DIE ERDE 139 2008 (1-2)
Special Issue: Fog Research
pp. 45-60
• Fog – Data interpolation – Regional climatology – Mexico
Fernando García-García and Víctor Zarraluqui (Mexiko City)
A Fog Climatology for Mexico
Eine Nebelklimatologie für Mexiko
With 8 Figures
Fog can be defined as a cloud in the vicinity of the earth’s surface that affects visibility. It
differs from a cloud only in that the base of fog is at the surface of the earth while clouds are
further above. Fog plays an important role in the hydrological cycle, mainly in the transport of
water from the atmosphere to the earth’s surface through wet deposition and interception by
trees and vegetation. It is considered also a natural hazard that causes low visibility (according to
the international, meteorological definition, fog reduces visibility at the ground below 1 km) and
is a particular danger for all varieties of air, land and water transportation. On the other hand, fog
can be also considered a potential non-conventional source of water supply when removed by
artificial methods for human consumption. Fogs of all types originate when the temperature and
the dewpoint of the air coincide. This may occur through cooling of the air to a little beyond its
dewpoint, as a result of advection, radiation or upslope movement of the air; or by adding
moisture and thereby elevating the dewpoint, thus producing so-called frontal fogs. These synoptic and mesoscale mechanisms are modified by local terrain features, such as topography, land
and vegetation cover and, in turn, small-scale circulation. Thus, varied climatic regimes result in
different distribution patterns of fog occurrence and development. In spite of its importance, the
impacts of fog formation, development and distribution have not yet been properly assessed
throughout the world. In particular, in Mexico there are very few specific studies on the topic
and there are none of national character known to these authors.
1. Introduction
Fog plays a major role not only in the hydrological cycle but also for many human activities, such
as agriculture and land, sea and air transport. Like
most hydrometeorological phenomena, fog occurrence strongly varies with geographical location
at both the local and the regional scale. In addi-
46
Fernando García-García and Víctor Zarraluqui
tion, fog observation and recording methods are
still very dependent on direct human presence and
perception, since its detection by automated instrumentation is not a widespread practice in
standard weather stations. These characteristics
make it difficult to develop detailed fog climatologies that cover the whole world.
The case of Mexico is no exception. Mexico is
a country with a great variety of climatic regimes that reflect the uneven distribution of
water resources throughout its territory. This
is one reason why there are no comprehensive
fog climatological studies on the national scale,
DIE ERDE
and most fog data are scattered across diverse
sources. Data availability is highly variable in
terms of quality and spatial and temporal coverage, and most existing studies have a regional character in addressing specific aspects of
the problem for particular applications. It can
be pointed out, for instance, that the National
Atlas of Mexico (Coll-Oliva 2007) does not include a single map devoted to fog.
The main purpose of the present study is to develop a detailed fog climatology for Mexico. The
procedure takes into consideration the inhomogeneous characteristics of the available database.
Fig. 1 Map of Mexico showing the locations of the 2,888 climatological stations used in the study. Each
symbol on the map represents one station. Note that the non-uniformity in the spatial distribution
of the stations is related to the difference in population density. Average data density is
approximately one station per 680 km2. / Karte von Mexiko mit den 2.888 Klimastationen, deren
Daten in der Studie berücksichtigt wurden. Jedes Symbol stellt eine Station dar. Die ungleichmäßige
räumliche Verteilung der Stationen ist auf die unterschiedliche Bevölkerungsdichte zurückzuführen.
Die durchschnittliche Datendichte beträgt etwa eine Station auf 680 km².
2008/1-2
A Fog Climatology for Mexico
These results are then used to classify regions
of fog incidence in terms of their main meteorological and physical formation and development
mechanisms. Thus, a secondary purpose is to
show the potential of the methodology used when
applied to different spatial and temporal scales.
47
ues were obviously dubious or questionable, they
were recalculated from the original daily records
also provided by the SMN (Quintas 2000). After
these data quality tests the resulting database,
consisting of the average monthly number of fog
days from 2,888 climatological stations with a nonuniform spatial distribution over the whole country (Fig. 1), was stored in electronic spreadsheets.
2. Data and Methodology
The database used for the present study was
standard climate records provided by the Mexican National Meteorological Service (SMN).
Standard normal values are in this context defined
as averages of weather observations – precipitation, air temperature and pressure at the surface
etc. – over consecutive thirty-year periods. This
is the most comprehensive and up-to-date public database of atmospheric records and products
available in the country and is available from the
National Water Commission (CNA 2007). In particular, standard average monthly fog days
(number of days with fog occurrence as reported
by an observer) were used. These were calculated
from daily observations in the period from 1961
to 1990 at the 3,300 climatological stations managed by the SMN (CNA 1999).
Due to the nature of the data, several corroboration checks and adjustments had to be performed.
