The Chinese meteorological records could be traced back to the oracle-bone inscriptions of the Shang Dynasty (c. 1600 bc–c. 1046 bc). For the past 3,000 years, continuous meteorological records are available in official histories, chronicles, local gazetteers, diaries, and other historical materials. Ever since the Qin Dynasty (221–207 bc), precipitation reports to the central government were officially organized; however, only those of the Qing Dynasty (1644–1912 ad) are extant, and they have been widely used to reconstruct precipitation variability. Modern meteorological knowledge began to be introduced in China during the late Ming Dynasty (1368–1644 ad). Modern meteorological observation possibly began in the 17th century, whereas continuous meteorological observation records go back to the mid-19th century. Previous researches have reconstructed the chronologies of the temperature change in China during the past 2,000 years, and the Medieval Warm Period and Little Ice Age were identified. With regard to precipitation variability, yearly charts of dryness/wetness in China for the past 500 years were produced. Several chronologies of dust storm, plum rain (Meiyu), and typhoon were also established. Large volcanic eruptions resulted in short scale abrupt cooling in China during the past 2,000 years. Climatic change was significantly related to the war occurrences and dynastic cycles in historical China.
Charles A. Doswell III
Convective storms are the result of a disequilibrium created by solar heating in the presence of abundant low-level moisture, resulting in the development of buoyancy in ascending air. Buoyancy typically is measured by the Convective Available Potential Energy (CAPE) associated with air parcels. When CAPE is present in an environment with strong vertical wind shear (winds changing speed and/or direction with height), convective storms become increasingly organized and more likely to produce hazardous weather: strong winds, large hail, heavy precipitation, and tornadoes. Because of their associated hazards and their impact on society, in some nations (notably, the United States), there arose a need to have forecasts of convective storms. Pre-20th-century efforts to forecast the weather were hampered by a lack of timely weather observations and by the mathematical impossibility of direct solution of the equations governing the weather. The first severe convective storm forecaster was J. P. Finley, who was an Army officer, and he was ordered to cease his efforts at forecasting in 1887. Some Europeans like Alfred Wegener studied tornadoes as a research topic, but there was no effort to develop convective storm forecasting. World War II aircraft observations led to the recognition of limited storm science in the topic of convective storms, leading to a research program called the Thunderstorm Product that concentrated diverse observing systems to learn more about the structure and evolution of convective storms. Two Air Force officers, E. J. Fawbush and R. C. Miller, issued the first tornado forecasts in the modern era, and by 1953 the U.S. Weather Bureau formed a Severe Local Storms forecasting unit (SELS, now designated the Storm Prediction Center of the National Weather Service). From the outset of the forecasting efforts, it was evident that more convective storm research was needed. SELS had an affiliated research unit called the National Severe Storms Project, which became the National Severe Storms Laboratory in 1963. Thus, research and operational forecasting have been partners from the outset of the forecasting efforts in the United States—with major scientific contributions from the late T. T. Fujita (originally from Japan), K. A. Browning (from the United Kingdom), R. A. Maddox, J. M. Fritsch, C. F. Chappell, J. B. Klemp, L. R. Lemon, R. B. Wilhelmson, R. Rotunno, M. Weisman, and numerous others. This has resulted in the growth of considerable scientific understanding about convective storms, feeding back into the improvement in convective storm forecasting since it began in the modern era. In Europe, interest in both convective storm forecasting and research has produced a European Severe Storms Laboratory and an experimental severe convective storm forecasting group. The development of computers in World War II created the ability to make numerical simulations of convective storms and numerical weather forecast models. These have been major elements in the growth of both understanding and forecast accuracy. This will continue indefinitely.
Storms are characterized by high wind speeds; often large precipitation amounts in the form of rain, freezing rain, or snow; and thunder and lightning (for thunderstorms). Many different types exist, ranging from tropical cyclones and large storms of the midlatitudes to small polar lows, Medicanes, thunderstorms, or tornadoes. They can lead to extreme weather events like storm surges, flooding, high snow quantities, or bush fires. Storms often pose a threat to human lives and property, agriculture, forestry, wildlife, ships, and offshore and onshore industries. Thus, it is vital to gain knowledge about changes in storm frequency and intensity. Future storm predictions are important, and they depend to a great extent on the evaluation of changes in wind statistics of the past. To obtain reliable statistics, long and homogeneous time series over at least some decades are needed. However, wind measurements are frequently influenced by changes in the synoptic station, its location or surroundings, instruments, and measurement practices. These factors deteriorate the homogeneity of wind records. Storm indexes derived from measurements of sea-level pressure are less prone to such changes, as pressure does not show very much spatial variability as wind speed does. Long-term historical pressure measurements exist that enable us to deduce changes in storminess for more than the last 140 years. But storm records are not just compiled from measurement data; they also may be inferred from climate model data. The first numerical weather forecasts were performed in the 1950s. These served as a basis for the development of atmospheric circulation models, which were the first generation of climate models or general-circulation models. Soon afterward, model data was analyzed for storm events and cyclone-tracking algorithms were programmed. Climate models nowadays have reached high resolution and reliability and can be run not just for the past, but also for future emission scenarios which return possible future storm activity.
