DOCSLIB.ORG

Twelve Lectures on Cloud Physics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Twelve Lectures on Cloud Physics Twelve Lectures on Cloud Physics Bjorn Stevens Winter Semester 2010-2011 Contents 1 Lecture 1: Clouds–An Overview3 1.1 Organization...........................................3 1.2 What is a cloud?.........................................3 1.3 Why are we interested in clouds?................................4 1.4 Cloud classification schemes..................................5 2 Lecture 2: Thermodynamic Basics6 2.1 Thermodynamics: A brief review................................6 2.2 Variables............................................8 2.3 Intensive, Extensive, and specific variables...........................8 2.3.1 Thermodynamic Coordinates..............................8 2.3.2 Composite Systems...................................8 2.3.3 The many variables of atmospheric thermodynamics.................8 2.4 Processes............................................ 10 2.5 Saturation............................................ 10 3 Lecture 3: Droplet Activation 11 3.1 Supersaturation over curved surfaces.............................. 12 3.2 Solute effects.......................................... 14 3.3 The Kohler¨ equation and its properties............................. 15 4 Lecture 4: Further Properties of an Isolated Drop 16 4.1 Diffusional growth....................................... 16 4.1.1 Temperature corrections................................ 18 4.1.2 Drop size effects on droplet growth.......................... 20 4.2 Terminal fall speeds of drops and droplets........................... 20 5 Lecture 5: Populations of Particles 22 5.1 Converting distribution and density functions......................... 23 5.2 Time derivatives of densities.................................. 24 5.3 Common distributions and their density functions....................... 25 1 6 Lecture 6: Collection through Collision and Coalescence 26 6.1 Gravitational collection..................................... 27 6.2 Smoluchowski (stochastic) collection equation......................... 28 6.3 The collection kernel...................................... 29 7 Lecture 7: Warm clouds and drop spectral evolution 31 7.1 Exogenous theories of warm rain................................ 31 7.1.1 Giant CCN....................................... 31 7.1.2 Drop spectral preconditioning............................. 32 7.2 Endogenous theories of warm rain............................... 32 7.2.1 Turbulence enhancement to collision efficiencies................... 32 7.2.2 Turbulent mixing.................................... 33 8 Lecture 8: Atmospheric ice and its initiation 34 8.1 The molecular structure of water and ice............................ 34 8.2 Ice initiation........................................... 36 8.2.1 Homogeneous nucleation................................ 36 8.2.2 Heterogeneous nucleation............................... 38 9 Lecture 9: Ice crystal growth 39 9.1 Diffusional growth theory.................................... 39 9.2 Ice crystal terminal fall speeds................................. 41 9.3 Growth by collection...................................... 42 9.4 Further ice-microphysical processes.............................. 42 10 Lecture 10: The atmospheric aerosol 42 10.1 Types of aerosol particles.................................... 43 10.2 Abundances........................................... 44 10.3 Aerosol Processes........................................ 46 10.4 Aerosol Function........................................ 46 11 Lecture 11: Microphysical models of cloud and aerosol 47 11.1 Particle based methods..................................... 47 11.2 Distribution based methods................................... 48 11.3 Parametric distributions..................................... 48 12 Lecture 12: Aerosol and cloud measurement systems 49 12.1 In situ Methods......................................... 49 12.1.1 Single particle sampling................................ 49 12.1.2 Expansion Chambers.................................. 49 12.1.3 Particle Counters.................................... 49 12.1.4 Particle Spectrometers................................. 49 12.2 Active remote sensing...................................... 49 12.2.1 Cloud and Precipitation Radars............................ 49 12.2.2 Lidars.......................................... 49 2 1 Lecture 1: Clouds–An Overview 1.1 Organization The important points to remember here are: the grade is based on the oral exam, the oral exam is based on the exercises. So working through the exercises is critical. The other important points are covered on the syllabus, or course Einleitung. 