First, in the case that a given observing station
had not reported a full thirty-year record, provisional normal values from data for at least ten
years within the study period were used. Reports
for stations with less than ten years of fog records
were rejected from the database. Second, occasionally it was found that some stations had either reported incorrect geographical coordinates
or changed their locations during the recording
period. In both these cases, station coordinates
were, whenever possible, adjusted against using
historical data from the National Statistics, Geography and Informatics Institute (INEGI 2008a),
or the corresponding data were not considered
for the study. Third, in cases when normal val-
Fog climatologies and their geographical patterns
were elaborated using the commercial contouring
and surface mapping program Surfer V8.01
(Golden Software, Inc, Golden, CO, U.S.A.) in the
MS Windows environment. This program allows
to choose from different data interpolation
schemes and to calculate “best fits” statistics. Various gridding methods were used to interpolate
and represent the data in digitised base-maps of
the Mexican territory – administrative boundaries,
general physical features, topography etc. – obtained from the National Commission for Biodiversity Knowledge and Utilisation (Conabio
2007). The tested gridding methods included
Kriging with different variograms (linear, quadratic and wave hole effect), triangulation with linear interpolation, and radial basis function (multiquadratic, inverse multiquadric and thin plate
spline). Kriging is one of the more flexible methods and is useful for gridding almost any type of
data set. In general, Kriging with a linear variogram is quite effective for most data sets, although it can be rather slow for larger data sets.
Triangulation with linear interpolation is fast but,
for small data sets, generates distinct triangular
faces between data points in their graphic representations. The radial basis function (RBF) is actually a diverse group of data interpolation methods. All of the RBF methods are exact interpolators that employ an equation dependent on the
distance between the interpolated point and the
neighbouring sampling points. In terms of the
ability to fit data and produce a smooth surface,
the multiquadric function is considered by many
to be best since it produces a good representation of small-sized samples (see for example Hardy
48
Fernando García-García and Víctor Zarraluqui
1971). The performance of the different interpolation methods mentioned above was tested and
evaluated, to finally produce fog-occurrence maps
for both spatial (national, regional) and temporal
(yearly, seasonal, monthly) scales.
3. Results
The macro-spatial, national-scale fog-occurrence maps were produced with yearly and seasonal (winter, spring, summer and autumn) time
DIE ERDE
resolution. Given the nature of the fog database
(see section 2) it was relatively easy to adapt it
to regional, smaller-scale studies provided that
the proper interpolation methods were used.
The choice of these methods depended very
much on the spatial distribution of the data and
their spatial density. In all cases it was generally found that the method of radial basis function, with an inverse multiquadric kernel used
to define the set of weights to be applied to the
data points when interpolating a grid node, rendered the best statistical results. Both the co-
Fig. 2 Relief map depicting the main orographic systems of Mexico: I. Sierra and Peninsula of Baja
California, II. Sierra Madre Occidental, III. Sierra Madre Oriental, IV. Trans-Mexican Volcanic
Belt, V. Sierra Madre del Sur, and VI. Sierra of Chiapas and Sierra of Guatemala. Black bullets show
the different locations mentioned in the text: 1. Mexico Basin, 2. Teziutlán, 3. Ensenada, and 4. Las
Alazanas (after Conabio 2007, INEGI 2008b and USGS/EROS 2006). / Reliefkarte mit den
wesentlichen orographischen Systemen von Mexiko: I. Sierra und Halbinsel Baja California,
II. Sierra Madre Occidental, III. Sierra Madre Oriental, IV. Transmexikanischer Vulkangürtel,
V. Sierra Madre del Sur und VI. Sierras von Chiapas und Guatemala. Die schwarzen Punkte zeigen
die verschiedenen im Text erwähnten Standorte: 1. Becken von Mexico, 2. Teziutlán, 3. Ensenada
und 4. Las Alazanas (nach Conabio 2007, INEGI 2008b and USGS/EROS 2006).
2008/1-2
A Fog Climatology for Mexico
49
Fig. 3 Fog climatology for Mexico: distribution of the annual average number of fog days in the country.
Isolines (red) are drawn every 50 fog days. The maximum annual average value for a single site is
about 280 fog days per year and registered in the Teziutlán region. / Nebelklimatologie für Mexiko:
Verteilung der durchschnittlichen Anzahl der Nebeltage pro Jahr. Die roten Isolinien bezeichnen
jeweils einen Abstand von 50 Nebeltagen. Der maximale Mittelwert tritt im Gebiet von Teziutlán auf
und beträgt ungefähr 280 Nebeltage pro Jahr.
efficient of determination (R2) and the F-test
statistics confirmed this. It was also found,
however, that sometimes other methods such
as triangulation and Kriging resulted in more
appealing graphic representations.
The maps representing the annual and seasonal distributions of the average number of fog
days in Mexico are shown in Figures 3 and 4.
Average values of fog occurrences above 50 fog
days per year are found more frequently in the
country’s main orographic systems (see Fig. 2),
i.e.the Sierra Madre Oriental, the Sierra Madre
Occidental, the Sierra Madre del Sur, the Sierra
of Chiapas and the Trans-Mexican Volcanic Belt
that runs from east to west across south-central
Mexico. There are also some coastal regions with
moderate incidence of fog, particularly the
northwest coast of the Baja California Peninsula around the Ensenada region. The maps show
the general lack of fog events in the northern
desert and semi-desert regions.
