Potter T.D., Colman B.R. (co-chief editors). The handbook of weather, climate, and water: dynamics, climate physical meteorology, weather systems, and measurements
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or wet snows are more difficult to detect than deeper snows containing little or no
liquid water. However, a clear advantage of this technology is that it is not greatly
affected by cloud cover, so measurements can be taken day and night during both
clear and cloudy conditions.
Gamma Radiation Remote Sensing
The soil near the surface of Earth constantly emits radiation to space in the form of
gamma waves. Snow cover attenuates this radiation in proportion to the water
content of the snow on the ground. This form of radiation is best detected over
relatively narrow bands by receivers mounted on aircraft. Levels of background
gamma emissions must be measured in the fall prior to snow accumulation and
then along the identical flight path at different times throughout the winter. This
method of mapping snow water equivalent is used operationally in several parts of
the United States where large river flooding from snowmelt is a common problem.
Acoustic Snow Depth Sensing
Point measurements of snow depth can be taken continuously and remotely. Sound
waves from an above-ground transmitter reflect off the snow surface. By measuring
the time for the reflected wave to reach the receiver, the distance can be measured
that corresponds to a snow depth. The depth of older snow is easiest to measure
since the surface tends to become smoother and harder with time. But recent
improvements in signal processing have led to accurate measurements of the
depth of fresh snow as well. Whil e heavy snow is falling, measurements may be
compromised as a por tion of the sound wave is reflected by ice crystals in the air.
Satellite Snow Depth Measurements
High-resolution mapping of the elevation of Earth’s surface is leading to the oppor-
tunity to do similar mapping of snow depth by computing the difference between the
elevation of a current observation with the known elevation of the ground from
previous satellite measurements. The accuracy of this met hod requires extremely
high-resolution background data and nearly perfect navigation of the data.
Portable Depth=Water Content Sensors
New sensors are being developed for use by ski areas and others concerned about
detailed spatial patterns of snow depth and water content. These devices can be sled
mounted and pulled by a skier. Using geographical positioning systems to
automatically map the sensors location, detailed maps of snow depth =water content
can be made.
946 CHALLENGE OF SNOW MEASUREMENTS
6 SUMMARY OF SNOW DATA CONTINUITY
More than 100 years of measurements of snowfall, snow depth, and water content
are available at hundreds of locations in the United States providing a remarkable
resource for meteorological, hydrological, environmental, engineering, and societal
applications. The data, however, are far from perfect. All the challenges to accurate
observations that are described here have been hand led from the very beginning of
quantitative observations with varying degrees of success. Observational consistency
has been hard to maintain due, in par t, to the fact the much of the data have been
gathered by volunteers who have received only modest training and who often can
take only one observation per day. Even at the nation’s primary weather stations,
many changes have occurred over time affecting observational consistency. The
large natural variability in snowfall sometimes hides the impact of observing
changes. Yet, in historical perspective, seemingly small observational changes
such as station exposure, time and frequency of observation, and observing proce-
dures do have profound impacts on historical time series. The example in Figure 8
for Sault Ste. Marie, Michigan, is fairly typical of snowfall time series found in the
United States. It can be very difficult to distinguish between actual climate variations
and true data inhomogeneities.
Perhaps the greatest change in surface observations was the deployment of the
Automated Surface Observing System (ASOS) by the Nationa l Weather Ser vice
during the 1990s as a part of a very extensive national modernization effort.
A change in precipitation gages and the automation of the measurement of visibility
Figure 8 Historic seasonal snowfall totals at Sault Ste. Marie, Michigan. A combination of
station moves, changes in exposure, and changes in observational procedures (some of which
have not been documented are superimposed on what appears to be a very significant long-
term increase in snowfall. Long-term snowfall time series for other parts of the country are
plagued by similar problems. Improving the consistency in observations would make it easier
to confidently identify important climate variations and trends (from Doesken and Judson,
1997).