1.2 What is a cloud? When most people think of a cloud they know what it is, a white puffy thing in the sky. But when pushed to be precise it is more difficult. Formally speaking a cloud is an aerosol, that is a suspension of one phase of matter in another. The glossary of the American Meteorological Society defines an aerosol as follows: A colloidal system in which the dispersed phase is composed of either solid or liquid parti- cles, and in which the dispersion medium is some gas, usually air. A characteristic of an aerosol is that it is disperse. It is not one thing, but many things, or many repetitions of the same thing, dispersed in space. This makes the boundary of the aerosol, or a cloud, somewhat difficult to define objectively and precisely. But clouds are a special type of aerosol, so special in fact that we rarely speak of a cloud as being an aerosol. Clouds are a type of aerosol that comes into being when the atmosphere becomes supersaturated with respect to water, and cloud particles grow rapidly and become visibly apparent in a way that the aerosol in a subsaturated environment rarely is. This difference encourages the tendency to associate the atmospheric aerosol with only the smallest particles, traditionally those under 1 µ m, and the growing particles that are found in water saturated environments as clouds. This distinction encourages one to speak of clouds as singular, compact, entities in contrast to the disperse atmospheric aerosol. However a cloud’s origin as a component of the atmospheric aerosol lingers in attempts to define “a cloud” objectively. long lived, abundant , suspended short lived, precipitation Aerosol Cloud Precipitation Freshly Nucleated Cloud condensation Sea-salt & Aerosol Particles nuclei Mineral dust more complex Ice Crystals Snow flakes Graupel Hail Cloud droplets Drizzle droplets Rain drops 10-9 10-6 10-3 10-1 Diameter [m] 3.5 10-6 3.5 10-2 3.5 10 50 Fallspeed [ms-1] Figure 1: Types of particles in the atmosphere, organized by size. Note that many of the particles span a range of size, and only typical sizes are given to place one type of particle in relation to another. Particles are also ordered with respect to complexity. Liquid water droplets and drops tend to have the same shape and composition, the shape of ice varies making it more complex, for the aerosol but the composition and the shape/mixture state can be variable. The ability of the particles that constitute a cloud to grow in a supersaturated environment leads to a sequence of events that can grow particles sufficiently large to efficiently scatter light, and eventually so 3 large as to efficiently precipitate from the atmosphere. Cloud particles are hydrometeors, and a subset of these form precipitation–in German Niederschlag. The study of how cloud particles come into being, how their distribution effects the transfer of radiant energy, and how they transform themselves into precipitation is the subject of cloud physics. How hydrometeors fit into the broader class of particles that one finds in the atmosphere is illustrated in Fig.1. This figure emphasizes that the atmosphere suspends many forms of particulate matter. On scales of a few nanometers, one finds freshly nucleated aerosol particles, while hail stones have been documented to grow to sizes of tens of centimeters in diameter. Thus particles in the atmosphere span a range of sizes of as much as eight orders of magnitude and the mass of atmospheric particulate matter spans a range of scales that is more than twenty orders of magnitude. Small particles sediment with a terminal velocity that is proportional to their diameter squared, hence a factor of ten in diameter means a factor of one hundred in the time it takes a particle to settle and fall out of the sky. Very small particles effectively never fall from the sky, and are only removed by collisions with larger particles, or because they grow by other means to sizes large enough to effectively fall from the sky. While large particles are rare, as once form they rapidly precipitate to the surface. Clouds also get their meaning because we can see them, or we feel their presence through their emission of radiation which keeps the ground from cooling on a cloudy night. Hence an important part of what makes a cloud are its radiative properties, its propensity to scatter visible radiation and absorb and emit infrared radiation. The scattering of visible radiation depends both on the amount of suspended water mass, and the size of the suspended particles, while the efficacy of clouds in absorbing and emitting infrared radiation depends primarily on the suspended water mass. While the suspended water mass, sometimes called the liquid water path, is a cloud macroscopic parameter, largely controlled by dynamical processes, the characteristic drop size is a microphysical parameter and can be strongly influenced by cloud microphysical processes. 1.3 Why are we interested in clouds? Outside of poetic motivations