Several representative cases in the main fog regions mentioned above were analysed for seasonal and monthly variation. For the sake of brevity,
only two of these regional cases are presented and
discussed in further detail in the following section:
the case of the Mexico Basin, where Mexico City
is located; and an area of the southern Sierra Madre Oriental, around the Teziutlán region, where fog
occurrence has its maximum value in the country.
50
Fig. 4
Fernando García-García and Víctor Zarraluqui
DIE ERDE
Fog climatology for Mexico: distribution of quarterly (seasonal) average number of fog days in the country:
spring (March, April, May), summer (June, July, August), autumn (September, October, November), and
winter (December, January, February). Isolines (red) drawn every 10 fog days. The maximum quarterly
average value for a single site is 82 fog days per season – in the summer season in the Teziutlán region.
2008/1-2
A Fog Climatology for Mexico
51
Verteilung der durchschnittlichen Anzahl der Nebeltage pro Jahreszeit in Mexiko: Frühling (März, April, Mai), Sommer
(Juni, Juli, August), Herbst (September, Oktober, November) und Winter (Dezember, Januar, Februar). Die roten
Isolinien bezeichnen jeweils einen Abstand von 10 Nebeltagen. Der maximale Durchschnittswert für ein einzelnes Gebiet
beträgt 82 Nebeltage je Saison – im Sommer in der Region Teziutlán.
52
Fernando García-García and Víctor Zarraluqui
4. Discussion
The general synoptic features involved in the
formation and development of fog in Mexico can
be inferred from analysing the seasonal fog climatologies presented in Figure 4. In most of the
Mexican territory the rainy season occurs during summer and fall, between May and October
(see Fig. 5). Thus, it is not surprising that the
least number of fog days in the year occurs in
spring, with a minimum in April. The occurrence
of fog increases towards the end of spring, coinciding with the beginning of the rainy and
hurricane seasons in both coastal areas of the
country (in May on the Pacific coast, and in June
on the Atlantic-Caribbean coast). The available
sources of humidity during summer (maximum
incidence of hurricanes and peak of the rainy
season) also coincide with the maximum seasonal frequency of fog days all over the country,
except for the Baja California Peninsula that
presents a Mediterranean climate and precipita-
DIE ERDE
tion regime. Autumn marks the transition between the end of the hurricane season and the
beginning of the season of cold frontal systems
affecting Mexico. The frequency of fog in the
northern regions diminishes whilst the seasonal
maxima concentrate in the mountainous, intertropical zone towards the south and east, in particular in the southern part of the Sierra Madre
Oriental and in the Sierra of Chiapas. Finally,
during winter fog incidence is almost exclusively found in the higher altitudes under the influence of the lower temperatures brought about by
nortes, which also advect humidity from the Gulf
of Mexico towards the continent (see below).
The synoptical and mesoscale characteristics
which prevail in Mexico and have an influence on
the development of fog during the dry and rainy
seasons are described in the following. In the summer, most of the Mexican territory gets under the
influence of the trade easterlies along the southwestern end of the semi-permanent Bermuda high-
Fig. 5 Winter (December, January, February) and summer (June, July, August, September) climatologies
of rain for Mexico, for the period 1958-2004 (after Vázquez 2007) / Niederschlagsverteilung in
Mexiko im Winter (Dezember, Januar, Februar) und im Sommer (Juni, Juli, August, September),
für den Zeitraum 1958-2004 (nach Vázquez 2007)
2008/1-2
A Fog Climatology for Mexico
pressure system (Fig. 6a). These east-northwest
prevailing winds gather humidity over the Gulf of
Mexico and, after moving over the Gulf Coastal
Plains, are orographically forced to ascend to
higher altitudes, thus producing typical cases of
upslope fog along the Sierra Madre Oriental. Two
examples of this are Teziutlán and Las Alazanas
regions (see Fig. 2). This circulation pattern is
commonly observed until autumn and also reaches the central part of the territory, including the
Trans-Mexican Volcanic Belt to the south and the
High Plateau to the north. On the western coast
the circulation pattern is very much dependent on
the dynamics of the intertropical convergence
zone, since the development of a warm water pool
over the northeast Pacific Ocean induces a region
of deep convection and propitiates the formation
of hurricanes that affect the Mexican coast.