6 SUMMARY OF SNOW DATA CONTINUITY 947
and precipitation type have resulted in discontinuous records at several hundred
stations. Furthermore, the measurement of snowfall was discontinued completely
at many stations since it was not a requirement of the Federal Aviation Administra-
tion at that time and did not lend itself to automation.
7 SOURCES OF SPECIALIZED SNOW DATA
Incredible resources about snow, historic data, new measurement technologies, and
applications are available, many via the World Wide Web. Some recommended
sources include:
National Weather Service, National Operational Hydrologic Remote Sensing
Center: http:==www.nohrsc.nws.gov
National Snow and Ice Data Center (University of Colorado in collaboration with
the National Oceanic and Atmospheric Administration: http:==nsidc.org
National Oceanic and Atmospheric Administration, National Climatic Data
Center: http:==lwf.ncdc.noaa.gov
U.S. Department of Agriculture, Natural Resources Conservation Service,
National Water and Climate Center: http:==www.wcc.nrcs.usda.gov
U.S. Army Corps of Engineers Cold Regions Research and Engineering
Laboratory: http:==www.crrel.usace.army.mil
National Aeronautics and Space Administration: http:==www.nasa.gov
Website addresses are as of autumn 2001.
REFERENCES
Bamzai, A. S., and J. Shukla (1999). Relation between Eurasian snow cover, snow depth, and
the Indian summer monsoon: An observational study, J. Clim. 12, 3117–3132.
Bergeron, T. (1935). On the Physics of Cloud and Precipitation. Proces Verbaux des Seances de
l’Association de Metiorolgie, UGGI, 5th assemblee generale, Lisbon, Sept. 1933.
Doesken, N. J., and A. Judson (1997). The Snow Booklet: A Guide to the Science, Climatology
and Measurement of Snow in the United States, Atmospheric Science Department,
Colorado State University, Fort Collins.
Doesken, N. J., and R. J. Leffler (2000). Snow foolin’, Weatherwise 53(1), 30–37.
Doesken, N. J., and T. B. McKee (2000). Life after ASOS (Automated Surface Observing
System)—Progress in National Weather Service Snow Measurement. Proceedings, 68th
Annual Meeting, Western Snow Conference, April 18–20, Port Angeles, WA, pp. 69–75.
Goodison, B. E. (1978). Accuracy of Canadian snow gauge measurements, J. Appl. Meteorol.
27, 1542–1548.
Goodison, B. E., and J. R. Metcalf (1992). The WMO Solid Precipitation Intercomparison:
Canadian Assessment, WMO Technical Conference on Instruments and Method of
Observation, WMO=TD No. 462, WMO, Geneva, pp. 221–225.
948
CHALLENGE OF SNOW MEASUREMENTS
Gray, D. M., and D. H. Male (Eds.) (1981). The Handbook of Snow: Principles, Processes,
Management and Use, Toronto, Pergamon.
Hobbs, P. V. (1974). Ice Physics, Bristol, Oxford University Press.
Holyrod, E. W. (1999). Snow Accumulation Algorithm for the WSR-88D Radar: Supplemental
Report, Report #R-99-11, USDI, Bureau of Reclamation, Technical Service Center, Denver.
Judson, A., and N. J. Doesken (2000). Density of freshly fallen snow in the Central Rocky
Mountains, Bull. Am. Meteor. Soc. 81(7), 1577–1587.
Mason, B. J. (1971). The Physics of Clouds, 2nd ed., Oxford, Clarendon.
McKee, T. B., N. J. Doesken, and J. Kleist (1994). Climate Data Continuity with ASOS—1993
Annual Report for the Period September 1992–August 1993, Climatology Report 94-1,
Atmospheric Science Department, Colorado State University, Fort Collins.
Minsk, L. D. (1998). Snow and Ice Control Manual for Transportation Facilities, New York,
McGraw-Hill.
Nakaya, U. (1954). Snow Crystals, Natural and Artificial, Cambridge, MA, Harvard University
Press.