A typhoon is a highly organized storm system that develops from initial cyclone eddies and matures by sucking up from the warm tropical oceans large quantities of water vapor that condense at higher altitudes. This latent heat of condensation is the prime source of energy supply that strengthens the typhoon as it progresses across the Pacific Ocean. A typhoon differs from other tropical cyclones only on the basis of location. While hurricanes form in the Atlantic Ocean and eastern North Pacific Ocean, typhoons develop in the western North Pacific around the Philippines, Japan, and China. Because of their violent histories with strong winds and torrential rains and their impact on society, the countries that ring the North Pacific basin—China, Japan, Korea, the Philippines, and Taiwan—all often felt the need for producing typhoon forecasts and establishing storm warning services. Typhoon accounts in the pre-instrumental era were normally limited to descriptions of damage and incidences, and subsequent studies were hampered by the impossibility of solving the equations governing the weather, as they are distinctly nonlinear. The world’s first typhoon forecast was made in 1879 by Fr. Federico Faura, who was a Jesuit scientist from the Manila Observatory. His brethren from the Zikawei Jesuit Observatory, Fr. Marc Dechevrens, first reconstructed the trajectory of a typhoon in 1879, a study that marked the beginning of an era. The Jesuits and other Europeans like William Doberck studied typhoons as a research topic, and their achievements are regarded as products of colonial meteorology. Between the First and Second World Wars, there were important contributions to typhoon science by meteorologists in the Philippines (Ch. Deppermann, M. Selga, and J. Coronas), China (E. Gherzi), and Japan (T. Okada, and Y. Horiguti). The polar front theory developed by the Bergen School in Norway played an important role in creating the large-scale setting for tropical cyclones. Deppermann became the greatest exponent of the polar front theory and air-masses analysis in the Far East and Southeast Asia. From the end of WWII, it became evident that more effective typhoon forecasts were needed to meet military demands. In Hawaii, a joint Navy and Air Force center for typhoon analysis and forecasting was established in 1959—the Joint Typhoon Warning Center (JTWC). Its goals were to publish annual typhoon summaries and conduct research into tropical cyclone forecasting and detection. Other centers had previously specialized in issuing typhoon warnings and analysis. Thus, research and operational forecasting went hand in hand not only in the American JTWC but also in China (the Hong Kong Observatory, the Macao Meteorological and Geophysical Bureau), Japan (the Regional Specialized Meteorological Center), and the Philippines (Atmospheric, Geophysical and Astronomical Service Administration [PAGASA]). These efforts produced more precise scientific knowledge about the formation, structure, and movement of typhoons. In the 1970s and the 1980s, three new tools for research—three-dimensional numerical cloud models, Doppler radar, and geosynchronous satellite imagery—provided a new observational and dynamical perspective on tropical cyclones. The development of modern computing systems has offered the possibility of making numerical weather forecast models and simulations of tropical cyclones. However, typhoons are not mechanical artifacts, and forecasting their track and intensity remains an uncertain science.
R. J. Trapp
Cumulus clouds are pervasive on earth, and play important roles in the transfer of energy through the atmosphere. Under certain conditions, shallow, nonprecipitating cumuli may grow vertically to occupy a significant depth of the troposphere, and subsequently may evolve into convective storms. The qualifier “convective” implies that the storms have vertical accelerations that are driven primarily, though not exclusively, by buoyancy over a deep layer. Such buoyancy in the atmosphere arises from local density variations relative to some base state density; the base state is typically idealized as a horizontal average over a large area, which is also considered the environment. Quantifications of atmospheric buoyancy are typically expressed in terms of temperature and humidity, and allow for an assessment of the likelihood that convective clouds will form or initiate. Convection initiation is intimately linked to existence of a mechanism by which air is vertically lifted to realize this buoyancy and thus accelerations. Weather fronts and orography are the canonical lifting mechanisms. As modulated by an ambient or environmental distribution of temperature, humidity, and wind, weather fronts also facilitate the transition of convective clouds into storms with locally heavy rain, lightning, and other possible hazards. For example, in an environment characterized by winds that are weak and change little with distance above the ground, the storms tend to be short lived and benign. The structure of the vertical drafts and other internal storm processes under weak wind shear—i.e., a small change in the horizontal wind over some vertical distance—are distinct relative to those when the environmental wind shear is strong. In particular, strong wind shear in combination with large buoyancy favors the development of squall lines and supercells, both of which are highly coherent storm types. Besides having durations that may exceed a few hours, both of these storm types tend to be particularly hazardous: squall lines are most apt to generate swaths of damaging “straight-line” winds, and supercells spawn the most intense tornadoes and are responsible for the largest hail. Methods used to predict convective-storm hazards capitalize on this knowledge of storm formation and development.
Ralf Weisse and Birgit Hünicke
A multitude of geophysical processes contribute to and determine variations and changes in the height of the Baltic Sea water surface. These processes act on a broad range of characteristic spatial and timescales ranging from a few seconds to millennia. On very long timescales, the northern parts of the Baltic are uplifting due to the still ongoing visco-elastic response of the Earth to the last deglaciation, and mean sea level is decreasing in these regions. Over centuries, the Baltic Sea responds to changes in global and North Atlantic mean sea level. Processes affecting global mean sea level, such as warming of the world ocean or melting of glaciers and of polar ice sheets, do have an imprint on Baltic Sea levels. Over decades, variations and changes in atmospheric circulation affect transport through the Danish Straits connecting the Baltic and North seas. As a result, the amount of water in the Baltic Sea and the height of the sea level vary. Similarly, atmospheric variability on shorter timescales down to a few days cause shorter period variations of transport through the Danish Straits and Baltic Sea level. On even shorter timescales, the Danish Straits act as a low pass filter, and high frequency variations of the water surface within the Baltic Sea such as storm surges, wind waves, or seiches are solely caused internally. All such processes have undergone considerable variations and changes in the past. Similarly, they are expected to show variations and changes in the future and across a broad range of scales, leaving their imprint on observed and potential future Baltic Sea level and its variability.