53
On the other hand, in the winter the region lies
in the Subtropical High and the synoptic situation is dominated by a deep trough in low latitudes that defines an elongated area of relatively low atmospheric pressure along its axis or
trough line (see Fig. 6b). This large-scale
trough may include one or more closed circulations of low pressure, or cyclones, that produce
northeasterly cold frontal systems which blow
towards the shores of the Gulf of Mexico. These
so-called nortes or northerns that result from
an outbreak of cold air from the north are a common disruption of the mean synoptic condition
in the winter. At this time of the year it is common to observe banks of stratus clouds near
the coast of the Gulf of Mexico, both over the
sea and over the coastal plains, that are advected inland by the dominant winds towards the
Fig. 6 Mean circulation in the Mexico region: (a) Mean patterns of omega-vertical wind at 700 hPa (shaded
areas in Pa s-1) and horizontal wind at 925 hPa (arrows in m s-1) during summer. (b) Mean patterns
of surface pressure (isobars in hPa) and horizontal wind at 925 hPa (arrows in m s-1) characteristic
of the passage of a norte during winter (after Magaña et al. 1999) / Vorherrschende Zirkulation
im Raum Mexiko: (a) Mittlere Stärke und Richtung des Vertikalwindes bei 700 hPa (schraffierte
Fläche in Pa s-1) und des Horizontalwindes bei 925 hPa (Pfeile in m s-1) während des Sommers.
(b) Mittlerer Luftdruck (Isobaren in hPa) und Horizontalwind bei 925 hPa (Pfeile in m s-1),
charakteristisch für den Durchzug eines „Nortes“ während des Winters (nach Magaña et al. 1999)
54
Fernando García-García and Víctor Zarraluqui
mountainous, high altitude (1,500 to 2,000 m a.s.l.)
areas, thus producing orographically modified
coastal fogs along the southern Sierra Madre
Oriental, often accompanied by drizzle and rain.
These frontal systems also advect cold air towards the central Mexican Plateau, where the
flow is modified by the local orography.
To illustrate the influence of mesoscale and local terrain features, two regional studies are discussed in the following. The first case corresponds to the Mexico Basin (Fig. 7), located in
the Trans-Mexican Volcanic Belt, covering an
area of about 30 km in radius centered roughly
at downtown Mexico City and at an average altitude of 2240 m a.s.l. The basin is mostly surrounded by mountains, including some of the
highest peaks in the country, like the Popocatépetl (5,462 m a.s.l.), the Iztaccíchuatl (5,286 m
a.s.l.) and the Ajusco (3,930 m a.s.l.) volcanoes,
except to the northeast. This latter area was
originally occupied by Lake Texcoco, the largest of a system of interconnected lakes in the
basin that have been systematically drained
since colonial times during the last four hundred years (see Fig. 7b). Fog events in the
Mexico Basin are not very frequent, reaching
average maximum local values of up to 7 fog
days per month throughout the year, except in
the summer and early fall (June to September)
when monthly maxima amount to up to 12 fog
days per month. However, when present, fog
has important economic impacts because it interferes with the operation of the major airport
in the country, especially during winter when
the fog events are more persistent and take
longer to dissipate. In the winter the frontal
systems described above advect cold air towards
the central Mexican Plateau, the flow being modified by the local orography, reaching the Mexico Basin and producing typical radiative-advective and post-frontal fog episodes with visibilities of less than 400 m in the early morning hours.
As the day passes by, solar radiation warms up
the lower atmospheric layers and the fog dissi-
DIE ERDE
pates within a few hours after sunrise. It is also
evident, however, that most relative fog-occurrence maxima are associated to local terrain features that modify and reinforce the synoptic and
mesoscale circulation. In particular, in fog areas
close to foothills there is an obvious influence
of a mountain-valley circulation that drains cool,
humid air to the lower lands overnight. For the
airport area, the additional presence of small
water bodies like the remnants of Lake Texcoco
provides an additional local source of low-level
atmospheric humidity. The general characteristics of fog formation and the consequences
of the location of the airport near small shallow
lakes (less than 10 km2 in surface area) have been
discussed by Magaña et al. (2002). The abovedescribed conditions, which are responsible for
the occurrence of fog episodes that force the
shutdown of all operations on the airport, agree
well with the general features of the fog map for
January presented in Figure 7a.
The second regional case study corresponds to
the Teziutlán area located in the southern Sierra
Madre Oriental, where the maximum annual fog
occurrence in the country is observed. Fog in this
region has been studied in some detail from different viewpoints that include: climate-vegetation relationship (Maderey et al. 1989; Ern 1972;
Lauer 1978; Vogelmann 1973), hydrological balance (Barradas 1983), chemical characteristics
and effects of fog water deposition (Báez et al.
1998), and some meteorological (Fitzjarrald 1986)
and microphysical aspects (García and Montañez 1991). The incidence of fog is particularly
high during autumn and winter, with a maximum
local average of up to 80 fog days per season.
Monthly fog maps for the Teziutlán region for
October and January, considered representative
of these two seasons, are shown in Figure 8.
These maps adequately represent the abovedescribed synoptic-mesoscale situation for the
formation of upslope fog throughout the year,
reinforced by the advection of stratus clouds from
the Gulf of Mexico and the coastal plains towards
2008/1-2
A Fog Climatology for Mexico
55
Fig. 7 a) Fog climatology for the Mexico Basin (left panel): average number of fog days in January. Each
symbol on the map represents one station, with data density being approximately one station
per 25 km 2. The underlying relief map indicates the approximate altitude of the basin floor (2,240
m a.s.l.) as well as the maximum elevation shown in the map of about 3,000 m a.s.l. (the Sierra
de Guadalupe) to the north.
b) Vegetation cover and land use in the Mexico Basin (right panel). Note that most of the region
is occupied by the metropolitan area of Mexico City (after INE 2007).
a) Nebelklimatologie des Mexiko-Beckens: durchschnittliche Anzahl an Nebeltagen im Januar.