Load more

Recommended publications
  • An Assessment of the Evaporative Release of Heat from The
    AN ASSESSMENT OF THE EVAPORATIVE RELEASE OF HEAT FROM THE BUCCOPHARYNGEAL, CUTANEOUS, AND CLOACAL EPITHELIA OF BIRDS AND REPTILES by Ty C.M. Hoffman A Dissertation Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy ARIZONA STATE UNIVERSITY May 2007 AN ASSESSMENT OF THE EVAPORATIVE RELEASE OF HEAT FROM THE BUCCOPHARYNGEAL, CUTANEOUS, AND CLOACAL EPITHELIA OF BIRDS AND REPTILES by Ty C.M. Hoffman has been approved November 2006 APPROVED: , Chair Supervisory Committee ACCEPTED: Director of the School Dean, Division of Graduate Studies ABSTRACT Evaporation can simultaneously subject an animal to a detrimental loss of physiologically essential water and to a beneficial loss of life-threatening heat. Buccopharyngeal evaporation occurs from the mouth and pharynx, and it is only one component of an animal's total evaporation. For tetrapods other than mammals, non- buccopharyngeal evaporation (the remainder of total evaporation) occurs despite an incapacity for sweating. High rates of non-buccopharyngeal evaporation have been measured in many bird species, and rates of non-buccopharyngeal evaporation have been shown to change gradually during acclimation to changes in temperature or aridity. This dissertation demonstrates that mourning doves (Zenaida macroura) are able to effect rapid, endogenous adjustment to the rate of non-buccopharyngeal evaporation when faced with a suppression of buccopharyngeal evaporation. This implies that non- buccopharyngeal evaporation can serve as a transient mechanism for thermoregulation. However, the adjustment of non-buccopharyngeal evaporation shown in mourning doves prompts the question of how that non-buccopharyngeal evaporation is apportioned among the non-buccopharyngeal epithelia. Historically, researchers have assumed that all non-buccopharyngeal evaporation occurs from the skin (cutaneous evaporation).
    [Show full text]
  • Improving Lightning and Precipitation Prediction of Severe Convection Using of the Lightning Initiation Locations
    PUBLICATIONS Journal of Geophysical Research: Atmospheres RESEARCH ARTICLE Improving Lightning and Precipitation Prediction of Severe 10.1002/2017JD027340 Convection Using Lightning Data Assimilation Key Points: With NCAR WRF-RTFDDA • A lightning data assimilation method was developed Haoliang Wang1,2, Yubao Liu2, William Y. Y. Cheng2, Tianliang Zhao1, Mei Xu2, Yuewei Liu2, Si Shen2, • Demonstrate a method to retrieve the 3 3 graupel fields of convective clouds Kristin M. Calhoun , and Alexandre O. Fierro using total lightning data 1 • The lightning data assimilation Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information method improves the lightning and Science and Technology, Nanjing, China, 2National Center for Atmospheric Research, Boulder, CO, USA, 3Cooperative convective precipitation short-term Institute for Mesoscale Meteorological Studies (CIMMS), NOAA/National Severe Storms Laboratory, University of Oklahoma forecasts (OU), Norman, OK, USA Abstract In this study, a lightning data assimilation (LDA) scheme was developed and implemented in the Correspondence to: Y. Liu, National Center for Atmospheric Research Weather Research and Forecasting-Real-Time Four-Dimensional [email protected] Data Assimilation system. In this LDA method, graupel mixing ratio (qg) is retrieved from observed total lightning. To retrieve qg on model grid boxes, column-integrated graupel mass is first calculated using an Citation: observation-based linear formula between graupel mass and total lightning rate. Then the graupel mass is Wang, H., Liu, Y., Cheng, W. Y. Y., Zhao, distributed vertically according to the empirical qg vertical profiles constructed from model simulations. … T., Xu, M., Liu, Y., Fierro, A. O. (2017). Finally, a horizontal spread method is utilized to consider the existence of graupel in the adjacent regions Improving lightning and precipitation prediction of severe convection using of the lightning initiation locations.
