The murder of cAli in 661 and the establishment of the caliphate of his rival Mucawiya, cousin of cUthman and Arab governor of Syria, is generally taken to mark the advent of the Umayyad dynasty, the first Islamic state built explicitly on the claims of one family (the Banu Umayya) to the right to rule. Mucawiya was succeeded in 680 by his son, Yazid, and then by members of collateral branches of the Umayyad family. In fact, however, the political situation was more complex, and its complexity reflects and is central to the process through which Islam emerged. The third caliph cUthman had appointed many members of his own clan to important administrative posts, provoking considerable opposition among Muslims who resented the favors granted to the family, particularly as many members of the Banu Umayya had been late and reluctant converts to Islam. cUthman's policy may have extended to efforts to ensure that he was succeeded as caliph by one of his sons. If that is the case, then the dynastic policies of the Umayyads could be regarded as having commenced earlier than the reign of Mucawiya, with the regime of cAli constituting a mere interregnum. On the other hand, no Umayyad “state” was firmly established and widely recognized for some time.

This book constitutes an attempt to describe and understand the slow emergence of a distinctively Islamic tradition over the centuries which followed the death of that tradition's founder, Muhammad ibn cAbdallah, in 632 CE. It is not a narrative history, although its analytical approach is (I hope) historical. I have cast the central questions as those of religious identity and authority. The question of what it means to be a Muslim requires, I believe, a dynamic answer. Had the question been posed to Muhammad, his answer (if indeed he would have understood the question) would have been quite different than that of a jurist in Baghdad in the ninth century, or of a Sufi mystic in Cairo in the fifteenth. From a historical perspective, no answer is better than any other, and none has any value except against the background of the larger historical factors that produced it. In the multicultural Near East, those factors have always included faith traditions other than Islam, and so I have tried throughout to give some account of the complex ties which, from the very first, have bound Muslim identities to those of Jews, Christians, and others.

The target audience for this book is quite broad, and therefore the target is, paradoxically, perhaps more difficult to strike squarely than with, say, a scholarly monograph of the usual sort, or a conventional introduction to “Islam”.

With the full development of sectarian movements within the Islamic umma, the stage was set for the crystallization of a specifically Sunni Muslim identity, which took shape largely in response to the threat of sectarian fragmentation. Khariji Islam survived in peripheral areas of the Islamic world, but in the central Near East in this period posed little threat. It did play some role in the revolt of African slaves (the “Zanj”) in southern Iraq in the late ninth century. This rebellion was driven by the appalling conditions in which slaves worked harvesting natron in the region's extensive and virtually impenetrable marshes, but it also relied heavily on its charismatic instigator, an enigmatic figure named Muhammad ibn cAli. The Khariji slogan la hukma illa lillah, “judgment is God's alone,” appeared on Muhammad's banners and coins which were minted in his name. But Muhammad was an opportunist, drawing on support wherever he could find it – at one point he claimed cAlid descent, and unsuccessfully sought an alliance with the Ismacili leader Hamdan Qarmat, whose name survived in that of the Qarmatians. As a result, the ideological orientation of the Zanj rebellion is somewhat confused. From hindsight, perhaps the most important aspect of the Zanj revolt was simply its timing, in the late ninth century, at just the moment that an active Ismacili movement appeared, the Imams most widely recognized by the Shica were disappearing, and the fragmentation of effective political authority called into question the precise significance of the cAbbasid caliphate.

It is conventional to speak of a “Sunni revival” in the eleventh and twelfth centuries. According to this view, militantly Sunni regimes such as that of the Saljuqs responded to the challenge of the “Shici century,” that period between the mid-tenth and mid-eleventh centuries when much of the central Muslim world was dominated by Shici regimes (the Fatimids, the Buyids) of varying stripes, by vigorously re-asserting – reviving – Sunni identity and claims to dominance. Like many grand historical themes, this one is perhaps a bit too neat and simple. On a political level, for example, the Saljuq seizure of power in Baghdad was not a restoration of a pre-Buyid political patterns. It is true that the Buyid amirs, whom the Saljuqs replaced, were Shicis, but their power had been in decline for some time previously. Moreover, relations between them and the cAbbasid caliphs, still the symbol of Sunni legitimacy, were often cordial; indeed, as the Saljuq armies approached Baghdad in 1055, the caliph intervened with the Saljuq leader, Toghril Beg, seeking protection for the Buyid amir al-Malik al-Rahim. Relations between the Saljuq leader and the cAbbasid caliph were hardly warm at the outset: Toghril Beg had been in Baghdad for thirteen months before he met the caliph.

If the notion of a Sunni “revival” is in some ways misleading, there were nonetheless extremely important developments at work that shaped the character that Sunni Islam would carry into the modern period.

Religious knowledge (cilm) was perhaps the central cultural lynchpin of the Islamic tradition and of the social patterns in which that tradition was experienced in the Middle Period. This knowledge was embedded in the rich and inter-related body of texts – principally the Koran, collections of hadith, legal treatises and textbooks, and commentaries on them – which formed the substantive basis for the training of those scholars who were known as the ulama. Our principal concern here, however, is less with the intellectual parameters of this cilm than with the social uses to which it was put, and with the way in which these uses helped to define Muslim identities and the nature of the ulama's authority.

