMERICAN METEOROLOGICAL SOCIETY

On a personal note, I first put the main ideas ex-

pressed here on paper in the fall of 1977 as part of a

potential thesis proposal. My advisor, E. N. Lorenz,

commented that this was an interesting idea but too

risky for a thesis topic. Control of the global atmo-

sphere is still a risky research topic, but there have

been substantial technological advances in many of

the supporting disciplines—computers, models, re-

mote sensing, etc. We believe there is a good reason

to pursue this research now.

The concept of global weather control raises a host

of sociological, ecological, and political issues. These

issues will only receive proper attention when global

weather control seems plausible. The questions raised

in these arenas will not be easy to resolve, and progress

is likely to be slow compared to the advance of tech-

nology. Therefore, it seems important to demonstrate

this plausibility now, long before technology advances

to the point of potential implementation, in order to

motivate a thorough discussion of whether or not, and

if so, to what extent and under what circumstances

we actually do wish to control the weather.

ACKNOWLEDGMENTS. I have benefitted from com-

ments on this paper by R. Rosen, K. Emanuel, J. Hansen,

R. Anthes, and an anonymous reviewer. This work was sup-

ported in part by the NASA Institute for Advanced Con-

cepts (NIAC) through a grant from the Universities Space

Research Association (USRA).

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Aberson S. D., and J. L. Franklin, 1999: Impact on hur-

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dropwindsonde observations from the first-season

flights of the NOAA Gulfstream-IV jet aircraft. Bull.

Amer. Meteor. Soc., 80, 421–427.

Beatty, J. K., 1999: Up in the sky! It’s a bird, it’s a plane,

it’s Znamya! Sky Telescope, p. 19. [http://

www.skypub.com/new/special/znamya.html.]

Bergot, T., G. Hello, A. Joly, and S. Malardel, 1999: Adap-

tive observations: A feasibility study. Mon. Wea. Rev.,

127, 743–765.

Birnbaum, J., and R. S. Williams, 2000: Physics and

the information revolution. Phys. Today, 53, 38–42.

Bishop, C. H., and Z. Toth, 1999: Ensemble transforma-

tion and adaptive observations. J. Atmos. Sci., 56,

1748–1765.

Cheung, K. K. W., and J. C. L. Chan, 1999: Ensemble

forecasting of tropical cyclone motion using a

barotropic model. Part I: Perturbation of the environ-

ment. Mon. Wea. Rev., 127, 1229–1243.

Courtier, P., 1997: Variational methods. J. Meteor. Soc.

Japan, 75, 211–218.

Dornheim, M. A., 1999: Inflatable structures taking to

flight. Aviation Week Space Technol., 150, 60–62.

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awarticle.html.]

ECMWF, 1999: A strategy for ECMWF, 1999–2008.

European Centers for Medium-Range Weather Fore-

casts, Reading, United Kingdom, 16 pp.

Houtekamer, P. O., and H. L. Mitchell, 1998: Data as-

similation using an ensemble Kalman filter tech-

nique. Mon. Wea. Rev., 126, 796–811.

Joly, A., and Coauthors, 1997: The fronts and Atlantic

stormtrack experiment (FASTEX): Scientific objec-

tives and experimental design. Bull. Amer. Meteor.

Soc., 78, 1917–1940.

Kalnay, E., S. J. Lord, and R. D. McPherson, 1998: Matu-

rity of operational numerical weather prediction: Me-

dium range. Bull. Amer. Meteor. Soc., 79, 2753–2769.

Kapitaniak, T., 1996: Controlling Chaos: Theoretical and

Practical Methods in Non-linear Dynamics. Academic

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cific experiment (NORPEX—98) targeted observa-

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Optical properties of contrail-induced cirrus: discussion of unusual halo phenomena.

Sussmann R.

Photographs of a 120 degrees parhelion and a 22 degrees parhelion within persistent contrails are presented. These phenomena result from hexagonal plate-shaped ice crystals oriented horizontally with diameters between 300 mum and 2 mm. From our observations and reinvestigation of previous reports, we conclude that a subset of the population in persistent contrails can consist of highly regular, oriented, hexagonal plates or columns comparable to the most regular crystals in natural cirrus clouds. This is explained by measured ambient humidities below the formation conditions of natural cirrus. The resulting strong azimuthal variability of the scattering phase function impacts the radiative transfer through persistent contrails.

PMID: 18253447 [PubMed - in process]

Multiple Contrail Streamers Observed by Radar

Thomas G. Konrad and John C. Howard

Applied Physics Laboratory, The Johns Hopkins University, Silver Spring, Md. 20910

(Manuscript received November 6, 1973)

DOI: 10.1175/1520-0450(1974)013<0563:MCSOBR>2.0.CO;2

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Effects of aircraft emissions on ozone, cirrus clouds, and global climate

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· Thomas G. Konrad

· John C. Howard

ABSTRACT

An unusual case of multiple streamers or filaments with the characteristic mare's tail pattern in vertical section has been observed by radar where the generating elements were condensation trails laid by high-altitude aircraft. The contrails were laid perpendicular to the wind and as they drifted a multitude of streamers formed along each trail. The streamers extended from 9 km to the ground. Numerous contrails were observed, each of which produced a sheet of streamers. RHI and PPI photographs at X and S band taken over a 2-hr period show the three-dimensional shape of the streamers due to the wind shear. Doppler measurements were also taken. The resulting velocity spectra are very narrow indicating little or no turbulence. Reflectivity factors were measured at various altitudes and show a decrease in reflectivity with distance from the generating line. Fall velocities based on the slopes of the streamer patterns varied from 0.4 to 1.4 m sec⁻¹. In general, the characteristics of the precipitation streamers were quite similar to those previously measured in naturally occurring cloud forms such as cirrus uncinus.