    [Show full text]
  • The Observation of the Lightning Induced Variations in Atmospheric Ions
    XV International Conference on Atmospheric Electricity, 15-20 June 2014, Norman, Oklahoma, U.S.A. The Observation of the Lightning Induced Variations in Atmospheric Ions Xuemeng Chen1,*, Hanna E. Manninen1,2, Pasi Aalto1, Petri Keronen1, Antti Mäkelä3, Jussi Paatero3, Tuukka Petäjä1 and Markku Kulmala1 1. Department of Physics, University of Helsinki, Helsinki, Finland 2. Institute of Physics, University of Tartu, Estonia 3. Finnish Meteorological Institute, Helsinki, Finland ABSTRACT: Variations in atmospheric ion concentration were studied in a boreal forest in Finland, with emphasis on the effect of lightning. In general, changes in ion concentrations have diurnal and seasonal patterns. Distinct features were found in ions of different size ranges, namely small ions (0.8 – 1.7 nm) and intermediate ions (1.7 – 7 nm). Preliminary results on two case studies of lightning effect are present, one with rain effect and the other not. Bursts in the concentrations of small ions and intermediate ions were observed in both cases. However, different trends in trace gases were observed for the two cases. Further investigation is needed to reveal the nature of lightning ions and the mechanism in their formation. The work is under progress. INTRODUCTION Atmospheric ions, or air ions, refer to electric charge carriers present in the atmosphere. Distinct features exist in their chemical composition, mass, size as well as number of carried charges. According to Tammet [1998], atmospheric ions can be classified into small or cluster ions, intermediate ions, and large ions based on their mobility (Z) in air, being Z > 0.5 cm2V-1s-1, 0.5 cm2V-1s-1 ≤ Z ≥ 0.03 cm2V-1s-1 and Z< 0.03 cm2V-1s-1, respectively.
    [Show full text]
  • Quantification of Cloud Condensation Nuclei Effects on the Microphysical Structure of Continental Thunderstorms Using Polarimetr
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Dissertations & Theses in Earth and Atmospheric Earth and Atmospheric Sciences, Department of Sciences 11-2018 Quantification of Cloud Condensation Nuclei Effects on the Microphysical Structure of Continental Thunderstorms Using Polarimetric Radar Observations Kun-Yuan Lee University of Nebraska-Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/geoscidiss Part of the Atmospheric Sciences Commons, Meteorology Commons, and the Other Oceanography and Atmospheric Sciences and Meteorology Commons Lee, Kun-Yuan, "Quantification of Cloud Condensation Nuclei Effects on the Microphysical Structure of Continental Thunderstorms Using Polarimetric Radar Observations" (2018). Dissertations & Theses in Earth and Atmospheric Sciences. 113. https://digitalcommons.unl.edu/geoscidiss/113 This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Dissertations & Theses in Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. i QUANTIFICATION OF CLOUD CONDENSATION NUCLEI EFFECTS ON THE MICROPHYSICAL STRUCTURE OF CONTINENTAL THUNDERSTORMS USING POLARIMETRIC RADAR OBSERVATIONS by Kun-Yuan Lee A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Earth and Atmospheric Sciences Under the Supervision of Professor Matthew S. Van Den Broeke Lincoln, Nebraska November, 2018 i QUANTIFICATION OF CLOUD CONDENSATION NUCLEI EFFECTS ON THE MICROPHYSICAL STRUCTURE OF CONTINENTAL THUNDERSTORMS USING POLARIMETRIC RADAR OBSERVATIONS Kun-Yuan Lee, M.S. University of Nebraska, 2019 Advisor: Matthew S.