National Research Council (1998). Future of the National Weather Service Cooperative
Observer Network, Washington, DC, National Academy Press.
National Weather Service (2001). Snow Measurement Video, prepared by Department of
Atmospheric Science, Colorado State University for National Weather Service, Silver
Spring, MD, 30 min.
Takahashi, T., T. Endoh, G. Wakahama, and N. Fukuta (1991). Vapor diffusional growth of
free-falling snow crystals, J. Meteorol. Soc. Jpn. 69, 15.
U.S. Dept of Commerce (1996a). Snow Measurement Guidelines (rev. 10=28=96), NOAA,
Silver Spring, MD, National Weather Service.
U.S. Dept. of Commerce (1996b). Surface Weather Observations and Reports, National
Weather Service Handbook No. 7, NOAA, Silver Spring, MD, National Weather Service,
Office of Systems Operations.
U.S. Dept. of Commerce (1997). Evaluation of the Reported January 11–12, 1997 Montague,
New York, 77-inch 24-hour Lake-Effect Snowfall, NOAA, Silver Spring, MD, National
Weather Service, Office of Meteorology.
Walsh, J. E., D. R. Tucek, and M. R. Peterson (1982). Seasonal snow cover and short-term
climatic fluctuations of the United States, Mon. Wea. Rev. 110, 1474–1485.
Yang, D., J. R. Metcalfe, B. E. Goodison, and E. Mekis (1993). An Evaluation of the Double
Fence Intercomparison Reference Gauge, Proceedings, Eastern Snow Conference, 50th
Meeting, Quebec City, Canada, pp. 105–111.
REFERENCES 949
INDEX
adiabatic process, 182
adiabatic reversible expansion, 194–203
aerosol particles (AP), 256–261
concentration, number and mass, 258
formation mechanisms, 256–261
Junge layer in stratosphere, 259
mass distribution, 261
number approximation, 261
number distribution, 260
sinks, 256
sizes, 256
sources, 256
surface distribution, 261
volume distribution, 261
aerosols, 256–261
cloud condensation nuclei (CCN),
256–261, 434
ice nuclei (IN), 256–261
solid or liquid particles, 256–261
ageostrophic flow, 509
air parcel, 7, 178–179, 180
air, composition of, 186–187
aerosols, 186–187
dry air gas constant, 186–187
dry air, 186–187
trace gases in dry air, 186–187
water, 186–187
air-sea interface measurements, 885
different time=space sampling, 885
in-situ, 885
satellites, 885
albedo of the earth, 350–351
function of incident radiation
wavelength, 350–351
albedo, 120–123
Alberta clippers, 519–531
Alter wind shield, 936
American Meteorological Society (AMS),
692
American Society for Testing Materials
(ASTM), 692
angular momentum, 32
local conservation of, 32
aphelion, 345–347
ARM Program, 802–803
cloud and radiation testbeds,
802–803
cloud-radiation interactions, 802–803
communications and Web, 802–803
DOE multi-lab program, 802–803
ASTM requirements, implementation of,
700–701
atmosphere, contents of, 119
Atmospheric Boundary Layer (ABL),
123–124
convection and mechanical mixing,
123–124
daytime ABL, 123–124
nighttime ABL, 123–124
atmospheric flow, 509–510
ageostrophic, divergent, 509–510
clouds and precipitation, 509–510
balanced, 509–510
geostrophic, non-divergent, 509–510
attractors, stable, 93
audits, 851, 858–859
Automated Hydrological Observing
System (AHOS), 742
Automatic Remote Collector (ARC),
743
951
Handbook of Weather, Climate, and Water: Dynamics, Climate, Physical Meteorology, Weather Systems,
and Measurements, Edited by Thomas D. Potter and Bradley R. Colman.