For the ulama, it was the active process of transmitting religious knowledge that was critical. As we have seen, the ulama were in fact socially quite diverse, and the only thing that marked them as a distinctive group was their command of these highly valued texts, and their control of access to them. In part this was simply a matter of education, that is, of transmitting to students a familiarity with essential texts which was necessary to the proper discharge of the responsibilities they might incur upon appointment to a range of offices – for example, that of the qadi, or that of professor (mudarris) in the myriad religious institutions which sprang up in medieval Islamic cities.

Virtually all accounts of the rise of an Islamic state and then empire in the seventh century stress its extraordinary character, the suddenness of the appearance on the scene of the Muslim Arabs and the wholly unexpected nature of their success – what Marshall Hodgson referred to as “a breach in cultural continuity unparalleled among the great civilizations.” Explanatory models for the Muslim success – at least those which do not focus upon the Arabs themselves, on the demographic, economic, or religious factors propelling them forward – tend to look for causes in the chaotic developments in the Near East in the late sixth and early seventh centuries. In this, of course, there lies the danger of an easy retrospective teleology, of the assumption that the Near Eastern civilizations experienced on the eve of the Muslim conquests a crisis which weakened them fatally, and so rendered those conquests (or something like them) virtually inevitable. The cautious historian should eschew such a dramatic viewpoint, tempting as it may be. On the other hand, conditions in the Near East in the early seventh century were indeed highly charged and unstable. From a broader perspective, they demonstrate, not the inevitability of the Muslim conquests, but the degree to which those events marked a stage in a longer-term process by which the Arabs were drawn into the cultural orbit of the Fertile Crescent and surrounding territories and, in their Muslim guise, contributed to its evolution.

Notes written from memory by Anders Persson (ECMWF) on 16 September 1999. The reader is encouraged to read P. D. Thompson's paper “Charney and the Revival of Numerical Weather Prediction”, reproduced, together with Charney's letters to Thompson in Lindzen et al., (1990).

History of NWP

In late 1945 Vladimir Zworykin, the “Father of Television”, who worked at RCA, joined with John von Neumann, the “Father of the Computer”, to suggest the use of the computer in meteorology. Zworykin's interest was in weather modification, and von Neumann's was in fluid dynamics. They also had the dream of connecting the TV and the computer into something we today know as a PC or Workstation. Their dream came partially true in Sweden in around 1955 when for the first time a forecast map that was made directly and automatically without any human intervention was produced on a screen (oscilloscope) (see Bergthorsson and Döös, (1955), Bergthorsson et al., (1955), also the Rossby Memorial Volume).

In early 1946 von Neumann contacted Rossby's group. They told von Neumann why a zonally averaged dynamical model would not work, and instead suggested a barotropic model which had been manually tested by Victor Starr in his 1941 book on weather forecasting for a 72-h forecast at 700 hPa. Von Neumann was not satisfied with the simple barotropic approach and in speeches in the spring of 1946 presented more ambitious plans. Von Neumann and Zworykin also appeared at the annual meeting of the AMS (see Bulletin of AMS (1946)).

If the numerical model forecasts are skillful, the forecast variables should be strongly related to the weather parameters of interest to the “person in the street” and for other important applications. These include precipitation (amount and type), surface wind, and surface temperature, visibility, cloud amount and type, etc. However, the model output variables are not optimal direct estimates of local weather forecasts. This is because models have biases, the bottom surface of the models is not a good representation of the actual orography, and models may not represent well the effect of local forcings important for local weather forecasts. In addition, models do not forecast some required parameters, such as visibility and probability of thunderstorms.

In order to optimize the use of numerical weather forecasts as guidance for human forecasters, it has been customary to use statistical methods to “post-process” the model forecasts and adapt them to produce local forecasts. In this appendix we discuss three of the methods that have been used for this purpose.

Model Output Statistics (MOS)

This method, when applied under ideal circumstances, is the gold standard of NWP model output post-processing (Glahn and Lowry, 1972, Carter et al., 1989). MOS is essentially multiple linear regression, where the predictors hnj are model forecast variables (e.g., temperature, humidity, or wind at any grid point, either near the surface or in the upper levels), and may also include other astronomical or geographical parameters (such as latitude, longitude and time of the year) valid at time tn.

Introduction

In general, the public is not aware that our daily weather forecasts start out as initial-value problems on the major national weather services supercomputers. Numerical weather prediction provides the basic guidance for weather forecasting beyond the first few hours. For example, in the USA, computer weather forecasts issued by the National Center for Environmental Prediction (NCEP) in Washington, DC, guide forecasts from the US National Weather Service (NWS). NCEP forecasts are performed by running (integrating in time) computer models of the atmosphere that can simulate, given one day's weather observations, the evolution of the atmosphere in the next few days. Because the time integration of an atmospheric model is an initial-value problem, the ability to make a skillful forecast requires both that the computer model be a realistic representation of the atmosphere, and that the initial conditions be known accurately.

NCEP (formerly the National Meteorological Center or NMC) has performed operational computer weather forecasts since the 1950s. From 1955 to 1973, the forecasts included only the Northern Hemisphere; they have been global since 1973. Over the years, the quality of the models and methods for using atmospheric observations has improved continuously, resulting in major forecast improvements.

Figure 1.1.1(a) shows the longest available record of the skill of numerical weather prediction. The “S1” score (Teweles and Wobus, 1954) measures the relative error in the horizontal gradient of the height of the constant pressure surface of 500 hPa (in the middle of the atmosphere, since the surface pressure is about 1000 hPa) for 36-h forecasts over North America.