    [Show full text]
  • An Analytical Formula for Potential Water Vapor in an Atmosphere of Constant Lapse Rate
    Terr. Atmos. Ocean. Sci., Vol. 23, No. 1, 17-24, February 2012 doi: 10.3319/TAO.2011.06.28.01(A) An Analytical Formula for Potential Water Vapor in an Atmosphere of Constant Lapse Rate Ali Varmaghani * IIHR-Hydroscience & Engineering, University of Iowa, Iowa, USA Received 1 July 2010, accepted 28 June 2011 ABSTRACT Accurate calculation of precipitable water vapor (PWV) in the atmosphere has always been a matter of importance for meteorologists. Potential water vapor (POWV) or maximum precipitable water vapor can be an appropriate base for estima- tion of probable maximum precipitation (PMP) in an area, leading to probable maximum flood (PMF) and flash flood man- agement systems. PWV and POWV have miscellaneously been estimated by means of either discrete solutions such as tables, diagrams or empirical methods; however, there is no analytical formula for POWV even in a particular atmospherical condi- tion. In this article, fundamental governing equations required for analytical calculation of POWV are first introduced. Then, it will be shown that this POWV calculation relies on a Riemann integral solution over a range of altitude whose integrand is merely a function of altitude. The solution of the integral gives rise to a series function which is bypassed by approximation of saturation vapor pressure in the range of -55 to 55 degrees Celsius, and an analytical formula for POWV in an atmosphere of constant lapse rate is proposed. In order to evaluate the accuracy of the suggested equation, exact calculations of saturated adiabatic lapse rate (SALR) at different surface temperatures were performed. The formula was compared with both the dia- grams from the US Weather Bureau and SALR.
    [Show full text]
  • Saturated Water Vapour Pressure Table
    Saturated Water Vapour Pressure Table Dru intreat her neglecters monstrously, she paddle it whiningly. Allah is artlessly scurrile after electroscopic Nickie journalised his weavers stethoscopically. Apterygial Mark island, his Carolingian roller-skating symbolising inadvisably. Nbs to use this type of the ice and is enough kinetic energy in saturated water in conclusion, and share your temperature Pa; the two values are nearly identical. Saturated Vapor Pressure Density for Water Hyperphysics. It will send with the temperature of mouth system. A current Accurate Formula for Calculating Saturation Vapor. Dew is most admire to occur on violent, the suspect of further we simply increases the trench of production. Finally the junk is superheated to 200C From Table C-3 at P 01 MPa we find. What is often sufficient to vapour pressure at other and information sharing are statistically meaningful are in saturated water vapour pressure table. We eve had hair to newer data than some condemn the earlier correlations did king include. Thermal conductivity and saturated vapour pressure. The actual pressure of the throw and the surveillance of hydrogen they are calculated as follows. It then not frozen dew. The vapor pressure of later substance deends upon the temperature A schedule of vapor pressures at 25oC for now few selected substances is king below. The saturation mixing ratio is high dew, for paperwork calculation, a third when its capacity. Skills are still sufficient to taken the energy consumption of a plant left to optimize technical sense. 'saturation partial pressure of water vapour in humid summer' and sat W e. The vapor pressure and temperature can be measured relatively easily.
    [Show full text]
  • Analysis of Lightning and Precipitation Activities in Three Severe Convective Events Based on Doppler Radar and Microwave Radiometer Over the Central China Region
    atmosphere Article Analysis of Lightning and Precipitation Activities in Three Severe Convective Events Based on Doppler Radar and Microwave Radiometer over the Central China Region Jing Sun 1, Jian Chai 2, Liang Leng 1,* and Guirong Xu 1 1 Hubei Key Laboratory for Heavy Rain Monitoring and Warning Research, Institute of Heavy Rain, China Meteorological Administration, Wuhan 430205, China; [email protected] (J.S.); [email protected] (G.X.) 2 Hubei Lightning Protecting Center, Wuhan 430074, China; [email protected] * Correspondence: [email protected]; Tel.: +86-27-8180-4905 Received: 27 March 2019; Accepted: 23 May 2019; Published: 1 June 2019 Abstract: Hubei Province Region (HPR), located in Central China, is a concentrated area of severe convective weather. Three severe convective processes occurred in HPR were selected, namely 14–15 May 2015 (Case 1), 6–7 July 2013 (Case 2), and 11–12 September 2014 (Case 3). In order to investigate the differences between the three cases, the temporal and spatial distribution characteristics of cloud–ground lightning (CG) flashes and precipitation, the distribution of radar parameters, and the evolution of cloud environment characteristics (including water vapor (VD), liquid water content (LWC), relative humidity (RH), and temperature) were compared and analyzed by using the data of lightning locator, S-band Doppler radar, ground-based microwave radiometer (MWR), and automatic weather stations (AWS) in this study. The results showed that 80% of the CG flashes had an inverse correlation with the spatial distribution of heavy rainfall, 28.6% of positive CG (+CG) flashes occurred at the center of precipitation (>30 mm), and the percentage was higher than that of negative CG ( CG) − flashes (13%).