ISBN 0-471-21490-6 # 2003 John Wiley & Sons, Inc.
baroclinic flows, 72–73
baroclinic fluid, 34
baroclinic instability, 43
baroclinic conversion term, 44
barotropic conversion term, 44
down gradient heat flux, 44
e-folding time, 47
growth of structures, 44
growth rate, 45
perturbation eddy energy, 44
stability theory, 44
barotropic flows, 72–73
barrier jets, 567
Batchelor, 5
Bay of Bengal low, 630
Beaufort scale, 889–891
Beer’s law, 318
Bendix aerovanes, 764
beta-plane approximation, 41
bistatic radar, 913–914
networks, 918
passive receivers, 913–914
Bjerknes, 3
blackbody radiation, 308
blizzards, 545
development of coastal surface lows, 545
storm of the century (March 1993), 547
threat regions, 545
blocked flow, 565
Brunt–Vaisala frequency, 565
effect on precipitation, 567–568
Bohr atom, 311
bombs: rapidly deepening lows, 526–528
Bora, 567
bore holes, 870
borehole temperatures, 874
1000 years ago was warmer than now, 874
warming past 300 years, 874
boundary layer
over terrain, 570–571
Boussinesq approximation, 69
balanced rotation and gravity effects, 70
Boussinesq equations, 79
bow echoes
morphology, 589–592
bow wave, 665
Bragg scattering, 900–902
brightness temperature, 309
Brunt–Vaisala frequency, 565
blocked flow, 565
buoyancy of parcel, 584
buoyant stability, 584
Bureau Internationale des Poids et Mesures
(BIPM), 701–707
canyon winds, 567
CAPE, 585
Carnot cycle, 194–203
efficiency of, 194–203
legs of, 194–203
model of tropical cyclone, 194–203
cavity radiation, 306–310
Celsius or Centigrade scale, 183
centrifugal acceleration, 14
chaos and nonlinear dynamics, 5, 85
chaotic system, 85
Charney, Jule, 5, 40
Chinook winds, 549, 567
circulation, 4, 21, 22
measure of flow strength, 23
rotation of fluid element, 24
Clausius–Clapeyron equation, 213–215
approximations: Magnus, Goff–Gratch,
and Tetens, 216–217
equilibrium vapor pressure, 213–215
ice and vapor, 213–215
liquid and solid, 213–215
liquid and vapor, 213–215
climate change, extremes and variability,
147
intense rainfalls, 147
interannual temperature, 147
temperature extremes, 147
temperature variability, 147
tropical cyclones in N. Atlantic, 148
climate change, radiation forcing, 148–149
CH
4
,NO
2
and halocarbons, 148–149
CO
2
, 148–149
O
3
, 148–149
climate change, 141
fundamental questions on, 141
climate forecasting, 91
climate system components, 119
cloud condensation nuclei (CCN), 264
activated droplets, 267
composition, 264
continental, 264
marine, 264
concentrations, 264
haze droplets, 267
Kelvin equation, 266
Kohler equation, 267
Raoult’s law, 266
supersaturation, 264
van’t Hoff factor, 266
cloud drop interactions, 286–287
accretion, 286–287
autoconversion, 286–287
droplet breakup, 286–287
952
INDEX
self-collection of large drops, 286–287
cloud droplets and ice crystals, 262–274
cloud seeding to increase snowpack,
844–846
cloud radiative forcing, 369–370
clouds, 255–256
definition, 387–388
composition, 255–256
humidity levels in, 255–256
importance of, 255–256
influence on:
aerosol composition, 255–256
atmospheric motions, 255–256
Earth’s climate, 255–256
hydrological cycle, 255–256
trace gas composition, 255–256
origin of current classification system,
388–389
particles, 387–388
pressures at, 255–256
structure, 387–388
temperatures of, 255–256
typical lifetimes, 387–388
clouds, classification of, 389–390
altitude regimes, 389–390, 255–256
categories, 389–390
composition, 389–390
dimensions of, 255–256
other attributes, 389–390
WMO cloud catalog, 388–389
clouds, high, 391–393
cirrus, cirrostratus, cirrocumulus,
388–389, 391–393
composition, 391–393