Jedes Symbol auf der Karte steht für eine Station mit einer Datendichte von etwa einer Station
pro 25 m². Die darunterliegende Reliefkarte zeigt die ungefähre Höhe des Beckenniveaus
(2.240 m ü. NN) sowie die maximalen Höhen im Norden, die ungefähr 3.000 m ü. NN erreichen
(die Sierra de Guadelupe).
b) Vegetationsbedeckung und Landnutzung im Mexiko-Becken. Ein Großteil der Region gehört
zum Agglomerationsraum von Mexiko City (nach INE 2007).
the region in the winter. In addition, they can be
easily related to modifications due to local features associated to the complex, high mountain
terrain and vegetation of the region.
5. Conclusions
A fog climatology developed for Mexico at various spatial and temporal scales was developed with
56
Fernando García-García and Víctor Zarraluqui
DIE ERDE
Fig. 8 Fog climatology for the southern Sierra Madre Oriental region of Teziutlán: average number of
fog days in: (a) October (monthly maximum local average of 24 fog days) and (b) January (monthly
maximum local average of 26 fog days). The maximum local annual average is about 280 fog days.
Each symbol on the map represents one station, with data density being approximately one
station per 160 km 2. The underlying relief map indicates that fog tends to concentrate in the
valley, the approximate altitude of Teziutlán is 1,920 m a.s.l.; it is surrounded by elevations of
up to about 3,000 m a.s.l. to the west. / Nebelklimatologie für die südliche Sierra-Madre-OrientalRegion von Teziutlán: durchschnittliche Anzahl der Nebeltage in: (a) Oktober (das monatliche
Maximum des örtlichen Mittels beträgt 24 Nebeltage) und (b) Januar (das monatliche Maximum
des örtlichen Mittels beträgt 26 Nebeltage). Der maximale lokale jährliche Durchschnitt beträgt
etwa 280 Nebeltage. Jedes Symbol auf der Karte steht für eine Station, die Datendichte beträgt etwa
eine Station pro 160 km². Die darunterliegende Reliefkarte zeigt, dass Nebel zu einer Konzentration in den Tälern tendiert; die Höhenlage von Teziutlán beträgt ungefähr 1.920 m ü. NN, die
Tallagen sind im Westen umgeben von Erhebungen mit bis zu 3.000 m ü. NN.
historical weather records. The corresponding database was constructed using monthly average
values of daily observations acquired over a thirtyyear period at about 2,900 climatological stations
of the Mexican National Meteorological Service
network. Different data interpolation schemes and
their performance were tested and evaluated in
order to produce fog-occurrence maps on various
spatial (national, regional) and temporal (yearly,
seasonal, monthly) scales. It can be concluded that
the program Surfer is a powerful tool for this type
of studies, provided the interpolation methods are
adequately chosen given the general characteristics of the data. In particular, radial basis function
2008/1-2
A Fog Climatology for Mexico
interpolation using the multiquadric method gave
good statistical results for the national scale but
lacked resolution for isolated data points. For the
regional, better-resolved scale, this method provided excellent results. It should be mentioned that in
some cases triangulation gridding with linear interpolation resulted in more appealing graphic representations. Needless to say, quality-assurance
techniques applied to the data were vital for obtaining these satisfactory results.
57
5. References
Barradas, V.L. 1983: Capacidad de captación de
agua a partir de la niebla en Pinus montezumae
Lambert, de la región de las grandes montañas del
estado de Veracruz. – Biótica 8 (4): 427-431
Báez, A.P., H.G. Padilla and F. García-García 1998:
Fog Water Chemistry at High Altitudes in Mexico. –
In: Schemenauer, R.S. and H. Bridgman (eds.): First
International Conference on Fog and Fog Collection:
Proceedings. – North York, Ontario: 77-80
Major regions of fog incidence in terms of the main
meteorological and physical formation and
development mechanisms were identified. These
results show the high variability of fog incidence
over the Mexican territory, both at the spatial and
temporal scales, and the difficulties that this implies for its proper and accurate handling, graphic representation and analysis. Finally, the described graphical representations were used to
better understand synoptic, mesoscale and local
features related to the formation and development
of fog. In particular, from regional studies local
characteristics related to topography and land
cover, including the presence of nearby water
bodies, can be inferred as modifying factors of the
larger-scales atmospheric conditions.