The impact of cruise altitude on contrails and related radiative forcing

Authors: Fichter, Christine; Marquart, Susanne; Sausen, Robert; Lee, David S.

Source: Meteorologische Zeitschrift, Volume 14, Number 4, August 2005 , pp. 563-572(10)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

Within the framework of the European Fifth Framework Project TRADEOFF, the impact of changing cruise altitudes on contrail coverage and corresponding radiative forcing was investigated. On the basis of the reference year 1992, a series of aircraft emissions inventories with changed flight altitudes was prepared. These emission scenarios provide flown distances, fuel consumption and NO_x emissions on a three-dimensional grid. The vertical resolution of these inventories was significantly increased over that used in former inventories. With a downshift of cruise altitude by 2000 ft(Throughout this paper we denote flight levels in ft. 2000 ft convert to approximately 610 m.), 4000 ft, and 6000 ft global annual mean contrail coverage is reduced in an approximately linear manner, reaching a maximum decrease of almost 45 % for a 6000 ft lower cruise altitude. Contrary to this, a slight increase by 6 % of global annual mean contrail coverage resulted for a 2000 ft higher maximum flight altitude. Relative changes of corresponding radiative forcing were shown to be very similar to those of contrail coverage. For changes in contrail coverage and radiative forcing associated with changes in flight altitudes, a strong seasonal and regional variability was found. This study only considers contrail radiative forcing. Trade-offs from other aviation related radiative impacts, e.g., from CO₂ or O₃, have not been studied.

Document Type: Research article

DOI: 10.1127/0941-2948/2005/0048

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BUT SOME CONTRAILS ARE MORE THAN JUST CONTRAILS !!!

STORMS WITHOUT LIGHTNING \: EXPLANATION

CHAFF CLOUDS

Journal of Applied Meteorology

Article: pp. 302–314 | Full Text | PDF (1.53M)

Intense Convective Storms with Little or No Lightning over Central Arizona: A Case of Inadvertent Weather Modification?

Robert A. Maddox, Kenneth W. Howard, and Charles L. Dempsey

NOAA, Environmental Research Laboratories, National Severe Storms Laboratory, Norman, Oklahoma

(Manuscript received February 5, 1996, in final form July 22, 1996)

DOI: 10.1175/1520-0450(1997)036<0302:ICSWLO>2.0.CO;2

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· Robert A. Maddox

· Kenneth W. Howard

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ABSTRACT

On 20/21 August 1993, deep convective storms occurred across much of Arizona, except for the southwestern quarter of the state. Several storms were quite severe, producing downbursts and extensive wind damage in the greater Phoenix area during the late afternoon and evening. The most severe convective storms occurred from 0000 to 0230 UTC 21 August and were noteworthy in that, except for the first reported severe thunderstorm, there was almost no cloud-to-ground (CG) lightning observed during their life cycles. Other intense storms on this day, particularly early storms to the south of Phoenix and those occurring over mountainous terrain to the north and east of Phoenix, were prolific producers of CG lightning. Radar data for an 8-h period (2000 UTC 20 August–0400 UTC 21 August) indicated that 88 convective cells having maximum reflectivities greater than 55 dBZ and persisting longer than 25 min occurred within a 200-km range of Phoenix. Of these cells, 30 were identified as “low-lightning” storms, that is, cells having three or fewer detected CG strikes during their entire radar-detected life cycle. The region within which the low-lightning storms were occurring spread to the north and east during the analysis period.

Examination of the reflectivity structure of the storms using operational Doppler radar data from Phoenix, and of the supportive environment using upper-air sounding data taken at Luke Air Force Base just northwest of Phoenix, revealed no apparent physical reasons for the distinct difference in observed cloud-to-ground lightning character between the storms in and to the west of the immediate Phoenix area versus those to the north, east, and south. However, the radar data do reveal that several extensive clouds of chaff initiated over flight-restricted military ranges to the southwest of Phoenix. The prevailing flow advected the chaff clouds to the north and east. Convective storms that occurred in the area likely affected by the dispersing chaff clouds were characterized by little or no CG lightning.

Field studies in the 1970s demonstrated that chaff injected into building thunderstorms markedly decreased CG lightning strikes. There are no data available regarding either the in-cloud lightning character of storms on this day or the technical specifications of the chaff being used in military aircraft anti–electronic warfare systems. However, it is hypothesized that this case of severe, but low-lightning, convective storms resulted from inadvertent lightning suppression over south-central Arizona due to an extended period of numerous chaff releases over the military ranges.

RADAR CHAFF USES AND TESTS

Journal of Applied Meteorology

Article: pp. 1101–1125 | Abstract | PDF (1.83M)

Chaff Seeding Effects in a Dynamical-Electrical Cloud Model

John H. Helsdon Jr.

Institute of Atmospheric Sciences, South Dakota School of Mines and Technology, Rapid City 57701

(Manuscript received January 24, 1980, in final form June 7, 1980)

DOI: 10.1175/1520-0450(1980)019<1101:CSEIAD>2.0.CO;2

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