clouds, low stratiform, 388–389, 399
clouds, low-based convective, 400–404
cumulus, 388–389
clouds, middle level, 393–398
altocumulus: water drops, 393–398
altostratus, altocumulus, nimbostratus,
393–398
altostratus: ice crystals and snow,
393–398
product of slow updrafts over large areas,
393–398
virga, 393–398
clouds, modification methods, 436–437
dynamic seeding, 436–437
microphysical, 436–437
seeding agents, 436–437
clouds, observations of
clinometers, 735–736
cloud height, 735–736
fixed beam ceilometers, 735–736
important for aviation, 735–736
rotating beam ceilometers, 735–736
CMOS logic circuit, 784–785
coalescence, growth by, 280–284
single drop hydrodynamics,
280–284
coherent turbulent structures, 76
2D enstrophy decay, 77
inverse cascading quasi-2D turbulence,
77
kurtosis, 77
cold air outbreaks, 544–545
movement in Northern Hemisphere,
544–545
cold rain process, 434–435
collection efficiency, 285
Comite Internationale des Poid et Mesures
(CIPM), 701–707
comma cloud signature, 48
Conditional Available Potential Energy
(CAPE), 585
conditional instability, 585
and vertical wind shear, 585
lift from surface outflows, 585
loaded gun sounding, 585
moisture and upward motion, 585
conservation of energy, 97
conservation of moisture, 97
Constant Altitude Plan Position Indicator
(CAPPI), 908
continuity equation, 3, 10, 97
convection, deep moist, 582–586
ingredients of, 582–586
free convection, 582–586
instability, 582–586
lift, 582–586
moisture, 582–586
convective available potential energy
(CAPE), 250
convective condensation level (CCL),
245–248
convective inhibition (CIN), 250
convective storms, 508, 586–587
air mass, 586–587
multicellular, 586–587
low-level wind shear, 586–587
squall lines, 586
pulse type, 586–587
supercells, 586–587
associated severe weather, 586–587
single rotating updraft, 586–587
convective temperature (CT), 245–248
coordinates, 7, 13, 14, 26
Eulerian, 7
INDEX 953
coordinates (Continued )
geopotential, 14
inertial, 13
Lagrangian, 7
rotating, 26
spherical, 14
coral bands, 870
Coriolis, 14
acceleration, 14
Coriolis force (Ferrel), 505
Coriolis parameter, 14, 39
beta-plane approximation, 41
latitude variation of, 40
coronas and iridescent clouds, 483–489
critical levels, 245–248
cryosphere,
albedo, 126
effect on changing sea levels, 126
snow, sea ice, glaciers, 126
cyclic process, 182
cyclogenesis, 526–528, 531
basic theoretical paradigm, 531
baroclinic instability, 531
other growth mechanisms, 531
cyclolysis, 526–528
cyclones, 526–528
semi-permanent large cyclones, 526–528
Dalton’s law of partial pressure, 184–185
data assimilation, 99–100
3D and 4D variational methods, 101
analysis schemes, 101
first guess of initial conditions, 101
main methods of, 99–100
objective analysis, 99–100
of radar data, 914
data logger, 791–792
cost and reliability balance, 791–792
direct result of quality, 791–792
lightning protection, 791–792
RF noise reduction, 791–792
test and repair personnel roles, 791–792
data retrieval, 792
cellular telephone, 794
dedicated cable, 793–794
on-site data storage, 792–793
satellite communications, 796–798
geosynchronous orbit (GEO),
796–798
low-Earth orbits, 796–798
middle-Earth orbit (MEO), 796–798
single frequency RF, 794–795
spread-spectrum RF, 795
switched telephone, 794
telecomm capability, 793
datalogger, 782–784
causes of measurement system failures,
782–784
inaccuracies of measurement systems,
782–784
Daubert test, 830
deep convection, 245
deformation depth, 46
derechos, 578–579
dew-point temperature, 226–227
diabatic process, 182
diagnosing stability on thermodynamic
diagrams, 249–250