CNA 1999: Normales Climatológicas Estándar y
Provisionales 1961-1990. – Unidad del Servicio
Meteorológico Nacional, Subdirección General
Técnica, Comisión Nacional del Agua. – Mexico
City. – available on CD
The results presented here represent the first attempt to develop a detailed national and regional
fog climatology for Mexico. In the future, the methodology will be tested and may be extended to other
highly localised hydrometeorological phenomena,
such as frost and hail incidence, for which there is
also a lack of detailed observational data.
Ern, H. 1972: Estudio de la vegetación en la parte
oriental de México central. – In: Comunicaciones
Proyecto Puebla-Tlaxcala 6: 1-6
Acknowledgements
Hardy, R.L. 1971: Multivariate Equations of Topography and Other Irregular Surfaces. – In: Journal
of Geophysical Research 76: 1905-1915
The authors are indebted to Jorge Luis VázquezAguirre and Dr. Víctor O. Magaña-Rueda for providing the original maps presented in Figures 5 and 6.
The underlying relief maps appearing in Figures 7a
and 8 were drawn with digitised data provided by
María de Lourdes Godínez-Calderón.
CNA 2007: Normales Climatológicas Provisionales
1971-2000. – Unidad del Servicio Meteorológico
Nacional, Comisión Nacional del Agua. – Mexico
City. – http://smn.cna.gob.mx/productos/normales/
estacion/normales.html
Conabio 2007: Metadatos y Cartografía en Línea. –
Subdirección de Sistemas de Información Geográfica,
Comisión Nacional para el Conocimiento y Uso de
la Biodiversidad. – Mexico City. – http://
conabioweb.conabio.gob.mx/metacarto /metadatos.pl
Coll-Oliva, A. (ed.) 2007: Nuevo Atlas Nacional de
México. – Instituto de Geografía, Universidad
Nacional Autónoma de México. – Mexico City
Fitzjarrald, D.R. 1986: Slope Winds in Veracruz. –
Journal of Climate and Applied Meteorology 25:
133-144
García-García, F. and R.A. Montañez 1991: Warm
Fog in Eastern Mexico: A Case Study. –
Atmósfera 4: 53-64
INE 2007: Vegetación y Uso del suelo 2000: Distrito Federal y Estado de México. – In: J.L. PérezDamián and I. Ramírez del Razo (eds.): Mapas del
Medio Ambiente de México. – Dirección General
de Investigación del Ordenamiento Ecológico y
58
Fernando García-García and Víctor Zarraluqui
Conservación de los Ecosistemas, Instituto Nacional de Ecología, Secretaría del Medio Ambiente
y Recursos Naturales. – Mexico City. – http://
www.ine.gob.mx/emapas/index.html
INEGI 2008a: Archivo Histórico de Localidades. –
Sistemas Nacionales Estadístico y de Información
Geográfica, Instituto Nacional de Estadística, Geografía e Informática. – Mexico City. – http://
mapserver.inegi.gob.mx/dsist/ahl2003/index.cfm
DIE ERDE
and Science Data Center, U.S. Geological Center. –
Sioux Falls, SD. – http://edc.usgs.gov/products/
elevation/gtopo30/gtopo30.html
Vázquez-Aguirre, J.L. 2007: Variabilidad de la Precipitación en la República Mexicana. – M. Sc. Thesis, Universidad Nacional Autónoma de México. –
Mexico City. – Available from TESIUNAM Database, Clasif. 001-03060-V2-2007 at http://
www.dgbiblio.unam.mx/
INEGI 2008b: Información Geográfica: Aspectos
Generales del Territorio Mexicano. – Sistemas Nacionales Estadístico y de Información Geográfica, Instituto Nacional de Estadística, Geografía e Informática. – Mexico City. – http://
www.inegi.gob.mx/inegi/default.aspx?s=geo&c=909
Vogelmann, H.W. 1973: Fog Precipitation in the
Cloud Forests of Eastern Mexico. – In: BioScience
23: 96-100
Lauer, W. 1978: Tipos ecológicos del clima en la vertiente oriental de la Meseta Mexicana. – In: Comunicaciones Proyecto Puebla-Tlaxcala 15: 235-244
Summary: A Fog Climatology for Mexico
Maderey, R.L.E., H. del Castillo G. y F.J. Cruz N.