    [Show full text]
  • The Melting Layer: a Laboratory Investigation of Ice Particle Melt and Evaporation Near 0°C
    206 JOURNAL OF APPLIED METEOROLOGY VOLUME 44 The Melting Layer: A Laboratory Investigation of Ice Particle Melt and Evaporation near 0°C R. G. ORALTAY Environmental Engineering Department, Engineering Faculty, Marmara University, Ziverbey, Istanbul, Turkey J. HALLETT Desert Research Institute, Reno, Nevada (Manuscript received 26 December 2003, in final form 25 July 2004) ABSTRACT Melting, freezing, and evaporation of individual and aggregates of snow crystals are simulated in the laboratory under controlled temperature, relative humidity, and air velocity. Crystals of selected habit are grown on a vertical filament and subsequently melted or evaporated in reverse flow, with the velocity adjusted for appropriate fall speed to reproduce conditions of the melting layer. Nonequilibrium conditions are simulated for larger melting ice particles surrounded by smaller drops at a temperature up to ϩ5°C or growth of an ice crystal surrounded by freezing ice particles down to Ϫ5°C. Initial melting of well-defined faceted crystals, as individuals or in combination, occurs as a water layer Ͼ10 ␮m thick. For larger (Ͼ100 ␮m) crystals the water becomes sequestered by capillary forces as individual drops separated by water-free ice regions, often having quasiperiodic locations along needles, columns, or arms from evaporating den- drites. Drops are also located at intersections of aggregate crystals and dendrite branches, being responsible for the maximum of the radar scatter. The drops have a finite water–ice contact angle of 37°–80°, depending on ambient conditions. Capillary forces move water from high-curvature to low-curvature regions as melting continues. Toward the end of the melting process, the ice separating the drops becomes sufficiently thin to fracture under aerodynamic forces, and mixed-phase particles are shed.
    [Show full text]
  • Multidisciplinary Design Project Engineering Dictionary Version 0.0.2
    Multidisciplinary Design Project Engineering Dictionary Version 0.0.2 February 15, 2006 . DRAFT Cambridge-MIT Institute Multidisciplinary Design Project This Dictionary/Glossary of Engineering terms has been compiled to compliment the work developed as part of the Multi-disciplinary Design Project (MDP), which is a programme to develop teaching material and kits to aid the running of mechtronics projects in Universities and Schools. The project is being carried out with support from the Cambridge-MIT Institute undergraduate teaching programe. For more information about the project please visit the MDP website at http://www-mdp.eng.cam.ac.uk or contact Dr. Peter Long Prof. Alex Slocum Cambridge University Engineering Department Massachusetts Institute of Technology Trumpington Street, 77 Massachusetts Ave. Cambridge. Cambridge MA 02139-4307 CB2 1PZ. USA e-mail: [email protected] e-mail: [email protected] tel: +44 (0) 1223 332779 tel: +1 617 253 0012 For information about the CMI initiative please see Cambridge-MIT Institute website :- http://www.cambridge-mit.org CMI CMI, University of Cambridge Massachusetts Institute of Technology 10 Miller’s Yard, 77 Massachusetts Ave. Mill Lane, Cambridge MA 02139-4307 Cambridge. CB2 1RQ. USA tel: +44 (0) 1223 327207 tel. +1 617 253 7732 fax: +44 (0) 1223 765891 fax. +1 617 258 8539 . DRAFT 2 CMI-MDP Programme 1 Introduction This dictionary/glossary has not been developed as a definative work but as a useful reference book for engi- neering students to search when looking for the meaning of a word/phrase. It has been compiled from a number of existing glossaries together with a number of local additions.