dissipation range, 74
Doppler velocity, 904–905
droplet spectra-broadening methods,
278–280
dry adiabatic lapse rate, 235–238
dry adiabat lines on thermo diagrams,
238
dry slot, 525–526
Eady model, 46
Earth’s surface radiative properties,
350–351
easterly waves, 621–623, 629
eddy diffusion of scalar fields, 79
eddy dissipation, 74
edge wave, Rossby, 47
effective gravity, 14
effective nuclei, 435
Ekman pumping, 32
El Nino and la Nina events, 59–60, 62, 163
shallow water mode theory (Matsuno),
63–64
El Nino Southern Oscillation (ENSO), 4,
59–60, 163
and climate change, 146–147
interannual variations, 163
dynamic coupling of ocean=atmosphere,
59–60
electromagnetic waves, 304
light in vacuum, polarization, 304
velocity, frequency, wavelength, wave
number, speed of, 304
emagram, 239–241
emissivity, 309
energy balance, 136
energy cascades, 74
energy fluxes, 136
ensemble forecasting, 89–90, 685
954
INDEX
enstrophy cascades, 74
basic physical cause of turbulence, 74
dissipative flows, 74
molecular dissipation, 74
enstrophy density, 71
enstrophy, 71
enthalpy, definition of, 191–193
entropy definition, 194–203
Environmental Protection Agency (EPA),
692
Quality Assurance Project Plans
(QAPP), 850–851
Prevention of Significant Deterioration
(PSD), 863
standards definitions and test methods,
692
equation of state, 97, 181, 184–185
equations of motion, 9, 97
equatorial plane, 345–347
equatorial wave theory, 64
diagram of shallow water low-latitude
modes, 65
equatorial Rossby radius, 64
equivalent depth, 64
internal gravity wave speed, 64
equatorial waves, 621–623
equatorially trapped, 632
equilibrium level (EL), 245–248
equinoxes, 345–347
equivalent potential temperature, 228–232
Ertel’s potential vorticity (see potential
vorticity)
Eulerian coordinates, 7
extratropical circulations, 39
extratropical cyclones, 519–531
associated weather, 519–531
bombs, 526–528
cyclonic circulations, 519–531
effects of mountains and coastlines on,
519–531
global distribution of cyclones, 526–528
life cycle, 519–531
orographic effects, 525–528
precipitation patterns in, 525–526
temperature patterns in, 521–524
scales of motion, 519–531
statistical climatology, 526–528
vertical structure, 528–529
convergence, 529
downshear, 528–529
mass conservation and vertical
motion, 529
typical tilt, 529
upshear, 528–529
vertical motion essential to
development, 529
wind patterns in offshore cyclones, 520
extratropical weather systems, 505
thermal theory of, 505
von Hann’s proof it was wrong, 505
Fahrenheit scale, 183
first law of thermodynamics, 3, 18,
188–193, 233–234, 504
first law of thermodynamics, enthalpy form,
223–224
flash floods, 579–580
forecast difficulties, 579–580
global occurrences, 579–580
related deaths, 579–580
floods
deaths from, 575
from convective storms, 586–587
Foehn, 567
forbidden entropy=energy process,
194–203
forensic meteorologist, 830
forensic meteorology, 829
case studies, 832–836
expert testimony, 830
role of, 829
weather data and info needed, 829
fossils, 870
freezing rain, 556
economic effects of, 556
synoptic conditions for, 556
frictional drag, 12
frontal circulations, 517–519
balanced vs. unbalanced ageostrophic
flow, 517–519
Sawyer–Eliassen equation, 517–519
frontogenesis, basis of, 48
advection of surface temperature, 48
anisotropic fronts, 49
confluent flow, 49
confluent regions, 48
deformation fields, 48
large scale flow effects, 49
frontogenetic mechanisms, 49
fronts, 513–517
anafronts, 513–514
atmospheric variables near fronts,
513–517
cloud distribution near fronts, 516–517
cold, 513–514
definitions, 513–517
katafronts, 513–514
INDEX 955