1989: Distribución del rocío y de la niebla: Fuentes
de humedad para la vegetación en la
República Mexicana. – Ciencia 40: 223-231
Magaña, V., J.L. Pérez, J.L. Vázquez, E. Carrisoza
y J. Pérez 1999: El Niño y el Clima. – In:
Magaña-Rueda, V.O. (ed.): Los Impactos de El
Niño en México: 23-66. – Universidad Nacional
Autónoma de México, Inter-American Institute
for Global Change Research, Secretaría de Gobernación, Secretaría de Educación Pública-Consejo Nacional de Ciencia y Tecnología. – Mexico City. –
online available at http://www.atmosfera. unam.mx/
editorial/libros/el_nino/
Magaña-Rueda, V.O., A. García-Reynoso, E. Caetano,
A. Jazcilevich, F. García-García y L.G. Ruiz-Suárez
2002: Estudio Preliminar para Determinar el Efecto
en la Formación de Niebla y en la Calidad del Aire
debido a la Creación de Cuerpos de Agua en la
Ubicación del Nuevo Aeropuerto Internacional de la
Ciudad de México. – Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México. –
Technical Report. – Mexico City
Quintas, I. 2000: ERIC II: Extractor Rápido de
Información Climatológica. – Instituto Mexicano de
Tecnología del Agua, Comisión Nacional del Agua,
México. – Version 2. – available on CD
USGS/EROS 2006: Global 30 Arc Second Elevation
Data GTOPO30. – Earth Resources Observation
The results of a fog climatology developed for
Mexico are presented. The study is based on
standard average monthly fog days calculated
from daily observations acquired over the
thirty-year period from 1961 to 1990, at the
3,300 climatological stations of the Mexican
National Meteorological Service network. After applying corroboration checks and adjustments to the data, different interpolation
schemes and their performance were tested and
evaluated in order to produce fog-occurrence
maps on various spatial (national, regional) and
temporal (yearly, seasonal, monthly) scales,
using the commercial contouring and surface
mapping program Surfer. For the data interpolation, it was found that the method of radial
basis function with an inverse multiquadric kernel rendered the best statistical results. These
indicate that average values of fog occurrences,
of more than 50 and up to 280 fog days per
year, are found more frequently in the country’s main orographic systems. It is also found
that the maximum seasonal frequency of fog
days in the country occurs during summer,
thus coinciding with the peak of the rainy season. These results are also analysed in view of
the synoptical and mesoscale characteristics
that prevail in Mexico during the dry and rainy
seasons and then used to classify major regions
of fog incidence in terms of their main meteorological and physical formation and develop-
2008/1-2
A Fog Climatology for Mexico
ment mechanisms. Finally, two regional case
studies are presented with the aim to illustrate
the influence that mesoscale and local terrain
features, such as topography and vegetation
and land cover, have on the formation and development of fog. This study represents the
first attempt towards a comprehensive and detailed fog climatology for Mexico. It is concluded that fog incidence over the Mexican territory shows high variability at both spatial
and temporal scales, showing the difficulties
that this implies for its proper and accurate
handling, graphic representation and analysis.
Zusammenfassung: Eine Nebelklimatologie für
Mexiko
Dieser Artikel beschreibt die Ergebnisse einer
Studie zur Nebel-Klimatologie Mexikos. Die Studie
basiert auf der Anzahl der durchschnittlichen
monatlichen Nebeltage, die berechnet wurde aus
Daten von täglichen Erhebungen an 3.300 Klimastationen des mexikanischen Wetterdienstes, welche über eine 30-jährige Periode, von 1961 bis 1990,
durchgeführt wurden. Nach Plausibilitätsprüfungen
und Anpassungen der Daten wurden verschiedene
Interpolationsverfahren und deren Ergebnisse getestet und ausgewertet, um Karten zu Nebel-Häufigkeiten auf verschiedenen räumlichen (national, regional) und zeitlichen (jährlich, saisonal, monatlich)
Ebenen zu erstellen. Hierzu wurde das kommerzielle
Konturierungs- und Kartenoberflächenprogramm
Surfer verwendet. Für die Interpolation wurde
festgestellt, dass das Verfahren der radialen Basisfunktion mit einem inversen multiquadratischen
Kern die besten statistischen Ergebnisse lieferte.
Diese zeigen, dass die Durchschnittswerte hinsichtlich des Auftretens von Nebel mit mehr als 50
bis zu 280 Nebeltagen im Jahr häufiger in den
wesentlichen Gebirgszügen des Landes liegen.
Ebenfalls fand man heraus, dass die maximale saisonale Häufigkeit von Nebeltagen im Land während
des Sommers auftritt und somit identisch mit dem
Höchststand der Regenzeit ist. Diese Ergebnisse
wurden außderdem mit Blick auf die synoptischen
und mesoskalen Merkmale analysiert, die in Mexiko während der Trocken- und Regenzeit vorherr-
59
schen, um die Hauptgebiete von Nebelvorkommen
bezüglich ihrer vorherrschenden meteorologischen
und physikalischen Konstellation sowie ihrer Entstehungsmechanismen zu typisieren. Schließlich
werden zwei regionale Fallstudien präsentiert mit
dem Ziel, den Einfluss der mesoskalaren und lokalen Besonderheiten des Raumes – wie Relief, Vegetation und Bodenbedeckung – auf die Bildung und
Weiterentwicklung von Nebel deutlich zu machen.
Die Studie stellt den ersten Versuch einer umfassenden und detaillierten Nebel-Klimatologie für
Mexiko dar. Sie macht deutlich, dass das Auftreten
von Nebel über Mexiko sowohl auf räumlicher wie
auch auf zeitlicher Ebene eine hohe Variabilität
aufweist. Ebenso zeigt sie die Schwierigkeit, diese
Daten sachgerecht und genau aufzubereiten, graphisch darzustellen und zu analysieren.