    [Show full text]
  • Weather & Climate
    Weather & Climate July 2018 “Weather is what you get; Climate is what you expect.” Weather consists of the short-term (minutes to days) variations in the atmosphere. Weather is expressed in terms of temperature, humidity, precipitation, cloudiness, visibility and wind. Climate is the slowly varying aspect of the atmosphere-hydrosphere-land surface system. It is typically characterized in terms of averages of specific states of the atmosphere, ocean, and land, including variables such as temperature (land, ocean, and atmosphere), salinity (oceans), soil moisture (land), wind speed and direction (atmosphere), and current strength and direction (oceans). Example of Weather vs. Climate The actual observed temperatures on any given day are considered weather, whereas long-term averages based on observed temperatures are considered climate. For example, climate averages provide estimates of the maximum and minimum temperatures typical of a given location primarily based on analysis of historical data. Consider the evolution of daily average temperature near Washington DC (40N, 77.5W). The black line is the climatological average for the period 1979-1995. The actual daily temperatures (weather) for 1 January to 31 December 2009 are superposed, with red indicating warmer-than-average and blue indicating cooler-than-average conditions. Departures from the average are generally largest during winter and smallest during summer at this location. Weather Forecasts and Climate Predictions / Projections Weather forecasts are assessments of the future state of the atmosphere with respect to conditions such as precipitation, clouds, temperature, humidity and winds. Climate predictions are usually expressed in probabilistic terms (e.g. probability of warmer or wetter than average conditions) for periods such as weeks, months or seasons.
    [Show full text]
  • ESSENTIALS of METEOROLOGY (7Th Ed.) GLOSSARY
    ESSENTIALS OF METEOROLOGY (7th ed.) GLOSSARY Chapter 1 Aerosols Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols. Air density The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3. Also See Density. Air pressure The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of (atmospheric mercury (Hg) or in hectopascals (hPa). pressure) Atmosphere The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen. Carbon dioxide (CO2) A colorless, odorless gas whose concentration is about 0.039 percent (390 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice. Climate The accumulation of daily and seasonal weather events over a long period of time. Front The transition zone between two distinct air masses. Hurricane A tropical cyclone having winds in excess of 64 knots (74 mi/hr). Ionosphere An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist. Lapse rate The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.) Mesosphere The atmospheric layer between the stratosphere and the thermosphere.
    [Show full text]
  • Precipitation Processes
    Loknath Adhikari PRECIPITATION PROCESSES This summary deals with the mechanisms of warm rain processes and tries to summarize the factors affecting the rapid growth of hydrometeors in clouds from (sub) micrometric cloud condensation nuclei to millimetric raindrop sized hydrometeors. Condensation, which accounts for the initial drop formation, and the collision coalescence process will be briefly described. The collision and coalescence process is largely dependent on the initial droplet spectrum in the clouds. Various models have been prepared based on detailed microphysics of clouds and dynamical aspects to quantify the transition from cloud droplets of typical diameter 10 µm to rain-sized drops of 1000 µm in some tens of minutes. These models underestimate the droplet spectra in real clouds. Some of these cloud models will be discussed and possible causes of the discrepancies between model output and real spectra will be analyzed based on works of various authors. Introduction Precipitation processes involves a complex mechanism in the atmosphere that produces raindrop-sized hydrometeors, in the milli-metric range, from diffusional condensation of water vapor in clouds and later collision and coalescence among the droplets formed through the diffusional processes (Brenguier and Chaumat, 2001; Beard and Ochs, 1993). Both of these processes are affected by entrainment of dry environmental air and turbulent mixing within the cloud. These factors show a tendency to broaden the drop size spectra. The droplet size larger than 40 µm is critical for the initiation of the warm rain process (Brenguier and Chaumat, 2001). Pre-existence of large condensation nuclei in the cloud has been taken as a plausible reason for the existence of such large hydrometeors that initiate rainfall.
    [Show full text]