Résumé: Une climatologie du brouillard pour le
Mexique
Les résultats d’une climatologie du brouillard développée pour le Mexique sont présentés. L’étude est
basée sur le nombre mensuel moyen des jours de
brouillard calculé à partir des observations quotidiennes acquises au cours des trente années de 1961
à 1990 sur 3300 stations climatologiques du réseau
du Service Météorologique National du Mexique.
Après l’application des contrôles de corroboration
et des ajustements des données, les différents régimes d’interpolation et leurs performances ont été
testés et évalués afin de produire des cartes de
l’apparition du brouillard sur diverses échelles
géographiques (nationale, régionale) et temporelles (annuelle, saisonnière, mensuelle), en utilisant
« Surfer », le logiciel commercial de contouring et de
cartographie de surface. Pour l’interpolation des
données, il a été constaté que la méthode de la
fonction d’une base radiale avec un noyau inverse
à élévation multiple au carré rend les meilleurs
résultats statistiques. Ceux-ci indiquent que ces
valeurs moyennes des événements de brouillard,
allant de plus de 50 jusqu’à 280 jours de brouillard
par an, se retrouvent plus fréquemment dans les
principaux systèmes orographiques du pays. Il est
également constaté que la fréquence saisonnière
maximale de jours de brouillard dans le pays se
60
Fernando García-García and Víctor Zarraluqui
produit au cours de l’été, ce qui coïncide avec le
maximum de la saison des pluies. Ces résultats
sont également analysés en vue des caractéristiques synoptiques et à échelle moyenne qui règnent
au Mexique pendant la saison sèche et la saison des
pluies, et qui sont ensuite utilisés pour classer des
grandes régions d’apparition de brouillard en termes de leurs mécanismes principaux de formation
et de développement météorologiques et physiques. Enfin, deux études de cas régionales sont
présentées dans le but d’illustrer l’influence que les
traits du relief, à échelle moyenne et au niveau local,
telles que la topographie, la végétation et la couverture de terre, exercent sur la formation et le développement de brouillard. Cette étude représente la
première tentative d’établir un inventaire exhaustif
et détaillé de la climatologie du brouillard pour le
Mexique. Il est conclu que l’apparition de brouillard
sur le territoire mexicain montre une variabilité
élevée aux échelles spatiale ainsi que temporelle,
démontrant les difficultés que cela implique pour
son traitement approprié et soigneux au niveau
d´une représentation graphique et de l’analyse.
Resumen: Una climatología de niebla para
México
Se presentan los resultados de una climatología
de niebla elaborada para México. El estudio se
basó en normales climatológicas mensuales de
días con niebla, calculadas de observaciones diarias realizadas durante el período de treinta años
1961-1990 en las 3,300 estaciones climatológicas
pertenecientes a la red del Servicio Meteorológico
Nacional. Luego de aplicar varias pruebas de corroboración y ajustes a los datos, se probó y evaluó el desempeño de diferentes esquemas de interpolación de datos para así producir mapas climatológicos de ocurrencia de niebla, tanto en escala espacial (nacional, regional) como temporal
(anual, estacional, mensual), mediante la utilización del programa comercial Surfer. Se encontró
que el método de función radial con kernel multicuádrico da los mejores resultados para la inter-
DIE ERDE
polación de los datos. Estos resultados se utilizaron para clasificar las principales regiones de incidencia de niebla en términos de los principales
mecanismos meteorológicos y físicos para su formación y desarrollo. Estos resultados muestran
que los valores promedio más grandes de ocurrencia de niebla, de entre 50 y hasta 280 días con
niebla al año, se dan en los principales sistemas
montañosos del país. También se observa que la
máxima frecuencia de días con niebla en el ámbito
nacional ocurre en el verano, coincidiendo con la
temporada de lluvias. Los resultados también se
analizaron en términos de las características de la
circulación, tanto sinóptica como de mesoescala,
prevaleciente en México durante las temporadas
de secas y lluvias, para así clasificar las regiones
de niebla identificadas con respecto a los principales mecanismos físicos y meteorológicos de formación de niebla. Finalmente, se presentan dos
casos de estudio a nivel regional con el fin de ilustrar la influencia que la circulación de mesoescala
y las características locales del terreno, tales como
la topografía y la cubierta de vegetación y el suelo, tienen en la formación y el desarrollo de la
niebla. El estudio representa un primer esfuerzo
de obtener una climatología detallada y completa
de niebla para México. Se concluye que existe una
gran variabilidad en la incidencia del fenómeno sobre el territorio mexicano, tanto en escala espacial
como temporal, y se muestran las dificultades que
esta variabilidad acarrea para su adecuado manejo,
representación gráfica y análisis.
Dr. Fernando García-García, Víctor Zarraluqui,
Centro de Ciencias de la Atmósfera, Universidad
Nacional Autónoma de México, Circuito de la Investigación Científica, Ciudad Universitaria, 04510
México, D.F., México, [email protected],
[email protected]
Manuskripteingang: 07.01.2008
Annahme zum Druck: 21.04.2008